FEDERAL DEMOCRATIC REPUBLIC OF ETHIOPIA MINISTRY OF WATER RESOURCES ERER DAM & IRRIGATION DEVELOPMENT PROJECT Final Detail Design Report Annex F: Road Infrastructure May. 2009 CONGER T ENGINEERING AND CONSULTING ENTERPRISE P.L.C (CECE) ENGINEERS WATER RESOURCES A AGRICULTURAL DEVELOPMENT PLANNERS EAX AOhlS AIIAIIA w-u-rx- x KPlnn In axMH’iulioti with Consultlnn En/iineerin/f Service (LT^DjQExecutive Summary Volume I : Dam & Appurtenant Structure Annex A: Dam Design Annex B: Dam Appurtenant Structures Annex C: Geotechnical Study Annex D: Hydrology' Volume 11: Irrigation & Drainage Annex E: Irrigation & Drainage Design Annex F: Road Infrastructure Annex G: Project Control Centers Annex H: Operation & Maintenance Manual Volume III: Project Worth AnalysisTable of Contents 1 Introduction...................................................................................................................................... 1 1.1 General...................................................................................................................................... 1 1.2 Location..................................................................................................................................... 2 1.3 Scope of the Report................................................................................................................... 6 2.0 Road Design................................................................................................................................... 7 2 1 Classification of Roads for the Project......................................................................................7 2.2 Typical Purposes of the Roads.......................................................................................... 7 2.2 Geometric Design...................................................................................................................... 9 2.3 Structural aspect and construction material selection.............................................................. 15 2.4 Drainage arrangement............................................................................................................. 19 3 0 Bill of Quantities and Specification............................................................................................. 24 3.1 General.............................................................................................................................24 3 .2 Bill of Quantities and Cost Estimate........................................................................................24 3.3 Specification.................................................................................................................... 24 4 0 Construction Schedule..................................................................................................................26Erer Dam Irrigation Project ZCECE & CES 1. Introduction 1.1 General Considering the importance of irrigated agriculture in all round development, the Government of Ethiopia had initiated action to bring more and more area under irrigated agriculture. To identify potential sources of water resources Preliminary Water Resources Master Plan for Ethiopia was got prepared by WAPCOS in 1990. Later on in 1998, Wabe Shebelle River Integrated Master Plan was drawn up and Erer irrigation project was identified as one of the potential scheme for development of irrigated agriculture. This project was found technically feasible, economically viable, environmentally sound and socially equitable and therefore recommended for implementation. The detailed designs are now being prepared to enable the government to implement the project with promptitude. The main objectives of this Consultancy Services are preparation of the Detail Engineering Design and Tender Document for the Erer Dam & Irrigation project. Thus, the Detailed Engineering Design is carried out to meet the economical approach and technically viable project as indicated in the Feasibility Study and as reviewed during the Inception phase and as proposed in Design Report. The service is carried out in accordance with generally accepted standards of professional practice and following recognized engineering procedures. The consultant’s scope of work is understood to cover all activities necessary to accomplish the stated objectives of these services, while adhering to the aforementioned procedures and practices. The scope of the services shall include all the services necessary to achieve the objectives described above. The road design for the Erer Dam and Irrigation project is part and parcel of the above objectives and the scope of works. The Feasibility Study carried out for the appraisal of Annex F: Road Infrastructure /Final Detail Design Report /2009 1Erer Dam Irrigation Project ZCECE & CES the project was commented during the Inception Phase prepared for the approval of the client including the Design Report. Basic concept on this report is adhered to the inception report and on the design proposed report except very minor change made on the cross slope of the roads to suit the condition and economical factor for the construction. In the Inception and Phase One Design Reports, the followings were considered for the design which is based on the Feasibility Study under taken by the consultant. Roads identified to serve the irrigation scheme are summarized as follow; • Primary canal length was 14.11 km • Secondary canals had two separate directions resulted Sl-P 6.8 Km and S2-P 9.53 Km • Other existing roads that were served the community prior to the project identification. • Tertiary and quaternary roads are those with lower design standards and would be implemented by the beneficiaries themselves in order to make the project economical and as well as for participation of community in the provision their own benefits. 