GENERATION INTEGRATED RURAL DEVELOPMENT CONSULTANT (GIRDC)
MOWIE, TBIWRDP
P.O.Box 5744
Tel. +251-116-633425
Fax No. +251-116-637038
GIRDC
Comet Building (5,h Floor) Haile Gebre Silassie Road, Addis Ababa, Ethiopia
P.O.Box 322 Code 1250 Tel +251 (0) 116 63 15 90/91
+251-911-63 41 95
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TABLE OF CONTENTS
1     INTRODUCTION.................................................................................................................1
2     OBJECTIVES AND SCOPE OF THE SURVEY.................................................................3
2.1     GENERAL OBJECTIVE................ ........................................................ ................;............. 3
2.2     SPECIFIC OBJECTIVES AND SCOPE OF THE SURVEY..................................................3
3     METHODOLOGIES AND EQUIPMENT USED FOR THE SURVEY.............................. .5
3.1     GENERAL APPROACH....................................................................... ...... ......... .................5
3.2     FIELD RECONNAISSANCE & ASSESSMENT OF MAJOR CHARACTERISTICS OF
THE AREAS..................................................................................................................... ....5
3.3    AWARENESS CREATION AND STAKEHOLDERS CONSULTATION............................  6
3.4     ORGANIZING SURVEY CREW AND ORIENTATION........................................................ 6
3.5     PERVIOUS WORKS, TOPOGRAPHIC MAPS, SATELLITE IMAGERIES AND PREPARATION OF BASE MAP........................................................................................  6
3.6    LINKING EMA GCP AND ESTABLISHING GEODETIC CONTROL POINTS.................... 7
3.7    TECHNIQUES OF DATA ACQUISITION AND COMPILATION.......................................... 9
3.8    QUALITY CONTROL SYSTEM............................................................................................ 9
3.9     EQUIPMENT USED AND LOGISTICS FOR THE SURVEY............................................... 9
3.10  SUMMARY OF TOPOGRAPHIC SURVEY METHODOLOGIES...................................... 10
4     STAFFING AND ORGANIZATIONAL SYSTEM.............................................................. 13
4.1     STAFFING..................................................................... .......................................................13
4.2     ORGANIZATION AND MANAGEMENT OF SURVEY WORKS......................................  13
5     MAJOR CHARACTERISTICS OF THE FLOODPLAIN AREAS...................................... 15
5.1     SURVEY AREA'S DESCRIPTION...................................................................................... 15
5.2     LOCATION OF THE FLOODPLAIN AREAS...................................................................... 15
5.3    ACCESSIBILITY OF THE FLOODPLAIN AREAS............................................................  21
5.4     SOIL, LAND USE LAND COVER AND FARMING SYSTEM.............................................21
5.4.1     Soil Types in the Project Areas........................................................................... 21
5.4.2     Land use /cover and Farming System........................................ 21
5.5     TOPOGRAPHIC NATURE AND DRAINAGE PATTERN IN THE SURVEY AREAS ....21
5.6     CLIMATE............................................................................................ .'................................ 22
5.7     SOCIAL AND PHYSICAL INFRASTRUCTURES........................... ..................................... 22
5.8    ASSESSMENT OF FOGERA AND DEMBIA FLOODPLAIN BOUNDARIES.............. ........ 22
6     REVIEW AND ASSESSMENT OF THE FLOOD PRONE AREAS................................... 27
6.1     GENERAL...................................... .......................................................... .......... ......... ...... ;27
6.2     FLOOD HISTORY...................... ......... ........ .................... .................. -................... •........... 27
6.3     HYDROLOGICAL MODELING........................ .......... ...................................................•...... 29
6.4     HYDRAULIC MODELING............................................ ................. .................. •........... .. ......35
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6.5      FLOOD PRONE AREAS ASSESSED FROM DIFFERENT STUDY REPORTS......................... 37
6.6      OTHER STUDIES......................................................................................................................... 40
6.7      EXISTING AND ONGOING FLOOD PROTECTION WORKS.................................................... 41
6.8     RECOMMENDATIONS................................................................................................................ 44
7     TOPOGRAPHIC FIELD SURVEY WORKS............................................................................... 45
7.1     GENERAL.....................................................................................................................................45
7.2     LINKING OF GCP OF EMA AND ESTABLISHMENT OF PERMANENT CONTROL
POINTS......................................................................................................................................  45
7.2.1      Identified EMA GCPs............................................................................................................ 45
7.2.2        Linking EMA GCP and Establishing Permanent Benchmarks........................................... 46
7.3      DETAIL TOPOGRAPHIC SURVEY WORKS..............................................................................51
7.3.1      Adopted Survey Technique and procedures........................................................................51
7.3.2       Linkage with Lake Tana Bathymetric Survey data.............................................................51
7.4     CROSS SECTIONS SURVEY WORKS......................................................................................51
7.5      SURVEY OF INFRASTRUCTURES............................................................................................53
7.6     SURVEY OF KEBELES, VILLAGES AND OTHER AREAS....................................................... 53
8     DATA PROCESSING, MAPPING AND VERIFICATION.......................................................... 55
8.1     SURVEY DATA PROCESSING...................................................................................................55
8.2     MAP AND DATA BASE OF THE SURVEY................................................................................. 55
8.2.1        Topographic Maps..............................................................................................................55
8.2.2        Data Base.......... .................................................................................................................56
8.3      INTEGRATION AND HARMONIZATION OF THE TOPOGRAPHIC DATA BASE TO
FLOOD MODELLING SOFTWARE'S..........................................................................................56
8.4     VERIFICATION OF THE TOPOGRAPHIC MAPS WITH EMA STANDARDS........................... 56
8.4.1        Verification through Linking to EMA National system........................................................56
8.4.2        Verification through Geometrical linking with control net works........................................ 56
8.4.3        Cartographic and Scale Verification...................................................................................57
9     ISSUES AND CONSTRAINTS.................................................................................................. 59
9.1     GENERAL.................................................................................................................................... 59
9.2      ISSUES AND CONSTRAINTS..................................................................................................  59
9.2.1        Survey Boundary.... .......................................................................................................... 59
9.2.2        Damage of the BM............................................................................................................. 59
9.2.3        High crops on the field.....................................................................................................  59
9.2.4        Rainfall..........................................................................................................................     60
REFERENCES................................................................................................................................. 61
APPENDICES.................................................................................................................................  63
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LIST OF APPENDICES
APPENDIX 1: Primary Permanent Benchmarks’ Location in Dembia FP Area........................................ 65
APPENDIX 2: Primary Permanent Benchmarks’ Location in Fogera FP Area......................................... 67
APPENDIX 3: Triangulation Points/GCPs Identified and Linked To the Suivey Area............................... 69
APPENDIX 4: Detailed Topographic Survey Data of the floodplain Areas............................................. .71
APPENDIX 5: Cross Section Data of Rivers & Gullies in the Floodplain Areas....................................... 73
APPENDIX 6: Specification of Differential Fixed GPS STotal Stations used for Survey.......................... 75
APPENDIX 7: Selected Photographs of BMs & GCP with Witness Diagram...........................................81
APPENDIX8:  Lake  Tana  Bathymetric  survey  Control  Points  (Adindan  Zone-37  UTM
Coordinates).................................................................................................................... 89
APPENDIX 9: Data Base Guides.............................................................................................................. 91
APPENDIX 10: Description of Services (TOR)......................................................................................... 95
LIST OF TABLES
Table 5-1: Administrative Locations and Area of proposed Floodplain survey            areas....................15
Table 6-1: Peak Flow Estimates for all Basins from Frequency Analysis (FA)               & HEC-HMS....... 30
Table 6-2: Design flood flows for Megech River........................................................................................ 33
Table 6-3 : Design flood flows for Gumara River....................................................................................... 33
Table 6-4 : Design flood flows.................................................................................................................... 34
Table 7-1: Locations of Identified EMA GCPs around the Project Area....................................................45
Table 7-2: Kebeles/Major Villages and Areas in Dembia Floodplain........................................................ 54
Table 7-3: Kebeles/Major Villages and Areas in Fogera Floodplain..........................................................54
LIST OF FIGURES
Figure  3-1:  Partial  View  of  flat  &  open  Survey  Areas  in  Fogera  (Left)  and  Dembia  (Right)  FP....8
Figure  4-1:  Adopted  Organizational  System  of  Lake  Tana  Floodplains  Topographic  Survey  ....14
Figure 5-1: Locations Map of the Lake Tana Sub-basin Floodplains Surveyed.........................................17
Figure 5-2: Map of Floodplain kebeles........................................................................................................ 19
Figure 5-3: Rib River old course......................................................................... ........................................ 22
Figure 5-4: Proposed Fogera & Dembia Floodplains Boundary................................................................. 25
Figure 6-1: Old and New courses of Megech River.................................................................................... 31
Figure 6-2: Interaction of new Gumara with the Shenzeli River north of project area................................ 32
Figure 6-3: Interpolation of the 1: 25 year’s peak flow................................................................................35
Figure 6-4: Lake Tana Floodplain................................................................................................................38
Figure 6-5: Existing flood extent for 1:50 and 1:100 year return period.....................................................40
Figure 6-6: Cut through dykes by Irrigators to minimize pumping head              and pipe length............. 42
Figure 6-7 : Uncontrolled movement of livestock has affected sustainability of the dykes.........................42
Figure 6-8; Flood extent with flood bunds in place for 1:50 and 1:100 year             return period............43
Figure 6-9 : Area benefitting from defenses in project area.................................................... ................... 44
Figure 7-1:    Location map of Identified EMA GCPs and Established BMs.............................................. 49
Figure 7-2:    Cross section Survey on Rib River....................................................................................... 52
Figure 7-3:    Layout of Surveyed Cross Sections of Rivers        courses  and Gullies.............................. 53
Figure 9-1:   Some of the Dismantled Bench marks..................................... ............................................. 60
Figure 9-2:High crops and dense perennial trees.....................................................................................  60
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List of Topographic Maps for Fogera & Dembia Floodplains (in MAP ALBUM: A1)
Map Number
TltleS Scale
TBS/TSF&D/01
Location Map of Lake Tana Sub-basin Floodplain Areas 1:175,000 (1 Nr)
TBS/TSF/02
Location of Established Permanent BMs in Fogera Floodplain, 1:50,000 (1 Nr)
TBS/TSF/03
Topographic Map of Fogera Floodplain 1:50,000 (1 Nr)
TBS/TSF/04
Detail Topographic Map of Fogera Floodplain, 1:10,000 (12 Nr)
TBS/TSF/05
Cross-Sections Map of Major Rivers in Fogera Floodplain (2 Nr) H 1:1000,V 1:100
TBS/TSD/06
Location of Established Permanent BMs in Dembia Floodplain, 1:20,000 (1 Nr)
TBS/TSD/07
Topographic Map of Dembia Floodplain 1:20,000 (1 Nr)
TBS/TSD/08
Detail Topographic Map of Dembia Floodplain 1:10,000 (4 Nr)
TBS/TSD/09
Cross-Sections Map of Major Rivers in Dembia Floodplain (4 Nr) H 1:1000,V 1:100
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ACRONYMS
A.A AMAX API BM BOA
Addis Ababa
Annual maximum
Areal Photo Interpretation Benchmark
Bureau of Agriculture
BOWRD                        Bureau of Water Resources Development
CAD CN DEM EMA
Computer Aided Design Curve Number
Digital Elevation Model Ethiopian Mapping Agency
ENTRO                         Eastern Nile Technical Regional Office
ERA EVI FAO FP FQ FTC GCP
Ethiopian Road Authority Extreme Value Type 1
Food and Agriculture Organization Floodplain
Flood Quantity
Farmer Training Center Ground Control Point
GIRDC                          Generation Integrated Rural Development Consultant
HEC HMS                     Hydrologic Engineering Centre Hydrologic Modelling System HEC-GeoRAS               HEC Geo-processing for River Analysis System
IDF ISIS LN
LP3 LEV
Intensity Duration Curve
Halcrow's in house 1D hydrodynamic modelling software Log Normal distributions
Log Pearson Type III Largest Extreme Value
MOW IE                        Ministry of Water Irrigation and Energy of Ethiopia
PA QCBS RFC RPCU SMEC SCS TaSBO
Peasant Association
Quality and Cost Based Selection Reinforced Concrete
Regional Project Coordination Unit Snowy Mountain Engineering Cooperation Soil Conservation Service
Tana Sub basin Organization
TBIWRDP                     Tana and Beles Integrated Water Resources Development Project
Tc
Time of Concentration
TIN
Triangular network model
TOR
Terms of Reference
USGS
United State Geological Survey
WB
World Bank
WVE
World Vision Ethiopia
WWDSE
Water Works Design & Supervision Enterprise
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1 INTRODUCTION
MOWIE-TBIWRDP
A   Lump-Sum   contract   agreement   was   signed   between   MOWIE   and   GIRDC   on   February11, 2014 to made detail Topographic Survey of Lake Tana sub -basin Floodplain Areas.
Flooding in the Lake Tana sub-basin has  caused havoc  and inconvenience to residents  in the area especially  over the last decades. The flooding has  been resulting in a loss  of several hundreds  of human lives  and several millions  worth private and public  property. As  per ENTRO 2010, these consequences  of flooding are complex  and far-reaching; among these consequences  direct damage to property  and structures, as  well as  disruption of economic activity  and displacement of affected population, with the attendant costs  of evacuation and temporary  accommodation which include loss  of agricultural productivity, including both opportunity  as  well as  direct damage to crops  in various  stages  of cultivation can be mentioned. The Government of Ethiopia, International organizations  and NGOs  have thus  put their concerted efforts in emergency, planning and developmental works to mitigate such effects.
The areas  affected by  flood around Lake Tana include parts  of all woredas  around the lake but Dara, Fogera, Libo kemkem and Dembia woredas  of South and North Gondar Zones  are areas currently  under consideration. In these four Woredas, people, livestock, farm and grazing land, social and physical infrastructures  were affected. In terms  of population, those of Dembia and Fogera have been among the most affected by  flooding. In 2007, the magnitude of the disaster rose to a higher level and required an emergency  response. As  these areas  were prone to recurrent flooding, frequent emergency  measures  were found to be not the most effective means  of dealing with the situation. As  the result a flood mitigation program was  started by MOWIE TBIWRDP with support from WB in collaboration with regional and other stakeholders. Accordingly  8 pilot floodplain kebeles  in the two largest flood risk  areas  of Fogera and Dembia were selected.
Flood risk mapping were conducted in these flood prone areas as it is important in:
•    Planning for early warning, flood preparedness and response,
•   Taking action at present, to reduce current and future destructions,
•    Developing infrastructure for reducing expected flood severity and damage, and
•    Guiding relevant development to avoid increased risk where hazard is frequent.
MoWIE in collaboration with other concerned stakeholders has been conducting different
studies in these areas to minimize flood risks resulting from flood and its consequences. In view
of that, topographic survey data for a pilot kebeles was required in order to be used as an input
in flood modeling, flood risk mapping and establish early warning system as flood problems are
more prevalent in the identified 8 kebeles around the lake in Dembia, Fogera, Libo Kekem, and
Dera woredas.
The consultant has  accordingly  conducted these survey  works  starting from collection of relevant data from concerned stakeholders  and identified and linked known national ground control points  which are established by  EMA. The survey  works  conducted have included; linking with EMA GCP and establishing permanent BMs, spot level survey, cross  section survey, infrastructures survey, etc.
This  final report with Map Album (in separate binding) presents; methodologies  of the survey Assessment and findings  of previous  Flood Studies, topographic  survey  data and outputs, of these two floodplain areas.
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2 OBJECTIVES AND SCOPE OF THE SURVEY
2.1     General Objective
The general objective of this  topography  survey  works  is  to gather sufficient topographic features  of both Fogera and Dembia Floodplain areas  so that it is  possible to carryout different hydrological modeling for flood studies  which shall lead to recommendations  to mitigate its negative impacts.
2.2     Specific Objectives and Scope Of The Survey
Specific objectives and scope of the survey works as stipulated in the TOR are as follow;
•      To  carry  out  detailed  topographic  survey  works  of  194km2    in  Fogera  and  70km2    in Dembia Floodplains;
•    To identify and gather every detail spot contours that improves the quality of risk maps;
•    To conduct cross section survey works in rivers and gullies crossing the project areas;
•     To carry out survey of infrastructures situated within the project boundary;
•      To  designate  environmentally  sensitive  areas  such  as  aquatic,  terrestrial  and  hillside areas, water courses and updated sensitive ecosystem inventory locations;
•      To  prepare  detailed  topographic  maps  @  a  scale  of  1:10,000  and  0.5m  contour  interval that   will   help  to   identify  the  existing  nature  of  all  the  Floodplain  features,  including specific  landscape  values  that  may  be  affected  by  different  level  of  floods.  This  work  will support accurate Floodplain modeling.
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3 METHODOLOGIES AND EQUIPMENT USED FOR THE SURVEY
3.1 General Approach
Three different methods of topographic surveys were proposed and evaluated as part of this survey planning:
(i)  LIDAR Techniques: This enables to cover larger area in shorter time but offers less technical advantage when the accuracy is compared with the ground survey method. Moreover, in our experience there is a high risk of uncertainty and delays in obtaining permits for a plane and eventual security approval for over-flights to be made. We discussed with EMA that; it is possible through them with the formal request of the client MOWIE. But the risk for delay is too high given the time frame of the study and the need to fast-track field work and surveys.
(ii)  High  Resolution  Stereoscopic  Satellite  Imagery:  In  this  case,  high  precision  data has to be ordered, over-flown (by satellite) and procured from a commercial, contracting satellite company. Accuracies obtained from this data meet the requirement of 0.5 m contour intervals required by the ToR for this study. This high resolution stereo data is not freely down loadable and is in fact costly to acquire, but provided all steps are carefully planned, timescales can be carefully managed and the risks of the delays associated with LIDAR techniques can be avoided. However, it requires to commission and contract the satellite to run in specific time and space by procuring an independent commercial provider of stereo satellite imagery such as Digital Globe, Geo Eye or Pleiades to undertake a dedicated satellite over-flight to provide Stereo SI. Halcrow- GIRDC was used this technique in Feasibility study of net 80,000 ha ENIDP (gross 168,000ha)  due  to  Halcrow  (U.K)and its  owning partner  CH2M  (USA)  commercial contact  with  the  imagery  firms.  However,  it  is  not  easy  for  us  and  the  current stakeholders to commercially negotiate and enter contract with these companies due to several reasons which are beyond the scope of this report to discuss them.
(unconventional ground based topographic  survey: This  is  a widely  used technique even though tedious and time taking. However, it gives the most accurate results as it involves collection of spot levels by looking and picking the actual nature of each physical feature. We believed that and was  possible to undertook  surveys  using conventional techniques by employing high accuracy Differential GPS and digital Total stations to get the required accuracy in the time specified under the ToR.
Based on efficiency  in time and cost, high accuracy, compatibility  of the data base and easiness to use and improve the data base (when required); method 111: conventional ground topographic survey was recommended, approved by the client. During negotiation the MOWIE had informed that, WB in its no objection to the assignment & contract award; advised the consultant to use ground topo survey technique with minimal use of satellite imageries only limited to preparation of Base map. Accordingly, we adopted this technique for carrying out the survey works. To this end the consultant organized, mobilized a significant number of field surveyors  with sufficient logistic  support in order to complete the topo survey  work  in a scheduled time frame (see section 4).
3.2    Field reconnaissance & assessment of Major Characteristics Of The Areas
The characteristics of floodplain survey areas, access & physical infrastructures, major bio physical and climatic features, soil, land use land cover, farming practices, socioeconomic and social infrastructures were assessed as the basis for this topographic field survey plan and field data collection. The major floodplain characteristics are discussed in section 5.
