Amibara Drainage Project Phase-II Soil Survey Summary

GOVERNMENT OF ETHIOPIA
MINISTRY OF WATER RESOURCES
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SOIL SURVEY/SO1L CLASSIFICATION DATA
<- Analysis
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ANNEX -4A
AMIBARA DRAINAGE PROJECT PHASE-II
PREPARATION OF DETAILED DESIGNS, TENDER DOCUMENTS.
PROJECT PREPARATION REPORT AND
ENVIRONMENTAL IMPACT ASSESSMENT REPORT
WATER AND POWER CONSULTANCY SERVICES (INDIA) LTD
(International Consultants in Water Resources)
KAILASH'. 26, KASTURBA GANDHI MARG ,
NEW DELHI - 110 001 .INDIAp
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I I I I I I I I I I I I I I I I
ISOIL SURVEY/SOIL CLASSIFICATION DATA/
ANALYSIS
ANNEX-4Ay
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ISOIL SURVEY STUDIES
CONTENTS
1          General Features or Study Area 
I            I Location
I            2 Geomorphology
1           3 Topography
14  Climate
15  Irrigation and Agriculture Development 1           6 Rationale for the study
1 7 Delineation of study area
Fages
1-1 to 1-3
2  Plan of Approach and Methodology for Soil Survey Studies 2-1 to 2-10
2.1       Introduction
2 2       Methodology of field soil survey and determining hydraulic properties
2.2 1    Auger bore study
i
Soil Colour
ii
Soil texture
in
Soil consistence
iv
Electrical conductivity of 1 2 soil-water suspension
V
Soil reaction (pill
vi
Free carbonates
VII
Mottling
vin
Concretions
IX
Relatively Impermeable layer Criteria and definition
ix           Depth to groundwater
xi          Groundwater EC & pH
xn        Soil profile description
2  2 2 Determining hydraulic properties in field - hydraulic conductivity and infiltration tests
2  2 2 1 Determining hydraulic conductivity using pour-in method
2  2 2 2 Determining hydraulic conductivity using bail-out method
2  2 2 3 Determining infiltration rate
3. Description of
 Soil Ty
pes in Project Area 
3-1 io 3-13
3
I
Introduction
3.2       Textural profiles
3           2 I Criteria for classification of textural profiles
3           2 2 Distribution of textural profiles in the Amibara project area
3.2 3 Distribution of textural profiles in the Melka Sadi
project area
3.3        Description of soil types
3           3 I Deep clay soils
3           3 2 Soils w ith appreciable amounts of clay oi silty clay in control section
3           3 3 Soils with medium and mixed texture
3           3 4 Relatively coarse textured soils
3           3 5 Coarse textured soils with sand or loamy sand more than 5 per cent in control section
3           3 6 Rock out- crop
ii4
Distribution of Soil Salinity in Project Area
4.1      Introduction
4  2 Criteria for classifying the salt affected soils
4  3    Saline soils
4  4    Sodic soils
4.5     Saline - Sodic Soils
4  6    Measurment of Soil Salinity in field
4  7 Determining EC of saturation extract in laboratory 4  8 Conversion of EC (12) to ECe
4 9 General distribution of saline soils
4 9 I Soil salinity in Amibara Area
4 9 2 Soil Salinity in Melka Sadi Area
5 Drainability Classes and Drains Spacing
5           1           Introduction
5.2     Soil factors influencing drainage
5           3           Soil parameters for drain spacing
5           3 I Auger bore logs
5           3 2 Field measurements of hydraulic conductivity 5           3 3 Depth to relatively impermeable layer
5           4           Determination of sub-surface field dram
4-1 io 4-10
5-1 to 5-16
depth and spacings
5
4 1 Drain depth Criteria for selection of drain depth
5
4 2 Drain spacings
5
4 2 1 Approach and criteria
5 4 2 2 Selection of hydraulic conductors
5 4 2 3 Selection of depth to relatively impermeable laser
and alternate criteria for selection of lateral spacing 5 4 2 4 Selection and method of calculation of drain spacing
in5 5 Drainabilily classes 5 5 1 Drainability class I
5 5 2   Drainability Class 11 5 5 3   Drainabilily Class 111 5 5 4      Drainability Class IV 5 5.5     Drainability Class V
6. Description of Soil Profiles
References
Maps
6-1 to 6-8
1-14
ivCHAPTER 1
GENERAL FEATURES OF STUDY AREA
1.1       Location
The study area is located at right bank of the Awash river, about 260 km east of Addis Ababa, adjacent to the Melka Warer and Melka Sadi towns in Middle Awash Valley Project area is about 8 km to the west of Awash-Melie highway and is connected with all weather road
1.2       Geomorphology
The study area is in the Rift Valley region, in which three main geomorphological units may be recognized as i) recent alluvial plains, ii) volcanic formations and iii) a series of old fluviatile terraces. The study area lies in the extensive flood plains formed recently by deposition of alluvial, volcanic and colluvial materials, including mainly sand, silt and clay in addition to basalt, tuff*, ash, gravel, cobbles etc.
1.3       Topography
The topography of the study area is an outcome of the geomorphological activities in the river basin forming an extensive alluvial plains The meandering course of the Awash forms the western boundary of the study area with levy formation along the bank and consequently the land slopes away from the river On the east, the ground slopes away from the Aledeghi escarpement towards the study area The ground elevation ranges from approximately 745 m in the south to 725 m in the nonh, in a overall streach of 36 km and width of some 8 to 2 km from west to east. Gradients are generally flat, in the range of
LI0 05 to 1 0 per cent There are a few evidence of past volcanic activities in the study area, where volcanic cones, such as Dinile and Amibara hills, rise abruptly from the flat plain
1.4         Climate
The study area has semi-arid climate with a mean annual, rainfall of about 560 mm with a considerable variation in precipitation from year to year. Annual rainfall is  bimodal with about 40 per cent of the annual mean occurring during the months of July and August and some 30 per cent during February to April
Mean monthly  temperature varies  from 22.5°C in December to 38.5°C in June Relative humidity varies from 58 per cent in August to 36 per cent in June The wind velocities are highest in June and July  exceeding 200 km/day  Annual sunshine hours  are in excess  of 3000 Annual evapotranspiration is estimated as 2400 mm.
1.5      Irrigation and agricultural development
Amibara and Melka Sadi state farms, in which study area lies, are irrigated by gravity flow by  diverting  the  Awash  river  water  through  weir  at  Melka  Sadi  Cotton  is  the  main  crop presently  grown  in  study  area  Some  small  part  is  under  maize  cultivation  also  Due  to drainage  and  other  problems  the  cropped  area  of  state  farm  has  reduced  considerably  to 8,400  ha  of  cotton  and  400  ha  of  banana  As  revealed  from  past  studies  the  cotton  yield has also decreased due to gradual increase in soil salinity and rising groundwater
1.6         Rationale for the study
For sustained crop growth a favourable salt and water balance in rooting zone depth is important. Previous  studies  have shown that over the period, on introduction ot irrigation, water level & its salinity have risen considerably in the project area Deptlvaf
1-2groundwater levels in Amibara under phase 1, as reported by Halcrow &. Panners, were within 300 cm below surface in an appreciable large area Similarly in phase II areas, where ground water level is within 300 cm of the surface have been included in the drainage programme which are contiguous to phase 1 areas Similarly, increase in soil salinity was also expected in surface and sub-soil in- phase II area Thus considering above aspects, the present study was undenaken to suggest an integrated drainage system to maintain groundwater and soil salinity at acceptable levels in phase II area
In order to assess quantitatively the drainage parameters related to soil types, soil and groundwater salinity, hydraulic  conductivity, depth to relatively  impermeable layer and other soil characteristics, the present study of the field soil survey was suggested in study area.
1.7       Delineation of study area
As per terms of reference the study area under phase II would be studied taking into consideration the existing groundwater level <3m from surface, soil salinity distribution, and other related aspects based on field data collected by consultant during the study The soil investigations were to be carried out in sufficient detail in areas having water table depth <3 m. Thus present study was carried out in such areas of about 4,000 ha
1-3CHAPTER 2
PLAN OF APPROACH AND METHODOLOGY FOR SOIL SURVEY STUDIES
2.1        Introduction
Periodic  supply  of irrigation water usually  results  in substantial changes  in soil physico chemical and hydraulic  properties. Principal associated changes  are generally  prolonged high water regimes  affecting root aeration and rise in salt content in soil profile Therefore, for sustained crop production in irrigated farming system, it is  exceedingly important to maintain a favourable oxygen - water - salt balance in rooting zone In order to achieve and maintain the above equilibrium the drainage facility may  follow or taken-up alongwith irrigation facilities, particularly in highly affected areas
In order to generate basic data required for drainage design and to characterise the soils of project area, in-situ soil investigations  were carried out. These include, field soil survey through studying log observations  of auger bores  at grid of 400 m x  400 m, soil profile observations  at selected locations, in-situ hydraulic  conductivity  determinations. Methodology and criteria in brief for above field studies are described below.
2.2  Methodology of field soil surv ey and determining soil hydraulic properties
2.2.1 Auger bore study
As  per  drainage  requirements,  project  area  of  Amibara  and  Melka  Sadi  State  farms  was demarcated  for  field  soil  survey  studies,  based  on  occurrence  of  high  water  table  regimes up to 300 cm bgl The density of all the observations was in the order of I per 16 ha. as widely used for detailed soil survey for project planning Thus the study area was divided
2-1into grids of 400 m x 400 m and intersect points were used as locations in field for auger bore study. The locations  for auger bore observations  alongwith other test sites  are depicted on maps
*
Each auger bore was studied in field up to a depth of 5 m. Throughout the depth, salient physical, chemical and soil water properties were recorded in field. These characteristics include soil colour, texture, consistence, electrical conductivity  (1.2 soil-water suspension), pH (1 2 soil-water suspension), reaction to HC1, occurrence of concretions &. mottlings
i) Soil colour
Soil colour as one of the improtant characteristics of soils, which provide ready clue to soil conditions and several important soil properties, was directly observed in field using Munsell soil colour chart. Soil colour for varying soil depths was recorded with notations of three variables  by  hue, value and chroma on auger bore description sheet The corresponding colour can easily  be read by  referring colour for respective notations  in Munsell chart e g 10YR3/3 refers dark brown colour of soil. It is to be mentioned that soil colour varies with respect to texture and soil moisture status as well
ii Soil texture
Soil texture which has direct bearing on pore-geometry (porosity) - the arrangement of macro and micro channels within soil mass responsible for draining the water, particularly through sub-surface drainage installations  for reclaming the land, was  judged by  'feel method' for respective soil depths. The feel method is  based on the expression of coarseness, fineness, hardness, stickiness, or plastic behaviour of soil as felt during rubbing moist soil between thumb and fingers. More common soil textural classes observed in
2-2field were silty  clay, silty  clay  loam, silt loam alongwith other fine, medium and coarse textural classes  In the present study, the different textural classes  are shown on'auger bore description sheets.
iii. Soil Consistence
Soil Consistence reflects  the expression of degree and kind of cohesion or resistance to deformation or rupture of soil material. Field study  of consistence is  made at three levels of moisture contents and specifically described as consistence when dry, consistence when moist and consistence when wet Consistence under dry  conditions  varies  from loose to extremely  hard, under moist conditions  from loose to extremely  firm and under wet conditions  from non sticky  non plastic  to very  sticky  very  plastic  Soil consistence in field was  assessed in field by  breaking or crushing the soil under dry, moist or wet conditions and according to feeling of hardness, looseness, friableness, stickiness  as  manifested by degree of cohesionness and resistance, and recorded on auger bore description sheet and soil profile format for respective depths and soil layers.