1.2 Location The Erer Irrigation Project (Figure 1) proposes to draw irrigation supplies from Erer River which is a tributary of Wabe Shebelle River. The project is located at about 530 km from Addis Ababa and 19 km from Harar town. The command area is situated on both sides of Harar-Jijiga road which is 11 km from Babile town towards Harar. The proposed dam site is situated about 6 km on left side of Harar-Jijiga road. Erer Irrigation Project is located in two Regional States, namely Regional State of Harari and Regional State of Oromia. In Oromia, project area is situated in Babile of the East Hararge Zone .In Harari it is situated in Erer and Soft Woredas. Annex F. Road Infrastructure /Final Detail Design Report /2009 2Erer Dam Irrigation Project ZCECE & CES MDEX MAP OF ERER IRRiOATlOU PROJECT Erit(*a Uganda Figi .0 Erer Irrigation Development Location map The command area starts from some distance downstream of the dam and extends only on right bank of Erer river. The command area is narrower and smaller near the dam site and becomes wider in the downstream side. The irrigable area is mainly situated below the bridge on Harar Jijiga road and extends beyond confluence of Erer River and Bidisimo stream covering only the right bank of the river. Although suitable areas are available on left side of the river also, due to limitation of water availability for irrigation only the command on the right bank of Erer River is chosen for this project. Annex F: Road Infrastructure /Final Detail Design Report /2009 3Erer Dam Irrigation Project ZCECE & CES The Primary Road section route generally traverses along similar landscape that varies in elevation from 1365m at the dam site to 1355m a.s.l. at the bifurcated to the two secondary canals. Both the secondary canal roads commenced at 1355m and traverses in two directions of which Sl-P runs to an elevation 1291m a.s.l. while S2-P terminated at around 1341m a.s.l. From the morphological set up of the area, the project route corridor has broadly cone major physiographic region of hilly section. Climatic conditions in Ethiopia, especially rainfall distributions, are largely governed by altitudinal variations and temperature variations. Based on Mean Seasonal Precipitation and Mean Seasonal Temperature variations, three operational seasonal periods are commonly known in Ethiopia These are named as “Bega”, “Belg” and “kiremt and are occurring in months of October - January, February - May and June - September, respectively. Using metrological data in the Atlas of Ethiopia 1984, the project area falls into Tropical Highland Climates region This could be classified as the area as an arid climate, locally known as “Kolla” zone with an altitude range of 700 - 1500 meters Mean annual temperature is in the range of 30°C - 40°C. The remarkable features of this climatic region are that, it has dry weather, rainfall is in summer (Kiremt) and evaporation generally exceeds precipitation. On the other hand the mean minimum seasonal temperature, see table below, ranges between 10°C - 15°C and occurs in the months of June to September. Table 1.1 Mean Seasonal Maximum and Minimum Temperature Phy. Reg. October - January (Bega) February - May (Belg) June - September (Kiremt) Max. Min. Max. Min. Max. Min. Eastern Lowlands 25°C - 30°C 20°C - 25°C 30 C - u 35°C 20°C - 25°C 25°C - 30°C 15°C - 20°C Annex F: Road Infrastructure/Final Detail Design Report /2009 4Erer Dam Irrigation Project ZCECE & CES The highest likely mean seasonal rainfall recorded along the eastern lowland is about 250mm and occurs in the month of June - September (Kiremt). Where as, in the central highland areas towards Bala area still receive their highest rainfall during the period of June - September (Kiremt), which is between 500 - 1000mm. Summary of the mean seasonal rainfall is given in Table below, Table 2.2 Mean Seasonal Rainfall (mm) Physiographic Regions October - January (Bega) February - May (Belg) June - September (Kiremt) Eastern Lowlands 10-50 50-100 100-250 Note. The temperature and rainfall data are only intended to give an insight about the climate of the project area and are not gauged The general layout of the road network (Figure 2) follows the irrigation scheme, which is the primary function of the road infrastructure The alignments of all roads except the existing ones are parallel to the primary and