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3.3       Awareness Creation and stakeholders consultation
This was the initial task accomplished as a prerequisite to plan and start survey. The team accompanied by  TBIWRDP M & E specialist and TaSBO staffs  to carryout inception and reconnaissance assessment of the project area. TaSBO internalized the flood problems of the area and has given due importance to the Topographic survey. The office promised to render support in all aspects up to completion of the survey work. Moreover, the TaSBO assigned the project communication head as  a focal expert to support the survey  team especially  in awareness  creation and assist in handling other administrative matters  related to the assignment.
The team consulted Regional Administration office, discussed with Amhara Regional State Advisor to the regional president, BOA, Bureau of Food security, Disaster Prevention and Early warning, BOWRD, North and South Gondar Zones Administration and respective four woredas administration and sectoral offices.
The field assessments were made in collaboration with concerned woreda staffs, namely: Dera, Fogera, Libo-kemkem and Dembia and also conducted awareness creation to the beneficiary farmers in the 8 pilot kebeles. The team consulted with the beneficiary communities on the flood problems, seasons of flood, psychological and physical damage including human and livestock  lives. Moreover, as  per the traditional approach it was  arranged with kebele administrations that; the awareness creation to be further strengthened by announcing during different religious and social occasions like on Sunday prayers, on community social gathering occasions like on “Idir”, “Ekub" and spiritual “Mehiber" or “Senbete" programs.
3.4       Organizing survey crew and orientation
In order to create common understanding of the scope and methodology of the assignment and detail survey works to be done by the team as a whole and make clear responsibility of each members of the team; two days orientation was given to the surveyors by the team leader and chief surveyor. Orientation and discussion were made on:
•    Methodologies and approaches to accomplish the survey in the required quality and the shortest time possible to avoid rainy season that can impede the survey,
•    Type of equipment used and level of accuracy of the equipment required for this survey
•   Quantity and quality of the topographic data to be surveyed
•   Integrations expected from the team during this field survey
•    Communications with the affected communities during the survey especially how to avoid  hostile  condition  and  create  smooth  relation.  It  was  underlined  and  reached consensus that the survey team should respect the local culture and be participatory.
•   Data acquisition, compilation and plotting
•   Logistics and supply system required for this field survey
•   All other issues relevant to field survey
3.5       Pervious works, topographic maps, satellite imageries and preparation of base
MAP
The consultant has  identified, collected available previous  flood investigation and impact studies, procured maps which are relevant to this assignment which included, 1: 50,000 and 1:250,000 scale topographic maps, land use land cover maps and other relevant information’s form MOWIE, ENTRO, EMA, MOA and other stakeholders. We found that 1: 250,000 scale
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map and others  listed are of insignificant use except to know the regional location. Besides  the 1:50,000 scales  which are as  old as  4 decades  had undergone significant manmade and natural changes  due to expansion of villages, infrastructures, cultivation, flooding, change of river and stream courses. Having realized this  self-demonstrable reality, we transferred 1:50,000 scale EMA map with reference to old and permanent features  like churches, big villages, roads  and other short-term unchangeable features  to digital format referenced to known feature point coordinates.
We then browsed and downloaded freely  available Satellite imageries  like Google Earth and linked with Global Mapper software from on line and calibrate based on known coordinate points  in the floodplain area by  identifying coordinates  recorded for existing/recent infrastructures such as main road, bridges, old church, congested areas like village etc.
Moreover our engineers, GIS & CAD experts, Chief surveyors  have accessed other free Satellite imageries  with 50 to 60m resolution such as  Quick  Bird, Land sat 7&8, Aster, Spot, SRTM DEM, Aster DEM . Digital Globe and used in the preparation of Topographic  base map for use in the field survey. The base map has  been distributed to all survey  crew. The image geo-referencing were checked using different site and drainage features  during reconnaissance field topographic  survey. It has  to be clear that, the output of these Topo map and Satellite imageries  interpretation including Global Mapper with DEM and other compatible software were used only for preparation of the base map which in turn was used for field survey planning and immediate reference during field survey.
On the other hand; use of satellite imageries  (other than for the base map) with the above mentioned resolutions  and even with more high resolutions  commercial imageries  have no value added output for this  level of high scale topo survey. This  is  due to the fact that, the current topo survey  used observation points  at 50mx50m and more ( in some places) is  of higher resolution than any available satellite imageries.
Therefore,   the   output   and   data   base   of   the   Lake   Tana   Floodplains   topo   survey   is   fully dependent on actual ground survey verified by GCP and permanent control points.
3.6 LINKING EMA GCP AND ESTABLISHING GEODETIC CONTROL POINTS
EMA GCPs  were identified from the National Topographic  maps  and from reconnaissance field assessment. The primary  control network  should be better of a density  that optimizes  but does not compromise the Real Time Kinematic  (RTK) GPS telemetry, i.e. the control stations  are not more than 20 km apart. This  is  because the RTK GPS radio telemetry  will not extend beyond approximately  15 km without line of sight. During linking, the more the distant (but not more than 20km), the more we took time of observation in order to increase the accuracy. Of several EMA GCPs, around Lake Tana Gonder area; only four were found available on the ground and these were procured from EMA and linked to the survey  area (see Table 7.1). Most of other points  do not exist on the ground due may  be soil deposition and dense vegetation coverage, destroyed by farmer ploughing, vandalism and other reasons.
In establishing Survey  Control Stations  and collecting other spot points, we adopted two Techniques: a Static  Survey  and RTK Techniques. In Static  surveys, a Reference Point was chosen and one or more Rovers  were allowed to operate with respect to it. Typically, a Rapid Static  Techniques  were used for increasing density  of data in existing networks, and for establishing control etc.
When starting survey work in an area where no GPS surveying has previously taken place, the first task is to observe a number of points, whose coordinates are accurately known in the local system. This  enabled a transformation to be calculated and hence, all points  measured with GPS in that area can be easily converted into the local system. At least 3 known points on the
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perimeter  of  the  area  of  interest  were  observed.  The  transformations  calculated  were  then  valid for the area enclosed by those points.
The Reference Receiver is  usually  set up at a known point and was  included in the calculations of the transformation parameters. If no known point is  available in WGS 1984 geographic coordinate, we allowed to set up anywhere within the network. The Rover receiver(s) then visit each of the known points. The length of time that the Rovers  must observe for at each point was  related to the baseline length from the Reference and the GDOP (dilution of precision or DOP).The receivers  were then allowed to collect data for a certain length of time. This  time is influenced by  the length of the line, the number of satellites  observed or DOP and the satellite geometry.
As a rule of thumb, the observation time is a minimum of 1 hour for a 20km line with 5 satellites and a prevailing GDOP of 8. Longer lines  require longer observation times. However we took 3.30hrs  to achieve high level accuracy  for each until we linked the points  with the Floodplain control point and other existing known BM. Once enough data has  been collected, the receivers were switched off. The Rover then was  moved to the next baseline and measurement was  once again commenced. The data was recorded and post-processed back at the office.
Control stations  were then established at 2km radius  mostly  on buried RFC centre drilled with nail and marked by  indelible paints. In addition to these permanent ground control points, in some cases  as  shown in the remark  of the attached lists  of survey  points, few of these stations were established on existing bedrock or in a few cases natural permanent tree stump.
The planned spacing of 2km BMs  may  be ± in the field due to natural topographic  features owning to flatness  as  well as  openness  of the survey  areas, appropriateness  of locations  and residence compounds, schools, churches, clinics  compounds, roads  other permanent structures, whenever encountered which is not safe to install.
The control stations  comprise permanent ground anchors  made of circular concrete structure 0.6 m deep and 0.3m diameter being drilled in with a 0.50 m long reinforcement bar whose part of it (5cm) left unburied so as  not to experience movement. The network  coordinate values along with the accuracy  and precision statistics  are tabulated and locations  are shown on the simplified contour map. The coordinate values  are set to be well within the specified tolerance of 0.010m ± 1 ppm for both the position and height values. Photos  and witness  diagrams  of these stations  have been shown for reference. GPS observations  were carried out at 5 second epochs  and baseline observation times  were proportional to the baseline length, such that all potential errors and biases are mitigated.
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Observations were made in the WGS84 coordinate system and transformed to Adindan UTM Zone  37N  grid  coordinates  while  processing.  The  height  datum  is  ellipsoidal  and  is perpendicular to the Clarke 1880 ellipsoid, at the surface of the ellipsoid. It should also be noted that for Ethiopia; there is an XYZ shift of +165m, +11m, and -206m respectively between the WGS84 and Clark 1880 ellipsoids.
3.7    TECHNIQUES OF DATA ACQUISITION AND COMPILATION
During data acquisition operations, static GPS receivers were positioned over stations at EMA Yifag GCP near Fogera, BM Hamuist, all other BM’sand Grid level data was acquired by fixing a leica system 1200 GPS using a post processed kinematic (PPK) GPS solution. The PPK solution involves the positioning of a static GPS receiver over a known coordinated point, whilst roving GPS, receivers log GPS Pseudo range and carrier phase data simultaneously.
These data are then post processed in Lieca Geomatics office (LGO) V 7.0 using real time kinematic  (RTK) GPS processing algorithms. This  period of stationery  data capture is necessary to allow integer ambiguities to resolve post processing. After this period the survey point indicated on the system Leica 500 GPS screen captured data in 1 second interval. This is sufficient to accurately capture data.
At the end of each data capture, as part of the procedures, the GPS receivers were down loaded in to LGo V7.0 where primary processing was carried out. Any poor quality data was deleted. These point data was imported, analyzed and plotted by the surveyors. All quality control procedures were carried out where practicably possible.
In general, topographic landscape features, rivers, gullies, ditches, embankments, wetlands infrastructures, etc. were surveyed on foot using Total stations. These point data were then imported into AutoCAD and analyzed by the surveyors on-site to determine: (i) day-to-day consistency  and quality; (ii) any  data gaps; (iii) to check  the reference (static) station coordinates; (iv) to check the consistency in the geodetic information; and (v) to ensure the entire site have been surveyed within the envisaged boundary.
Terra Modeler and AutoCAD are then used to create a triangulation model. This is then edited to remove any unnecessary triangles such as those outside the survey boundary, or those triangles created around missed clustered points. This triangulation model was then contoured at 0.5 m. Further editing is then carried out on the triangulation model to remove any spurious triangles where such cases are found.
3.8    Quality control system
Our quality  control started with topographic  survey  planning, designing of methodology, selection of up to date digital equipment and orientation of the topographic surveyors and survey coordinators. The team leader and the chief surveyor made frequent field supervision. In addition to, on field daily plotting and checking by each surveyor, it is arranged in such a way that the field survey team send their data every two days to our team leader and chief surveyor for checking. The supervisors then checked and sent their feedback including corrections to be made.
3.9    Equipment Used And Logistics For The Survey
For the GCP & BM crew, dual frequency Differential RTKGPS with full accessories was made available. Moreover, a laptop with appropriate GPS survey processing software’s which provide survey output as X, Y and Z data suitable for import into other software were made available. In addition, other ancillary equipment to support survey works such as hand held GPS for basic
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navigation  and  tracking  were  given  to  each  surveyors.  We  were  also  made  available  other equipment like digital camera, meter, etc.
To make more specific, each of the mobilized topographic survey crew had:
•    One Digital Total Station with full accessories and six Leica Digital Total Stations with 5"  accuracy  are  used  in  Fogera  Floodplain  topographic  survey,  whereas  3  Sokkia Digital Total station are used in Dembia Floodplain Topographic survey.
•    Communication  mobiles  with  extra  power  sources to  enable internet  communication too
•   CDMA for Internet,
•   One Toshiba laptop computer with different appropriate software,
•   One hand held GPS for counterchecking and closing some polygons like villages ,
•   One compass and
•   One Digital Camera
•   One rolled Meter (50/100m size)
Moreover, all other field survey logistics were made available. Of all worth to mention in here is; six 4-WD vehicles were made available one for two survey crews and one vehicle for BM crew. In addition to this, one more shuttle vehicles were made available which were used by the team leader and chief surveyor for supervision.
In office to process data for reporting and mapping we used computers with different software’s, Plotter, and other office equipment and tools.
3.10   Summary of Topographic Survey Methodologies
In summary, methodologies adopted for this survey works include:
•   Carrying out initial field reconnaissance survey works;
•   Preparation of survey crew and orientation based on reconnaissance survey findings;
•   Collection of pervious works, 1:50,000 topographic maps Asatellite imageries;
•   Preparation of base map;
•   Making available survey equipment and other logistics
•   Identification and procurement of EMA GCP;
•   Linking EMA GCP with survey area
•   Establishing permanent benchmarks;
•   Carrying out detailed topographic survey works;
•   Carrying out survey works of infrastructures;
•   Conducting cross sections survey works;
•   Connecting the surveying works at different sites of the project to each other by close traversing method;
•   Topographic survey to envisage the configuration of the terrain and location of both natural and human made objects from the known/fixed permanent benchmarks;
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•  Encoding the collected surveying data to different computer programs  and then processing to produce topographic  maps, profiles, layout and boundary  mark  using, AutoCAD, Surfer and Civil designer software'.
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4    STAFFING AND ORGANIZATIONAL SYSTEM
4.1    Staffing
The surveyors crews were organized in to two groups: one group each for Dembia and Fogera and to nine field survey sub-groups: three of these crews for topographic survey works on Dembia Floodplain and six  crews  for topographic  survey  works  on Fogera Floodplain. Besides one GPS team was assigned to establish permanent Bench Marks and link them with EMA’s permanent GCP. In addition to this one Water resource engineer (team leader), one chief surveyor to organize technical aspects of survey works have been assigned to coordinate and control overall survey works.
4.2    Organization And Management of Survey Works
The organization of the team for Lake Tana floodplain Topographic survey was strategically designed to enable efficient field work and coordination within and among the team members. GIRDC assigned one of its senior permanent staff members to be the team leader and work in close coordination with the chief surveyor who is responsible for technical matters of the survey. Moreover, two senor surveyors are assigned each to coordinate Dembia and Fogera floodplain overall field topographic surveys.
The team leader was directly liaison with the Clients Project coordinator, RPCU and other stakeholders on all matters pertaining to the assignment. A system has been created for the groups to closely interact in conducting the survey in order to achieve the required quality and consistency of the data collected on every day.
The chief surveyor in collaboration with the team leader and the water Resource Engineer were responsible to follow up the field survey and control the quality, quantity of the work and progress of topographic data collection in reference to the scheduled time table designed for this purpose. The adopted organizational system of the Lake Tana Floodplain Topographic survey is shown in Figure 4.1 below.
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5    MAJOR CHARACTERISTICS OF THE FLOODPLAIN AREAS
5.1   Survey Area’s Description
These pilot Floodplain survey  areas  were delineated in reference to flood prone kebeles  in consultation with the MOWIE; Hydrology and Water Quality Directorate of the client. These areas were delineated and measured using Arc GIS version 10.1 with projection- UTM; datum-WGS84; Zone-37. The list of first proposed Kebeles and areas of each is given in Table 5.1 below.
Table 5-1: Administrative Locations and Area of pi
areas
Nr
Project
name
Zone
Woreda
Kebele
Proposed Area for survey
Km2
Ha
1
Wagera
42.88
4,288
2
Fogera
Nabega
43.05
4,305
3
Jegina
27.74
2,774
4
Fogera
Floodplain
South
Gonder
Dera
Mtsilina Tana
52.18
5,218
5
Libo Kemkem
Genda Wuha
17.49
1,749
6
Teza Abba
12.41
1,241
Subtotal Fogera FP
195.75
19,575
7
Dembia
Debr Zuria
21.52
2,152
8
Seraba
34.64
3,464
9
Dembia
Floodplain
North
Gonder
Achera
14.75
1,475
Subtotal Dembia FP
2
4
70.91
7,091
Total
264.36
26,436
boundary; by GIRDC GIS
5.2   Location of the Floodplain Areas
Both Dembia and Fogera floodplains are located around the Lake Tana, which is the largest lake in Ethiopia that is found in the north-west mid highlands of Ethiopia. It is located within the ranges of UTM projection of about 281,71 ON, and 1.281.740E to 349.560N, and 1,359,830 EWGS84 datum. The Lake is situated at about 564 km from the national capital town Addis Ababa.
Administratively the floodplains are located in Amhara National Regional State; Fogera Floodplain being in South Gonder Zone, Fogera, Dera & Libo Kemkem Woredas and is consisting of six Kebeles whereas, Dembia Floodplain is located in North Gonder Zone Dembia Woreda consisting of three Kebeles on the northern side of the lake (See Figure 5- 1: Location Map of the Floodplain areas and Figure 5.2 Map of Floodplain kebeles)
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5.3    Accessibility of the Floodplain Areas
Dembia Floodplain is accessed through A.A - Bhair Dar - Gonder asphalt road, 793 km from Addis Ababa and then 60 km after Gonder to Kola Diba capital town of the woreda. Similarly, Fogera Floodplain is accessed through Bahir Dar-Gondar asphalt road at about 624km near the town of Woreta. There are scattered tracks to access within these Floodplains. However, these roads/accesses in the project area are limited to dry season and impassable during even small rainy season.
5.4    Soil, Land use land cover and Farming system
5.4.1      Soil Types in the Project Areas
Vertisols are the major soil types followed by Fluvisols and Gleysols prevailing in these project areas. Vertisols  occupy  the very  flat landscape part where there are areas  subjected to seasonal inundations. The Fluvisols  are found mainly  along the Floodplains  adjacent to the rivers identified in the project areas. The Gleysols are found in the waterlogged areas along the shores of Lake Tana and depressed areas. These soils especially the vertisols are very difficult soil to work on during rainfall and for sometimes after rainfall.
5.4.2      Land use /cover and Farming System
Generally  the land use is  under crop production, grazing, villages  and infrastructures  under ownership of mainly  private farmers  and community. Mixed farming (crop and livestock production) is  the common agricultural practices  that have been undertaking in the survey areas. These areas area under intensive crop cultivation and as a result the natural vegetation has almost been cleared completely. Teff, Wheat, Lentils, Check Pea and vegetables are the major crops grown in the area. Rice (paddy and highland varieties) is being introduced in the area. The cropping calendar is  from July  to January. Crops  planted in September/October following flood recession are harvested in February/March. Eucalyptus as homestead plantation is the most common tree species in the area especially around villages. Moreover, Croton and Cordia are the most common natural tree species found around the home stead’s and religious centers.
5.5    Topographic nature and drainage pattern in the survey areas
Most of these survey areas are characterized by flat (plain) topography, with average slope ranging from 1- 2%. The extensive flat plain has numerous subdued facets (depressions),
which are predominantly water ways and seasonal wetlands. There are some relatively gentle areas where most villages and service infrastructures are located.
Lake Tana is  the source of the Blue Nile River and has approximately 15,000 km2 drainage areas, of which the lake itself covers 3,060 km .The average elevation of the lake surface area
2
is 1,786masl.
Physical observation, map and imageries  interpretation have shown that, there are several seasonal and permanent rivers, streams  and gullies  draining to the main rivers  namely: Megech, Dirma, Rib, Gumera and their tributaries and thereby to Lake Tana.
The drainage system is  characterized by  instability  of silty  river banks  on Gumara, Ribb, Megech and other rivers particularly around the curves while they meander. This stream course nature is  one of the sources  of flooding problems  observed and reported by  the local community. The rivers erode outer part of the curved course and deposit silt on the inner side. This resulted in instability of the river course. In addition to this, effort to irrigate by gravity in the dry season by cutting across the banks has contributed to this problem as it creates weaker
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spots  for flooding during rains. This  causes  rivers  like Rib and Megech changed their course in the last decade, which resulted in technical and social damages  and conflicts  in land & water use (See figure 5.3 for Rib and Figure 6.1 for Megech).
5.6      Climate
The survey  areas  of this  project fall within the traditional Woina Dega agro-climatic  zones, which can be classified as  sub-humid tropical highland climate. It’s  mean annual rainfall, ,is about 1000 mm and the rainy  season is from June to September, during which more than 85% of the annual rainfall is  received, with dependable rainfall of about 850 mm. Its  average daily temperature varies from 23 °c in May to 19 °c in August, with a mean value of 20 °c. Similarly, the mean annual evapo-transpiration in the sub-basin is  indicated to be in the range of 1200 to 1400 mm. The ideal time for the topographic survey in the area has been found to be from mid February to end of May.