iv. Electrical conductivity of 1:2 soil-water suspension
Electrical   conductivity   measurements   in   field   were   carried   out   using   12   soil-water suspension  In  order  to  diagnose  the  salinity  occurrence  in  soil  profile  EC  (12)  was measured  at  three  varying  depths  for  each  auger  hole  site  EC  of  surface  soil  was measured  by  drawing  soil  sample  between  0  to  30  cm.  depth,  while  two  other  EC measurements  of  sub-soil  were  recorded  at  30  -  100  cm  and  100  -  200  cm  soil  depths respectively  EC  was  measured  using  portable  digital  electronic  meter  of  soil  suspension prepared  by  mixing  one  pan  of  soil  (volume  basis)  in  two  pans  of  water  Soil  salinity maps  were  prepared  by  plotting  EC  values  of  surface  soil  and  sub-soil  and  depicted  on maps no 3 and 10 for Amibara and Melka Sadi areas respectively
2-3V.            Soil reaction (pH)
Soil reaction, pH, was also measured of 1:2 soil-waler suspension at three respective depths alongwith EC measurements using digital pH meter after its calibration in standard buffer solutions.
vi.        Free carbonates
The presence of free carbonates in soil was tested with diluted HC1 The presence of carbonates  in soil is  distinguished by  nil, slight, strong or violent effervescence HCI reaction with soil was tested at all varying soil depths for respective auger bore and soil profile depths and recorded in auger bore and soil profile sheets.
vii.       Mottling
Presence of mottles in soil profile indicates the occurrence of waterlogging conditions for prolonged period resulting in reduction processes. Mottling was  described by  noting colour of principal mottles using Munsell soil colour chart. The presence and magnitude of mottels wherever observed within 5 m soil depth were recorded in auger bore and profile sheets
viii.   Concretions
Concretions generally formed from local accumulation of materials like calcium carbonate, magnesium carbonate, iron or manganese oxides with soil panicles Magnitude and size of concretions  were observed by  feeling on crushing or rubbing soil Whenever coneretions noted were recorded in auger bore and profile sheets In addition to above soil propenies, other important parameters which are exceedingly important for drainage design such as:
2-4a. depih to relatively impermeable layer,
b depth to groundwater,
c. EC and pH of groundwater, and
d site description
The above parameters have also been recorded on auger sheets for respective auger bores.
ix.         Relatively impermeable layer: Criteria & definition
To identify  the relatively  impermeable layer, while logging the auger bore up to a depth of 5 m is very important as it has a direct bearing on drainage design of sub-surface drains. For drainage purposes, a relatively  impermeable layer has  been defined as  a layer which has  a hydraulic  conductivity  of less  than one-tenth of that of the immediately  overlying layer. By  another definition (USBR, 1964) the drainage barrier has  a permeability  value less  than one-fifth the average of the horizons  above it. However, as  it is  extremely difficult to determine hydraulic  conductivity  at large number of sites, except with an alternative to assume K values  as  cited in literature for different soil textural classes, it is necessary  to adopt more practical approach for characterizing the relatively  impermeable layer
It's  worth  mentioning  that  relatively  impermeable  layer  as  a  parameter  for  sub-surface  field drains design usually acts as a drainage barrier which causes a saturated zone or build-up of  perched  water  table,  and  sets  a  limit  to  the  depth  of  permeable  material  It  restricts  the downward  water  movement  and  causes  lateral  flow  either  to  natural  slope  or  installed  field laterals  and  thus  causing  more  close  spacing  of  drains  On  the  contrary  when  there  is  no occurrence  of  such  barrier  or  it  occurs  sufficiently  deep  most  of  the  water  flow  may  be vertical   below   the   drains   and   thus   allowing   widely   spaced   laterals   in   field.   The construction costs of tile drains become very costly when such barrier stratum is less than
2-5275 cm from the surface Therefore, an accurate and practical approach to identify the relatively impermeable layer is very important to drainage cost estimates.
Keeping in view the above aspects, in present study, the relatively impermeable layers have been identified as  having i) a texture of clay  or silty  clay  with overlying more permeable medium or coarse textural layers and, ii) a firm, very firm or extremely firm consistence when moist, or a hard or very hard consistence when dry.
As revealed from auger logs a compact layer usually occurs within 30 to 50 cm soil depth from surface, which are caused by  using particular diameter of discs driven by  heavy tractors repeatedly over each tillage operation thus only pulverizing the soil up to disc size and compacting such layer just below. These layers  were not considered as  relatively impermeable
The inference and distribution of relatively impermeable layer with regard to drainability classes are described in subsequent chapter Contour maps of relatively impermeable
layers were prepared separetly for Amibara & Melka Sadi areas and depleted on map no. 6 and 13 respectively
x.         Depth to groundwater
Depth to groundwater was measured using specially designed water level recorder with two positive and negetive terminals extended through a flexible cable at lower end and connected other end of the cable to the multimeter As  the lower terminals  touch the water table in the hole there is  an instant direction in multimeter indicator This particular device functions accurately in field to provide an accurate measurement of waler table depth. Using above data water level contours were prepared at 100 cm. intervals and shown on maps no 4 and 11 for .Amibara and Melka Sadi areas respectively
2-6xi.  Groundwater EC & pH
Groundwater EC and pH were measured for each auger hole using portable digital EC and pH meters. Groundwater EC and pH were recorded for all auger bores excluding the sites where depth to groundwater is below 5 m. Groundwater salinity map was prepared by plotting the EC values both for Amibara and Melka Sadi areas and depicted on maps 5 and 12 respectively
xii.  Soil Profile Description
Some 10 per cent of auger bore holes observations were made in profile pits The sites for profile examination were selected based on representing the prevailing area. Care was taken to locate the profile within field to avoid the influence of field canal, field boundary, road etc Profile pits were excavated to a depth of about 2 m. The length and width as 2 m & I 5 m. were kept to the east - west and north - south directions respectively in order to get sufficient sunlight to read the profile horizon characteristics. The profile excavated sides  were kept straight vertical and even. As  per FAO guideline, soil profile was examined and following details  were recorded in field, i) horizon depth, ii) soil colour matrix  under dry, moist and wet conditions  iii) soil texture iv) consistence under dry, moist and wet conditions, v) structure, vi) EC 12, vii) pH, viii) HCI reaction - presence of carbonates, ix) pores  x) mottling and other important features  including groundwater depth, groundwater EC, & pH, depth to relatively  impermeable layer, site description and other notable features Soil samples were also collected from profile pits to analyze rhe samples for ECe and texture for correlating and confirming the estimation of texture in field. The procedure for examining all the above characteristics have been detailed in auger bore description section. The location of profile pits is depicted on maps.
2-72.2.2     Determining hydraulic properties in Geld - Hydraulic conductivity and
infiltration test
Hydraulic conductivity tests
As per TOR the hydraulic conductivity tests have been carried out at selected profile pus Methodology adopted for determining hydraulic conductivity in absence of water table
was pour-in test as described in FAO 42 soils bulletin, 1979, and bail-out method below water table as described in ILRI publication. However, for ready reference, the procedure
in brief for above tests is described below
2.2.2.1 Determining Hydraulic conductivity using pour-in method
This method was used to determine hydraulic conductivity for two successive depths at 0 - 1 m and 1 to 2 m where water table was not within the test zone depth Initially an auger hole was drilled on selected location using post-hole auger of 10 cm. dia to a depth of I meter Care was taken to drill the whole as straight as possible While drilling the inner surface of the hole is slightly compacted causing sealing of some pores. In order to avoid such  smearing  the  inner  hole  surface  was  scraped  wnh  a  locally  prepared  scraper  by winding spirally a piece of barbed wire on a wooden slick at one end covering a length of about  20  cm  The  hole  was  carefully  scraped  While  drilling  the  hole  a  complete  log including texture, colour, consistence and structure was obtained. A water container for supplying  water  to  the  hole  was  placed  nearby  Waler  was  discharged  into  the  hole through attached hose and a constant water level was maintained manually in the hole using water level recording device. With lapse of lime, quantity of water discharged into hole  was  recorded.  The  test  was  continued  till  relatively  constant  conductivity  value (stable  conductivety  rate)  was  achieved.  A  care  was  taken  that  minimum  quantity  of waler over the period must flow into hole to meet the conditions set-up in conducting test The hydraulic conductivity was computed using nomographs for condition I or condition
2-8Il (as  applicable), as  shown in FAO Soils  bulletin 42, 1979 The associated parameters as radius of hole (r), depth of water maintained in hole (h), h/r ratio, depth of water table or impervious  strata from surface of water maintained in hole (Tu), total quantity  of water flown in hole (m1), rate of water flowing into hole, q, (nV/min), and textural class  were used to compute hydraulic conductivity
Hydraulic  conductivity  using  pour-in  method  was  carried  out  at  eight  selected  profile  sites The results of K - values alongwith other associated parameters are presented in table 5 I
2.2.2.2       Determining hydraulic conductivity using bail-out method
The bail-out method was  employed for determining K - values  for soil layers  below water table. These tests  were also conducted at eight selected locations  at soil profiles  In this method a hole of 8 cm. dia was  drilled into soil using post-hole auger inside the profile pit A log of entire 2m depth including texture & consistence was  obtained Sufficient water approximetly  2/3rd depth was  bailed out from the hole using bailer Immediately after removal of water from hole, the rise of water level with respect to time interval was recorded using specially  designed water level recorder and stop watch In present study the depth of water recovery  in hole was  fixed and corresponding time in seconds  was recorded from stop watch. The readings were terminated as soon as 25% bailed out water was  replaced in the hole By  that time 5 to 8 readings  were recorded to obtain the relatively stable values.
Finally K - values were computed using following relation
h
K= C ................... .. .............................................................. I t
2-9whereas,
K = hydraulic conduntivity, md
C = geometry factor, obtained from Ernst nomograph as per occurrence of impermeable
layer
Ah = rate of rise of water level in the auger hole cm. sec-1
Al
The K values using bail - out method is given in Table 5 2.
2.2.2.3      Determining Infiltration rate
Two infiltration tests were carried out at a selected location in Amibara project area In
present study infiltration rates were measured using double-ring infiltrometers having inner
and outer dia 30 cm and 45 cm respectively The length of rings was 45 cm
The procedure for measurement of infiltration rate involved following steps
a)     The  double-ring  infiltrometers  were  installed  at  representative  site  in  the  field  The rings  were  driven  into  the  soil  approximately  to  25  cm  soil  depth  by  hammering  the driving  plate  placed  on  top  of  the  cylinders  Approximately  20  cm  height  of  cylinders remained projected above the ground level.
b)   Initially water was filled in the outer buffer zone to avoid horizontal flow and to ensure the vertical movement of water into the soil. Later, water was added in rhe inner-ring and instantaneous  observation  of  water  drawdown  was  recorded  using  float,  stop  watch  and graduated water reservior attached to the infiltrometers