secondary canals. The commencement of the road is at the crest of the dam at the extreme left side where it would be connected to the existing road serves the community along the reservoir area. This road needs realignment, not to inundate by the water reservoir water by the proposed dam. However, the final road standard and realignment is dependent up on the future resettlement plan. The other road component under this report is the one which connects the truck road of Harar - Babile road to the camp for Munschen fur Munschen The road connects several villages and settlements but it is far from the proposed new roads. It also has good engineering structure, thus needs only rehabilitation work. Annex F: Road Infrastructure /Final Detail Design Report /2009 5Erer Dam Irrigation Project /CECE & CES 1.3 Scope of the Report This report is prepared in connection with the detail road design works of Erer Irrigation project. It elaborated the application of the design under discussion and confirms the proposed design during the Inception and Phase One Reports. The first part of the report tried to show the general appearance of the road and its location in respect to the dam and irrigation scheme. The second part of the report shows some design approach, modification and deviations from the stated design due to economical reasons. It also elaborates the road design which is adhered to the existing ERA design manuals of specific classes and component within the design parameters. This part of the report also discusses the purposes of each of the road infrastructures and their major functions in order to make economical construction and maintenance of the road in each category. Discussion also made on the provision of local material for the use of the road construction and the drainage aspect of the irrigation scheme. The third part of the report is dealt with the specification of road construction under the bill of quantities for the work items Based on the bill of quantities cost estimations were made to indicate the required budget for the roads under the contract. The last part of the report indicates the schedule for the provision of the road infrastructure in respective of the dam and other construction. Annex F: Road Infrastructure /Final Detail Design Report /2009 6Erer Dam Irrigation Project ZCECE & CES 2.0 Road Design 2.1 Classification of Roads for the Project The classification of the road that had been designed to facilitate the purposes of the dam and irrigation scheme was discussed in detail in the design phase report. To summarized and high light the important parameters under consideration are, • The Ethiopian Roads Authority’s Standard Specification 2000 would be the bases for the design. • However, The ERA standard maybe modified for lower design roads where the beneficiary themselves may undertake the construction and maintenance works of such structures as may be appropriate to be outside the scope of the contractor. • Factor influencing the road design standards, in particular the design speed, is the volume and composition of traffic. Thus, the design of a road should be based at least in part on factual traffic volumes. • The importance of geometric standards for low volume roads, as in the case of this project, is minimal. Thus, in such circumstance, it is appropriate to adopt inexpensive standards that enable the development of feeder roads with minimal cost. • The basic road infrastructure network would generally follow the irrigation layout. • Social and economical centers in the Weredas under the influence area would be considered in order to meet the requirements of the beneficiaries 2.2 Typical Purposes of the Roads While designing road in Ethiopia, in accordance with to ETA standards, road is classified according to the function it serves. This functional classification in the country recognizes five functional classes. Additional factor influencing the development of road design standards, in particular the design speed, is the volume of traffic and composition of traffic. For our case, the most appropriate classes of road in the farm and access road to the farm could be categories as Feeder Road where the AADT in most cases is less than 100 vehicles per day. The design of a road should be based in part on factual traffic Annex F: Road Infrastructure/Final Detail Design Report /2009 7Ercr Dam Irrigation Project ZCECE & CES volumes. However, the existing (factual) traffic volume may alter the design standard of the road Traffic volume may affect features of design, such as width, alignments, and gradients. The different functional roads serving different purposes will have its own standard that will consider the volume of traffic expected during the operation of the farm. The network will be connected to either the major road or the near by town for further connectivity with other outlets. Hierarchy of road network could be categorized according to their major functions All roads would be provided with adequate side drains from runoff water and disposed at the nearest natural channels. The amount of water discharge