5.7      Social and physical infrastructures
Both Dembia and Fogera Floodplains  are mainly  in flatter levels  thus  several villages  in these areas  are sited on relatively  higher/elevated grounds. Moreover, there are churches, schools, clinics, market places, Kebele centers  (including FTC), recently  constructed emergency shelters  (within the schools  premises) and other social and physical infrastructures. All these are surveyed and mapped as part of this assignment.
5.8        ASSESSMENT OF FOGERA AND DEMBIA FLOODPLAIN BOUNDARIES
MOWIE prepared Floodplain pilot kebeles  map based on the level of the kebele to flood prone. The delineation of the pilot kebele in some places  has  followed administrative boundary  rather than flood lines. During Contract negotiation MOWIE advised the consultant to identify  all flood hot spots  beyond the given boundary  as  the boundary  is  arbitrary  given in both Floodplains. Accordingly  the team examined imageries, DEM and supported by  field assessment to delineate flood affected areas  in Fogera and Dembia Floodplains. There is  neither highest elevation nor criteria given to the consultant to delimit the boundary  of the Floodplain. The flood prone area boundary  of other studies  like RIVER SIDE 2010, SMEC 2006, and WVE-FAO 2010 covers larger areas than currently delineated kebeles.
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It has  been found that the most extreme level corresponding to the given edge of the boundaries is 1793m for Dembia FP and 1801m for Fogera FP areas in reference to DEM. In reference to these boundaries, there are still additional areas below these levels which is prone to flood (8032 ha) on Dembia FP and (37,7000ha) on Fogera FP areas. In summary about 45,732 ha area is on the lower level prone to flood.
On the other hand, there are still areas which are located at elevated areas (1789 to 1850m) in Tana Mistili Kebele, which was excluded. On the contrary additional area surveyed to cover some flood prone areas at lower level along the Lake, Rib River downstream of the bridge and Megech River near Robit Village. The above findings and corresponding areas; are presented in Table 5-5 & figure 5-4. MOWIE and the flood modeling consultant have to investigate more as to how to handle these other flood prone areas.
Table 5-5: Assessment of Dembia and Fogera Topographic Survey Floodplain Areas
No
Description of Area
Area, ha
Fogera
Dembia
Subtotal
1
MOWIE Proposed floodplain areas for topographic survey
19,575
7,091
26.668
2
Area excluded due to higher elevation& slope
2715
0
2715
3
Additional area surveyed to cover some flood prone areas
2829
425
3254
5
Total area topo Surveyed
21,829
8,096
29,925
4
Other additional area prone to flood due to lower topography & slope
37,700
8,032
45,732
Topographic Survey in Lake Tana Sub-Basin Floodplain Areas
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6   REVIEW AND ASSESSMENT OF THE FLOOD PRONE AREAS
6.1    General
There are several studies conducted on Lake Tana sub basin Floodplains. However detailed review has been made for only those relevant to Lake Tana Floodplains Topographic Survey mainly focused on Flood History, Hydrological modeling works and main findings, assessment of flood prone areas  and findings, existing and ongoing flood protection works  and recommendations. The previous studies reviewed are:
•    Flood Risk Mapping Consultancy for Pilot Areas in Ethiopia; July 2010 by River Side, USA   in   association   with   Tropics   consulting   engineers   and   Shebele   Consulting Engineers of Ethiopia for ENTRO.
•    ENTRO-Project Preparation, Flood Preparedness and Early Warning study; Dec. 2006 by SMEC International for ENTRO.
•    Design Review Report of Megech Seraba Pump Project by BRL in Association with Generation Integrated Rural Development Consultant (GIRDC)for MOWIE: 2012
•    Feasibility  Study  Report  of  Megech  Robit  Pump  Project  By  Halcrow  In  Association With GIRDC for MOWIE: 2011
•   Other studies
>    Lake Tana Area Flood Protection Works Impact Evaluation, 2010 by GIRDC for WVE.
>     Lake  Tana  Bathymetric  Survey;  2012  by  OMEGA  Development  Service  for MOWIE
> Lake Tana sub-basin Dams  (Gigel Abay, Jamma, Rib and Megech) and Irrigation development study  and design project 2009/10 by  WWDSE in association with Tahal and GIRDC, DH & other National Consultants for MOWIE
>   Gumera Dam and Irrigation Project feasibility Study; 2008 by WWDSE in
association with ITC India and GIRDC and other National consultants for
MOWIE
The current study had also made its own assessment of the flood prone areas based on DEM and consultation with the communities. This flood assessment and analysis of pervious works is not within the scope of the current assignment and the consultant made as a basis to delimit floodplain boundaries (as discussed in section 3.2 above) plan the topographic survey work of the pilot kebels, prepare base map. Moreover, the review and assessments done will help the planned flood modeling as an information base.
6.2    Flood History
The causes of severe flooding in the Fogera and the Dembia floodplains are believed to be:
•   ponding of excess rainfall in floodplain depressions
•   Rise of lake level and
•   overflow of the rivers like Rib, Gumera, Megech Rivers draining into the lake
In the Fogera plain, flooding occurs from the Gumera River near the southern end of the plain, and the Ribb River approximately 15 km to the north. Both rivers flow west across the plain, extending approximately 12 - 15 km south-east from the lake shore to the highway between Bahir Dar to Gonder. Separated floodplains extend further up of both rivers for many kilometers upstream of the highway. Inadequate cross-drainage through the highway embankment has
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aggravated iocal upstream catchments  flooding in past years, but this  has  been partly  corrected by  recent addition of culverts. Floods  occur annually  and high flooding occurs  approximately every 4 years. Water depth will range between 0.5m and 1.2m (Knee to Chest height) and flow velocity  is  moderate and slow, and flooding speed will take several hours  for flooding their by the farm fields and houses inundated. Main Flood duration is typical about 2-3 days, but can be much more than longer in years  of high flood, particularly  if lakes  levels  are higher than average. Although flood levels  will subside, heavy  rains  throughout the season will result in ongoing, periodic inundation (SMEC 2006).
In  Dembia  Floodplain,  the  flood  occur  annually  between  July  and  September,  flood  peak  are  in August.  Due  to  the  predominance  of  black  cotton  soils,  village  at  risk  become  completely inaccessible  at  the  onset  of  rains.  Water  level  will  characterize  reach  shoulder  height  and  can remain  3-5  weeks.  During  exceptional  high  floods  boat  are  mobilized  from  Bahir  Dar  city  and distributed  food  and  medicines  to  isolated  villages  using  Lake  Tana  as  their  access  point.  The main  problem  with  flooding  in  Dembia  Floodplain  is  loss  of  agricultural  production  and  their  by income.  Damage  of  upstream  watershed  has  caused  chronic  siltation  of  rivers  which  result  in change  of  Megech  River  courses  eight  years  ago.  Flooding  of  the  Megech  has  consequently begun  to  affect  entirely  new  kebeles  and  now  flows  directly  through  the  town  of  Robit  dividing part  of  the  town.  In  recent  years,  the  town  has  been  completely  inundated  (SMEC  2006). According  to  SMEC  2006,  other  studies  and  our  discussion  with  the  local  people  the  following are some of problems caused by the flood in the prone areas:
Road  Access Problem: During the flood time the Fogera plain will be inundated and the road accesses  become impassable and affected people is  only  communicated by  swimming. Also farmers are unable to transport produce to the markets
Shelter Problem: In some of the most affected flood risk  areas, people have to live in chest- high water levels for short periods and others will leave the area. For example, in 1996, the high floods  inundated the Kebele of Kedista Hana for 3 months  and around 650 households  were evacuated by  motor boat or helicopter and housed in temporary  shelters  on the main road. However, some refused to leave their houses  for fear of losing their land. During the flood season, where access  is  available most of the cattle will be moved to higher ground, only calving mothers will remain behind.
Unserviceable of social services: During Serious  flood all social services  like school, clinics and road will close down, but most of the time flood time (July  to September, peak  in August) overlap with school vacation period. However, some of the worst affected kebele will only resume school in October/November. The School are particularly  vulnerable to floods  as  they are built near the village and constructed.
Susceptible to  Water Borne Diseases: People in area where flood frequently  inundated were particularly  susceptible to malaria and other flood-related water borne diseases  brought about by contaminated or stagnant waters.
Sedimentation  of the river bed: Siltation of the Floodplains  and sedimentation of the river are severe and reduced discharge capacity  of the river channels  and led to increased inundation of the plains.
Disturbance of Boundaries of Woreda and  Kebles: Gumara River is  the boundary  between Dara and Fogera Woredas. Due to increased siltation of the river channel towards  its  entry  to the lake in the last one decade, the course of the river was changed for about 250 m in favour of Fogera Woreda as  per the information from the Woreda and the study  by  the project. Moreover, the change of the course resulted in creation of a barrier between communities  and the church during rainy  season. Similarly  many  waddies  were formed by  the rivers  and stream at confluence with Lake Tana who created communication and related issues. Similarly Rib
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River  change  of  river  course  with  a  boundary  between  Fogera  and  Libo  kemekem  woreda created similar issues
Some of the worst floods history occurs as per the different reports and our discussion with the local inhabitants include:
A serious flooding occurred in 1964, 1988, 1993, 1994 and in 1995 (when 44 people lost their lives) by which large numbers of people were affected. The flood of 1988 is worth citing at this point and has  caused a massive evacuation of the residents  and damage to crops  on the agricultural land.
Flooding of Libo Kemkem and Fogera Woredas on 7 August 2006 by Overflow of Gumera and the Ribb Rivers resulted in one life loss and displacement of 30,000 people
Flooding  of  Twenty  administrative  units  of  seven  Woredas  surrounding  Lake  Tana  on  30 August 2006 by rising lake levels in which more than 10,000 people were displaced
At the same time in the Fogera plains, floods  killed three people, made 36,000 people homeless, inundated over 6,600 hectares  of cropland, destroyed more than 320 beehives, damaged a school and several water points, spoiled stored seeds, and deposited large volume of gravel and sand on farmlands.
6.3    Hydrological Modeling
Different hydrological studies of the project/target area have been made under different project in different time. Some of the major previous studies referred by the consultant are summarized as follows:
I.  Flood  Risk  Mapping  Consultancy  For  Pilot  Areas  In  Ethiopia  (ENTRO  2010)  By RIVERSIDE    in    Association    With    TROPICS    CONSULTING    ENGINEERS    & SHEBELLE CONSULT
The purpose of study was  to develop discharges  for each rivers  (Gumara, Ribb, Megech & Dirma) that are representative of peak flow for range of probabilities and the scope of the works are hydrological analysis  of four drainage sub-basin of Lake Tana area to estimate the magnitudes  of peak flood corresponding to 2, 5, 10, 50 & 100 year return period. The two methods used for hydrological analysis are:
Flood Frequency Analysis: Out of the seven historical data available four of them: at Gumara near Bahir Dar; Ribb near Addis  Zemen; Megech near Azezo and GilgelAbay  near Merawi which are found in inflow to the lake were used as inflow input data for determining appropriate d/s boundary condition to develop the model.
Log Pearson Type III (LP3) distribution and Extreme Value Type I (EVI) distribution were fitted to the available peak of Gumara, Ribb & Megech River flow data. The US Geological Survey (USGS) computer program Peak  FQ was  used for the LP3 distribution statically  analysis. However, due to the lack of stream flow data on Dirma River, the flow of Dirma was estimated by transporting flows from Megech Basin which has similar land use; soil type characteristics; and subject to the same meteorological regimes. An inspection show that the LP3 distribution provides a good fit to the observed data for the Gumara and Megech gages, while the EVI distribution provides  a better fit for the Ribb. For consistency  in selection of a frequency distribution for the flood risk mapping, the LP3 distribution is used for all basins. The final result of the analysis summarized in Table 4-1 below.
Rainfall - Run off Response Model (HEC HMS): The Hydrologic Engineering Center Hydrologic Modeling System (HEC HMS) model was selected to perform event based rain fall - run off
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
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simulation for Gumara, Ribb, Megech and Dirma Basin. The watershed in each rivers were sub divided in to different sub watershed and the Basin located b/n Gumara and Ribb Watershed, Fogera Middle Basin, was  included as  one of sub basin (sub basin 5); in the Ribb basin schematics  and the Dembia Middle Basin, the basin in between the Megech and Dirma watershed was included in the Dirma basin schematics as one Sub Basin, Sub Basin 5.
For estimating infiltration loss; transformation of excess  precipitation into surface runoff; representation of base flow contributions  to sub basin outflows  and simulation of routing flows in open channels; Loss  Rate Method: Soil Conservation Service (SCS) curve number; Transform Method: User-specified unit hydrograph; Base flow Method: Constant monthly; Routing Method: Lag and Precipitation Method and Frequency  Storm methods  were selected respectively  based on data availability  and primarily  objectives  of the modelling component of the project.
The  available  stream  gage  location  was  used  as  outlet  sub  Basin  1  in  the  Megech  catchment and as outlet sub Basin 2 in Gumera and Ribb Basin. The Dirma basin does not have a gage. However,  for  analysis  purposes  a  gaged  site  was  chosen  at  the  outlet  of  Sub-basin  1,  which comprises  the  mountainous  terrain  of  the  catchment.  Frequency  Storm  Method  was  used  to input   precipitation   data   for   various   duration   and   exceeding   probabilities.   The   IDF   Curve (developed  by  ERA  2002)  for  Region  A2  which  includes  Gumera,  Ribb,  Fogera  Middle  Basin, Megech,  Dirma  &  Dembia  Middle  Basin  were  used  as  in  put  in  HEC  -  HMS  Model.  Since rainfall  events  generally  last  more  than  2  hours  during  the  rainy  season,  the  IDF  curves  were extended  to  include  24  hour  intensity  duration  frequency  data  available  from  the  Ribb  Dam Hydrological  Study  and  the  Megech  Dam  Final  Feasibility  Study  developed  by  Water  Works Design  &  Supervision  Enterprise  (WWDSE 2007 and  2008 respectively). HEC HMS requires 3, 6  and  12  hours  depth  duration  data  which  were  obtained  by  visually  interpolation  between  the available  2  hour  and  24  hour  data.  The  area  of  each  Sub  Basins  were  delineated  in  GIS Program  using  90m  SRTM grid data and curve numbers were determined from soil group and land use combination obtained from GIS layer in each sub Basin. The composite curve number for different hydrological soil groups were found in ERA Drainage Design Manual (ERA 2002).
HEC-HMS was run using the 2, 5, 10, 50 and 100 yr design storms with a one hour time step for a total of six days. Based on the inspection of daily stream flow data, it was concluded that generally  the largest flows  occur in the month of August. Consequently, the simulation dates were set in August and the August monthly  base flow values  were used in the simulations. Cumulative peak  flow values  at the outlet of each sub-basin are listed together with the discharge volumes  at the outlet of the gauged sub-basins  and the outlet of each river basin. The results for all Basins are summarized in Table 6-1 below.
Table 6-1: Peak Flow Estimates for all Basins from Frequency Analysis (FA) & HEC-HMS
Station Name
2 Year
Peak(Cms)
5 Year
Peak(Cms)
10 Year
Peak(Cms)
50 Year
Peak(Cms)
100 Year
Peak(Cms)
Gumara (gagged area = 1354 km2)
FA
329
404
448
539
574
HMS
236
422
592
803
914
Ribb (gagged area = 1625 km2)
FA
148
188
212
262
282
HMS
113
325
411
612
729
Megech (gagged area = 514 km2)
FA
177
278
346
491
550
HMS
99
229
330
500
579
Dirma (gagged  area = 158 km2)
FA
69
108
135
191
214
HMS
40
88
125
188
217
Source: ENTRO 2010
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II. Feasibility Study Report OF Megech Pump (ROBIT) Projects By Halcrow In
Association With GIRDC: 2011
The project area lies within the natural drainage basin of Lake Tana which is fed by the Megech River and four main local rivers that cross the project area of Megech Pump (Robit), from west to east, the Shenzeli, Gumara, Sara and Firkit. The main course of the Megech River now runs through the village of Robit having shifted its course sometime between 1998 and 2000. The original alignment of Megech River now comprises a dried and cut-off river course whereas and the new water course is considerably wider and deeper, see figure 6-1.
Old course of Megech River
New course of Megech River
Outside the project area, the upper and middle parts  of the Megech river basin are characterized by mountains, steep slopes and deep valleys with a maximum altitude of 3,000 masl. The Megech River has  a catchment area of about 725 km2 and flows  in a southerly direction towards Lake Tana. The main tributaries of the Megech River are the West Fork and Angereb and the Megech River is gauged near the town of Azezo at the road bridge roughly 5 km downstream of the Megech Dam site currently  under construction as  part of upstream Megech Gravity  Scheme. The catchment area to the gauge is  about 462 km2 with an area upstream of Megech dam of 425 km .
2
The Shenzeli channel in this area is larger than the Gumara but has a smaller catchment area
(163 km ) and smaller design flows compared to the large Gumara catchment area (198 km ).
2
2
This is likely to be the result of the flow in the Gumera recently moving to a new channel about 6km upstream of the project area then joining up with the Shenzeli channel, thereby augmenting flows in the Shenzeli at the expense of flows on its old water course. The location where this new course of the Gumera joins up with the tributaries of the Shenzeli is shown in Figure 6.2 after which their combined flows  travel south towards  the project area deepening and scouring out a wider channel.
Topographic Survey in Lake Tana Sub-Basin Floodplain Areas
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Figure 6-2: Interaction of new Gumara with the Shenzeli River north of project area
MOWIE-TBIWRDP
Gumara joins with
tributaries of
Shenzeli
New Gumara
Shift from
old Gumara
to new
Combined
flow in deep
wide
Shenzeli
Old Gumara
Proposed       main
Canal about 2 km
to south
Source: Feasibility Study Report of Megech Pump (ROBIT) Projects, by Haicrow Group and GIRDC: 2011
Flood peaks for these tributaries, and for the Shenzeli and Gumara rivers are generated using a combination of rainfall-runoff modelling and design rainfall depth estimated from frequency analysis.
Flood peaks for these tributaries, and for the Shenzeli and Gumara rivers are generated using a combination of rainfall-runoff modelling and design rainfall depth estimated from frequency analysis which are summarized as follows.
Flood Frequency Analysis
Flood  frequency  analysis  is  used  to  estimate  the  design  peak  flows  for  return  periods  from  1:2 year up to a 1:100 year return period and performed using maximum annual daily flow from the gauge  stations  on  the  Megech  River  and  the  Gumara  River.  Flood  frequency  analysis  for  the Megech River at Azezo gauge is performed on 30 years of data from 1978 to 2007. The annual maximum  (AMAX)  daily  flows  after  1978  were  used  as  these  are  considered  more  reliable.  A shorter  annual  maximum  daily  flow  series  of  17  years  is  used  for  flood  frequency  analysis  for the  Gumara  River  at  the  gauging  station  near  Maksegnit.  With  records  of  30  years  at  Azezo frequency  analysis  is  restricted  to  about  1:50  to  1:100  years  events  but  no  higher  on  the Megech  River.  The  17  years  of  AMAX  daily  flows  at  Maksegnit  gauge  is  too  short  to  estimate design  events  in  the  order  of  1:50  year  and  1:100  year  return  period  with  any  confidence  so estimates are subject to large uncertainties.
Flood frequency analysis was performed using probability distributions the Logistic (L) Gumbel (GU), Largest Extreme Value (LEV), and Log Normal distributions (LN), and Gamma (G) distributions in order to estimate the 1:2, 1:5, 1:10, 1:25, 1:50, and 1:100 years flood peaks. The result of flood frequency analysis show that, for short return periods (i.e. < 10 yr) estimated flows are similar between probability distributions, fitting well to the AMAX daily flow data, but
Mi
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for larger return periods this separation increases. For return period of < 1:50 years the GU and LEV Type 1 distributions fit the AMAX daily flows well, the latter suited to model extreme maximum distributions; including high extremes such as flood heights. However, design flows from the GU distribution are selected as these best fit the AMAX daily flows in both cases, and the GU flood frequency curve plots in the middle of family of probability distributions. Also, Gumbel or Log Pearson III analyses is the preferred method as outlined in the ERA (2001) provided there is at least 10 years of continuous or synthesized record for 1:10 year discharge estimates and 25 years for 1:100 year discharge estimates.
The design flood flows estimated from flood frequency analysis for the Megech and Gumera River for various return periods are tabulated in the following Tables 6-2 & 6-3:
Table 6-2: Design flood flows for Megech River
Discharge return period, T
Design flow LEV(m s-1)
3
Design flow GU(m s-1)
s
Q2
151
123
Q5
229
232
Q10
281
295
Q25
346
372
Q50
394
428
Q100
442
483
Source: Feasibility Study Report of Megech Pump (ROBIT) Projects, by Halcrow & GIRDC: 2011 Table 6-3 : Design flood flows for Gumara River
Discharge return
period, T
Design flow LEV
(m s-1)
3
Design flow GU
(m’s-1)
Flow upstream of main canal
(GU)*(m s-1)
3
Q2
37
34
38
Q5
62
86
96
Q10
78
116
129
Q25
99
152
170
Q50
114
180
199
Q100                                129
206
229
Source: Feasibility Study Report of Megech Pump (ROBIT) Projects, by Halcrow & GIRDC: 2011
Design flood hydrographs
Rainfall runoff modelling is used to transform the design rainfall to design flood hydrographs for a range of return period floods using rainfall runoff models in HEC-HMS version 3.2 Hydrologic Modelling Systems software. The rainfall excess is estimated based in the methodology known as Curve Number (CN) developed by the Soil Conservation Service (SCS). For the rainfall runoff transformation, the unitary  hydrograph methodology  developed by  Clark  (two parameters) was used. For the routing of flood waves in channel sections, the Muskingum- Cunge method was applied.
This methodology uses CN to estimate catchment retention which is estimated based on the Ministry of Water Resources ETHIO-GIS digital soil map, as well as FAO land use and land cover datas obtained from different topographic maps and field observations. This approach is widely  used in estimating effective rainfall and design hydrographs. Specific  catchment characteristics are needed to generate flood hydrographs in HEC-HMS rainfall-runoff models. Sub-catchments are created to account for the spatial variability of the hydrological process. Catchment characteristics are determined from the DEM acquired from SRTM (Shuttle Radar Thematic Mission) data with a resolution of 90 m . Catchment characteristic determined from