c)    The measurements of water fall with respect to  time were continued at suitable time intervals  until  stable  rate  was  achieved  which  was  generaly  obtained  in  5  to  6  hours duration.
2-10CHAPTER 3
DESCRIPTION OF SOIL TYPES IN PROJECT AREA
3.1        Introduction
The soils  of the project area were studied and classified through conducting field soil surveys  in identified area of phase II As per TOR the criteria for identifying area for soil survey  was  based on existing groundwater level below 3 meter from bgl and soil salinity occurrence Soil survey  includes  description of auger holes  and soil profiles  pits. Auger holes were studied up to 5 m depth unless a hard layer was encountered at a shallower depth through which augering was  not possible. Auger holes  were made and studied at 400m x 400m gnd in order of 1 per 16 ha. Some ten per cent of the observations were studied by  excavating profile pits  of dimensions  2 x  I 5 x  2 m length, width and depth respectively  From bottom of profile pit deeper layers  were also studied through further augering up to a depth of 5 m
In present study 229 new auger holes including 172 in Amibara and 57 in Melka Sadi, and 8 profile pits  at selected locations  were studied In addition 28 observations  oCauger holes  and profile pits  studied by  previous  cosultants  including Ital consult, 1969,71, Sir William Halcrow &. Panners, 1981 & 85 were also used in soil study Thus soil survey was carried out in more than 4000 ha in Amibara and Melka Sadi areas.
Auger holes, with respect to drainage characteristics, were examined in detail for their morphological, physico-chemical and hydraulic  propenies  which include colour, texture, consistence, electrical conductivity, soil reaction (pH), mottling & presence ot concretions  In addition salient characteristics  as  depth to relatively  impermeable layer, groundwater - depth, EC and pH alongwith site description for each auger hole were
3-1studied. The detailed description of all auger holes including above properties is presented in separate Annexure. The methodology  for examining all the above properties  is described in preceeding chapter
As per FAO guidelines each profile was examined in detail for their morphological,
physical, chemical and hydraulic properties including site description. The salient characteristics included, horizon depth, soil colour, consistence, structure, EC. pH, HCI reaction, porosity, mottling and other site characteristics as depth to relatively impermeable layer, groundwater depth, EC and pH. Detailed description of soil'profiles examined in Amibara and Melka Sadi areas are presented in profile description sheets 
The field soil survey studies including determining hydraulic conductivity and infiltration tests were carried out between October 10th, 1995 to February 7th, 1996 in project area located at Amibara and Melka Sadi cotton stale farms adjacent to Melka Warer and Melka Sadi towns in the Middle Awash Valley about 8 km. to the west of all weather Awash-
mille highway at about 260 km east of Addis Ababa.
The comprehensive data of detailed auger hole studies, profile examination, laboratory analysis, and hydraulic conductivity tests were used to classify soils of project area into different soil types and to provide salient information for drainage investigaiton
Therefore, in order to generate valueable daia base for drainage investigation particularly for sub-surface design these data were analysed and interpreted Following self explantory maps were prepared.
i)          Map no     I   -    Soil classification of Amibara
ii)
Map no
2
-   Soil textural groups of Amibara
iii)
Map no
3
-  Soil salinity of Amibara
iv)
Map no 4
- Depth to groundwater of Amibara
v)
Map no. 5
- Groundwater salinity of Amibara
vi)
Map no. 6
- Depth to relatively impermeable layer of Amibara
3-2vii) Map no. 7 - Soil drainability &, drain spacing of Amibara
viii)         Map no      8   -      Soil classification of Melka Sadi
ix)          Map no      9   -       Soil textural groups of Melka Sadi
x)           Map no. 10-            Soil salinity of Melka Sadi
xi)
Map no.
11-
Depth to groundwater of Melka Sadi
xii)
Map no.
12-
Groundwater salinity of Melka Sadi
xiii)
Map no
13 -
Depth to relatively impermeable layer of Melka Sadi, and
xiv)
Map no.
14 -
Soil drainability and drain spacing of Melka Sadi
In sequel order, first soil textural profiles  and soil classification of project area are described below The details  pertaining to rest of the above studies  are discussed in subsequent chapters.
3.2      The Textural Profiles
Texture is  an expression to indicate the coarseness  or fineness  of the soil and it is  one of the single most foundamentai and permanent characteristics  that has  direct bearing on pore-geometry  which determines  the water transmission behaviour of soil Infact, texture provides  the open spaces  in soil mass  used for retaining and draining of water alongwith nutrients  and air As  it is  extremely  difficult to determine quantitatively  the intricate and most torturous  pathways  constituted of voids  which transmit water, instead, are evaluated through correlating with texture The analysis  of textural properties, therefore, assumes great significance particularly  to the occurrence and specifically  thickness  of more permeable sandy  and least permeable-clayey  layers. For the design of drainage system the extent and distribution of different soil layers  of varing textural composition, particularly around the sub-surface drains which transmit water, are required. For practical purposes,particularly, for drainabilily evaluation the soil textural profile classification which is 
primarily based on dominant texture and occurrence of relative thickness of poorly or
highly permeable strata in control section is important The conrol section is defined as 
the depth of composite soil layers which extends from soil surface to the surface of
relatively impermeable layer or in absence of such layer to the bottom of auger hole
3.2.1. Criteria for classificaion of textural profiles
The criteria, for classificaion of textural profiles with respect to drainability, is based on varying proponion of texture occur in auger hole depth up to 5 m, as described below
i)        The dominant texture of profile, this may be
a)         fine : Silty clay loam or finer
b)         Coarse     Silt loam, silt, sandy loam or coarser
c)         Mixed      About equal thickness of fine and coarse textured layers.
ii)         Relative thickness of clay or silty clay layers in the conrol section.
iii)        Relative thcikness of sand and loamy sand in control section
Based on above.criteria, in present study, following types of textural profiles have been classified.
I) Clay                         Profiles which have at least 200 cm of clay or silly clay at surface
A maximum of 20 cm of coarser textured soil may be present in this surface layer
2) F+                           Profiles in which fine textured layers (silty clay loam, or finer) are dominant and which have clay or silty clay in at least 20 per cent of the control section
3-43) F
Profiles in which fine texured layers (silty clay loam or finer) are dominant and which have clay or silty clay in less than 20 per cent of the control section
4)           M+                       Profiles with more or less equal thickness of fine and coarse
textured layers and which have clay or silty clay in at least 20 per
cent of the control section.
5)           M                         Profiles with more or less equal thickness of fine and coarse
textured layers and which have clay or silty clay in less than 20 per
cent of control section
6)          C                         Profiles  in  which  coarse  textures  (silt  loam,  sandy  loam  or  coarser) are dominant and which have sand or loamy sand in less than 5 per cent of the control section
7)          Cs
Profiles in which coarse textures (silt loam, sandy loam or coarser) are dominant and which have sand or loamy sand 5% or more in the control section
3.2.2     Distribution of textural profiles in the Amibara project area
The distribution of textural profiles  in Amibara area is  presented in soil textural group map No.2. Soil profiles  composed of varying texture ranging from fine to coarse texture groups are widely  distributed in the project area. As  revealed from the auger hole logs  and soil profiles  examination, nearly  45 per cent area is  characterised by  the soil profiles  in which fine texture layers  (silty  clay  loam or finer) are dominant having more than 20% of clay and silty clay in the control section.
3-5About 30 per cent soils  of the area are occupied by  medium textured soil profiles  with more or less  equal thickness  of fine and coarse texture layers  The remaining about 25 per cent soils  have coarse textured profiles  which are dominantly  occupied by  silt loam, sandy loam or coarser texture
The extreme southern pan of the project area, adjacent to Melka Warer town, is 
predominantely occupied by mixed textured profiles with clay or silty clay in less than
20% of the control section. On the contrary, the soils of the extreme nonhern pan are
composed of coarse textured profiles having with dominant texture of silt loam, sandy 
loam or coarser with sand or loamy sand in less than 5% of the control section
Interestingly the relative impermeable layers in this zone are also deeper, below 350
cm from soil surface.
The soils of central pan extending from south to nonh generally have fine texture profiles 
A small patch of about 10 per cent area of the eastern zone is distinctly occupied by deep
clay profiles which usually exhibit cracking and superficial self mulching powdery material
often drops to the bottom of the fissures These soils also have prolonged high water
regimes particularly at deeper depths with poor internal drainage as well
3.2. 3 Distribution of textural profiles in the Melka Sadi Project area
The distribution of textural profiles  in Melka Sadi Project area is  presented in textural group map No 9 As revealed from the auger hole logs and profile examination the profiles in which fine textured layers predominantly occupied by silty clay, clay and silty clay loam are widespread About 65 per cent area is  composed of fine textured soil profiles  with clay and silty clay dominant texture with more than 20 per cent clay or silty clay in control section. Mixed profiles with more or less equal thichness of fine and coarse textured layers occupy  about 25 per cent area Coarser textured soils  with sill loam, sandy  loam or coarser layers occupy only about 10 per cent area Infact there are several bands with fine
3-6textured    materials    Soils    with    thicker    clay    layers    (F+    and    M+)    occur    extensively Invariably a clay .layer is encountered at deeper layers about below 350 cm bgl.
Clay  profiles  which have more than 200 cm. clay  or silty  clay  at surface are present in small patches  in eastern pan These profiles  account about 14 per cent area In general thickness  of the individual layer is  variable. These soils  are mainly  alluvial in nature characterized with deposition of river sediments
3.3         Description of Soil types
The  extent  of  soil  types  (units)  as  distinguished  in  both  Amibara  and  Melka  Sadi  areas  are presented in Table 3 1
Table 3.1 Extent of different soil types in Amibara and Melka Sadia areas
Soil Mapping
Unit
Area in
Amibara (ha)
Area in Melka-
Sadi (ha)
Total Area
(ha)
Percentage
V
M+
M
C
CD
R
341
1286
414
280
473
13
124
504
119
52
64
-
465
1790
533
332
537
13
12 7
48.8
14.5
90
14 6
0.4
Total
2807
863
3670
100 0
Phase II Area
not                 Soil. Surveyed
220
40
260
Grand Total
3027
903
3930
3-73.3.1 V : Deep Clay Soils (465 ha)
This unit comprises areas which have at least 200 cm of clay or silty clay at surface In most of the locations the composed layer of silty clay and clay extends up to a depth oi about 300 cm Occassionally  a maximum of 20 cm coarser texture material is  present within that depth Invariably, the underlain layers  are composed of silt dominated texture including silty clay loam, silt and sill loam
The soils of this class are characterised by the surface cracking, self mulching, subangular
blocky and blocky structure and poor internal drainage The profiles of these soils contain
high amount of montmorillonite type of clay which causes swelling and shrinking
characteristics of these soils. Generally they are identified in field by appearance of
relatively dark colour (10 YR 3/1 or 10 YR 3/2), very loose powdery material at surface
which is known as superficial self-mulching material drops to the bottom of the fissures