in each drain during the occurrence of high storm would be considered in order to make sure of their drainage capacity. Three categories of road types are identified in the irrigation scheme to serve different purposes with different standards. The very basic, as indicated in the Inception Report, is to follow the country’s established standards so as to ease the road construction and maintenance economics. The first and the highest road in the project is adopted from the DS-6 standard while roads which are already serving the community will be in the standard for the DS-7. The lowest hierarchy in the road standard (DS-9 or DS-10) is for those roads which are out of the scope of the contractor and construction and maintenance would be implemented by the beneficiaries The DS-6 standard road (Figure 2) will follow the primary and the two secondary canals that are designed as per the specification. The DS-7 is a rehabilitation of existing roads within the irrigation scheme without alignment change. These roads are connected villages in the areas and to the main highway road and will also serve during the project implementation and in the irrigation development. Annex F: Road Infrastructure /Final Detail Design Report /2009 8Erer Dam Irrigation Project ZCECE & CES TYROL SECTICN (ter primary cylitaPt jJO ahead & wc ant<) WIDENING TABLE SLOPE RATIO TABLE rtagrrtd Stope (m) Cut (H:V) WIDEN NG DUE TO HghW HoQhtcf M WWmnQ ktaten* (MV) ELrtn Sal 00 - 1.0 2:1 3.1 0 l 0 - 2.0 2:1 21 00-3.0 Over 2.0 2.1 3.2 3 0-6 0 0.3 Rock 00-20 05 1 1.25 I 6 0-90 0.6 Over 2.0 0.25 1 1•1 over 9 0 0.9 Figure 2 0 Typical Road Cross-sections 2.2 Geometric Design Using road functional classification selection and design traffic flow, in the Erer Irrigation project, the feeder road standards was selected as indicated in the Design Report made for the client. Table 2-1 below was reviewed to highlight the class of road under discussion. The feeder road with the design standards and expected AADT has five road design standards. Annex F: Road Infrastructure/Final Detail Design Report/2009 9Erer Dam Irrigation Project /CECE & CES Table 2-1 Design Standards vs. Road Classification and AADT Road Functional Classification Design Standard No. Design Traffic Flow (AADT) Design Speed (krn/hr) Flat Rolling Mountainous Escarpment DS6 50- 100 60 50 40 30 F E E D E R ■ DS7 30-75 60 50 40 30 DS8 25-50 60 50 40 30 DS9 0-25 60 40 30 20 DS10 0-15 60 40 30 20 The geometric design of the road project has been carried out as per ERA Geometric Design Manual - 2002-class DS6 as recommended on the design standard report. During the selection of horizontal and vertical alignment the design criteria and controls, which have been agreed between the client and the consultants, have been utilized in conjunction to safety requirements. The design has been conducted by the use of computer-aided design using soft desk and Eagle Point software. The software generates every detail with regard to horizontal alignment, vertical alignment, super elevations, etc. Annex F: Road Infrastructure /Final Detail Design Report /2009 10Erer Dam Irrigation Project ZCECE & CES Cross-Section Basic requirements for the road cross-section have been incorporated in a typical cross section drawing that has shown on the drawings (please refer to the drawing album.). • Carriageway and shoulder widths • Normal camber/cross fall details (for the reason of economical design this elements were modified to suit the canals’ layout) • Position of grade line and super elevation pivot point • Fill slopes at various embankment heights • Typical side drain geometry • Cut slopes in different materials • Details for transition from low fill to shallow cut • Benching details for high fills and deep cuts (if appropriate) • Nominal topsoil stripping depth • Thickness and extent of top soiling of earthworks slopes • Pavement layers thickness, widths, materials and construction specifications. Horizontal and Vertical Alignment The geometric design of the roads project has been based on the results of the study carried out during the detail design process. During the selection of horizontal and vertical alignment, the design criteria and controls, which have been agreed between the client and the consultants, have been utilized, wherever possible, in conjunction to safety requirements (please refer to drawing album). In this particular road design the controlling condition of the road elements is the layout of the canal system. This has been particularly where the water in the canal should be lowered than the road bed or sub-grade. Hence applying the balancing of earthwork quantities and setting of road cross sections with regard to super elevation, cut and fill Annex F: Road Infrastructure /Final Detail Design Report /2009 11Erer Dam Irrigation Project /CECE & CES slopes, longitudinal drains and cross drainage structures are governed by the layout of canals to minimized the maintenance cost. The approved geometric design standards for each agreed design speed have been applied to the design of the horizontal and vertical alignments using Computer