2
the DEM include: Catchment boundaries; Catchment area (km2); Length of the longest watercourse (km); and Catchment average slope (m/m). Each catchment is schematized into sub-catchments based on their drainage network. On the Megech River Muskingum and Cunge hydrological routing is used to phase the tributaries hydrographs together and then propagate the flood wave downstream.
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The Megech River has a catchment area of 725 km2 and at the Megech dam the contributing area is  about 425 km2 and an elevation range from 1,900 to about 2,950 mask  The main tributary  upstream of the dam is  the Angerb River. Downstream of Megech dam there is  a
significant right bank  tributary  of the Dimaza River (92 km2) which enters  the main Megech River just upstream of the gauge station. Further downstream the Berg river (71 km2) joins the Megech in its  mid-section, and a right bank  tributary  (85 km2) joining in its  lower section just north of the command area. This  combined with area of catchment through command area totals  85 km2. The Shenzeli and Gumara rivers  are represented as  lumped catchments. Each river or reach is  represented using Muskingum and Cunge routing in order to propagate the flood wave through the command area.
Improved flood protection is requires through the command area along the river courses of the Megech, Shenzeli and Gumara. The HEC-HMS hydrological model is  used to generate the hydrographs for a range of return period design storms for locations upstream of the proposed main canal which borders  the command area. The rainfall-runoff models  are set up using the catchment characteristics, applying rainfall hyetographs  based on design depths  with durations set to the estimated Tc for each catchment. Hydrographs are fed into the hydraulic river models to determine peak  water levels  along these rivers  as  they  pass  through the command area. Estimated flood flows from rainfall-runoff models for the three main rivers for each return period are tabulated in Table 6-4 below. The design flows  for the Megech River take into account future attenuating effects  of the upstream Megech storage reservoir currently  under construction. Encouragingly, design flows  for the Gumera river estimated using rainfall runoff modelling, when compared to flows estimated from flood frequency analysis, has a difference of only +9% and +10% for the 1:50 year and 1:100 year, respectively
Table 6-4 : Design flood flows
Discharge return
period,T
Design
Megech*(m’s-1)
Design
Shenzeli(m’s-I)
Design
Gumara(m s-1)
3
Q2
46.9
23.9
24.9
Q5
95.6
65.7
69.3
Q10
129.5
95.2
101.9
Q25
173.2
130.6
145.4
Q50
206.8
159.3
179.6
Q100
240.8
188.6
215.0
Source: Feasibility Study Report OF Megech Pump (ROBIT) Projects, 2011
III. Design Review Report of Megech Seraba Pump Project by BRL in Association
with GIRDC & ADSWE: 2012
Feasibility  Study  Report for Megech Seraba Pump Project prepared by  Tahal Engineering Consultants  was  reviewed and revised by  by  BRL-GIRDC. The Megech PCA part of the Dembia Floodplain consists  mainly  of recent alluvial deposits  from a series of rivers of which the main rivers flow from North to south are:
•   Old Megech River at the eastern boundary,
•   Nededit River in the middle,
•   Dirma River in the western part
All the river flood during the rainy season and carry huge quantities of sediment load, which are deposited along their banks and in the buffer zone near the Tana Lake Peak flows on major :n?rarnXSa“y **** "’r°USh
•   Rational method for catchment smaller than 0.5km2;
•   SCS or Curve Number method for catchment from 0.5km2 up to 50 km2
Topographic Survey in Lake Tana Sub-Basin Floodplain Areas------------ -------------------------------------- -------------- ---------------------------------------------
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• More complex hydrological models for catchment of more than 50 km2
The peak flow of Dirma River was done using SCS UH method in feasibility study, however this method is recommended for catchment area in between 0.5 km2 and 50 km , but catchment area of Dirma River at its outfall at Lake Tana is about 550 km2. It should be noted that use of the CN method for such catchment generally leads to overdesign. For such catchment areas it is  recommended to determine peak  flows  through either hydrological modelling or frequency analysis  of observed annual peak  flows. The hydrological model is  selected and the final analysis output described using the following graph.
Source: Design Review Report of Megech Seraba Pump Project by BRL in Association with GIRDC& ADSWE
6.4 Hydraulic Modeling
The  following  are  the  summary  of  the  hydraulic  model  done  in  previous  studies  in  the  target area, as referred by the consultant:
I.          Flood Risk Mapping Consultancy for Pilot Areas in Ethiopia (ENTRO 2010) by RIVERSIDE, TROPICS CONSULTING ENGINEERS and SHEBELLE CONSULT
The Hydrologic  Engineering Center River Analysis  System (HEC-RAS) program was  used to perform both one-dimensional steady  flow and one-dimensional unsteady  flow analysis  The unsteady  flow analysis  was  added at the request of stakeholders  to determine the effects  of storage in the basin on the inundation extents and to evaluate the duration of flooding. The four rivers  tributary  to Lake Tana used the lake as  the downstream boundary  condition, with an evaluation of appropriate lake levels  corresponding to various  return period flows  for the tributaries; RAS-Mapper was  used to predict inundation extents  and water surface elevations including information on depths  and velocities  that enable identification of flood hazard areas for floods up to and including the 100-year return flood event. Also HEC-RAS provides the
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means  to  generate  predictions  of  flow  velocity  in  the  channel  and  across  the  floodplain  under flood conditions and will thus produce useful hazard data for this risk assessment.
As  described in summary  of Hydrological Modeling of the report, four tributaries  to Lake Tana were included in the hydraulic  analysis, the Rib, Gumera, Dirma, and Megech. The upstream extents  of the modeled reaches  were estimated at locations  where the historical flows  would not overflow the channel banks  and create significant flooding. These upstream extents  were determined during the field survey & the selection was verified by the hydraulic modeling.
Combination  of  Arc-GIS  and  HEC-GeoRAS  were  used  to  create  geometry  input  files  for  the HEC-RAS  models.  The  river  centerline,  bank  lines,  flow  paths,  levee  alignments,  and  cross sections were digitized  in  HEC-GeoRAS  to  match  the  channel  centerline with field survey data. Once  the  digitization  process  was  complete,  the  HEC-GeoRAS  data  was  imported  into  HEC- RAS.  To  develop  the  hydraulic  model,  an  attempt  was  made  to  identify  appropriate  flow  paths that would be expected in the portions of each floodplain that are at an extended distance from the rivers, and to draw the cross sections in such a way that they would be perpendicular to the flow, should it extend that far in such a way that the water surface across the width of the cross section could be expected to be at the same elevation.
In Fogera Plain, the Gumera River model reach is 37 km long and contains 118 cross sections with an average distance between cross  sections  of 320 m while the Ribb River model is comprised of the following two separate reaches  connected by  a lateral structure that represented the existing ground between the two reaches;
•   the current Ribb River which is 30 km long and contains 90 cross sections with an
average distance of 330m between cross sections.
•   the old alignment of the Ribb which is 21 kilometre long and contains 36 cross sections 
with an average distance of 580m between cross sections. This reach is to model the interception of run-off by the old Ribb River as well as to represent overflow from the
main Ribb River into the old alignment of the river during high flow conditions.
Also in Dembia Plain, the Dirma River model reach is 32 km long, contains 225 cross sections with an average distance between cross sections of 142 m. The Megech River model reach is 15 km long, contains 68 cross sections with an average distance between cross sections of 220 m. A separate hydraulic model reach was defined for the central portion of the Dembia plain is drained by  a separate channel that originates  within the plain and has  a small drainage area, but which is  potentially  inundated by  flow from the Dirma River, so connected to Dirma River with lateral connections.
A combination of ineffective flow, levees  and blocked obstructions  were used to reflect flow to the effective flow areas  of the cross  section for both left and right Floodplains. Structures  like Bridge and lateral structures  observed during survey  were also included in the model: two bridges  on the road connecting Woreta and Bahir Dar in the hydraulic  model areas  of the Fogera Plain, on the Ribb River and the other on the Gumara River. The bridge parameters 
oX6
d based °" the results of ^e field survey and the elevation model was used to
mnd2?And nnfnn r bL P Fl°odp,ain In addition three lateral structures, two on Dirma river model and one on Ribb River model were included.
XTs^XpX233^^»± ,
vvaterbuppiy Haper 2339 (Arcement and Schneider, 1989). Peak flow data for ? s m sn and
d US!?9c,LO,h field survey and a melhod °‘-»<’d in USGS
100 year discharges were used for the steady flow analysis and th J f
t 2’ 5’ !°’ 5O’an°
elevations were used as the downstream
at d the Lake Tana water surface
periods corresponding to the various return nArinri Ik nd,f,ons us,ng lake levels with return
for both high and low lake levels in each of tha riv
each of the rivers indicated that the effect is not significant.
O fl°*t A° analysis of water surface profiles 
Topographic Survey in Lake Tana Sub-B^nHoodplain Areas'
Final Report 36GIRDCCf-p__________________________________________________________________ MOWIE-TBIWRDP
By the time peak flows reach the area of influence of the lake in the channel and floodplain, the flow has spread sufficiently to exhibit large flow areas and low velocities.
II.    Feasibility Study Report OF Megech Pump (ROBIT) Project by Halcrow&
GIRDC-.2011
Flood hydrographs of varying return periods are fed into the hydraulic river model constructed using ISIS software to represent the main rivers intersecting the project area. ISIS models (Halcrow’s in house 1D hydrodynamic modelling software) are constructed for the new Megech, Shenzeli, Gumara, Sara, and the Wayin Areb rivers. In the ISIS models the river channel are represented using river cross section surveyed at between 250 and 500 m intervals. The upstream ISIS model limit for each watercourse is the main irrigation canal. The ISIS model for the upstream portion of the Shenzeli River about 4 km was extended up to the main canal using interpolated sections. Model attempts to represent the river floodplain interactions in the Megech (Robit) command area. The floodplain for the most part is schematized mostly using extended river cross sections, and in their lower portions by reservoir units; areas where flood water pond.
Elevation data used to extend river cross section in to the floodplain and to produce the stage volume curve used in the reservoir units is taken from the digital elevation model (DEM) of the Megech project area generated from the topographical survey. Reservoir units were typically only used to represent areas adjacent to river channels and Lake Tana. Spills connect these reservoirs  to  river  cross-sections,  and  a  spill  connects  the  reservoir  into  a  boundary representing Lake Tana; spills allow water to move between model units. Roughness or manning values for the model were selected based on photographs of the site, and personal accounts from site visits. Values of 0.03 were selected for the channel, and 0.05 for the floodplain. The models downstream boundary is Lake Tana. Since its construction in 1996 water levels in Lake Tana have been controlled by the Chara-Chara weir. Peak lake levels tend to peak in October following the rainy season. Analysis of the peak water level records show that water levels in September, one of the month during which peak river flows tend to occur, are typically about 1787 masl. Therefore, this level has been used for the downstream flow boundary to represent the effect of a high lake level coinciding with a large flood event. The existing ISIS river models that represent the current conditions were modified to represent the semi-retired flood protection bunds along the river courses. Models are run for the existing conditions (assume Megech dam in operation) and for after flood protection scheme in place. The water levels above the heights of river banks after the flood bunds are put in place within the  models  are  used  to  determine  the  actual  height  of  the  required  flood  protection embankments plus freeboard.
III.    Design Review Report of Megech Seraba Pump Project by BRL in Association with GIRDC and ADSWE:2012
Since the Old Megech River does not spill over its banks as the active river changed its bed and dam is under construction in the upstream part, it can as such be accepted not to propose flood protection banks along the Old Megech River. So the detailed Design Report limits river training works to Dirma and Nededit Rivers. The hydraulic design of the river training for main river and small gullies have done using HEC-RAS software and manning equation on excel program; the cut part was designed for Q 5years and the fill part of composite section was designed for Q 10 years.
6.5 Flood Prone Areas Assessed From Different Study Reports
The project area, the Dembia & Fogera Floodplains lies within the natural drainage basin of Lake Tana fed by different main rivers including Dirma & Megech in case of Dembia Floodplain and Gumera and Ribb in Fogera Floodplain. The Lake Tana area floodplains are described using figure 6-4:
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
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Flood affected area for Fogera and Dembia Floodplains  are described in different sources/Flood studies reports as different area extent. Some of the sources that described the flood affected area in Fogera and Dembia Wereda referred by consultant are summarized as follows:
I. ENTRO- Project Preparation, Flood Preparedness and early Warning Study; 2006
by SMEC International for ENTRO
According to this report, particularly Flood prone areas in the Fogera Floodplain that are most at the risk by flooding are located between the Gumera and Ribb Rivers which covers almost quarter of the Woreda, 6-7 kebeles: Shana, Kuhar Mincheal, Abena Kokit, Wagtera, Kidist Hana, Nabega, & Shaga kebeles in Fogera Wereda, South Gondar Zone and Shana Tsion, Bambik, Gendassa, Tega Amba, Kaba, Tebaga, Bura and Agidana Kiring kebeles are those most devastated in Libo Kemkem Wereda, North Gondar Zone while in Debimbia Woreda of North Gondar, the kebeles most affected by flood are Tana Woyina Abo, Achera, Robit, Debir Zuriya Adisge, Arebiya Kesge Aba Libanes, and Gurama amba Mikael.
Topographic Survey in Lake Tana Sub-Basin Floodplain Areas
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II. Flood Risk Mapping Consultancy for Pilot Areas in Ethiopia (ENTRO 2010) by
RIVERSIDE, TROPICS CONSULTING ENGINEERS and SHEBELLE CONSULT
Both result of steady and unsteady hydraulic models indicated very similar flood elevations and extents  of the prone areas. The unsteady  model simulates  the attenuation of peak  flows, but the resulting reduction in peak  flow is  not large in percentage terms  perhaps  because total hydrograph volumes  are large enough to fill storage areas  on the rising limb, leaving only modest incremental volume to store and attenuate peak flows. Moreover, because of the large flooded area, differences in peak water level are even less noticeable than differences in peak flows  between the steady  and unsteady  models. These differences suggest that, for purposes of future flood risk  assessment and mapping, uncertainties  associated with the simplifications required for steady  modeling are not large; however, the steady  model appears  to provide reasonable estimates of flood depths and velocities, the results from the unsteady models are useful in assessing the duration of flooding at multiple locations within the floodplain.
In Dembia Floodplain, the model results  for the Dirma River show that during a 2-year flood water start to cross  from the Dirma Basin into the Dembia middle basin (Shenzli River) and during larger flood events significant amounts of water flow into the Dembia middle basin. This flood water, in combination with local runoff from the middle basin results  in large inundated areas  in the Dembia floodplain. The modeling results  for the Megech River show that flood waters not only follow the Megech River towards Lake Tana, but also use a flow path west of the River. During the 2-year flood some minor flooding alongside the river and western flow path should be expected, whereas  during the 100-year flood, significant portions  of the floodplain are inundated in both the eastern (left) and western (right) floodplains.
In Fogera Floodplain inundation maps of the Gumera River indicated that flooding is expected in the overbanks  relatively  close to the river. During the 2-year flow the inundation area is extensive, but flooding depths in most locations are limited to approximately half a meter and during the 100-year flow, some additional areas are flooded, and the flooding depth in certain areas is in excess of two and a half meters. These uniformly large flow depths suggest that the channel should remain relatively stable and is unlikely to experience a major re-alignment that would result in abandonment of a large length of the channel. The inundation maps of the Ribb River indicate that flood of 2 year occurrence interval has  significant flooding along the alignment of the current Ribb River and the 100 years outflow of the Ribb River is more than six times larger than the 2-year flow but the difference in water elevation between the 2-year and the 100-year flow is on average considerably less than a meter. Moreover, due to the flat terrain the flood waters spread considerably, resulting in large inundated areas.
IV. Feasibility Study Report OF Megech Pump (ROBIT) Project by Halcrow &
GIRDC:2011
Flood mapping is carried out using ISIS Mapper an extension of the ISIS (Halcrow's in house 1D hydrodynamic modelling software) river software. Modelled maximum water levels are used to generate a flood water surface as a Triangular network model (TIN). ISIS Mapper generates flooding extents by intersecting the DEM with the TIN for a given return period. Flood mapping approach maps flood water within river cross sections, and flood water stored within reservoirs. It does  not, however, map overland flow routes  represented in the model by  spills  and floodplain sections. These flow routes  were incorporated by  editing the flood extents  to represent the likely flow path, based on model maximum water levels and the topography. The extent of the 1:50 and 1:100 year return period flood in the command area under existing conditions has exhibited no significant difference for the 1:50 and 1:100 year return period flood in the command area under existing conditions is shown in Figure 4-5
Notable features  of the modelling include the interaction between the Shenzeli and Gumara Rivers. Spilling between the two channels in the upper reaches of the model sees significant volumes of water passing from the channel of the Shenzeli into the Gumara in the command
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
Final Report 39GIRDcOr*______________________________________________________________________________ MOWIE-TBIWRDP
are. This  can in part be attributed to the channel connecting the two water courses; however the majority  of the water spills  across  the area between the watercourses  upstream of this connecting stream. As  a result flows  in the lower Gumara are much higher than flows  in the lower Shenzeli, leading to large scale out of bank flooding for the former and limited out of bank flooding for the latter. Flooding from the Megech River is  significant on the left bank; however, the long embankment on the right bank  prevents  anything other than localized flooding on the right bank. For all return periods  the channel through the village of Robit contains  the flow, though a significant proportion of the flow passes down the flow route to the east of the village. For lower flows the main river channel takes the majority of the flow, whilst for higher flows the majority flows to the east of the village (see figure 6-5).
T
*
w
Ml
to
to
6.6 Other Studies
to
WVE, Lake Tana Area Flood Protection Work  Impact Evaluation, by  GIRDC 2010 was  also reviewed. The project was  aimed at mitigating and minimizing vulnerability  of the community from flood disasters  and risks  through provision of physical and biological flood mitigation measures  on three major rivers  (Gumera, Rib and Megech Rivers) and their tributaries, which include de-silting, construction of embankments, biological measures, and redefining river courses  so as  to prevent damage on lives  and livelihoods  of community  while preserving the environmental benefits  of floods. This  study  indicated that flood marks  of larger return periods need to be identified during surveying works around these rivers.
It  is  indicated  in  the  study;  the  overall  impact  of  the  project  was  evident  in  number  of  people, livestock,  area  of  farm  and  grazing  land,  physical  and  social  infrastructures  protected.  As  a result  182,754  people,  110,923  heads  of  livestock  and  16,955ha  of  farm  land  have  been protected   through   construction   of   about   97   km   of   dykes   and   related   interventions.   The effectiveness of the dykes varies from one woreda to the other and also within a woreda. But in general,  the  areas  under  consideration  have  been  effectively  protected  from  the  havoc  of  flood disaster.  However,  some  breaches  have  been  observed  which  have  affected  few  hectares  of cropland   but   caused   no   human   and   livestock   displacement.  Some  of   the  causes  of  such breaches  are;  instability  of  silty  river  banks,  abstraction  of  river  water  to  irrigate  by  gravity  and motor  pumps  by  cutting  across  the  dykes  and  banks,  heavy  deposition  of  silts  under  bridges, heavy  flooding  during  peak  discharge  and  lack  of  cross  drainage  works  for  streams  and  flows from  adjacent  catchments.  Such  incidences  are  expected  from  the  emergency  nature  of  the project.
to
Topographic Survey in Lake Tana Sub-Basin Floodplain Areas
Final Report 40GIRDC O1-^
MOWIE-TBIWRDP
Lake Tana sub-basin Dams (GligelAbay, Jamma, Rib and Megech) and Irrigation development study  and design project 2009/10 by  WWDSE in association with Tahal, GIRDC and other National Consultants for MOWIE and Gumera dam and Irrigation Project feasibility Study; 2008 by WWDSE in association with ITC India and GIRDC and other National consultants were also reviewed.
The study  concentrated on water resource and Hydro-metrological analysis. Moreover, both studies  revealed that the construction of the storage dams  in the upstream will mitigate the prevalent flood hazards  in the downstream. To this  end the construction of Megech and Rib dam is ongoing which will contribute to reduced flood hazards in Dambia and Fogera Floodplain respectively.
Last but not least Lake Tana Bathymetric Survey; 2012 work was also reviewed. The main work which was  the bathymetric  survey  of Lake Tana enabled to know the lake water level and checked maximum elevation of the lake. They  made both lake level survey  and topographic survey of the lake shore. The current topo survey work has linked their BMs.
6.7 Existing And Ongoing Flood Protection Works
Different biological and physical measures that have direct or indirect impact on the flooding to bring relief from flooding problems have been proposed, some of them were constructed and others  are under construction. Some of flood remedial works  taken in and the vicinity  of the Flood area include:
Dyke along Gumara and Bwaza Rivers in Dara Wareda