These soils  generally  remain moist particularly  in deeper horizons  for appreciably  long period after irrigation However, due to surface cracking the upper layer of few centimetres  of soil profile dries  up During soil survey  pressure faces  and slickensides were also observed Gilgai is  common. Owing to above characteristics  these soils, as per 7th approximation, are classified as  deep Vertisols  Sometimes  soil strucrture becomes massive in nature causing extremely low permeability and accumulation of perched water above these layers, which act as relatively impervious strata These soils have very limited suitability for sub-surface drainage
Such clay soils occur in patches in both the Amibara and Melka Saddi areas In Amibara area these soils are confined to the eastern boundary where shallower, less than 300 cm . relatively  impermeable layers  are present While augering it was  also observed that on puncturing through these layers water table rises which indicates that water remains under
3-8pressure in such areas. In Mclka Sadi area these soils also occur in extreme eastern pan As revealed from EC measurements of surface and sub-soil horizons, soils are not affected by salinity, however, the groundwater is highly saline with EC > 7 dSm-1 at most of the
locations
3.3.2 M+ ;
Soils with appreciable amounts of clay or silty clay in control section (1790 ha)
Soils  of this  unit are composed of soil profiles  in which fine textured layers  (silty  clay  loam and finer) are dominant. Alongwith fine textured profiles  some mixed profiles  having nearly  equal thickness  of fine and coarse textured layers  are also present Clay  or silty  clay occupies 20 per cent or more of the control section in profiles of these soils.
These soils  are widely  distributed occupying about 50 per cent area in both Amibara and Melka Sadi. In several cases  more or less  compact layers  were observed at a depth of 30 - 60 cm. These are caused by  mechanical cultivation and are assumed to be easily eliminated with regard to the relatively  impermeable layer for drainage design purposes because
i)   They occur in conjuction with layers less 10 times of hydraulic conductivity
ii)   They can often be disturbed by deep cultivation
Nearly 60 per cent of the profiles are characterised by finer textured layer with more than 20 per cent clay & silty clay in control section These soil units are composed of F+ and F textural groups Vertic characteristics in the surface horizon are common with self mulching and cracking behaviour of these soils. The structure is often subangular blocky Slickensides are also present in clayey horizons. Having above characteristics these soils are classified as the Vertisols
3-9As revealed from profiles examination about 40 per cent area of this unit is composed of profiles with more or less equal thickness of fine and coarse textured layers and which have clay or silty clay in at least 20 per cent of the control section. These profiles have the characteristics of M+ textural group These soils do not crack on drying and have both finer and coarse textured layers These soils may be included in the Entrsol order
Soils of this unit are widely distributed, occupying central part extending from south to north in Amibara area, whereas in Melka Sadi, these are intermixed with more finer and coarser units  With respect to drainage, these units  are moderate to poorly  drained As revealed from EC measurements this unit in general is not affected by salinity having ECe <4.0 dSm-1 However, some patches  sparsely  distributed in the vicinity  of western & eastern boundaries, are affected with moderate salinity
3.3.3    M : Soils with medium and mixed texture (533 ha)
This unit comprises the profiles of medium and mixed texture and composed of more or less equal thickness of fine and coarse textured layers and which have clay or silty clay in less  than 20 per cent of control section. These medium textured soil are distributed in small patches covering about 15 per cent area in each Amibara & Melka Sadi
As revealed from auger bore logs the fine and loam textured soil layers occur in
succession may be rather indifferent with variable thickness. Generally, these units are not affected by soil salinity However, in many places, groundwater is relatively saline The relatively impermeable layer is intercepted at varying soil depth ranging from 200 to 400
cm. bgl
These soils  usually  do not exhibit marked swelling and shrinking properties, however, minor cracks appear at soil surface These soils have much resentbleness with the alluvial soils
3-103.3.4     C : Relatively coarse textured soils (332 ha)
Soils  of this  unit are characterised by  the profiles  in which coarse textures  (sill loam, sandy loam or coarser) are dominant and have sand or loamy  sand less  than 5 per cent in control section. Soils  of this  unit generally  have a sequence of layers  with invariably  coarse, silt loam or sandy horizons with variable depth
These soils  are orginated from Awash river action during recent times. As  evident from the bail-out hydraulic  conductivity  tests  soils  are relatively  more permeable with K - values exceeding 3 m d-1
Few fine concretions  of calcium carbonate with occasional occurrence of snail shells  were also observed. Silty  and sandy  materials  predominate on finer sediments  which occur as  a rule in these profiles  Based on above characteristics  these soils  may  be broadly  classified as the Entisols
Majority   of   soils   of   this   unit   occur   in   scattered   patches   in   central   pan   of   Amibaia Generally soil consistence is friable and effervescence of HC1 reaction is usually strong.
Groundwater in these areas  generally  varies  between 250 - 350 cm bgl. Soil salinity  is very  low to low The depth to the relatively  impermeable layer in this  unit is  generally encountered below 200 cm bgl and in very  few locations  it is  present at more than 400 cm depth. Groundwater is  slightly  saline with EC variying between 0 75 to 1.5 dSm-1 (I 2 soil-water). However, at few locations  groundwater is  exceptionally  more saline where EC exceeds 10 dSm-1
3-113.3.5    CD : Coarse textured soils with sand or loamy sand more than 5 per cent
in control section
This unit is similar to the C group except having more coarse sand and loamy sand texture in control section These soils  are rather uniform with some differences  in texture which grades from sandy to loamy sand and in some cases sill loam to silty clay loam In general the thickness  of the individual layer is  variable and the succession may  be rather indifferent Coarse texture with appreciable loamy sand and sandy layers are predominant in this particular unit.
These sediments were orginated from river action during recent times The consistence of most of the layers is friable to very friable and sometimes loose to very loose as well Fine concritions of calcium carbonate with strong to violent HCI reaction are also observed Interstingly a gritty type of sound was generally noticed while augering in the sandy zones of these profiles which indicats the presence of sand deposits originated from Awash river flood action
The permeability of these soils is high sometimes exceeding 5 m d-l As these soils have been developed recently and may be classified as the Entisols
This unit predominantly occurs in northern part with few scattered patches covering entire area of Amibara Occurrence of these coarse textured soils is limited in Melka Sadi area.
The depth to the relatively impermeable layer in this unit is normally between 300 and 450 cm Depth to the groundwater varies between 300 and 400 cm bgl Groundwater quality is moderately saline to highly saline with large variation in EC values However, the soils of this unit are not affected by salinity which may be attributed to appreciable leaching of soluble salts from highly permeable soil strata to groundwater
3-123.3.6      R : Rock out-crop (13 ha)
Very  small patch of about 13 ha area affected by  hard rocky  substrata with limited 60 cm soil cover was  observed This  unit is  also characterized by  exposed rocky  surface patches in the vicinity The area is abandoned and occupied by scattered acacea bushes.
3-13CHAPTER 4
DISTRIBUTION OF SOIL SALINITY IN PROJECT AREA
4.1 Introduction
Occurrence of salinity, affecting adversely  the crop growth, is  probably  the most widespread phenomenon particularly in arid and semi-arid irrigated areas The build-up ot soil salinity  in rooting depth is  associated with excessive irrigation and poor drainage facilities  As  irrigated soils  receive considerable quantity  of dissolved salts  through irrigation water, for instance, EC of irrigation water used in Amibara and Melka Sadi farms is O.35dSm-i which corresponds to 210 mg/litre of soluble salts (mainly NaCI) with annual application rate of 1 ha-m, up to 2 I m tonnes of salt per ha would be accumulated in the soil (or added to groundwater) every  year In the arid and semi-arid climate transportation and leaching of salt by  natural drainage cycle is  incomplete due to scanty rainfall and high rate of evaporation The presence of impermeable soils and sub soils also impede the leaching and drainage of salts  If no artificial drainage is  provided the salinity build-up from continuing application of surface irrigation waler is generally inevitable
The primary  deleterious  effect of excess  salinity  is  to raise the concentration of soil solution consequently  the flow of water into the plant roots  is  affected. It is attributed io the fact that the total water potential in soil solution as induced by low osmotic potential is reduced than that of plant roots  causing reduction in water potential gradient and finally reduces the water uptake by plants eventhough the soil has enough water content With further increase in salt concentration in soil which causes  more reduction in the water potential gradient and sometimes reversing the same the flow of water may take place in opposite direction i e from plant root to soil solution In addition, some ions  particularly sodium, chloride and sulphate have specific toxicity for certain crops.
4-1Criteria Tor classifying the salt affected soils
Salt   affected   soils   include   saline,   saline-sodic   or   sodic   soils.   The   criteria   for   classifying above salt affected soils is based on mainly three properties as:
i)   Salinity of saturation extract as measured by electrical conductivity (ECe) at 25° C
ii)     The  Exchangeable  sodium  percentage  (ESP)  as  defined  by  the  degree  ot  saturation  ot soil exchange conmplex with Na-r and may be calculated using following relation
Exchangeable Na-r (mcq./lUUg of soil)
ESP =    ---------------------------------------------------------------------------------X 100
Calion Exchange capacity (meq./lOOg of soil)
However, another property  SAR (Sodium Adsorption Ratio) is  frequently  & conveniently used in place of ESP In fact the SAR is  statistically  correlated with the ESP and experimentally  this  value is  more readily  obtained than ESP A SAR value of 13 corresponds roughly to an ESP value of 15
iii. Soil reaction (pH)
The degree of acidity  and alkalinity  of a soil is  usually  expressed as  a pH value which is defined as  negative logarithm of H-r activity  It is  also used to distinguish the salt affected soils. The criteria for classify ing salt affected soils is given in Table 4 1
Table 4.1. Criteria for classifying salt affected soils
Property
normal
Saline
Sodic
Saline-Sodic
ECe (dSm-1)
<4
>4
<4
>4
SAR
< 13
< 13
> 13
> 13
PH
70
7 0-8 5
8.5-10.0
8 5-10.0
4-24.3       Saline Soils
Saline soils are often recognized by the presence of a white crust on the surface The
absence of a white crust, however, does not preclude the existence of a saline soil. The
SAR value of less than 13 reflects relatively low level of adsorbed sodium, whereas the
high salt concentration gives a saturation extract of ECe value of greater then 4 dSm- I
The soil pH is less than 8.5 The Cl" and SO« " “ ions are the principal anions, with
smaller amount of HCOj  . The principal cations are Ca2-r and Mg2+ with lesser amount
of Na+ ion The presence of compounds with soils as gypsum (CaSO* 2H2O) and calcium carbonate  (CaCCh)  and  magnesium  carbonate  (MgCCh)  are  common.  The  high  salt concentration  keeps  the  soil  in  a  flocculated  conditon  and  water  permeablity  is  high Reclamation is usually required for satisfactory crop yields The reclamation of saline soils is relatively simple It requires adequate drainage to leach the excess soluble salts from the profile, since leaching salt from the soil is a process of dissolution and downward transport of ions through the root zone. Traditional basin method of salinity reclamation is based on salt  transport  under  saturated  flow  conditions.  Ponding  of  water  is  continuous  for  a period of 60 - 100 days, then the soil is allowed to go through a drying cycle. Drying of soil  lends  to  promote  structure  that  is  beneficial  to  permeablity  and  also  it  discourages microbial  growth,  which  when  present  on  soil  surface  reduces  water  infiltration  Field studies  have  shown  that  continuous  ponding  for  leaching  of  salt  is  not  as  effective  as intermittent ponding.