Aided Design (CAD) techniques. Drawings have been produced as an output from the software package used. The horizontal and vertical alignments are interdependent, and as far as possible these elements have been co-coordinated to produce an aesthetically pleasing combination of the two. Safety considerations have been applied to the alignment design Points at even increments of length of 100 meters along the centerline, tangent points and such other critical points as may be required have been fully defined relative to the stations of the baseline by coordinates and offsets suitable for setting out the centerline All points have been coordinated to the national survey grid to which the project has been referenced. The digital terrain model has enabled cross sections to be determined along the length of the road centerline at each 100-meter station and as required (Figure 3). Annex F: Road Infrastructure /Final Detail Design Report /2009 12Erer Dam Irrigation Project /CECE & CES Figure 3.0 Typical Road Plan and Profile Annex F: Road Infrastructure/Final Detail Design Report /2009 13Erer Dam Irrigation Project ZCECE & CES • • The Design Speed is used as an index which links road function, traffic flow and terrain to the design parameters of sight distance and curvature to ensure that a driver is presented with a reasonably consistent speed environment. In practice, most roads will only be constrained to minimum parameter values over short sections or on specific geometric elements. The DS-9 and DS-10 standard was applied for road section for the tertiary canals as well as for quaternary canals respectively. The DS-9 and DS-10 are the lowest standard under the design standards. The singled lane width of the road would be 3.3 meters where in most cases farm tractors and carts may use the road section frequently A passing lane would be provided within a sight distance or at every 400 to 500 meters alternatively if two directions is occupied one against the other. The width of the lane could be widened at village section where there would be a need for parking lanes as well as pedestrian walk way The surface could also be paved if there is necessity with natural gravel to be effective during the wet seasons otherwise if there is no need of using during the rainy season the surface may be kept as natural soil surface. The constructions of these roads are left to the beneficiaries using labor based road construction method and thus it is out of the scope of the contractor’s duties. The higher hierarchy road network would be the road provided for the primary and secondary canals and other social and economical centers under the scheme. All roads of the DS-10 will be connected to these roads and more intensive canal maintenance required. Furthermore, farm inputs and outputs would be transported through these routes before and after every farming and harvest periods respectively. Thus, there would be a need for higher and more durable road standard. The higher level of the road network under the Erer irrigation project is the connection of the above roads to the higher standard of roads or to the nearest town where the Ethiopian road network existed. This level of the road network could be design to the DS-6 standard. This standard connects all the lower roads of the scheme to the outside world by which more trucks are expected during the operation of the farm. Annex F: Road Infrastructure /Final Detail Design Report /2009 14Ercr Dam Irrigation Project /CECE & CES 2.3 Structural aspect and construction material selection In conjunction with the soil and material requirements, assessment has been conducted to locate suitable construction material within the Project area The activities include; • Natural granular material for surfacing. • Quarry Stone for crushed aggregate and masonry works • Borrow material for embankment and improved sub grade • Water for compaction and concrete work. • Sand for concrete and mortar works. The basic material under the structure of any road is the sub-grade characteristic along the road corridor where all pavement structure depend on The sub-grade of the vicinity under the irrigation scheme is predominantly consists of sandy soil except at the end of the two secondary canals. This exhibited bearing capacity of more than adequate for the road classes under consideration. For the soil having more than CBR value of 7%, the sub-grade would be compacted according to the specification directly from the embankment while for the others less or equal to this value, as per the ERA design manual The following table recommends compaction thickness according to the results of the sub-grade CBR values (the result obtain from site soil tests). Table 2.2 Various CBR value and the corresponding thinkness. G7 of 25% IImmpprroovevedd susubbggrraaddee wwiitthh aa mmiinniimmuumm 44 -- ddaays ys sosoaakekedd CCBBRR ooff 77%% Annex F: Road Infrastructure /Final Detail Design Report /2009 15Erer Dam Irrigation Project ZCECE & CES Gravel materials that fulfill the minimum requirements as surfacing would be obtained outside of the irrigation