Construction of dykes using largely de-silted material from the river course was proposed and constructed by  International NGOs  and government along Gumara and Bwaza Rivers  in Dara Wareda. Five crossings/foot bridges  were also planned across  Bwaza River and four of them were completed. Large part of the dyke is constructed with relatively sizable berm and it is in satisfactory condition. However, tendencies of silting on the inner side of the curve and erosion on the outer side are visible. To stabilize the river banks and dyke slopes, planting of grass and shrubs  were recommended and planted. However the following problems  were observed after dyke construction:
•    Instability  due  to  silty  river  banks  of  Gumara  particularly  around  the  curves  while  it meanders which increases the width of the river helping in mitigating the flood which would have resulted in loss of land.
•    The  consultant  realized  that  the  flood  protection  dykes  and  embankment  works  were not  based  on  standard  designs  and  specifications.  Of  all  the  structural  works  are not compacted and subject to light flood and human impact damages.
•    Pumped irrigation is quite common along Gumara River in the dry season. When the suction  head  substantially  increases  due  to  the  dykes,  the  farmers  cut  through  the dyke  making  it  vulnerable  to  the  next  flooding  unless  it  is  plugged  before the  floods see figure 6-6.
• • •   ’
c
, I
• ' * . *• "*
Topographic Survey in Lake Tana Sub-Basin Floodplain Areas
-<*
Final Report 41GIRDCO-f^
MOWIE-TBIWRDP
Figure 6-6: Cut through dykes by Irrigators to minimize
umping head and pipe length
•  Lack  of  cross  drainage  works  for  streams  and  runoff  flows  from  adjacent  catchments is  also  one  of  the  problems  that  cause  ponding  of  water  and  dyke  failures  at  some sections.
Dyke along Ribb Rivers in Fogera Floodplain
Dykes  using largely  de-silted material from the river course was  proposed and constructed along Rib Rivers  in Fogera Floodplain. In order to stabilize the river banks  and dyke slopes, planting of grass  and shrubs  were recommended and planted. The rate of survival of the dykes and biological measures  is  low due to limited care and protection given by  the community  and open grazing practiced in the area, See Figure 6-7.
Source: Lake Tana Area Flood Protection Works Impact Evaluation, 2010 by GIRDC for WVE
Topographic Survey rn Lake Tana Sub-Basin Floodplain Areas
Final Report 42GIRPCO'T*'________________________________________________________________________ MOWIE-TBIWRDP
Construction of Megech Dam, river trainings and drainage system
As discussed above the construction of Megech Dam (ongoing) on the Megech River will bring some relief from flooding problems on Floodplains area when completed. Also construction of river trainings and drainage system proposed and under construction to protect the command area of Megech gravity project has a positive remedies on problems arise due to flood.
Construction of Ribb Dam, River trainings and drainage system
Like Megech gravity  project, the Ribb project which is  on the construction consist of Dam, headwork, river trains  works  and drainage system to protect the command area which will reduce the magnitude of peak flood in the target area and also will mitigate the flood during peak flow.
Construction of River trainings Works and drainage system in Megech Seraba Project
In order to protect the command area of Megech Seraba Pump Project command areas Drainage and Flood training works have been designed and on construction along the Dirma River, small river like Kirist and other small gullies in command area. Therefore parts of the Floodplain areas  which are found on the left side of Dirma River in Seraba PA will later expected to be relieved from flood.
Proposed  Construction  of  protection  bunds  along  new  Megech,  Shenzeli,  and  Gumara Rivers by Megech Robit project
Flood protection bunds were proposed along new Megech, Shenzeli, and Gumara Rivers for 50 and 100 years return period flood peak in the command area of Robit Megech project and the extent of 1:50 and 1:100 year return period flood after construction of bunds are shown in figure 6-3. It is clear that when flood protection bunds are in place the flooding is significantly reduced and is contained within the flood channel (see figure 6-.8 and 6-9).
Source: Feasibility Study Report OF Megech Pump (ROBIT) Project by Halcrowi GIRDC: 2011
The areas benefiting from the flood protection bunds can be seen on the figure 6-4 (in white color) and is a huge benefit to the communities. The benefits are include: (i) a lower risk to people from flooding; (ii) a reduction in damage to settlements and infra-structure; and (iii) a reduction in crop losses and gullying, and together with drainage will prevents environs which encourage waterborne diseases (i.e. malaria, and schistosomisis).
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
Final Report 43GIRDCC-y
Figure 6-9 : Area benefiting from defenses in project area
MOWIE-TBIWRDP
Source: Feasibility Study Report OF Megech Pump (ROBIT) Project by Halcrow & GIRDC: 2011
6.8 Recommendations
•      While   doing   hydrology   and   hydrological   modeling   in   next   assignment,   the   main tributaries   (like   Dameza,   shinta,   Angrebe...etc   for   Megech   River,   the   corresponding main  tributaries  for  Dirma,  Rib  and  Gumera)  missed  in  the  currently  reviewed  reports should be incorporated.
•     Better  if  more  Hydro-metrological  data  and  river  data  like  the  gauging  station  data  at Kola Deba Town Under the Bridge should be incorporated in analysis
•     Better to use 30m resolution currently available in public domains over the 90m x 90m resolution   for   hydrologic   modeling   and   catchments.   Also   preferable   if   more   finer resolution land cover data will be used for analysis.
•    As  described  in  review  parts,  hydrological  and  hydraulic  modeling  have  done  using  1D modeling, but despite the complexity of the modeling better if 2D modeling will be used for the next assignment so that the real situation is more described with accuracy.
•     Almost  in  all  of  the  work  done  in  target  area,  only  the  negative  impact  of  flood  is assessed,  but  better  if  the  positive  impact  will  also  assessed  and  it's  findings  will incorporated in final recommendation for flood protection.
•      The   flood   protection   structures   to   be   practiced   should   be   to   the   standard   and compacted
•      The   flood   protection   works   implemented   in   the   area   indicate   that   dykes   were constructed  in  area  without  considering  interest  of  farmers  especially  to  divert  water  for irrigation  during  dry  time.  As  a  result  farmers  dig  the  banks  to  minimize  the  suction head  of  the  pump  (figure  6-6).  Therefore  consultation  should  be  made  with  the  farmers and structures to allow diversion of water included in the design and construction.
•    Rehabilitation of existing flood protection works, periodic and regular maintenance of the flood protection works shall be in place
•    Hydrological modeling and Storage Reservoir operation system should also take into account downstream flood occurrences.
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
Final Report 44girdcG1
7 TOPOGRAPHIC FIELD SURVEY WORKS
7.1 General
MQWIE-TBIWRDP
Detailed topographic surveys were done for the existing features on the ground such as rivers/channels (old and new or existing river courses), congested areas, embankments, and boundaries of features (like Lake Tana in the pilot Kebeles’, settlement areas, hills and the like), depressions, swampy areas and other relevant features in the project areas. As discussed in section 3 above, the topographical survey works include among others the following main survey works:
•    Identification and Transfer of Ground Control Points/GCP/ from the national grid located in and around the project area to the survey sites;
•    Establishing permanent Bench Marks at appropriate scale and points (two at each
station);
•    Detailed topographic survey of flooded project area;
•    Detailed topographic survey of the existing & old river route/courses;
•    Detailed topographic survey of alignments of dike, swamp area,etc.;
•    Topographic surveys of natural drainage lines, river cross section survey, and
•    infrastructures like villages, school, churches, clinics/health centers, etc.;
•    Other survey works
Detail activities of each are discussed as follow.
7.2       Linking of gcp Of EMA and Establishment of permanent control points 7.2.1     Identified EMA GCPs
EMA GCPs were identified from the National topographic maps, in discussion with EMA and from reconnaissance field assessment and transferred to the project area and then established new permanent GPS points. Such primary control networks should be better of a density that optimizes but does not compromise the Real Time Kinematic (RTK) GPS telemetry, i.e. the control stations were selected such that they are not more than 20km apart (two GCPs per project). This is because the RTK GPS radio telemetry cannot extend beyond approximately 15km without line of sight. Of several EMA GCP around Lake Tana and Gonder area; only four were found at the time of survey on the ground and these were procured from EMA (see Table 7-1 below and Figure 7.1). The others identified ten primary BM points do not exist on the ground probably owing to soil deposition and dense vegetation coverage, destroyed by farmer while ploughing, vandalism and/or other reasons.
Table 7-1: Locations of Identified EMA GCPs around the Project Area
EMA's
National BM
EASTING
NORTHING
ELEVATION
REMARK
Identified for
BPN51
323959.730
1282424.937
1787.771
Bahir Dar
Yifag
348618.800
Fogera FP
1340427.257
1833.00
Near Fogera
BNP56
317638.897
1291685.042
1785.40
Near Zege
BNP39
313986.733
1368473.957
1868.10
Between Kola Deba & Gorgora
BNP41
323686.590       1375497.253
2018.30
Between Kola Deba & Gorgora
Source: Procured from EMA
These specifically at: GCP Stations BNP51at Bahir Dar BNP56 at Zege, and the other at
Dembia FP
• •- -
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
Final Report 45GIRDCfr-y__________________________________________________ _______________________MOWIE-TBIWRDP Yifag were identified for Fogera FP topographic survey. However, the reading of GCP BPN 51 at Bahair Dar was found unstable due to unknown reasons and later on canceled.
Stations,  BNP  39  and  BNP41  GCP  in  between  Kola  Diba  and  Gorgora  were  identified  for Dembia FP topographic survey. Location of the GCP is shown in Figure 7.1.
7.2.2      Unking EMA GCP and Establishing Permanent Benchmarks
The assigned survey crew for GPS survey works have linked the identified GCPs to our project area and established permanent BMs  using differential RTKS GPS. Several permanent benchmarks were established being founded on the established GCP which is fixed again in reference to the national benchmarks  of EMA. The locations  of benchmarks  have been selected based on relative locations, accessibility, convenience for conducting any  other topographic survey tasks and the extent of the intended ground survey requirements.
After linking these EMA's  GCPs  to our floodplain survey  area, we then established two permanent control points at each site, readings of which were taken with the following features (based on source data):
•   Grid:                                                  UTM zone 37
•  Projections:
•   Spheroid:
Transverse Mercator
Clarke 1880(Modified)
•   Unit Measurement
Metre
•   Meridian of origin:
39° 00 East of Greenwich
•   Latitude of origin:
Equator
•   False Coordinates of origin:
Easting -500000 m
•   Northing:
Nil
•  Scale factor at origin:
•   Datum:
0.9996 Adindan (30th Arc)
Reasons behind our selection of GPS system were:
•   Position or X, Y, Z coordinates of points can be determined directly with high accuracy.
•   Indivisibility between ground station is unnecessary
•   Measurement may be carried out, day and night anywhere in the world at any times in any type of weather condition
•   Able to provide the service to an unlimited number of users
•   Low cost, low power but high quality surveying
In general, with this  selected coordinate system we have established a network  of new permanent primary benchmarks throughout the project area at an average distance of 2km interval, each of which is tied in to the nearest Primary National EMA GCP. The 2 km interval of the BMs is selected for this level of detail/scale and considering the topographic nature of the Floodplain. It has to be known that EMA even for cadastral survey in towns where there is dense housing and infrastructure uses 1 km interval BMs. Based on this appropriate level, 89 primary permanent benchmarks' were established for Fogera Floodplain. In here few of them have been located as additional outside of the project area aside and east of asphalt road crossing the project boundary for safety as the installed ones were under destruction by
Topographic Survey in Lake Tana Sub-Basin Floodplain Areas
Final Report 46GIRDCCf f~*
MOWIE-TBIWRDP
local people. Similarly  42 primary  permanent benchmarks’ were established for Dembia Floodplain areas. On top of this, we have checked and re-established some of previously established permanent benchmarks (i.e. for bathymetric surveys as available on the ground) relative to the newly permanent primary benchmarks established throughout the project area.
The established BMs are in concrete poles being nails drilled and buried on it or on rock when available and painted. Description & Photos  of all these BMs  locations  as  confirmed and established in the field with their findings are presented in a tabular form in Appendix-1 and Appendix-2 for Dembia and Fogera FP respectively of this final report.
>
I
Topographic Survey In Lake Tana Sub-Basin Floodplain Areasmowie-tbiwrdp
GIRDCOt~t~>
Final Report 48Notes :
331000
336000
341000
346000
351000
361000
366000
371000
376000
1.  ALL DIMENSIONS AND ELEVATIONS ARE IN METERS UNLESS OTHERWISE SHOWN.
2. DESCRIPTIONS OF FEATURES AS SHOWN
IN THE LEGEND.
1355000
■
1350000
1350000
1320000
1315000
0     4000       8000       12000     16.000 20.000m SCALE 1400,000
CL,ENT; @
FEDERAL DEMOCRATIC REPUBLIC OF ETHIOPIA
MINISTRY OF WATER IRRIGATION AND ENERGY
LEGEND
-Lake Tana Boundary -Island
—River
-Road
A -EMA GCP BMs 
-Bathymetric BMs -Proposed BMs 
for floodplain (2) -Towns
PROJECT:
TBIWRDP
TOPOGRAPHIC SURVEY IN LAKE TANA SUB BASIN
FLOOOPLAJN AREAS
1290000
SRaWMG TiTlE------------------------ -------------
LOCATION OF EMA GCP AND PROPOSED BMS
1280000
301000       296000       291000      286000       281000
316000       321000
336000
341000       346000       351000       356000       361000       366000       371000
1275000 376000
DESIGNED A 2
CHECKED 7c”
SCAIE. AS SHOWN
DRAWING No
DRAWN: 8 K
APPROVED AC
DATE: Oecambor.2014
FIGURE 7.1
SHEET NO
1OF1*?
r .          -•
■
-i
n
n
IGIRDCOy
MQWIE-TBIWRDP
■ft
7.3 Detail topographic survey works
7.3.1     Adopted Survey Technique and procedures
In detailed topographic survey works, we adopted a static survey, where a reference point is chosen and one or more rovers  were allowed to operate with respect to it. Typically, Rapid Static Technique was used for increasing density of data in existing networks, for establishing control points, etc. After the main control survey points were observed and completed, these detailed survey works were carried out both in Dembia and Fogera FP in order to pick natural floodplain features for topographic mapping.
This survey was carried out in grids of 50m by 50m to 25m by 25m in some flood hot spot areas, depending on its necessity on terrain features as it varies from location to location. In some areas additional points were also taken in the middle depending on encountered ups and downs of land features such as depressions and/or hills. We also collected spot levels within the project areas  at edges  of the proposed grids  and within the grids  depending on its necessity. Refer for the detailed topographic surveyed data carried out in the project area in Appendix-4 of this report.
In carrying out this detailed topographic survey, we used positioning accuracies of:
•   U+l-2 H: 3mm + 0.5ppm and V: 5mm + 0.5ppmin Static Method
•   Lj+L2 H: 10mm + 1ppm and V: 15mm + Ippmin RTK Method
In case of Fogera FP site we
•   Started from BMS DAR- BM Hamusit 25 km Air distance and data were captured at 1 second interval with in 3:30 hours
•   From BM HA (Hamusit town) - Bend of woreta-welidiya Road/WWR BM 25 km
captured data at 1 second interval within 3:30 hours
•   From WWR BM to BM10 11km Air distance captured data at 1 second interval within
2:30 hours.
In case of Dembia FP site we:
•   Started from JANGS BASE BMS, to M001-BM 13km Air distance captured data at 1 second interval with in 2:30 hours
•   From M001-BM to BM-17 1.2km captured data at 1 second interval within 1/2 hours.
•   From M001-BM to BM-16 1.7km Air distance captured data at 1 second interval within
1/2 hours.
7.3.2    Linkage with Lake Tana Bathymetric Survey data
Our permanently  established BMs  were also linked with fixed coordinates  of the Bathymetric Survey data e.g. GPS_05A of coordinates 313942.6880 E and 1353483.5324 N and height of 1832.223m Adindan UTM zone 37. The list of Bathymetric  survey  BMs  around Lake Tana shore are attached in Appendix 8 for future reference and use with the current survey.
7.4 Cross Sections Survey Works
Survey works for taking cross sections were also carried out in all the channels/rivers courses and gullies crossing the floodplain areas under consideration. These cross sections were taken from right to left while looking downstream i.e. in the direction of flow. In collecting these data
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
Final Report 51------------------------------------------------------------------------------------------------------------------------------MOWIE-TBIWRDP
we took at least five levels: river banks both left and right, river centers at thalweg points top
and bottom (on the external) of dykes and some 50 to 100m away from river banks as found
necessary. These traced center lines (profiles) of all existing drainage channels & qullies 
throughout the project area were done including mapping of the major cross sections (See
figure 7.2 for typical cross section survey on progress, 7.3 for the general layout and map for
detail actual major cross section profile).
p
To mention the major ones: cross-sectional survey of the Gumera, Rib, Megech, Dirma and other smaller streams and drainage lines at every 50m to 100 m interval and or less than this including meandering of the rivers and at 50m away from their banks on both right and left banks over a distance stretching within the floodplain project boundaries were done.
These cross section surveys were undertaken right from entrance to the project boundaries on the upstream to down the point where each river joins the Lake Tana or point where it stops in the project boundary itself. The surveyed cross sections data can be referred in Appendix-5 for both Dembia and Fogera FP.
We would like to make clear that: from the existing cross section survey over several hundreds o cross section profiles can be plotted. Therefore we recommend using these attached cross 
surveyed data; detail profiles at additional sections of denser distance/intensity can be p o e and map prepared for any required purpose during the course of flood modeling.
Topographic Survey in Lake Tana Sub-Basln Flo^^----------------------------------------------- -----------------------------------------------
FinaTReport 52MOWIE-TBIWRDP
GIRDO* t *_____________________________________________________________ ____ _—• 
Figure 7-3: Layout of Surveyed Cross Sections of Rivers courses and Gullies
'
7.5 SURVEY OF INFRASTRUCTURES
The  survey  teams  have  identified  lots  of  existing  infrastructures  in  the  project  area.  These infrastructures were surveyed in detail which included:
•    Survey  and  bounding  including  mapping  of  location  of  schools,  clinics,  churches, market places, grave areas, emergency shelters, etc. again including closing of open polygons by Handheld GPS calibrated with the traverse points and BMs
•    Survey & gap filling using handheld GPS ( of all existing main access roads or tracks) throughout  the  project  area  including  mapping  the  layout;  there  were  no  standard gravel roads observed within these survey boundaries
•    There are no permanent structures of irrigation canals laid in the survey area though temporary canals/ditches which are subjected to ploughing at every season were seen here and there which is difficult to define.
•    Similarly, temporary foot paths within crop land were observed but difficult to define their access route and then survey and present them on the map. We checked that foot paths and crossings on EMA 1:50,000 maps are in most cases not exist. We had been  convinced  that  it  is  misleading  to survey  these  undefined  temporary  footpaths and  crossings  which  are  at  times  even  changing  before  end  of  the  season  due  to claim of the individual land and village communities ownership right.
•   It has been tried to locate and survey flood depth measuring poles established by MOWIE under flood control project. However, only very few of them were observed afterward being in marshy - swampy areas. Consequently it was unable to read the points.
7.6 SURVEY OF KEBELES, VILLAGES AND OTHER AREAS
Topo survey  and delineating the boundaries, mapping of all villages/settlement areas  and other congested areas  of habitation; including closing of open polygons  by  handheld GPS calibrated with the traverse points and BMs were done.
The area occupied by Villages and associated infrastructures in Fogera Floodplain is 3,254 ha. Swampy areas and receded lake shore areas occupied 581 ha and 985.5 ha respectively. The balance area is under farm land, grazing and infrastructures.
Area occupied by  Villages  and associated infrastructures  in Dembia Floodplain is  1067 ha; whereas receded lake shore areas occupied 506 ha. The balance area is under farm land, grazing, community service and etc. (see Table 7-2 & 7-3)
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
Final Report 53GIRDCGt~t~>'
Table 7-2: Kebeles/Major Villages and Areas in Dembia Floodplain
MOWIE-TBIWRDP
Kebele & Villages surveyed
Area ( ha)
Achera
1045.23
Arebia Dibakesge
279.07
Awiha Abona
549.61
Debirzuria Adisgetsion
1950.24
Robit
91.00
Guramba Batana Chanqua
215.15
Seraba Dablo
3419.89
Total
7550.19
Seasonal water & Lake boundary (seasonal)
502.00
Grand Total
8052.19
Table 7-3: Kebeles/Major Villages and Areas in Fogera Floodplain
Kebele &" Village surveyed
Area( ha)
Kab
1141
Tezanba
1179
Genida Wuha
1380
Banibiko Sedeya
1402
Tibaga
427
Shina Tsyon
493
Nabega
2803
Tihua Enakokit
177
Shina
2041
Kdist hana
2230
Wagetera
3976
Kuhar Mikael
481
Mtslina Tansa
1121
Zarina Jegina
2767
Total
21619
Seasonal water & Lake boundary (seasonal)
986
Higher slop area
403
Grand Total
23008
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Final Report
54GIRDC Of*
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8 DATA PROCESSING, MAPPING AND VERIFICATION
8.1    Survey Data Processing
All the collected reference and roving receiver data from RTKS GPS and digital Total Stations of high accuracy level were retrieved in to LGo V 7.0 the reference station coordinates using Map source-pro software then we manually changed to the correct values as in this case initial values  are always  of low accuracy  navigated solutions  and the roving receiver data is  then processed and appropriate GPS solution is  computed using the RTK algorithm in a post processing environment. These points  were then sorted, such that all points  where integer ambiguities were not resolved are highlighted and these points are then deleted. They are then exported from LGo as comma delimited CSV files. The CSV files are then all served as tab delimited txt files. The txt files were then imported in to Terra Scan which is micro station bolt on software package.
In  processing  these  data  we  also  used  different  computer  programs  like  excel,  AutoCAD, Surfer, Terra Model, Civil designer and Leica geo office software.
Using Leica geo office tools, datum and map in the WGS1984 geographical coordinate system (longitude, latitude, ellptoidical height) were transformed in to Adindan UTM zone 37 (easting, Northing, orthogonal height or Elevation) for final adoption.
8.2    Map and Data Base Of The Survey
8 2.1 Topographic Maps
Detail topographic survey and cross section data processed above were then plotted/mapped using AutoCAD and/or Arc GIS 10.1 with the help of geo-referenced data taken in the area. A range of these maps were produced to have understanding of the floodplain areas. Overview maps  showing the whole project area on one sheet is  produced which enables  the whole scheme to be shown on a single A1 paper. The major output; detailed maps at 1:10,000 scale with control interval of 0.5m were prepared.