4.4      Sodic Soils
Sodic Soils are characterised by low salinity of soil water The SAR values are larger than 13 indicating that a greater amount of exchangeable Na+ exists in saline soils The
exchangeable Na^ hydrolyses, forming NaOH in the soil solution which then reacts with 4-3dissolved COi to form Na? COj Under these conditions  the pH of sodic  soil may  increase to 10 At these high pH values, calcium and magnesium ions  are precipitated as  carbonals because of relatively  high concentration of COa ions. The prominent cation is  Na+, with some Ca?i-, Mgz-r and k+ present The high ESP is  manifested by  a disperssed (deflocculated) clay  system, which greatly  reduces  both air and water entry  into soil. The reclamation of sodic  soils  presents  more difficulties  than the reclamation of saline soils Three processes occur during the conversion of sodic soils to an agromnomic resource
a)   Na+ is replaced by Ca-r on the exchange complex
b)   The hydraulic conductivity increases
c)   The sodium salts are leachd from the system
The source of C<u+ ions  that replaces  exchangeable Na+ can originate in soil minerals, for example, gypsum and lime. It can be added as  a natural constituent ion in the irrigation water, or it can be added to the soil in the form of chemical amendments  that Ca2-t- or react with the soil minerals to release calcium.
An important indigenous  soil mineral that is  beneficial for sodic-soil reclamation is gypsum The factors  that govern the effectiveness  of any  given ammendment are principally  the soil lime (carbonate) content and soil pH value Since a low hydraulic conductivity  is  distinctive property  of a sodic  soil, reclamation can be a time consuming process. The choice of a chemical amendment to be used for sodic  soil reclamation depends  on the type of soil, the time available for reclamation, the amount of water available for leaching, the extent of reclamation and economic considerations
4.5      Saline - Sodic soils
Saline-Sodic  soils  have chemical properties  of both saline and sodic  soils  The SAR is greater than 13 whereas  the soluble salt concentration is  also high EC > 4 dSm-1 The presence of the excess  salt maintaining the soil permeability  as  a high level and acts  to reduce the pH value (pH < 8 5). If the excess salts are leached from the soil, the
4-4properties may or may not change to those of sodic soil depending on the type of salts present  Reclamation  requires  salt  removal  and  decreasing  the  amount  of  exchangeable
Na+ before a good crop growth is realized
4.6       Measurement of soil salinity in Geld
In order to diagnose the salinity occurrence in soil profile EC was measured in field using 1 2 soil - water suspension on volume basis at surface (0-30 cm) and two measurements of subsoil at 30 - 100 and 100 - 200 cm soil depths EC was measured using portable digital electronic EC meter at 240 auger and profile sites covering more than 700 tests
Determining  EC  in  field  using  1.2  soil  -  water  suspension  was  used  for  following  two reasons
i.  Same ratio is used in previous studies including Master Plan and Sir Macdonald studies
ii.    By  avoiding  the  use  of  vacuum Alteration  needed  to  obtain  saturation  extract, it does not require any apparatus except graduated sampler, beaker and stirrer
Most international systems for interpreting soil solinity are, however, based on the saturated extract (ECe) which is discussed below
In  present  study,  in  order  to  convert  the  EC  (1.2)  soil-water  suspension  to  ECe,  soil samples  covering  the  range  of  EC  (1.2)  from  low  to  high  were  collected  from  the  field with  known  EC(  1  2)  values  This  soil  samples  were  dried  &  properly  labeled  indicating sample location, EC (1 2) value, depth of sample, textural classes (feel method), and date of  sampling  These  samples  were  brought  to  the  laboratory  of  the  Ministry'  of  Water Resources for ECe measurements.
4-5Determining electrical conductivity of Saturation Extract (ECe) in laboratory
Step  1  -  Each  sample  was  dried,  crushed  gently  in  a  pestle  &  mortar  and  sieved  through  a 2 mm sieve
Step  2  -  A  saturated  paste  was  prepared  by  adding  sufficient  water  to  100  g  of  soil  in  a beaker Water was added to dry soil until soil is saturated and just slides off the spatula
Step  3  -  The  saturated  paste  has  transferred  to  Buchner  -  funnel,  previously  fitted  with filter paper. The extract was collected on applying suction through vaccum pump
Step 4 - EC of extract was  measured by  using electronic  EC meter Simultaneously  room temperature was  also recorded and finally  EC values  were adjusted to standard temperature of 25° C using factors  for conversion of conductivity  values  to 25° C (FAO soil bulletin no 10, 1976)
4.8 Conversion of EC (1:2) to ECe
The EC values  of soil extract (ECe) thus  obtained from laboratory  were plotted against EC ( 1:2) values  obtained in field on a log-normal graph paper and a relationship between two sets  of values  was  obtained in form of a bell-shaped curve as  shown in Fig 4 I The correlation was  similar to that of Master Plan Study  The equivalent EC 12 and ECe values for the standard USBR (1954) salinity classes is shown in following Table 4 2
4-6EC(1.2soil-walersuspension), dSm1
I
LEGEND
Phase DEC values Nister plan EC values
z
•O VERY HIGH
HIG -1
3
I
MOOI RATE • -
oo
3 C-
EC I Saturation Extract dSni1)
on & saturation extracr-
fig-4.1 Relationship between electrical conductivity of 1-2 Suit water suspensi
WAPCOS (11 ^d.
feb 1996Table 4.2 - Soil salinity classes for ECe and EC 1:2
Soil Salinity class
ECe dSm-l
EC (1.2)dSm-l
Very Low
Low-
Moderate
High
Very High
0-2
2-4
4-8
8-16
> 16
0-0 75
0.75 - 1.50
1.50-3 00
3.OO-5.OO
> 5.00
4.9 General distribution of Saline Soils:
Soil  salinity  in  project  area  was  broadly  classified  into  three  classes  including  i)  non-saline soils which have very low (VL VL/M,VL/H) and low (L,L/M,L/M/M-H) salinity classes,
>
ii) moderately  saline, and iii) highly  saline which includes  high and very  high salinity classes. Sub-divisions  of the non-saline units  as  indicated above considered the salinity occurrence in sub-soil layers  also. Above all salinity  units  are shown on salinity  maps  no 3 and 10 for Amibara and Melka Sadi areas  respectively  Distribution of soil salinity  in study area is presented in Table 4 3
4-7Table 4.3 - Soil salinity distribution in study area
Soil Salinity Classes
Area in Amibara
(ha)
Area in Melka Sadi (ha)
Total area
(ha)
Percentage
Very Low
VL
VL/M .
VL/H
1716
288
12
425
31
™
2141
319
12
58
9
0.3
Low
L
L/M
L/M-H
279
147
38
227
57
-
506
204
38
14
0
1
Moderate
207
98
305
8
High & Very High
120
25-
145
37
Total
2807
863
3670
Phase 11 area not soil
survey
220
40
260
Grand Total
3027
903
3930
4.9.1   Soil Salinity in Amibara area
As evident from EC values measured at three varying depths at each auger bore sue. fairly large pan of Amibara area, about 72 per cent, is  non-saline with very  low (VL) salinity values  < 0 75 dsm-1 (12 soil-water suspension) In most of the locations  there is  no appreciable difference in surface and sub-soil salinity  values  However, in some area salinity  slightly  increased with depth Occurrence of sub-soil salinity  is  probably  attributed to the presence of saline groundwater
4-8Occurrence of very  low salinity  is  widely  distributed thoughout the area, however, northern pan are generally  non - saline. Soils  in this  area are coarse textured and grc  ind water depth is  also relatively  deeper than 350 cm. bgl Relatively  impermeable layers  also encounter at deeper depths below 400 cm The groundwater salinity is also > 3 dSin-l
About 16 per cent area is occupied by low salinity (0 75 - 1.5 dSm-l) and distributed
widely thoughout the area. However, their occurrence is relatively more in northern part
where coarse textured soils are predominant. Infact low salinity areas are generally 
adjacent to very low salinity (non-saline) areas.
Very  little area about 7 per cent is  affected by  moderate salinity  (1.5 - 3 0 dSm-l). These soils  occur mainly  along western boundary  with highly  saline patches. There are very  few isolated patches  about 5 per cent where salinity  effects  are clearly  visible even without determining the EC. Such areas  may  have a damp 'slick' surface appearance. The ECe values  of these isolated slick  patches  exceeds  8 dSm-l These spotes  are located in isolation along eastern and western boundary  The groundwater EC is  also exceptionally very  high ranging from 8 to 16 dSm-l. Soil profiles  in these areas  are dominated by  fine texture including silty clay loam, silly clay and clay
4.9.2 Soil salinity in Melka Sadi area
About 53 per cent area has very’ low salinity in soil profiles. Such areas are widely 
distributed and composed of large blocks. Profiles in these areas are mainly fine textured
Depth to groundwater varies from 250 - 350 cm bgl. The ground- water is relatively 
saline with large EC variation from 1 5 to 8 dSm-l
Soils of low salinity occur in central pan of the area adjacent to very low salinity patches Such slightly affected areas are nearly 33 per cent Soil of these areas are characterized by
4-9fine texture with more than 20 per cent silty clay and clay in control Groundwater is relatively saline with large EC variations
Moderately saline area occurs in small patches at only two locations and occupies about 11 per cent area Highly saline area is negligible less than 3 per cent and occurs in very small isolated patches along boundary areas. The groundwater is exceptionally saline with EC > dSm-1 Some of these spots also exhibit damp and slick surface appearanceCHAPTER 5
drainability classes and field drains spacing
5.1          Introduction
Soil properties  ' are of fundamental importance for drainage design and drainage performance Water flow towards  the drains  is  controlled by  the soil Basically, the profile characteristics  up to a depth of 5 m and hydraulic  conductivity  of respective horizons are exceedingly important for computing drain spacings
5.2      Soil Factors influencing drainage
i. Uniformity of Soil
ii    The depth of different layers in soil profile
iii    The hydraulic conductivity of different layers 
iv. Depth to relatively impermeable layer, if any
There   are   some   secondary   factors   which   also   influence   the   drainage   behaviour   These include:
i)      Soil stability to water
ii)     Panicle- size distribution
iii)    Chemical propenies
iv)    Infiltration etc
Drainage   design   is   more   accurate   under   uniform   soil   in   the   soil   profile   having   minimum spatial variability However, it is unlikely to have uniformity in natural system
5-1
•-
■nDifferent textural layers in soil profiles are observed in field through excavating the soil profile pits or auger borings. In fact, the significance of these layers is based on their hydraulic  conductivity, because sub-surface drainage is  influenced by  the nature of the layers in the vicinity of drains and those of the layers occurring up to the depth of the relatively impermeable layer.
The hydraulic conductivity is one of the important properties in drainage study. Lower hydraulic conductivity values, all other factors remaining some, mean higher waler table at mid point of drain spacings and steep fall of hydraulic head adjacent to drains 
w V-
The other secondary factors like soil stability through water, pore-size distribution, chemical properties including collapse of loose soil material near the drain, and the chemical properties like CEC & ESP also affect the drainage
5.3     Soil parameters for drain spacing
5.3.1    Auger bore logs
Description of all 229 auger bores including 172 in Amibara and 57 in Melka Sadi were described in detail and presented in a separate annexure
5.3.2    Hydraulic Conductivity
Hydraulic conductivity at selected eight locations was determined in field at three varying depths as 0 - I, 1-2 and 2 - 4 m In absence of water table, hydraulic conductivity was determined using pour-in method and in presence of waler table by bail-out method Detailed procedure for determining hydraulic conductivity for both the methods is described in chapter 2 The results of K - values for pour - in and bail-out methods are presented in following Tables 5 I and 5 2 respectively
5-2r
t
* • *
TABLE 5.1 HYDRAULIC CONDUCTIVITY DETERMINED USING POUR - IN METHOD
Location
Radius
of hole.
Depth of .T. or
(mpenluus SlnU
from surface of
water maintained
In hole, Tu i m)
Water
maintai
ned in
hole, h
Condition
T u > Jh
F5 < 10
MB II A
Vnibin
knuhirj
Amibira
. Vnib.ui
Condition I!
Jh >Tu >h
Applicable
Total quantity of water Ho»*n In hole (mJ)
F9 J 170
Amibira
Applicable
NA