scheme along the hills. This however should to be tested and approved prior to the use as surface material. The major excavation requirement would be for the construction of the dam structure hence suitable material could be selected from such excavation for the surface material. The gravel wearing course shall be either of the following table as shown below. Table 2.3 Recommended Particle Size Distributions for Mechanically Stable Natural Gravels and Weathered Rocks for Use as Base Course Material (GB2, GB3) Test sieve (mm) Percentage by mass of total aggregate passing test sieve Nominal maximum particle size 37.5 mm 20 mm 50 100 - 37.5 80- 100 100 20 60-80 80-100 10 45-65 55-80 5 30-50 40-60 2.36 20-40 30-50 0.425 10-25 12-27 0.075 5-15 5-15 Furthermore the wearing course gravel shall fulfill the requirement shown in table below. Table 2.4 Complementary Materials Requirement for the Gravel wearing Course Materials Property Requirement % Passing 37.5 mm mi. 100 Shrinkage product, SP SP = LS x (%pass 0.425mm) 120-400(1) Grading Coefficient GC (2) 16-34 Field dry density, (%MDD), Modified AASHTO Min 95 Compacted thickness Min 125 mm Max 200 mm Compaction moisture, Modified AASHTO 80- 105% (1) In built up areas a maximum SP of 270 is desirable to reduce dust problem. (2) GC = ((%passing 28mm - %passing 0.425mm) x (%passing 5 mm))/100 Annex F: Road Infrastructure /Final Detail Design Report /2009 16Erer Dam Irrigation Project ZCECE & CES Taking-into account the need for construction of major and minor drainage structures, rock exposures that could be used as sources of crushed aggregate for cement concrete and masonry works have been observed. Suitable quarry stones are fairly available within the project area, in favour of the geological setting and physical nature of the rocks. Most of the quarries identified are made up of basalt and rhyolite. The joint spacing of the rock mass was also noted as an indication of workability and potential weathering. In general potential quarries have been assessed based on the following criteria • Ease of mining and development of quarry faces; • Ease of erecting crusher plant, • Minimum overburden; • Outcrops with minimum variability in strength characteristics, • Proximity to the alignment, and those with existing access, or those simple for opening access; • Those with sufficient quantity; and • Those with little impact upon the environment and local settlements Most of the quarry sites located as potential and additional sources could also be used as sources of masonry stones. Majority of them are strong enough to full fill the strength requirement as masonry stone as observed from field assessment. The design of the roads, particularly the primary and the two secondary canals, are laid parallel to the canals and attain higher elevation than that of the water flow in the canals resulted for more borrow to fill activities. The amount of fill required would be obtained along the right side drains proposed for excavation. Additional material could be also obtained on the hill side outside the scheme. Due to the nature of the soil in the area excavation for borrow material to haul out of the free distance is not necessary. It is therefore provision is not included in the bill items Annex F: Road Infrastructure/Final Detail Design Report /2009 17Erer Dam Irrigation Project ZCECE & CES ♦ During the field survey, potential water sources for compaction and concrete work has been identified from the Erer River and also found at Dicho River but the amount of water during the prolonged dry season need to be fetched from other sources. Potable water would be hauled from the Harar Town or Besidimo Village. Sand sources for mortar and concrete works are available within the project area, it seems their resistance to soundness test is satisfactory. Erer and Dicho River sands could be used as sources but river sand has characteristics of renewable whose properties could be changed from season to season. Hence the required tests as indicated in the specification, should be done at different sources and seasons. In general the following tests are recommended prior to the use of particular material for the permanent construction; Sub grade Material • AASHTO soil classification, Liquid Limits (AASHTO T89 - 94) and Plastic Limits (AASHTO T90 - 94) including sieving on 2.0, 0.425 and 0.075mm sieves at intervals of lkm. • 1 - Point CBR tests at every 2 km (AASHTO T193-93), 4 days soaked, light hammer compaction • Natural moisture content in areas with darker sub-grade soils Natural Gravel Sources • 3 - point CBR (AASHTO T193 - 93) at modified compaction (AASHTO T180-93), 4 days soaked • Grading, T27 - 93 • AASHTO soil classification, Liquid (AASHTO T89 - 94) and Plastic (AASHTO T90 - 94) Limits Annex F: Road Infrastructure /Final Detail Design Report /2009 18Erer Dam Irrigation Project ZCECE & CES Rocks for Crushing • L A Wear, AASHTO T 96 - 94 • Soundness (sodium sulfate), AASHTO T104 - 94 • Aggregate crushing value according to BS- 812 part 110:199 • Flakiness Index Sand • Organic Impurity, AASHTO T-21-91 • Grading, AASHTO