The followings are map output of surveying works both in hard & soft copies:
(i)  TBS/TSF&D/01; Location Map of Lake Tana Sub-basin Floodplain Areas (both Fogera and Dembia Areas) including pilot kebeles at 1:175,000 scale (in 1 sheet)
(ii) TBS/TSF/02; Location of Established Permanent BMs in Fogera Floodplain at 1 50 000 scale (in 1 sheet)
(iii) TBS/TSF/03; Topographic Map of Fogera Floodplain at1:50,000 scale (in Isheet) to show the general topographic features all together.
(iv) TBS/TSF/04; Detail Topographic Map of Fogera Floodplain at, 1:10,000 scale (in 12 sheets) at 0.5 contour interval.
r
(v) TBS/TSF/05; Cross-Sections Map of Major Rivers in Fogera Floodplain (in 2 sheets^ at H 1:1000,V 1:100 scale
1
(vi) TBS/TSD/06; Location of Established Permanent BMs in Dembia Floodplain at 1:20,000 scale (in 1 sheet).
(vii)       TBS/TSD/07; Topographic Map of Dembia Floodplain at 1:20,000 scale (in 1 sheet) to show the general topographic features all together;
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
Final Report 55
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MOWIE-TBIWRDP
(viii) TBS/TSD/08; Detail Topographic Map of Dembia Floodplain at 1:10,000 scale (in 4
sheets) at 0.5 contour interval.
(ix) TBS/TSD/09; Cross-Sections Map of Major Rivers in Dembia Floodplain (in 4 sheets) at
the scale of H 1:1000, V 1:100
8.2.2   Data Base
The following Data bases are presented
Excel data Base: all Topographic features surveyed, river cross sections data's collected, BMs, GCPs are compiled in Excel for both Dembia and Fogera Floodplains
CAD Data Base: Rivers cross sections of Dembia and Fogera Floodplains are presented in CAD. 14
GIS Data Base: MXD and SHAPE files of all maps and attributes are complied in ARC GIS10.1 for reference, further use and analysis by the client and the flood modelling experts
PDF:  All  CAD  and  GIS  maps  are  compiled  in  PDF  format  for  ease  of  retrieval,  reference, recording, printing etc.
Photographs:   Selected   photographs   of   GCP,   primary   BMs   with   description   and   geo referenced information are presented for reference.
Simplified  Data  Base  users  guides  is  prepared  and  attached  with  compiled  data  base  in separate folders and also here in Appendix 9.
8.3    Integration and Harmonization of the topographic Data Base to Flood
MODELLING SOFTWARE’S
The flood modelers  used Arc  GIS. We prepared the floodplain topographic  maps  and data base, infrastructure and other features, cross sections and profiles data's to be compatible and convertible to Arc GIS. The excel data of all features is available in soft copy and can also be exportable to different software’s to be used by the Flood Modelers.
8.4    VERIFICATION OF THE TOPOGRAPHIC MAPS WITH EMA STANDARDS
We made technical discussion with EMA surveying, remote sensing, cartography  section experts  and technicians  before commencement of the survey  work. Moreover, we verified our work  and output with EMA and other known international survey  standards  using the following procedures;
8.4.1       Verification through Linking to EMA National system
We verified the survey  works  on the ground through linking with EMA GCP by  adopting acceptable methodology  and accuracy  of linking. As  discussed above we proved that, our distance (20Km) and time of observation (3:30hrs) during GPS survey  was  more than the accuracy required by EMA and other survey standards.
8.4.2    Verification through Geometrical linking with control net works
a dopted
m of traverse closing to each point with control net works
(BMs) and other known established points. The traverse linking or closing resulted in picking
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas’
Final Report 56GIRDCOf-*_____________________________________________________________________________________MOWIE-TBIWRDP
the existing natural geometrical pattern of points and polygons. As a standard the data from topographic survey conducted without traverse closing should not be considered reliable.
8.4.3    Cartographic and Scale Verification
We have checked our cartographic presentations with EMA and other standards. This includes legend construction, symbols  of different topo features  & infrastructures  such as main roads, access, bridges, villages, schools, churches, clinics, rivers/streams, major and minor control lines representation, spot heights, delineation of boundaries, northing, grid references, map title and map No..etc.
We checked the scale of mapping and presentation of location map, topographic map at control interval of 0.5m, river cross sections...etc (as given in the map) including input data quality and quantity.
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Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
Final Report 57mowie-tbiwrdp
GIRDCCfrT*
Topographic Survey in Lake
--------- --------------- - ---------------------------------------------------- --------*'n
MOWIE-TBIWRDP
GIRDC srr
9 ISSUES AND CONSTRAINTS
9.1 General
A number of issues and constraints had been encountered during the field topographic survey.
But the consultant and the field survey team have handled most of them in discussion with the
TBIWRDP, TaSBO, Regional, Zone, Woreda and Kebele stakeholders  including the beneficiaries themselves. The team appreciates the cooperation of all the stakeholders. Major issues are presented as follow for experience and handling as appropriate.
9.2 Issues and constraints
9.2.1      Survey Boundary
MOWIE prepared Floodplain pilot Kebeles map based on the Kebele administrative boundary rather than flood levels/lines. This study during the course of the field survey found that; there are additional areas highly flood prone. On the other hand, there are areas which are located at elevated areas like in Tana Mitsili Kebele, and was excluded an equivalent flood prone area located at lower level along the Rib River was included.
The change of survey boundaries has made the team to lose some data collected mainly 12 BMs  already established and connected to GCP and establishment of additional BMs in the newly proposed areas.
It was observed Dembia that the given survey boundary did not reach new Megech River bank in Robit Village area. Thus, we extended to additional survey works on about 420ha to include the major flood line on the ground.
Moreover, the field survey  supported by  the office topographic  maps  and DEMs  analysis reveals that; there are still high flood prone areas not included in the pilot flood study system. Specifically Awhia Abona and Tana Weyina kebele of Dembia Floodplain and a large area of Fogera floodplain which are found to be within the high flood prone plain. The study found that over 45,000 ha’s  prone to flood in addition to the already  delineated pilot kebeles  of about 30,000 ha. We recommend the MOWIE and the Flood modeler consultant shall investigate the issue more and handle the issues.
9.2.2      Damage of the BM
The  local  communities  have  dismantled  a  number  of  the  MBs  for  unknown  reasons.  An example of dismantled BM in Tizamba Kebele is shown in Figure 9-1.
The consultant has  made discussion with the woreda and kebele administrators. They promised to handover the BMs to local militias or alternatively to give responsibility to the owner of land if the land is private and to the surrounding communities if the land where BM located belongs to the communities or on the road. However, it has been difficult to identify who owns the land where the bench mark  is  established. As  a response to this  problem additional permanent benchmarks  were established along the asphalt road from Behir Dar to Gondar, crossing the survey area. This indicated that, more community consultation works have to be done at all levels.
9.2.3      High crops on the field
High-rise crops mainly maize, dense and dense Eucalyptus trees resulted in difficulty to take reading through them (see figure 9-2 below). The survey crew overcame this problem by mounting the reflector on high rising pipe stand.
Topographic Survey in Lake Tana Sub-Basin Floodplain Areas
Final Report 59GIRDCOt-*-
MOWIE-TBIWRDP
Figure 9-1: Some of the Dismantled Bench marks Figure 9-2:High crops and dense perennial trees
9.2.4    Rainfall
Assessment of the climatic  condition of the area and information from local inhabitants  has revealed that the belg rain starts in end of April or early May. However, unexpected intermittent rain for a days at the end of March and early April falls which resulted in runoff on the fields and making muddy  especially  on heavy  clays  to the degree making walking difficult. Moreover, crossing streams  & rivers  had been impeded which makes  especially  cross  section survey difficult. The survey  team overcomes  the problem by  concentrating the work  in villages  and infrastructures until the field dry up. It has to be learned that the topographic survey and other field survey works shall be planned with a completion target before any rainy season.
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Topographic Survey in Lake Tana Sub-Basin Floodplain Areas-------------
Final Report 60GIRDC Of*
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REFERENCES
•     MOWIE-GIRDC;  Topographic  Survey  in  Lake  Tana  Sub-Basin  Floodplain  Areas: Inception Report; Feb.2014 and Interim Report; April 2014
•    Flood Risk Mapping Consultancy for Pilot Areas in Ethiopia; July 2010 by River Side, USA   in   association   with   Tropics   consulting   engineers   and   Shebele   Consulting Engineers of Ethiopia for ENTRO.
•    ENTRO-Project Preparation, Flood Preparedness and Early Warning study; Dec. 2006 by SMEC International for ENTRO.
•    Design  Review  Report  of  Megech  Seraba  Pump  Project  by  BRL  in  Association  with Generation Integrated Rural Development Consultant (GIRDC) for MOWIE: 2012
•    Feasibility Study Report of Megech Pump (ROBIT) Projects By Halcrow In Association With GIRDC for MOWIE: 2011
•   Lake Tana Area Flood Protection Works Impact Evaluation, 2010 by GIRDC for WVE.
•   Lake Tana Bathymetric Survey; 2012 by OMEGA Development Service for MOWIE
•     Lake  Tana  sub-basin  Dams  (Gigel  Abay,  Jamma,  Rib  and  Megech)  and  Irrigation development  study  and  design  project  2009/10  by  WWDSE  in  association  with  Tahal and GIRDC, DH & other National Consultants for MOWIE
•    Gumera  Dam  and  Irrigation  Project  feasibility  Study;  2008 by WWDSE in association with ITC India and GIRDC and other National consultants for MOWIE
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
Final Report 61MQWIE-TBIWRDP
GIRDCC^Xl
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Topographic Survey in Lake'S!
GIRDC(3*~t~>
MOWIE-TBIWRDP
APPENDICES
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Final Report 63
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MOWIE-TBIWRDP
APPENDIX 1: Primary Permanent Benchmarks’ Location in Dembia FP Area
Sn
Point ID
EASTING
NORTHING
- ELEVATION
V ; REMARK S
1
M001
323723.951
1358343.210
1787.940
2
BM-1
314351.661
1363404.503
1805.393
ROCK
3
BM-1A
314403.080
1363406.290
1807.331
ROCK
4
BM-1B
314479.582
1363417.960
1803.503
ROCK
5
BM-2
316393.950
1363453.570
1791.930
CONCRETE
6
BM-2A
316428.500
1363764.200
1791.670
CONCRETE
7
BM-3
318323.651
1363429.733
1791.614
CONCRETE
8
BM-3A
318321.851
1363501.035
1791.807
CONCRETE
9
BM-4
320429.340
1363442.770
1792.600
CONCRETE
10
BNMA
320136.570
1363434.430
1795.430
CONCRETE
11
BM-5
324238.140
1363432.470
1794.880
CONCRETE
12
BM-5A
324219.520
1363533.030
1796.220
CONCRETE
13
BM-6
314315.340
1361499.550
1790.130
CONCRETE
14
BM-6A
314227.420
1361479.930
1790.125
CONCRETE
15
BM-7
316360.900
1361298.220
1788.810
CONCRETE
16
BM-8
318392.990
1361364.500
1789.320
CONCRETE
17
BM-8A
318394.790
1361437.810
1789.760
CONCRETE
18
BM-9
320335.960
1361430.240
1789.590
STONE
19
BM-10
322319.870
1361430.110
1789.550
CONCRETE
20
BM-10A
322403.640
1361448.270
1790.370
CONCRETE
21
BM-11
324305.629
1361442.112
1790.060
CONCRETE
22
BM-12
314347.120
1359424.550
1787.930
CONCRETE
23
BM-12A
314365.640
1359324.940
1787.840
CONCRETE
24
BM-13
316346.820
1359392.830
1788.340
CONCRETE
25
BM-14
318514.480
1359521.910
1787.690
CONCRETE
26
BM-14A
318571.120
1359619.240
1787.680
CONCRETE
27
BM-15
320304.600
1359417.890
1787.530
CONCRETE
28
BM-16
322337.780
1359437.560
1788.530
CONCRETE
29
BM-16A
322268.990
1359445.620
1788.810
CONCRETE
30
BM-17
324307.938
1359454.358
1787.314
CONCRETE
31
BM-18
314369.760
1357493.690
1787.860
CONCRETE
32
BM-18A
314358.660
1357584.400
1788.050
CONCRETE
33
BM-19
316536.160
1357505.360
1787.250
CONCRETE
34
BM-20
318330.251
1358138.423
1787.346
CONCRETE
35
BM-20A
318332.559
1358368.989
1787.234
CONCRETE
36
BM-21
320502.800
1358374.530
1787.170
CONCRETE
37
BM-22
322592.740
1357390.940
1786.980
CONCRETE
38
BM-22A
322687.150
1357362.530
1787.090
CONCRETE
39
BM-23
324221.480
1357477.940
1788.160
CONCRETE
40
BM-DR
314350.662
1356727.111
1802.563
STONE
41
BM-GPS-05
314365.413
1353829.992
1810.863
ROCK
42
BM-GPS-05A
313945.256
1353483.476
1824.738
ROCK
Source: Adindan UTM Zone-37
Topographic Survey In Lake Tana Sub-Basin Floodplain AreasMOWIE-TBIWRDP
Final Report 66GIRDCO-y
APPENDIX 2: Primary Permanent Benchmarks* Location in Fogera FP Area
MOWIE-TBIWRDP
Sn
Point id
Easting
Nothing
Elevation
REMARK
1
BM-HA
343207.845
1302941.067
1934.953
Hamusit town
2
WORETA
357908.490
1318444.922
1823.591
Woreta town near to Blue hotel
3
BM-WWR
359432.711
1321204.307
1793.256
Woreta Weldia road
4
BM-1
347516.901
1328864.237
1787.965
concrete
5
BM-1A
347511.725
1329031.970
1788.133
concrete
6
BM-2
349000.001
1328877.318
1788.986
concrete
7
BM-3
351112.725
1328905.197
1789.100
concrete
8
BM-3A
351081.750
1328806.146
1788.706
concrete
9
BM-4
347029.864
1327082.523
1788.704
concrete
10
BM-4A
346870.816
1327138.921
1788.530
concrete
11
BM-5
348994.124
1326801.570
1789.184
concrete
12
BM-6
350998.976
1326909.267
1788.968
cut of tree
13
BM-6A
351143.400
1326872.115
1788.482
cut of tree
14
BM-7
353154.984
1326769.994
1789.145
concrete
15
BM-8
344854.627
1325712.335
1788261
concrete
16
BM-8A
345175.310
1325845.026
1788.588
concrete
17
BM-9
347102.348
1325087.467
1788.173
concrete
18
BM-10
349072.335
1324934.058
1788.009
concrete
19
BM-10A
349016.804
1324620.011
1788.624
concrete
20
BM-11
351194.031
1324945.947
1788.688
cut of tree
21
BM-12
353034.864
1324882.954
1789.502
concrete
22
BM-12A
352752.475
1324935.230
1789.242
concrete
23
BM-13
345713.032
1322736.838
1787.767
concrete
24
BM-13A
345646.692
1322669.748
1787.891
concrete
25
BM-14
346999.343
1323004.611
1788.372
concrete
26
BM-15
348978.561
1322891.454
1788.397
concrete
27
BM-15A
348908.339
1322679.265
1788.289
concrete
28
BM-16
350899.901
1322915.367
1787.819
concrete
29
BM-17
345114.230
1321994.810
1788.146
concrete
30
BM-18
346967.088
1320908.059
1788.620
concrete
31
BM-18A
347057.493
1321090.607
1788.973
concrete
32
BM-19
348766.456
1320846.769
1788.383
concrete
33
BM-20
343657.858
1318928.376
1788.580
concrete
34
BM-20A
343657.858
1318760.683
1788.653
concrete
35
BM-21
344958.070
1318869.102
1788.879
concrete
36
BM-22
341730.634
1316776.336
1788.839
concrete
37
BM-23
343036.999
1316861.757
1789.710
concrete
38
BM-23A
343293.257
1316762.168
1789.787
concrete
39
BM-24
345016.342
1316922.895
1789.010
concrete
40
BM-26
341530.700
1314837.451
1788.241
concrete
41
BM-27
343004.703
1314895.415
1788.594
concrete
42
BM-27A
343040.188
1314873.860
1788.943
concrete
43
BM-28
344977.144
1314629.796
1788.753
concrete
44
BM-30
341100.368
1313156.036
1788.381
concrete
45
BM-31
342991.085
1312884.452
1788.444
concrete
46
BM-31A
342982.693
1312768.424
1789.562
concrete
47
BM-32
345063.342
1312956.543
1790.064
concrete
48
BM-33
347056.453
1312935.762
1789.741
concrete
49
BM-37
344965.915
1310728.786
1788.155
concrete
50
BM-38
347012.457
1310886.294
1790.001
concrete
51
BM-38A
347041.722
1310913.767
1790.049
concrete
52
BM-39
348822.847
1310860.690
1791.108
concrete
53
BM-42
345486.903
1309264.238
1802.008
Rock
54
BM-42A
345518.538
1309296.719
1790.331
Rock
55
BM-43
347004.719
1308923.213
1789.716
concrete
56
BM-44
349009.139
1308907.990
1791.872
concrete
1
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas 
Final Report 67MOWIE-TBIWRDP
GIRDCC/^-
Sn
S7
Point id BM 45
Easting 351006.047
Nothing 1306921.433
Elevation 1797.375
REMARK
concrete
58
59
350633.415 350461.641
BM-48 347030.236 BM-49 348920.oU/
-
BM-45A
BM-45B
1308031.051 476
1795.232
1795.979
concrete
1RO6R20 726
1835.281
Rock
60
1306309 282
1798.848
cut of tree
61
1306315 658
1797.288
cut of tree
62
BM-49A dDmlVr'DI'bQ   OU
349011.560
351162 586
1308952.176
1794.122
concrete
63
r o-
RM-GPS-50A
351207.085
1308897.146
Gumara river Briadge
65
BM-GPS-51
353175 598
1310898.950
1796.132
stone
66
BM-GPS-51 A
353219.287
1310915.924
1794.706
1796.658
1807.309
stone
67
BM-GPS-52
354566.661
1314228.149
stone
6R
BM-GPS-52A
354598.043
1314319.814
1807.957
69
BM-GPS-53
359567.174
1325981.105
1794.499
stone
Rebe river briadge
76
BM-GPS-53A
359553.826
1325924.198
1794.774"
Rebe river briadge
71
BM-GPS-54
359492.783
1325272.889
1793.862
on Culvert
72
BM-GPS-54A
359471.978
1325211.849
1792.683
Rock
73
BM-A1
346688.537
1316064.137
1789.665
concrete
74
BM-A1B
346685.980
1316021.889
1788.693
concrete
75
BM-A2
348699.604
1314926.853
1789.731
concrete
76
BM-A3
350290.473
1314085.470
1790.344
concrete
77
BM-A3B
350314.321
1314170.504
1789.900
concrete
78
BM-A4
352037.121
1313167.516
1791.075
concrete
79
BM-A5
353000.012
1328925.078
1790.1401
concrete
80
BM-A6
354719.250
1328842.996
1790.551
concrete
81
BM-A6B
354678.070
1328852.413
1790.588
concrete
82
BM-A7
355087.818
1326659.256
1790.900
concrete
83
BM-A7B
355180.811
1326605.941
1790.630
concrete
84
BM-A8
356989.208
1325839.324
1792.924
concrete
85
BM1-K
348707.971
1329353.765
1802.116
Rock
86
GPS Base
363132.390
1334577.484
1832.191
Rock
87
YIFAG
348618.800
1340427.257
1833.000
Rock
88
BM-M001
359891.152
1327284.436
1793.859
Rock
89
BM-M002
360020.216
1327592.292
1793.748
Rock
Source : Adindan UTM Zone-37GIRDcOf^
MOWIE-TBIWRDP
APPENDIX 3: Triangulation Points/GCPs Identified and Linked To the Survey Area
STATION
EASTING
NORTHING
ELEVATION
REMARK
BNP56
317638.897
1291685.042
1785.4
Near Zege
BNP39
313986.733
1368473.957
1868.1
Between Kola Deba & Gorgora
BNP41
323686.590
1375497.253
2018.3
Between Kola Deba & Gorgora
YIFAG
348618.800
1340427.257
1833.0
Near FogeraM2W!e-tb]vvrdp
Final P0poflGIRDCOp
APPENDIX 4: Detailed Topographic Survey Data of the Floodplain Areas
MOWIE-TBIWRDP
Note: Detailed topographic surveyed data of the project area are in softcopies (as it is too large to attach it here)
'• 
A
•
•  -■
i
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'<•
■ .■
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i
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♦:
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Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
■MQWIE-TBIWRDP_
GIRDCCfT _____________________ ________
>
Topographic Survey in Lake Tana Sub-Basin Floodplain Areas
'7inaiRePortGIRDCOy____________________________________________________________________ MOWIE-TBIWRDP APPENDIX 5: Cross Section Data of Rivers & Gullies in the Floodplain Areas
Note: Cross Section data of Rivers & gullies in the project area are in softcopies (as it is too large to attach it here)
4
Topographic Survey in Lake Tana Sub-Basin Floodplain Areas
Final ReportGIRDCCf"t~>
MOWIE-TBIWRDP
Final ReportNo
GIRDCOy_________________________________________________________ __________ MOWIE-TBIWRDP APPENDIX 6: Specification of Differential Fixed GPS &Total Stations used for Survey
Appendix 6.1 Specification of Adopted GPS
y Component.
Description.
1
Receiver
Sported GNSS system
GPS L2
Standard
GPS L5
Standard
Glonass
Standard
Galileo
Standard
RTK performance
Standard
DGPS/RTCM
Standard
RTK up to 5KM
Standard
RTK unlimited
Standard
Network RTK
Standard
Position update & data recording
Standard
5Hz positioning
Standard
20Hz positioning
Standard
Row data logging
Standard
RINEX logging
Standard
NMEA out
Standard
Addition features
RTK reference station functionality
Standard
Performance
Advanced measurement engine
Technology
Jamming resistant measurements
High  precision  pulse  aperture  multipath  correlator  for pseudo range measurements
Excellent low elevation tracking
Very low noise carrier phase measurements with <0.5mm precision
Minimum acquisition time
120 channel
No of channel
Max. simultaneous tracked satellites up to 60 satellites simultaneously
On two frequencies
Satellite signals tracking
GPS LI. L2, L2C L5
Glonass L1, L2
Galileo (TEST);GIOVE B
Galileo El E5a, E5b ..AIE-BOC
Compass
SBAS, WAAS.EGNOS, GAGAN. MSAS
GNSS measurements
Fully independent code and phase measurements of all frequencies
GPS carrier phase full wave length , code IC/A. P.C code
Glonass,  carrier  phase  full  wave  length,  code  IC/A.P narrow code
Galileo carrier phase full wave lenqth, code
Measurements time
Reacquisition time
<1 sec
Antenna
Standard survey antenna
Types
Technology
Smart track
Ground plane
Built - in ground plane built in ground plane
Dimensions(diameter height)
170mmx62mm
Weight
0.4kg
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
Final Report 75MOWIE-TBIWRDP
GIRDCC^V
No
Component
Description
Gain
Typicaly27 dbi
Temperature operation range
40*c to+70‘c
Humidity
100% - .. - .
Protection against water  sand
,
IP66.IP67
Drop& topple over
Withstand   1.5mdrop   on   to   hard   surface   and   survives topple over from 0.2m pole on to hard surface
Vibration
Withstand    vibration    during    operation    on    large    civil construction machine
Compliance with ISO 9022,36-08and mil-sto-514.5 cat 24
Choke-ring Antennas
Type
Atso4 GG
Satellite signal tracking
GPS L1. L2
Glonass
Design
Dome Margolin. JPL Design
Protection Radom
Optional
Dimension & diameter height)
380mmx 140mm
Weight
4.3kg
Gain
Typically 27 dbi
Measurement performance accuracy
Accuracy(RMS)code different at with DGPS , RTCM
DGPS , RTCM
Typically 25cm (RMS)
Accuracy(RMS)with real time (RTK)
Standard of compliance
Compliance with ISO 17123.8
Rapid static (phase)
Horizontal 5mm+0.5ppm (RMS)
Static mode after initialization
Vertical 10mm+0.5ppm (RMS)
Kinematic(phase)
Horizontal 10mm+1ppm (RMS)
Vertical 20mm+1ppm (RMS)
ACCURACY (RMS)WITH POST PROCESSING
Staticf phase )with long observation
Horizontal 3mm+0.5ppm (RMS)
Vertical 6mm+0.5ppm (RMS)
Static &rapid static(phase)
Horizontal  5mm+0.5ppm  (RMS)/vertical10mm+0.5ppm (RMS)
Kinematic (phase)
Horizontal 10mm+1ppm (RMS)/vertical 20mm+1ppm
(RMS)
On the fly(OTF) Initialization
*■               t
RTK Technology
Smart check technology
Reliability of OTF initialization
Better than 99.99%
Time for initialization
Typically 8 sec
Receiver
Hardware
Weight &Dimension
5.4 kg Standard RTK Back-pack rover including CFU RTK device, controller Buttons
Weight
Pole and bracket
Environmental Specification
502.4-11.MIL STD 810F-501.4
Femperature operatinq
40cto+65c compliance with IS09022-10-08.IS09022-11 SPECIAL mil STD 81 OF
i
Humidity 
r
100% compliance with IS09022.13-06.IS09022 12-04 and nil STD 810f-507.4-1
F
’roof against water, sand & dust
-------------------- -------------- ----------------------r F
r
r
P67  According  IEC  60529and  mil  STD  810F  510.4-1and nil STD 810f 512.4-1
V
'ibration
'y
’rotection against blowing rain and dust
Yotection  against  temporary  s  submersion  in  to  water max. depth Imblowing rain and dust
Vithstands strong vibration during operating compliance
Topographic Survey in Lake Tana Sub-Basin Floodplain AreasGIRDC<fry
MOW1E-TBIWRDP
No?
Component
Description
with ISO 9022.36-08 and mil std 81 Of-514.5 -cat 24
Drops
v
vithstandsl .0m drop on to hard surfaces
Functional shock
z
IOq/15 to 23 msec compliance with mil std 81 Of-516.5-1
r
i
'Jo lose of lock to satellite signal when used on a pole set jp and submitted to pole bumps up to 150 mm
Power electrical
Supply voltage
‘
Nominal 12v DC
Ranqe 10.5-28v DC
Power consumption
F
Internal power supply 
Rechargeable      Aremovable       Li-ion       battery       4.4 <jh/7.4v2batteries
Internal power supply
l500h receiving RTK data with standard radio
Operation Time
300h transmitting RTK data with standard radio
1
l400h   RTK   via   GSM/GPRS   connector   with   2intemal catteries
Certification
ccompliance to FCC.CE
i
c
cal  approval  for  IC  Canada,  c  tick  Australia  Japan  , ochina
External power supply 
r
echargeable external NIMh battery 9Ah/12v
Memory & data recording
Memory Medium                                        r
emovable and 1Gb
i
1Gb is typically sufficient for about GPS &GLONASS(8+4 satellite
Data capacity
280 days row data logging at 15s rate
data recording
Type of data
3n board recording of
3NSS row data
Rinex data
Recording rate
up to 20 Hz
User interface
Buttons
Dn/off button & Function button