Applicable
Kpplicable
Rale of How, <| (m3 mln-1)
0 000010 0   000015 0000071
0   000090 0   000020
0   000015
0   000021
0.000100
0 000060
K-value (md I)
Soil Tetfural
clauei
ZCLZL
ZU CL
ZC.ZCL
ZCLZL ZC
MB.’00
Annlnn
Applicable
Applicable
Fl 28 47
MellraSaJi
Applicable
Applicable
Fl J JJ
Mcllu Sadi
Applicable
■ Kpplicable
\ plicible
oooo no
0.0000J 2 Q000100
0  00011  0 0   000035 0000169
0 000200
ZL.ZC
ZL____
ZCLZL ZLZ.SL
ZC. ZL ZCL C. ZC ZCLZC, SCL ZC.FSL
NV
Not    Vpplka
ble,    Z    Silt.    ZL    :    Sill    Loom.    ZC    Siltx    Cl«    ZCL
FSL
Silts Cl.is Loam. C
Fine Sjmh Lo
im. CL Cl.n Loom. SL SonJi Loom
Cla\ SCL Sands Clas Loam.Table 5.2 Hydraulic conductivity using bail-out method
Profile no
Test depth (cm)
K md-1
Soil texture
p-l
200 - 350
2 15
SL, ZCL
P-2
200 - 400
625
ZCL , ZL, LS, FSL
P-3
175 - 335
1 79
ZCL, LS, SL
P-4
240 - 370
2 82
S. LS, Z, ZC
P-5
300 - 380
5 87
LS. Z
P-6
170 - 350
5 29
ZL. ZCL, SL
P-7
280 - 380
1 60
“SL
P-8
240 - 380
1 72
ZCL, FSL
Z    Silty,    ZL    Silt    Loam,    ZCL    Silly    Clay    Loam,    S    Sand,    SL    Sandy    Loam, FSL : Finer Sandy Loam, LS Loamy Sand,
5.3.2   Field measurements of Hydraulic Conductivity
As per TOR hydraulic conductivity was determined in field using procedure as described in section 2 2.2 Hydraulic conductivity results revealed the following conclusions
i) Hydraulic conductivity values as measured from bail - out tests were invariably higher than  those  derived  by  pour-in  tests  However,  large  variation  is  also  attributed  to relatively coarse texture strata within the test zone depth at deeper layers between 2 - 4 m In  addition,  the  vertical  flow  ot  water  also  contributes  to  the  radial  movement  of  water causing more rapid flow of waler from surrounding areas into the hole During the course of conducting bail-out test it was observed that water rushes into hole very rapidly even a thin layer of coarse texture (sand layer) is present During the process of bailing-out the pores also get cleaned by removal of silt panicles through repealed bailing-out of water from hole
5-4On the contrary, the hydraulic conductivity tests using pour-in method were carried out in lop 0-1 and 1-2 metres depth. The surface horizons are usually composed of fine texture silty clay and silty clay loam. These soil layers also have verxic characters which generally exhibit swelling and shrinking properties. During tests, when water flows from auger hole into surrounding soil the possibility of swelling may not be ruled out which may affect the porosity resulting in lower K-values. Smearing of inner auger surface during augering is unavoidable, although its effects in terms of restricting the rate of water entry into the test section was reduced by scraping the hole with locally made scraper. Further, canal water was used in which suspended silt panicles may also lend to block very fine pores in the soil, thus  funher restricting the flow rate. The combined effect of above factors  may lower down the K - values.
The results  of K-values  thus  obtained from conducting field tests  were correlated with published standard K-values  for different textural classes  (R.J. Winger (1985). These standard K-values for different textural classes are presented in Table. 5.3
Table 5.3:Hydraulic conductivity and textural classes (Winger 1985,after FAO,1979)
Textural groups
Hydraulic conductivity md-i
Very hard clay
001
Hard  clay,  hard  silty  clay,  hard  clay  loam, hard sandy clay loam
0.08
Clay,  silly  clay,  silty  clay  loam,  clay  loam, sandy clay loam, sandy clay
0 30
Sill loam, silt, loam, very fine sandy loam
1.00
Loamy sand, sand, sandy loam, fine sandy loam
2.00
Coarse sand, loamy coarse sand
6.00On comparing (he the K - values obtained in present study by determining in field and
above standard values following inference was drawn
During field survey the observed K - values as obtained from pour-in test and bail - out methods, were correlated with texture of test zone depth Extremely poor correlation was observed between K-values  and texture As  revealed from the results  of K-values  in table 5.1 that hydraulic  condutivity  varies  widely  for the same texture For instance, the hydraulic conductivies were as 0 10 and 0.020 md-1 for the same silty clay loam texture, which shows  wide variations  in conductivities  even in same textural group As  the corrlation between K-values  and the texture was  very  poor (no correlation), the determination of hydraulic  conductivities  in field were terminated The principal reason for this  variability  is  probably  the complex  and highly  stratified soil textured layers occurring in the soil profile, which influence the K - values to a great extent
Therefore, for designing the field laterals  spacing and classifying the soil drainability, the standard values of hydraulic conductivity of Table 5 3 were used in the present study as the same were also adopted in ADP phase I. However, as per TOR, number of hydraulic conductivity tests were carried out in field
For drain spacing calculations  the hydraulic  conductivity  values  in the vicinity  of drains and below 1 25 cm up to the depth of relatively  impermeable layer are of primary importance.5.3.3      Depth to relatively impermeable layer
Based on the criteria as  described in section 2 the relatively  impermeable layers  were identified in the field for each auger bore location and accordingly  depth of relatively impermeable contour were prepared and depicted on maps  6 and 13 for Amibara and
Melka  Sadi  areas  respectively  The  relatively  impermeable  layers  varied  from  200  to  500
cm  depth  from  the  surface  and  at  some  places  no  relatively  impermeable  layer  could  be identified  within  the  bore  depth  of  500cm.  As  revealed  from  these  contours,  there  is  no definite   trend   or   pattern   in   their   configurations   However,   in   southern   part   of   Amibara relatively  impermeable  layers  occur  at  shallower  depths  i  e  from  200  to  300  cm  below groundsurface   and   in   northern   pan   they   are   encountered   at   deeper   depths   There   are some  isolated  locations  where  it  occurs  at  much  deeper  depth  In  Melka  Sadi  it  varies from 200 - 500cm bgl
5.4 Determination of sub-surface field drain depth and spacings
5.4.1 Drain Depth : Criteria for selection of drain depth
The criteria for selection of an optimum drain depth is based on following factors
i)     Adequate root aeration i.e rooting zone free from waterlogging
ii)    To restrict the secondary salinization
iii)   Economic considerations i.e minimizing the installation cost of laying laterals as influenced by macliinary. equipment, excavation (earth work) cost, etc
iv)    Satisfactory outfalls conditions, taking into consideration complete dramage system originating from field through secondary and main drams.etc up to outfall in the rivet
Relatively deepening of laterals may cause excessive deepening of drain lines up to the remote final outfall location
5-7Keeping in view the above factors a compromise depth of I 8 m bgl has been selected for laterals for the sub-surface drains, particularly with the consideration that the phase II area
is also contiguous to phase I in which laterals have already been laid at 1 8 m depth
5.4.2    Drain Spacings
As discussed in preceeding paragraphs, drain spacing in the present study is based on a comprehensive approach taking into consideration the field observations  (soil survey studies) of auger - bore logs, depth of relatively  impermeable layers  and hydraulic conductivity  interpretations. In brief the methodology, criteria and procedure for computing dram spacings of laterals is summarized below
5.4.2.1 Approach and Criteria
i) Review of earlier studies:
In order to find out optimum drain spacings  as  influenced by  in-situ water transmission characterisics, soil textural variability, depth to relatively  impermeable layer and other associated factors, the criteria used in previous  studies  were reviewed. In Master Drainage Plan (1985), lateral spacings  were determined according to drainability  classes bassed on estimated hydraulic conductivity and measured depths to relatively impermeable horizons These were broadly classified as follows
5-8Table 5.4 Master Plan drainability classes and hydraulic conductivity values
Drainability Class
Soil Texture Range
Mapping Symbol
Design H C , md-l
I
Silt      loam,      sandy loam or coarser
Cs
2.0
11
Other               profiles except ones with
> 2.0 m of clay or
silty clay
C. M, M+, F+
14
Ill
2.0 m of clay or silty clay
Clay
In above study, texture and hydraulic  conductivity  have been broadly  classified into two groups  for computing lateral spacings  (third group of clay  was  not considered for drain spacing) In this  approach, the comprehensive representation has  neither been given io
varying  textural  layers  (highly  stratified  soil  profiles,  in  which  even  up  to  as  many  as  I  5
layers  were  observed)  occurring  in  soil  profiles  of  large  number  of  auger  bores  nor  to varying hydraulic conductivity values of respective textural classes.
The above two classes of drainability were further subdivided into four sub-groups on the basis of depth to relatively impermeable layer with a total of all eight drainability classes in the Master Drainage Plan. Phase 1 of ADP suggested a different method as discussed below
5.4.2.2    Selection of hydraulic conductivity
One of the most important factors for determining the lateral spacings is to take into account the water transmission behav.our of layers just in the vicinity of the drains. Near
5-9the drains, flow converges and there is increased rate of head loss. Keeping in view the above following two conditions  for selecting soil profile depths  and their most representative hydraulic conductivity values were considered
a)   First, the representative hydraulic conductivity, one meter soil profile depth 0 5 in
above and 0 5m below the drain line is considered As laterals are laid down at a depth of
1 8 meter, the soil profile extending from 1.3 metre below the surface up to 2.3 meter
depth is considered for this.
b)   Secondly, the representative hydraulic conductivity of profile depth extending from
1 25 m bgl to the top of the relatively impermeable layer, if present, otherwise to the
bottom of the bore
5.4.2.3    Selection of depth to relatively impermeable layer and alternative criteria
for selection of lateral spacing
Two methods are employed to find out the depth of relatively impermeable layer The
first one is by visual inspection of profile log and the second is based on USBR criteria
Through visual inspection of auger log, the soil layer of very hard clay or having similar characteristics  is  choosen as  the relatively  impermeable layer. In the present study  the relatively impermeable layer is generally coposed of clay or silty clay texture
The second method is as recomended by USBR As per drainage manual of USBR, a relatively impermeable layer or "barrier zone is a layer which has a hydraulic conductivity one-fifth or less of the weighted average of the hydraulic conductivity of the soil above it”
The spacing of the laterals is of great importance in the sub-surface drainage design It has been worked out for four conditions as adopted in phase I Considering the laterals
5-10are  placed  18m  below  the  ground  surface,  these  are  based  on  the  following  weighted mean hydraulic conductivity and depth of relatively impermeable layer combination
i)    Weighted  mean  hydraulic  conductivity  between  the  depths  of  1  3  m  and 2 3 in below ground  surface  and  the  depth  of  relatively  impermeable  layer  below  drain  level  determined by visual inspection
ii)  Weighted mean hydraulic conductivity between the depths of 1.3 m and 2 3 m below
ground surface and the depth of relatively impermeable layer below drain level determined
by USBR method
hi) Weighted mean hydraulic  conductivity  between the depth 1 25 m below ground surface up to the relatively  impermeable layer and the depth of relatively  impermeable layer below drain level determined by visual inspection of soil profile
iv)   Weighted   mean   hydraulic   conductivity   between   the   depth   1   25   m   below   ground surface  up  to  the  relatively  impermeable  layer  and  the  depth  of  relatively  impermeable layer below drain level defined by USBR method
As  both,  the  hydraulic  conductivity  of  soil  close  to  the  sub-surface  drain  and  the  depth  of the relatively impermeable layer below drain level play important roles in determinimz the
mCliil/U , ...k tii.iiioii ui Ut.un
After  computing  the  drain  spacings  based  on  above  mentioned  criteria  four  values  of spacings were obtained The optimum value was selected using following criteria
5-111) If the spacings are within 10 per cent variation then the average valaue is taken