T-27-93 • Soundness (Na2SO4), AASHTO T-104-94 Water • Chloride content • Sulfate content • pH value 2.4 Drainage arrangement The provision of efficient and adequate drainage system is extremely important for the life of the road and surrounding thereby This will reduce maintenance cost and preventing adverse environmental impacts Inadequate drainage design will contribute highly to deterioration of the pavement structure Areas to which attention should be given could be categorized as surface and subsurface drainage along the road and cross drainage (adjacent territory drainage) The design of longitudinal drains, culvert capacities and waterway openings have been governed by the criteria specified in the ERA Standards (2002) Annex F: Road lnfrastiucture/Final Detail Design Repoit Z20O9 WErer Dam Irrigation Project ZCECE & CES The surface drainage system, which will take care of rain water from the pavement surface, adjacent cut slopes and the ground cross fall have been treated by proper cambering of the roadway and by introduction of side drains. Minor drainage structures (structures less than 6m wide) have been specified as standard structures and have been recommended based on hydraulic efficiency, type of terrain and foundation material Wherever possible, standard drawings have been adopted unless and otherwise special type of design is required. Field visit has been conducted and the nature of the catchments areas, the type of terrain and soil & land use pattern have been assessed after the locations of the streams are identified with hand held GPS and subsequently ground survey has been carried out. The type and size of drainage structure specified for a particular location is often determined based on structural selection criteria Bridges are used where they are more economical than a culvert, perhaps due to the need to bury a culvert under a high level of fill. They are also employed to satisfy land use requirements, to mitigate possible environmental harm with a culvert, to avoid floodway or irrigation canal encroachments, and to accommodate large debris. Culverts are used where bridges are not hydraulically required, where debris is tolerable, and where they are more economical than a bridge. Concrete box and slab culverts are constructed with a square or rectangular opening, and with wing walls at both ends. They are usually specified for larger flows, where the area of the opening is larger than that available for manufactured concrete or metal pipe culverts. > They may also be used where the cost estimate indicates that concrete box/slab culverts Constructed on site are less expensive than manufactured and/or imported pipe culverts. Annex F: Road Infrastructure /Final Detail Design Report /2009 20Erer Dam Irrigation Project ZCECE & CES Lining of ditches has been recommended where the occurrence of erosion is anticipated It has been recommended on the hydrologic study to implement lining where ditch velocities exceed certain values. Additionally, considering the different types of sub grade material to be encountered and the limitation that normally corresponds with the velocity of the flow, the construction of ditch lining has been set for section of the road with greater than or equal to 5% slope. The details of this have been attached on plan/profile sheets. (Please refer to drawing album) Delineation of drainage catchments crossing the road were defined on 1:250,000 & 1:50,000 scale topographic maps for all catchments and subsequently worked out at detail level. The areas of the delineated catchments were determined by the use of digital planimeter. The catchments parameters such as slope, length of the longest water course, difference in elevation between the crossing point and water divide were all determined from the above mentioned topographical maps. The hydrological fieldwork is comprised of i) Hydrological survey of the alignment to determine sections of the route with unstable hydrological conditions (erosion, water logging, landslide, etc) and to investigate their causes ii) Asses the land cover conditions of the drainage of rivers and streams crossing the alignment and catchments parameters During field survey, the following important observations were recorded: • The roads’ alignments of both the primary and the two secondary canals are traversing through hilly cut need several crossings of different openings. Annex F: Road Infrastructure/Final Detail Design Report /2009 21Erer Dam Irrigation Project /CECE & CES________________________________________ . In order to minimize construction cost, the culverts crossing the canals also crossing the roads’ alignments on which both structures are integrating within the same type of culverts. . The canals and the roads are aligned parallel to each other resulted with inlets of all culverts from the streams are served both structures (The canals and the road sections), hence the road crown slope would be in one direction toward the outlet. The hydrology study for the project as a whole carried out in the same report for the design under the dam and irrigation report and hence