Buttons Functionality
Function button
easy switch between rover/base mode
easy here positioning functionality
Led status indicator
Blue  tooth  position  ,RTK,  status,  data  logging  detailed power status
Additional user interface
integrated  web  interface  functionality  provides  full  status indicator and configuration option
Communication
Communication Point
2x seriamol RS232 Lemo
1xUSB/RS232 Lemo
1XSPIN Lemo external power
simultaneous data links
1x Bluetooth port Bluetoothv200+EDR.CLASS2
up to 3data licks can be attached and used simultaneously
2real   time   out   put   interfaces   via   Independent   ports providing
Identical or different RTk /RTCM formats
External data link
Radio modems
support of any suitable UHF/VHF radio with RS232 inte
face
r
and operating in transparent mode
.Satellite 3As GFU housing, fully sealed and protectei
IP67
1
GSM/UMTS (HSDPA)phone modems
Support            of            any GSM/GPRS/UMTS(HSDPA)modem
suitabl
e
SIEMENS MC75 IN                 GFU HOUSING, QUA( 850/900/1800/1900Mz fully sealed and protected IP 67
3
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
Final Report 77GIRDCCfr-f-*
MOWIE-TBIWRDP
No
Component
Description
CDMA Phone Modems
SUPPORTED ANY SUITABLE CDMA MODEM
Multitask mtmmc CDMA IN GFU HOUSING, DUAL BAND 800/900/mhz,1xRTT
FULLY SEALED AND PROTECTED IP 67
Landline Phone modems
SUPORT    OF    ANY    SUITABLE    LANDLINE    PHONE MODEM
Communication Protocols
Real    time    data    formats    for    data transmission and reception
Proprietary format .CMR.CMR+
Real  time  data  formats  according  RTCM standard for data
Transmission and reception
RTCM2.1.RTCM2.3, RTCM3.0.RTCM3.1
NMEA out put
NMEA 0183V2.20AND PROPRIETARY
0
r-
■ • -' - •
-
Final ReportGIRDC^-P
MOWIE-TBIWRDP
Appendix b.2 No
opecincaiion or nuupieu uuiua ivun
. Component
5»i£gfi'4S^SSlDSiiicjripti6hW*
Angular Measurement
1
rotal Station with Laser plumment with 2 keyboard with touch screen, standard applications and optional Application .user nanual and container (set) internal battery & riemory card)
Accuracy Hz
.
?>"(0.025mgon)
display resolution
t
).1”(0.1mgon)
Method
?absolute, continuous, diametrical
Compensation
<Duadruple axis compensation
Compensator setting accuracy 
<)■.5"(0.2mgon)
Distance Measurement
Distance Measurement (PRISM)
Round prism
'
3500M(12000ft)
3 Round prism
*
5400m (17700ft)
360’prism
-
2000M(7000ft)
360’prism
1000m(3300ft)
Mini-prism
2000m(7000ft)
Reflective tape (60mm*60mm)
250m(800ft)
Accuracy 3.4 measurement time
Standard
1mm+1.5ppm
Fast
3mm+1.5ppm
T racking
3mm+1.5ppm
Averaging
1mm+1.5ppm
Typical measurement time
0.8s
Distance Measurement (Any Surface)
pin pointR30/R400/R1000
30M(98ft)/400m (1310ft)/1000m(3280ft)
Accuracy 3,7 measurement time
pin pointR30/R400/R1000
2mm+2ppm/typ.3s
Distance measurement (Long-range)
Long-range2,4
AA
10000m( 32800ft)
Accuracy 3,6 measurement time
Long-range
5mm+1.5ppm/typ2.5s
GENERAL
Display resolution
0.1mm
Short measurable distance
1.5m
Method
System analyzer based on phase shift measurement(coaxial, visible red laser)
Laser dot size (Non-prism)
Telescope
At30m;7mm*10nim.at 50m;8mm’20mm
Magnification
30x
Free objective aperture
40mm
Field of view
Focusing range
r30’(1,66gon)/2.7mat100m
1.7mtoinfinity
Keyboard & Display
Display
backlight*touch screen
Keyboard
keys, illumination
Position
face/standard/face/optional
Memory, ports & communication
Internal memory/memory devices
Stick
Interface
RS232,Bluetooth@wireless-technology  USB
mini AB OTG
>
Operation
... .
Sensitive of circular level
672mm
Centering accuracy of laser plummet
1.5mm at 1.5m
Number of drives
1 horizontal/1 vertical
Power Management
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
Final Report 79GIRDCOt*________________________________ _______________________________________ MQWIE-TBIWRDP
No
Component
Description
Internal battery
Lithium Ion
Operating time
5-8h(GEB221)
Voltage /capacity
7.4h /4.4Ah
Weight & Dimensions
Weight of total station /battery /Tribach
5-7kg
Environmental specifications
Working/storage temperature range
20*cto+50'c/-40 cto+70'c
Dust/Water(IEC60529)/Humidity
IP55/95%,non-condensing
Guide Light (EGL]
Working Range
5-150m
Positioning accuracy
5 cm at 100m
Topographic Survey in Lake Tana Sub-Basin Flood^aln Area?
Final ReportgirdcGJXL
APPENDIX 7: Selected Photographs of BMs & GCP with Witness Diagram
MOWIE-TBIWRDP
Description:
Surveyed by: GIRDC
Adlndan UTM Z37N : E 320335.960,N 1361430.24
Description: near to Dlrima River
Surveyed by: GIRDC
AdlndanUTM Z37N :E 314479.582, N 1363417.96
Heiqht(m) Clarke 1880:1789.59
Height[mj Clarke 1880: 1803.5033
Description:
Surveyed by: GIRDC
Adlndan UTM Z37N : E 318392.990, N 1361364.500
Height(m) Clarke 1880:1789.320
Description: near to old Megech River
Surveyed by: GIRDC
AdlndanUTM Z37N :E 320136.570, N 1363434.430
Helght(m) Clarke 1880:1803.5033
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
Final Report 81girdc
MOWIE-TBIWRDP
Description:
Surveyed by: GIRDC
Adindan UTM Z37N : E 314365.640, N 1359324.940
Description:
Surveyed by: GIRDC
AdindanUTM Z37N :E 316360.900, N 1361298.220
Surveyed by: GIRDC
Adindan  UTM  Z37N  :  E  324305.629.  N  1361442.112 Height(m) Clarke 1880:1790.060
Description: near to Dirima River
Surveyed by: GIRDC
AdindanUTM Z37N :E 314369.760, N 1357493.690 Height(m) Clarke 1880: 1787.860
Topographic Survey in Lake Tana Sub-Basin Floodplain Areas
Final ReportGIRDCOT*
MOWIE-TBIWRDP
BM 6
Description:
Surveyed by: GIRDC
Adindan UTM Z37N : E 314315.340. N 1361499.550 Height(m) Clarke 1880:1790.130
BM 6A
Description:
Surveyed by: G1RDC
AdindanUTM Z37N :E 314227.420, N 1361479.930 Height(m) Clarke 1880: 1790.125
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
Final Report 83GIRDC Of-*
MQWIE-TBIWRDP
Description:
Surveyed by: GIRDC
Adindan UTM Z37N : E 347516.901, N 1328864.237
Description:
Surveyed by: GIRDC
AdindanUTM Z37N :E 353034.864, N 1324882.954
Height(m) Clarke 1880: 1787
Heiaht(m) Clarke 1830: 1789.502
Description: near to lake Tana
Surveyed by: GIRDC
Adindan  UTM  Z37N  :  E  344854.627,  N  1325712  335 Helght(m) Clarke 1880: 1788.261
Description:
Surveyed by: GIRDC
AdindanUTM Z37N :E 345646.692, N 1322669.748 Height(m)
Topographic Survey In Lake Tana Sub-Basin Floodplain AreZ?
Final Report 84girdcHJ^
MOWIE-TBIWRDP
Description:
Surveyed by: GIRDC
Adindan UTM Z37N : E 345114.23, N 1321994.81 Height(m) Clarke 1880: 1788.1456
Description:
Surveyed by: GIRDC
AdindanUTM Z37N :E 345486.903, N 1309264.238 Height(m) Clarke 1880: 1802.008
Description:
Surveyed by: GIROC
Adlndan UTM Z37N : E 349009.139, N 1308907.99 Helflht(m) Clarke 1880: 1791.872               _______
Description:
Surveyed by. GIRDC
AdindanUTM   Z37N   :E   348978.561,   N   1322891.454  Height(m) Clarke 1880: 1788.397
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
Final Report 85GIRDC CF-f^
MQWIE-TBIWRDP
Description:
Surveyed by: GIRDC
Adindan UTM Z37N : E 350899.901, N 1322915.367
Description:
Surveyed by: GIRDC
AdindanUTM   Z37N   :E   347004.719,   N   1308923.213   Height(m)
Clarke 1880: 1789.716
Description:
Surveyed by. GIRDC
Adindan UTM Z37N : E 3454AR -Hejflhtfm) Clarice 1880:J8y nn« ' *
Description:
3      1309264 238
Surveyed by: GIRDC
u-Jaht/m)
AdindanUTM  Z37N  :E  344977.144,  N  1314629.796  He  0
Clarke 1880:1788.753             __________________GIRDCOT*
MOW1E-TBIWRDP
APPENDIX 8: Lake Tana Bathymetric survey Control Points (Adindan Zone-37 UTM
Coordinates)
S.N
POINT ID
EASTING
NORTHING          ELEVATION
1
2
3
4
5
6
7
8
9
10
£1
12
13
14
BDN____
PAR
GPSO 5A
GPSO6
324056.879
323959.730
313942.688
288267,522
GPSO 6A
GPSO-1
GPSO-1A
GPSQ-2
GPSO-2A GPSQ-2B
GPSQ-3
GPSO-3A GPSO-3B
GPSO-4
288202.811
326909.669
326651.815
331002.462
331209.204
341115.722
286209.201
286084.969
275643.421
351288.644
1278166.926
1282424.937
1353483.530
1348243.028
1348131.824
1282867.911
1283191.822
1300520.855
1300692.717
1300458.218
1313088.229
1313244.867
1293779.384
1340194.196
1798.924
1787.771
1832.687
1733.951
1733.691
1816.059
1800.372
1818.150
1825.545
1974.990
1710,211
1710.870
1916.928
1903.769
POS.+ HT.
QUALITY
0.0184 0.0298 0.0197 0.0242 0.0235 0.0229
0.0223
0.0236
0.0415
0.0221 0.0434 0.0404 0.0183 0.0351
Topographic Survey in Lake Tana Sub-Basin Floodplain Areas
Final Report 87MOWIE-TBIWRDP
GIRDC OT
1
■ ■«,
v-
.a •,
Topographic Survey in Lake Tana Sub-BasinFloodplainAre^MOWIE-TBIWRDP
GIRDCCy-t^
APPENDIX 9: Data Base Guides
Lake Tana Sub basin Floodplains Topographic Survey Database
Simplified Users Guide (Dembia)
Main Directory: ‘Database’
There are two sub-directories:
1.   Dembia
2.  Fogera
1. Dembia
There are five folders:
1.1. CAD
1.2. GIS
1.3. PDF
1.4. EXCEL
1.5. Photographs
1.1         . CAD
Under  ‘CAD’  folder  there  is  File  called:  ‘TBS_TSD_09_Cross-Sections  Map  of  Major  Rivers  in Dembia Floodplain (4 Nr) H 11000, V 1100.dwg’
1.2.        GIS
Under ‘GIS’ folder there are two sub-folders:
1.2.1   MXD
1.2.2   Shp
1.2.1   MXD
Under 'MXD’ folder there are six files:
>   TBS_TS 06 -20,000_Location of Established Permanent BMs in Dembia
FloodPlain.mxd
>   TBS TS _07 -20,000_Topographic Map of Dembia FloodPlain.mxd
>   TBS_TS _08 -10,000_Detail Topographic Map of Dembia FloodPlain_1-4.mxd
>   TBS_TS _08 -10,000_Detail Topographic Map of Dembia FloodPlain_2-4.mxd
>   TBS_TS _08 -10,000_Detail Topographic Map of Dembia FloodPlainJM.mxd
>   TBS_TS _08 -10,000_Detail Topographic Map of Dembia FloodPlain_4-4.mxd
1.2.2 Shp
Under ‘Shp’ folder there are several files that help to read/open ‘MXD' files.
Topographic Survey in Lake Tana Sub-Basin Floodplain Areas
Anal Report 89GIRDCCy-fr-*
1.3. PDF
Under ‘PDF folder there are again six files:
MOWIE-TBIWRDP
>    TBS_TS _06 -20,000_Location of Established Permanent BMs in Dembia FloodPlain
>    TBS_TS _07 -20,000_Topographic Map of Dembia FloodPlain
>    TBS_TS _08-10,000_Detail Topographic Map of Dembia FloodPlain_1-4
>    TBS_TS _08-10,000_Detail Topographic Map of Dembia FloodPlain_2-4
>   TBS_TS _08-10,OOO Detail Topographic Map of Dembia FloodPlain_3-4
>    TBS_TS _08-10,000_Detail Topographic Map of Dembia FloodPlain_4-4
1.4.  EXCEL
Under this EXCEL folder there are four files:
Primary Permanent Benchmarks’ Location in Dembia FP Area Triangulation Points/GCPs Identified and Linked To the Survey Area
Detailed Topographic Survey Data of Project Area
Cross Section Data of Rivers & gullies in Dembia Floodplain Area 1.5.  Photographs
There is one file of selected photographs in Dembia Floodplain.MOWIE-TBIWRDP
GIRDCOy
Main Directory: ‘Database’
There are two sub-directories:
1.  Dembia
2.   Fogera
2. Fogera
There are five folders:
2.1. CAD
2.2. GIS
2.3. PDF
2.4. EXCEL
2.5. Photographs
2.1         . CAD
Under 'CAD' folder there are two Files called:
>
>
Figure 7.1_Location of EMA GCP and Proposed BMs.dwg
TBS_TSF _05 _Cross-Sections Map of Major Rivers in Fogera Floodplain (2 Nr) H
11000, V 1100.dwg
2.2
GIS
Under ‘GIS’ folder there are two sub-folders:
2.2.1    MXD
2.2.2    Shp
2.2.1 MXD
Under MXD’ folder there are nineteen files:
The first three files are A3 maps for both Demia & Fogera the rest 17 files are all for Fogera
> A3 Figure 5.1_Location Map of Lake Tana Sub-basin Floodplain Survey Areas.mxd
> A3 Figure 5.2_Map of the Floodplain Kebeles.mxd
> A3 Figure 5.4_Proposed Fogera and Dembia Floodplain Boundary.mxd
> TBS_TS _01 -175,000_Location Map of the Project .mxd
> TBS_TS _02 -50,000_Location of Established Permanent BMs in Fogera Floodplain.mxd
> TBS_TS _03 -50,000_Topographic Map of Fogera Floodplain.mxd
> TBS_TS _04 -10,000_Detail Topographic Map of Fogera Floodplain_1-12.mxd
> TBS_TS _04 -10,000_Detail Topographic Map of Fogera Floodplain_2-12.mxd
> TBS_TS _04 -10,000_Detail Topographic Map of Fogera Floodplain_3-12.mxd
> TBS_TS _04 -10,000_Detail Topographic Map of Fogera Floodplain_4-12.mxd
> TBS_TS _04 -10,000_Detail Topographic Map of Fogera Floodplain_5-12.mxd
> TBS_TS _04 -10,000_Detail Topographic Map of Fogera Floodplain_6-12.mxd
> TBS_TS _04 -10,000_Detail Topographic Map of Fogera Floodplain_7-12.mxd
Topographic Survey In Lake Tana Sub-Basin Floodplain Areas
Final Report 91GIRDC
MOWIE^BIWRdp
r | OO IO Ut ~ i
■— |--
i
-.
> TBS_TSF _05 _Cross-Sections Map of Major Rivers in Fogera Floodplain (1-2).mxd
> TBS_TSF _05 Cross-Sections Map of Major Rivers in Fogera Floodplain (2-2).mxd
2.2.2 Shp
Under *Shp’ folder there are several files that help to read/open ‘MXD’ files.
2.3 .PDF
Under ‘MXD’ folder there are twenty files:
The first four files are A3 maps for both Demia & Fogera the rest 17 files are all for Fogera
>   A3 Figure 5.1_Location Map of Lake Tana Sub-basin Floodplain Survey Areas >   A3 Figure 5.2_Map of the Floodplain Kebeles
>   A3 Figure 5.4_Proposed Fogera and Dembia Floodplain Boundary
>   A3 Figure 7.1_Location of EMA GCP and Proposed BMs
>   TBS_TS _01 -175,000_Location Map of the Project .mxd
>   TBS_TS _02 -50,000_Location of Established Permanent BMs in Fogera
Floodplain.mxd
>   TBS_TS _03 -50,000_Topographic Map of Fogera Floodplain.mxd
>   TBS_TS _04 -10,000_Detail Topographic Map of Fogera Floodplain_1-12.mxd
>   TBS_TS _04 -10,000_Detail Topographic Map of Fogera Floodplain_2-12.mxd
>   TBS_TS _04 -10,000_Detail Topographic Map of Fogera Floodplain_3-12.mxd
>   TBS_TS _04 -10,000_Detail Topographic Map of Fogera Floodplain_4-12.mxd
>   TBS_TS _04 -10,000_Detail Topographic Map of Fogera Floodplain_5-12.mxd
>   TBS_TS _04 -10,000_Detail Topographic Map of Fogera Floodplain_6-12.mxd
>   TBS_TS _04 -10,000_Detail Topographic Map of Fogera Floodplain_7-12.mxd
>   TBS_TS _04 -10,000_Detail Topographic Map of Fogera Floodplain_8-12.mxd
>      TBS_TS _04 -10,000_ Detai I Topographic Map of Fogera Floodplain_9-12.mxd
>      TBS_TS _04 -10,000_Detail Topographic Map of Fogera Floodplain_10-12.mxd
>      TBS_TS _04 -10,000_Detail Topographic Map of Fogera Floodplain_11-12.mxd
* TBS.TS _04 -10,000_Detail Topographic Map of Fogera Floodplain_12-12.mxd >      TBS.TSF _05 -Cross-Sections Map of Major Rivers in Fogera Floodplain (1-2). r TBS_TSF _05 -Cross-Sections Map of Major Rivers in Fogera Floodplain (2-2).
2.4.     EXCEL
Under this EXCEL folder there are four files
L
2.5.    Photographs
Jhere is one file of selected photographs in Fogera FloodplainMOWIE-TBIWRDP-
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APPENDIX 10: Description of Services (TOR)
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Topographic Survey In Lake Tana Sub-Basin Floodplain Areas 
Final Report 93Contract Agreement for Consultancy Service for Topographic Survey in Lake Tana Sub-basin Floodplain Areas—
Description of Services (TOR)
1
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Ir.nn^d Agreement for Consultancy Ser^ceforTopog^SgH^Contract Agreement for Consultancy Service for Topographic Survey in Lake Tana Sub-bay Floodplan
Table of Contents
1
2
3
4
5
Flood Problems....................................................... Project Background
Description              of
study              Area
Project Location and Pilot Study Areas Objective of the consultancy 
30
6      Scope of Work
7      Preparation of Topographic Survey 6 Reports 
..31
9      Deliverables.............................................................................................................................  31
10    Time schedule„31
11    Expertise required and Qualifications_...................................................................................... 31
12    Administration
32
List of Figures
Figure 1: Lake Tana location north-west of Ethiopia high lands, 12°00N .37*15, E...„..2S
Figure 2: Lake Tana pilot study areas’
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Figure 3: Pilot communities in Lake Tana areas'................................................................................ 29
Ministry of Water Irrigation and EnergyContract Agreement for Consultancy
Service for Topographic Survey in
Lake Tana Sub-basin Floodplain Areas
1. Flood Problems
Ethiopia, recent floods have been caused
ScX  a«eded ove?'^oTpeopte. including 16.000 displaced, and over summer 2007 floods were reported to be equally devastating, causing s 
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reg?onaf    states    of    Amhara    and    Gambella.    affecting    over    60.000    people    and    destroying farmlands, road, and homes.
Historically, the flow of Blue Nile and its  tributaries  (including the inflow to the Lake Tana) reaches  its  maximum peak  flow during the rainy  season (from June to September). The blue Nile contributes  about two thirds  of water to the main Nile River and is  contributed from such short period of high volume of flow. Despite the beneficial use of the flood flow, the flooding regime in the Lake Tana sub-basin has  been causing haoc  and inconvenience. Severe flooding along populated areas, have had devastating effects  on lives, livelihoods, and properties. Infrastructure, agricultural land, and other resources  at risk  from floods  can be vast, and include residential, commercial and industrial property, and public  service infrastructure, including water supply, farmlands  and crops. The flood plains  of Lake Tana area are particularly  vulnerable to such frequent and damaging flooding problems  which cause significant loss  of life and economic  damages. Despite attempts  to develop both physical dykes  and flood warning system, the flooding situation hasn't yet proved. The poorly  constructed dykes  have been observed deteriorating. Recently  developed flood forecasting models  have had limitation of calibration data as  well as  fails  to capture the required topographic  details. Therefore, the main objective of this  TOR is  to developed detailed topographical maps  of the flood plain areas  of Fogera, Dembia and Gilgel Abbay flood plain through ground surveying.
2. Project Background
The  Tana  and  Beles  Integrated  Water  Resources  Development  Project  (TBIWRDP)  Sub Component B2, Flood Management
The subcomponent flood management around Lake Tana area will build on activities  started under the Flood Prevention and Early  Warning Project Phase I financed under the NBTF which started implementation by ENTRO in June 2007.
This  supports  improved community-based flood management and adaptation strateqies  around the shores  of Lake Tana through flood preparedness  strategies  including paSto™  ?^ management planning and local risk  mapping; flood mitigation measures  through^maTscale biSn hrmeah7es  such”as  elevated access  ways, drains, secure water supply  capacity building through training, improved information system and data acquisition and proces^ino for
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3. Description of study Area
r thP Blue Nile River and has approximately 15.000 km total d
rainage
Lake  Tana  is  the  source  of  the  Blue  Nil               1,786  m  amsl.  The  lake  is  the
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Figure 1: Lake Tana location north-west of Ethiopia high lands, 12°00N .37°15, E
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4. Project Location and Pilot Study Areas
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Ministry of Water Irrigation and Energy ~Contract Agreement for Consultancy Service for Topographic Survey in Lake Tana Sub-basin Floodplain Areas
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Figure 2: Lake Tana pilot study areas
There   are   three   floodplain   areas   needed   to   be   surveyed   are:   Fogera   floodplain   and   Dembia
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floodplain with respective approximate coverage areas of 70 km  and 194 km .!
Contract Agreement for Consultancy ServiceforTopograph.c SurveyinLake TanaSub-basj, F|00d^in
5. Objective of the consultancy
The main objectives of the topographic survey are:
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ore detailed topographic map U
~ scale T 10,000 and 0.5m contour intervalth^ J  A
f)ood p!ain features, including
1. T0||help to identify the existing nature of
landscape values that may be affected by different level
accurate flood plain modeling.
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2. To identify every detail spot contours that improves the quality of nsk maps
6. Scope of Work
The detailed activities should include but not limited to the following activities:
1)  Site description including plan number Kebele and Gott number and district number.
2)   Location map at appropriate scale indicating the regional setting.
3)  Site map at appropriate scale indicating the layout of project.
4)  Controls, vertical and horizontal references.
5)  Site  profiles  and  cross  sections  @  50m  interval  in  suffciant  number  to  demonstrate terrain  conditions  have  to  be  prepared.  A  spot  height  grid  100m*100m  has  to prepared.
6)  Site plans/ sketches/ color photographs indicating project location, site featuiresand activities identified in relation to easily identifiable landmarks such as those
accompanying maps.
7)     Proximity   to   designated   environmentally   sensitive   areas   such   as   those identified.  This  includes  aquatic,  terrestrial  and  hillside  areas,  watercourses sensitive ecosystem inventory locations.
8)  All image and data sources will be appropriately referenced and clearly indicat
when this information was developed to certify that the most up-to-date
Information available was used in completing the relevant assessments.
9)  A topographic survey has to be made to all 8 pilot kebeles of Dembiai flood P                   shoW km ) and Fogera flood plain (area to be covered -a e
of floods This work will supW ... x .
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10) Maps should be presented in A0 size, color format and that must be printed
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Ministry of Waler Irrigation and Energy^tnHAoreement for Consultancy Service for Topographic Survey in Lake Tana Sub-basin Floodplain Areas--------------------------
8.   Reports
The consultant will prepare and submit the inception and final reports
Inception report
The consultant will prepare and submit inception report containing the Topographic  Survey  on Floodplain Areas  of Lake Tana. This  will be submitted within 45 days  from the commencement date.
Final report
The consultant will prepare and submit final report containing the Topographic  Survey  on Floodplain Areas  of Lake Tana. This  will be submitted at the end of 6 months  from the commencement date.
9.   Deliverables
The  Final  products  of  this  consultancy  are  listed  below  and  will  be  delivered  to  the  Ministry  of Water and Energy (MoWE)
»  A  detailed  Topographic  Survey  map,  (both  in  digital  as  well  as  in  hard  copy,  at  the end   of   the   contract   period.   The   topographic   map   should   clearly   integrate   the   flood plain as well as the river channel geometry.
o    Detailed    topographic    survey    that    incorporates    the    detailed    features    analysis    on areas of Lake Tana Floodplain presented in the scope of the study section
•  The  deliverables  should  be  in  GIS  that  is  compatible  format  with  flood  plain  modeling as will be advised by the flood modeler.
» Final Report at the end of 6 months
The consultant shall supply  10 bounded copies  of the report and 10 maps  with one electronic copy  in both Microsoft Word and Adobe PDF formats  on CD-ROM for the report and the map at appropriate software.
10.        Time schedule
The   time   for   the   Consultancy   service   is   6   months.   The   time   frame   for   implementing   this consultancy is detailed as follows:
JTime schedule
Activity
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M-4
M-5
M-6
Inception report
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Prepare and submit topographic  survey map rm.-___
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peTti^e required arid Coalifications
Minist^ of Water irrigation and EnergyContract Ao.^eni in.
u , curvev in Lake Tana Sub-basin Floodplain Areas 
. MSc. in Water Resource Engineer Fnoineering as a team leader and have 10 years and above experience.
•     3 experienced survey Chief Surveyor - haveing y
, nrc With a diploma in surveying and
-m upars and above experience in topographic surveying
Senior Surveyor - haveing y
r vears and above expenence in topographic surveying.
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Junior Surveyor- haveing 6 years and above experience in topograph,c surveying.
one GIS expert for storing, manipuiating and property managing the data in digit,,
•     Sa?a nd h?v. to yearn and above expenence.
12. Administration
Ministry  of Water and Energy  (MoWE) is  the designated representative of the Client and will be responsible for work  oversight and contract administration. The consultant is  expected to work closely  with Ministry  of water Energy  (MoWE) staffs. All reports  will be addressed to Ministry  of water Energy (MoWE)
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Summery