2) In case the alternative spacings were found to have divergent values, subjective judgement was applied to consider the most suitable value
Drain spacings were computed using following steady state Hooghoudt’s tlow equation as
SKdli
4 Kir
or S2 =
( 8Kdh + 4Kh2 )
-----------------------  ---------------------------------------- 2 q
where q            =          discharge rate per unit surface area In present study 
q = 2.5 mm/day.
K =           Representative weighted hydraulic conductivity md-l
h =         Hydraulic head (m) or water table elevation above drain level midway between the drains
s =         Drain spacing (m)
d = Thickness of the so called equivalent layer which depends on the depth. Do, from drain level to the relatively impermeable layer, drain spacing S and welted perimeter of drain U
5-12The equivalent depth'd' upto impervious layer
Do
d =        ------------------------------
KDo            Do
------- Ln ---------- t- I
KS             U
The symbols used in above equations are given in following Fig 5 I
I , "zvs
’
’ *■
■■ t
Fig 1 Symbols used in flow equation
U = Wetted perimeter including envelope
'd'  is  computed  using  a  nomograph  for  Hooghoudt's  d-value  as  given  in  FAO  28,  1984  or by direct computation by trial.
Using the Hooghoudt's  equation, the spacings  were computed for the 4 alternative conditions  for each auger log, and the spacing to be adopted was  decided on the considerations already discussed The spacings thus computed were made for all the
5-13auger bore logs and values of the corresponding spacings were transferred on auger hole location map Based on various spacings, 5 different classes of 30, 45, 60, 75 and 100 m spacings were obtained and depcted on maps 7 &. 14 for both Amibara and Melka Sadi areas respectively
5.5 Drainability Classes
Drainability classes, drain spacing and dominant textural classes are presented in following Tableno 5.5
Table 5.5 Drainability classes and drain spacing alongwitli dominant soil texture in study area
Drain
ability
class
Drain
spacing
(m)
Amibara area
Melka Sadi area
Total for study area
Domi
nant soil
texture
Area
(ha)
Percent
age
Area
(ha)
Percent
age
Area
(ha)
Percent
age
class
1
30
576
19
284
32
866
22
V, F+
11
45
317
11
243
27
566
14
F, Mt
111
60
1632
54
301
33
1925
49
M-r M
IV
75
393
13
20
2
408
11
C, M
V
100
109
3
55
6
165
4
CD
Total
3027
903
3930
5-145.5.1      Drainability Class 1 ( 866 ha)
Drainability  class I is predominantly  occupied  by  clay  and  fine texured  V and  F+ soil profiles which  have at least 200  cm of clay  or silty  clay  at surface.  In  most of the locations the layers are composed  of clay  and  silty  clay  extending  up  to  a depth  of about 300  cm Invariably, the underlain layers are consisted of silt and clay dominated textures
This class occupies 22  per cent area in  both  Amibara and  Melka Sadi It is distributed  in small patches all over the area in  Amibara,  however,  its location  is confined  to  extreme north-east pan of Melka Sadi
5.5.2      Drainability Class II ( 566 ha)
Class II is dominantly occupied by F and M+ soil textural classes and characterized by 
profiles in which fine textured layers (silty clay loam or finer) are predominant and which 
have clay or silty clay in less than 20 per cent of control section
This class is sparsely  distributed  in  small patches all over the area,  however,  with  wide patches occur in  northern  part of Amibara area.  Whereas in  Melka Sadi area this class is confined  to  southern  part only  It occupies little area about 14  per cent in  both  Amibara and Melka Sadi
5.5.3      Drainabliiy Class III ( 1925 ha)
Drainablity Class III is composed of soil profiles in which fine textured layers (silty clay loam and finer) are dominant alongwith finer textured profiles. Some mixed profiles having nealy equal thickness of fine and coarse textured layers are also present
5-15This class is widely distributed and occupies largest area i.e about 50 per cent in both Amibara and Melka Sadi The predominant textural classes are M+ and M constituting about 85 and 15 per cent area in this class respectively
Class III drainability occupies the centra! pan, extending from south to nonh in Amibara area, whereas in Melka Sadi, these are intermixed with more finer and coarser units This class is moderately drainable having drain spacing of 60 m
5.5.4   Drainability class IV ( 408 ha)
Drainability class IV comprises profiles in which coarse textures (silt loam, sandy loam or coarser) are dominant and have sand or loamy sand less than 5 per cent in control section This  class  occupies  about  11  per  cent  area  Soils  of  this  class  are  more  permeable Relatively  impermeable  layers  occur  al  deeper  depth  Owing  to  above  characterstics  the spacing is also as wide as 75 m Majority of this class are distributed in isolated parches in central  pan  of  Amibara  area  In  Melka  Sadi,  negligible  area  (about  2  per  cent)  is occupied by this class becauase majority of soil profiles are composed of finer textured layers with relatively shallower deepth of relatively impermeable layers.
5.5.5 Drainability class V ( 165 ha)
Characteristically  drainability  class V comprises of the profiles dominated  by  coarse textural layers and  mostly  confined  to  Amibara area Soils of this class are highly permeable and accordingly spacing is also as wide as 100 in This class occupies only 4 per cent area. The profiles of this class have more proponion of sand and loamy sand with coarse texture in  control section  This class is confined  to  some patches which  are sparsely distributed throughout the study area
5-165
Ml
Ml
■iI
■ai
*
*DESCRIPTION
OF
SOIL PROFILESi
■d
■I
■n
■I
■I
■I
I
■s
di
di
ad
di di id id
i
IExplanatory Notes
Boundary 
a
abrupt
s
c
clear
g 
gradual
w
i
smooth wavy 
irregular
d 
diffuse
b
broken
Colour
Colour in Munsell notation
Mottling
Quantity
Size
vf
very few
f :
fine
f
few
m :
medium
c
common
m
medium
m
many
Colour
RB          reddish brown
Structure Form*
sbk subanguiar blocky abk angular blocky 
pr        prismatic
cl        columnar
pl        platy
m        maassive
sg       single grain Pores.              Quantity as mottling Texture
YB yellowish brown Size
grade 1 size
f m c vc 2 3
fine medium coarse very coarse weak moderate strong
as mottling
C        clay
ZC silty clay CL . clay  loam L  loam
SC     sandy clay SCL  sandy clay loam SL     sandy loam
LS     loamy sand
ZCL   silty clay loam ZL      silt loam
Z        silt S        sand
(F - fine, VF very* fine, C coarse)Explanatory Notes (Continued)
Consistence.
Dry
1       loose
s.      soft
Moist
1    loose
vfr very friable
sh.
slightly hard
fr:
friable
h
hard
fi
firm
vh;
very hard
vfr
very firm
e(x)h
extremely hard
e(x)fi.
extremely firm
Wet;
ns/so
non sticky
np/po.
non plastic
ss
slightly sticky
ps
slightly plastic
s.
sticky
P
plastic
vs:
very sticky
vp
very plastic
Concretions
Quantity 
As mottling
Size
As mottling
Salts
Reaction to HCI
Electrical conductivity in deci Siemen per in (dSm-1)
eo         nil
e         slight es         strong ev         violent
2Amibara Drainage Project Phase II, Soil Profile Characteristics
1  Profile No
2  Field No
3  Area
■4 Site Description
P-1
F5A/I0
Amibara cotton state farm
5  Groundwater Depth (cm)
6  Groundwater EC (dSm-1)
7  Groundwater pH .. 
. 175 0 82 7 49 , 
8  Date 9  Author luucpin
18 1095
Dr Dhan Pal
r
Fairly good cotton growth, even plant density , plant height varies about 80-100 cm picking 
stage, free from local weeds, profile site 30m east of irrigtion field canal
10  Depth to Rel Impermeable Layer (cm) 440
I Xo I Horizon
I Jcpthfan)
| 1          1 0-2 5
1  c
n
I Dn
olour
talrix
Texture
Coruistci
kc
Structure
1 EC(I.2) 1 ECe
pH
HCL
Pores
Concretions
Mottling
Remark
1 Boundan
| ConJiliun 1 1’ s
On
Moist
U el
form
Size
1 Grade
| dSm-l
reaction
Quantity
Size
Quanlitx
Size
Quanlitx
Size
1
1 I0VR
7f'
sh
Ir
32
1 •»        1 22 70
s
P
sbk
f
|2
1 ’ 22
7 86
co
c
f
-
Il | 70 1 10
1
10\  R JJ
ZCL
Mr
S$
-E?
sbk
tn
T2
To 12
7 72
ev
c
c
f
1
1£*
3J IQYR
ZL
ic
Ir
L
m
j2
To 14
P»
7 69
ex
c
III
f
f
Feu Hue roots
Present up to
1 1 110 1’0
| < Il ’0-1
34 JO'i R
L-O /I
M
ns
-2!£
'g
c
|1
[0 15
7 71
e\
c
c
f
r
ti
| o          1 I J*.|so
34 | 0> R
C1
ss
p»
[sbk
m
|2
0 22
7 23
ev
c
ni
fi
31
ss
P'
sbk
f
2
Io 16
7 67
e
c
f
f
r
•
Augerii
’g
.
p 1 -M) 1J0
r 7         1 i <o  ■’op
|
JJ IO> R
OYR
Cl
Ir
7CI
J2
st
ir
JJ lO'l R
sS
£S
co
1 ')         1 1 JO 4 40
SI
[ |ii              1
13
|n\ R
IK
"P
es
Ven feu fine voncretions of
CaCo3
III           1   l» 4l < ’f)
3J
1 O'! R
zc
7|
li
r
es
.
ZC intermixed
uith S & 7
■K
3|
cs
6-1Amibara Drainage Project Phase II, Soil Profile Characteristics
1 Profile No
2  Field No
J .Area
4 Site Description
•P-2 
.’F5B/I1A
5 Groundwater Depth (cm) 205
6 Groundwater EC (dSm-l) 175
Amibara cotton state farm            7 Groundwater Ph 
7 43
:  Medium  cotton  growth,  plant  height  varies  from  80-100  cm  ,  first  picking completed, free from local weeds
8  Date               1 11 95
9  Author           Dr Dhan Pal
10  Depth to Rel Impermeable Layer (cm) 320
1 Nu
Huri/on
Depth
Boundarx
Condition
Colour
Texture
Structure
ECe
PH
Pores
Concretions
Dex
Moi a
Drx
Moist
Wet
Form      | Size
Grade
FC(I     2) dSm-l
IICL
reaction
Quantitx
Sire
Quanlilx
Size
Qujn Citx     1 Size
Remark 1
11
0-60
83
HH R
32
ZC
th
it
s
P
sbk
1m
3
1 54
7 31
co
c
f
12
Soil >.Tack J continue 1 up to 50 I cm depth I
60 ’0
g3
lb'xR
4J
ZCI.
xfr
ss
P'
sbk
m
2
1 31
7 19
eu
*•’
1»
zJ
7O-H5
S3
I0YR
42
ZL
fr
st
abk
rn
2
0 16
7 81
cs
c
rn
14
K5-I5O
10*1 R
J2
ZC
fr
____
s J’
sbk
m
1
044
761
eu
c
f
Dec
Au germ g
I5
I5O-2IO
tot r
3J
ZC( ZL
fr
ss
Ps
e
16
210-250
I0YR
J2
LS
(15
nP
e
I7
2<0 120 [
I0YR
3 J
FSL
ns
"£
e
1*
J 20 J90
10^ R
3 2
ZC          1
fi
s
Ps
e
Due tu hardness of lax er further augeruig xxas n<4 possible
6-2J Profile No
2  Field No
3  Area
4  Site Description
P- 3 
F5B/14
Amibara Drainage Project Phase II, Soil Profile Characteristics 5  Groundwater Depth (cm)                      175
Amibara cotton state farm
6  Groundwater EC (dSm-l)
8 Date
Amibara cotton state farm 7 Groundwater pH ' 
1 24
S ’in 
13 11 95
Dr Dhan Pal
Medium cotton growth cotton al picking r • ! j •   °
8
from field canal in cotton field 
* g germination, surface so.I dry witJh slight crack, location about 10m west
d , , "r "nan ™
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Dr Dhan Pat
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Melka Sadi cotton state farm                7 Groundwater pH
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6  Groundwater EC (dSm-l) 7  Groundwater pH
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I
IREFERENCES
All India Soil and Land Use Survey Organization
FAO FAO FAO
FAO
ILR1
Sir M MacDobnald & Panners Ltd
Sir W Halcrow & Panners
1970 Soil Survey Manual, 1 A R 1, New Delhi
1965    Report on Survey of the Awesh River Basin, Vol 2, Soil Science
1977   Guidelines for Soil Profile Description (second edition)
1979   Soil Survey Investigation for Irrigation, FAO, Soils Bulletin No 42 , Soil Resources Management and Conservation Service Land, and Water Deveiope- ment Division, FAO, Rome
1984    Drainage Testing, FAO Irrigation and Drainage Paper, No 28, FAO, Rome
1972 - 1974     Drainage Principles and Application Vol I-IV
1LRI, Wageningen, The Netherlands
1989 Amibara Drainage Project 1, Drainage Specialist Filed Visit Repon, WRDA, Addis Ababa.
1985 Master Drainage Plan for Melka Sadi and Amibara Areas. Final Repon, Vol 3, Annex Al Soils and Drainability Classes, WRDA, Addis Ababa
United States Department of Agriculture
Winger, R J
1964 Diagnosis and Improvement of Saline and Alkali Soils. Agricultural Handbook No bO (Reprinted 1969)
1985 Unpublished Review Report of the Master
Drainage Plan for Melka Sadi and Amibara Areas World Bank , Eastern and Southern Africa Projects Department.**
>)
ii)
LIST OF MAPS
Map no 1        - Soil classification of Amibara Map no 2 - Soil textural groups of Amibara
1
iii)        Map no 3 - Soil salinity of Amibara
iv)        Map no 4 - Depth to groundwater of Amibara
V)        Map no 5 - Groundwater salinity of Amibara
Vi)       Map no 6 - Depth to relatively impermeable layer of Amibara
vii)       Map no 7 - Soil drainability & drain spacing of Amibara
viii)      Map no 8 - Soil classification of Melka Sadi
ix)       Map no 9 - Soil textural groups of Melka Sadi
X)        Map no 10- Soil salinity of Melka Sadi
xi)       Map no 11- Depth to groundwater of Melka Sadi
xii)      Map no 12- Groundwater salinity of Melka Sadi
xiii)       Map no 13 - Depth to relatively impermeable layer of Melka Sadi xiv)       Map no 14 - Soil drainability and drain spacing of Melka SadiI
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SOiORAINABILITY CLASSES & DRAIN SPACINGSNo* or Stccnoxr C»omSOIL TEXTURAL MAP MELKA SADIDEPTH TO GROUNDWATER
MELKA SADIGROUND WATER SALINITY MELKA SADI1 FGf NO
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Summery