here it is referred only the final analysis for the road drainage structures There are 33 culverts provided to accommodate the runoff water and the natural streams crossing the canals and roads. The hydrological analysis of the study is carried out as per ERA Drainage Design Manual (DDM) 2002 and AASHTO Highway Drainage Guidelines. a) Catchments Size. The following design criteria have been adopted; 2 i) For small catchments areas up to 0.5 km , provided that the catchments generally has uniform slope, soil and land cover simple rational formulas have been adopted ii) For main catchments areas of ungauged rivers SCS unit hydrograph, area velocity, Regional Regression formula and TRRL methods have been adopted. b) Return Periods. The selection of the return period on the design floods is commonly based on experience and economic consideration. Considering the guidelines mentioned above, the following return periods are considered for the present analysis. • 25 year return period-'for short span bridges and check for 50 year return period of over-toping for DS5 road standard, Annex F: Road Infrastructure /Final Detail Design Report /2009 22Erer Dam Irrigation Project ZCECE & CES • 50 year return period for medium bridges and check for 100 year return period of over-toping, • 100 year return period for main bridges and check for 100 year return period of over toping • 10 year return period for culverts and check for 25 year over-toping. The discharge capacity estimation for culverts will be made by the formula proposed by D. Fiddes and L.H. Watkins, “Highway and Urban Hydrology in the Tropics” and compared with the software HY8 This empirical method suggests formulas for two cases, i.e long and short culverts (i) Span< 2m; and (ii) 2m< Span<6m). In the long culverts, friction loss is a major factor, while in the short culverts, entry conditions are critical. The Formula for Short Culverts Q = CdA >1 (2gd) The Formula for Long Culverts Q = A0 (2Gh/(ke + kf + 1)) Tables for coefficients used for calculating discharge by this method will be directly taken from the reference book mentioned above. Depending on the Design capacity estimation, the design flood comparison proposal for new culverts will be recommended. The minimum diameter of 750mm for pipe culverts as recommended by ERA Manual is also pursued. Annex F: Road Infrastructure /Final Detail Design Report /2009 23Erer Dam Irrigation Project ZCECE & CES-------------- ----------------------- ------------------- < 3.0 Bill of Quantities and Specification 3.1 General The design of the roads is reflected on the bill of quantities (BOQ) on which estimation of works have been established. The BOQ, the specifications of works and the drawing should be read concurrently during the bidding process and as well as during the construction period. The specification of works governs the work methods, payment term and quality requirements under each bill items. The final drawings as working drawings are expected from the prospective contractor and approved by the supervisor prior to the commencement of any works. All take of on actual site works would be the final measurements for payment approval. 3.2 Bill of Quantities and Cost Estimate The quantities set out in the Bill of Quantities are estimated quantities and are used for computation of tenders and awarding contract It should be clearly understood that only the actual quantities of work done or material supplied measured for payment, the billed quantities may be increased or decreased. 3.3 Specification The scope of the works for this technical specification has two distinctive objectives; • Construction of new roads for the Erer Dam and Irrigation project and • The rehabilitation of existing roads within the project scheme. The technical specification for the road construction has five sections according to the work to be under taken to complete the contract. < • Section 1 Clearing and grubbing of the road • Section 2 Earthwork Section 3 Pavement works Annex F: Road Infrastructure /Final Detail Design Report /2009 24Erer Dam Irrigation Project ZCECE & CES_________________________________ 1.0 Section 4 Drainage works 2.0 Section 5 Daywork ERA Standard Specification 2002 is the technical specification for all the works under the road works. Where ever applicable particular condition governs. Annex F; Road Infrastructure /Final Detail Design Report /2009 25Erer Dam Irrigation Project /CECE & CES 4.0 Construction Schedule The workload for the road sub project of the Erer dam and irrigation project has about 34 km of new construction and 11 km of rehabilitation. The sub project is not meant to be treated separately rather part of the total project. The construction of the drain, canals and roads could be done concurrently with few stretches of one to the other. Hence the construction of the road sub project should be part and parcel of the other infrastructure. The estimated construction period is 22 calendar months as shown in figure 4.1. AnnexF: Road Infrastructure/FinalDetailDesign Reporf/2669 26
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