Topographic Survey in Lake Tana Sub-Basin Floodplain Areas - Summary

Topographic Survey in Lake Tana Sub-Basin Floodplain Areas - Final Report Summary

1. Introduction

The report details a topographic survey conducted in the Lake Tana sub-basin floodplain areas of Ethiopia, focusing on Dembia and Fogera regions. The survey was commissioned by the FDRE Ministry of Water, Irrigation and Energy (MOWIE) as part of the Tana & Beles Integrated Water Resource Development Project (TBIWRDP). The work was carried out by Generation Integrated Rural Development Consultant (GIRDC) between February and December 2014.

2. Objectives

General Objective

To gather sufficient topographic data for hydrological modeling and flood studies to mitigate negative flood impacts.

Specific Objectives

Conduct detailed topographic surveys of 194km² in Fogera and 70km² in Dembia floodplains
Identify detailed spot contours for improved risk maps
Conduct cross-section surveys of rivers and gullies
Survey infrastructure within project boundaries
Prepare detailed topographic maps at 1:10,000 scale with 0.5m contour intervals

3. Methodology

The survey employed conventional ground-based techniques using:

Differential GPS (Leica System 1200) for control points
Digital Total Stations (Leica and Sokkia) for detailed surveys
Post-processed kinematic (PPK) GPS solutions

Key Activities:

Field reconnaissance and stakeholder consultation
Linking with Ethiopian Mapping Agency (EMA) Ground Control Points (GCPs)
Establishing permanent benchmarks (89 in Fogera, 42 in Dembia)
Detailed topographic surveys at 50m x 50m grids
Cross-section surveys of major rivers (Gumara, Ribb, Megech, Dirma)
Infrastructure and village surveys

4. Key Findings

Floodplain Characteristics

Parameter	Dembia Floodplain	Fogera Floodplain
Area Surveyed	70.91 km² (7,091 ha)	195.75 km² (19,575 ha)
Major Rivers	Megech, Dirma	Gumara, Ribb
Soil Types	Vertisols, Fluvisols, Gleysols
Average Slope	1-2%

Flood History

Major floods occurred in 1964, 1988, 1993-1995, and 2006-2007, causing:

Loss of lives (44 in 1995, 600+ in 2006)
Displacement of thousands
Damage to crops, infrastructure, and property
River course changes (Megech and Rib rivers)

5. Deliverables

Maps Produced

Map Number	Description	Scale
TBS/TSF&D/01	Location Map of Lake Tana Sub-basin Floodplain Areas	1:175,000
TBS/TSF/03	Topographic Map of Fogera Floodplain	1:50,000
TBS/TSF/04	Detail Topographic Map of Fogera Floodplain (12 sheets)	1:10,000
TBS/TSD/07	Topographic Map of Dembia Floodplain	1:20,000
TBS/TSD/08	Detail Topographic Map of Dembia Floodplain (4 sheets)	1:10,000

Data Formats

Excel databases of survey points
CAD files of cross-sections
GIS shapefiles and MXD files
PDF versions of all maps
Photographic documentation of benchmarks

6. Challenges

Destruction of benchmarks by local communities
High crops and dense vegetation obstructing surveys
Unexpected rainfall making fields inaccessible
Survey boundaries not fully aligned with actual flood-prone areas

7. Recommendations

Use higher resolution (30m) data for hydrological modeling
Implement 2D hydraulic modeling for more accurate results
Consider both negative and positive flood impacts
Improve flood protection structure standards
Include farmer consultation in design of flood mitigation structures
Expand surveys to cover additional flood-prone areas identified