Project: Amibara Drainage Project Phase-II - Detailed Designs, Tender Documents, and Environmental Impact Assessment

Location: Right bank of Awash River, 260 km east of Addis Ababa, Ethiopia

Consultant: Water and Power Consultancy Services (India) Ltd.

Study Area: Approximately 4,000 ha in Amibara and Melka Sadi state farms

1. Study Area Characteristics

Geomorphology: Rift Valley region with alluvial plains, volcanic formations, and fluviatile terraces
Topography: Flat alluvial plains with elevation 725-745m, gradients 0.05-1.0%
Climate: Semi-arid (560mm annual rainfall), bimodal precipitation, high evapotranspiration (2400mm/year)
Current Land Use: Primarily cotton cultivation (8,400ha) with some maize and banana

2. Soil Survey Methodology

Comprehensive soil survey conducted from October 1995 to February 1996:

229 auger holes (172 in Amibara, 57 in Melka Sadi) at 400m x 400m grid (1 per 16ha)
8 detailed soil profile pits (2m depth)
Field measurements included:
- Soil color, texture, consistence
- Electrical conductivity (EC) and pH
- Depth to groundwater and impermeable layers
- Hydraulic conductivity tests (pour-in and bail-out methods)

3. Soil Classification and Characteristics

Soil Type	Area (ha)	Percentage	Key Characteristics
V: Deep Clay Soils	465	12.7%	>200cm clay/silty clay, vertic properties, poor drainage
M+: Soils with appreciable clay	1,790	48.8%	Fine textures dominant, >20% clay in control section
M: Medium/mixed texture	533	14.5%	Equal fine/coarse layers, <20% clay
C: Coarse textured	332	9.0%	Silt loam/sandy loam dominant, <5% sand
CD: Very coarse textured	537	14.6%	>5% sand/loamy sand, high permeability
R: Rock outcrop	13	0.4%	Shallow soils over bedrock

4. Soil Salinity Distribution

Salinity Class	EC (1:2) dS/m	Area (ha)	Percentage
Very Low	0-0.75	2,472	67.3%
Low	0.75-1.5	748	20.4%
Moderate	1.5-3.0	305	8.3%
High/Very High	>3.0	145	3.9%

5. Drainage Recommendations

Drainability Class	Drain Spacing (m)	Area (ha)	Percentage	Characteristics
I	30	866	22%	Clay soils, poor drainage
II	45	566	14%	Fine textures, moderate drainage
III	60	1,925	49%	Mixed textures, good drainage
IV	75	408	11%	Coarse textures, very good drainage
V	100	165	4%	Very coarse textures, excellent drainage

Key Drainage Design Parameters:

Recommended drain depth: 1.8m below ground level
Design discharge rate: 2.5mm/day
Depth to impermeable layer varies 200-500cm
Hydraulic conductivity ranges 0.01-6.0 m/day depending on texture

6. Conclusions

Soil salinity and rising groundwater are major concerns affecting agricultural productivity
About 12% of area has severe drainage limitations (Class I)
Nearly half the area (49%) has moderate drainage characteristics (Class III)
Drain spacing recommendations range from 30-100m based on soil characteristics
Integrated drainage system needed to control salinity and waterlogging