Amibara Drainage Project Phase-II Soil Survey Summary

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SOIL SURVEY/SOIL CLASSIFICATION DATA/
ANNEX-4A
kSOIL SURVEY STUDIES
CONTENTS
Pages
1 General Features of Study Area 
1.1 Location
1.2 Geomorphology
1.3 Topography
1.4 Climate
1.5 Irrigation and Agriculture Development 1.6 Rationale for the study
1.7 Delineation of study area
H
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.
iii.
Soil texture
Soil consistence
iv.
Electrical conductivityof 1:2 soil-water suspension
v;
Soil reaction (pH)
vi.        Free carbonates
vii.       Mottling
viii.       Concretions
ix. Relatively Impermeable layer: Criteria and definition
ix..        Depth to groundwater
xi.         Groundwater EC & pH
xii.         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 Types in Project Area
3.1        Introduction
3.2        Textural profiles
3.2.1     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
3.3.1      Deep clay soils
3.3.2     Soils with appreciable amounts of clay or 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
3-1 to 3-13
ii4          Distrib
ution of Soil Salinity in Project Aiea
4-1 to 4-10
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 (1:2) to ECe
4.9       General distribution of saline soils 4.9.1    Soil salinity in Amibara Area
4.9.2    Soil Salinity in Melka Sadi Area
5 Drainability
 Classes and Drains Spacing 
5-1 to 5-16
5.1
Introduction
5.2
Soil factors influencing drainage
5.3       Soil parameters for drain spacing
5.3.1    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 drain
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 conductivity
5.4.2.3  Selection of depth to relatively impermeable layer
and alternate criteria for selection of lateral spacing 5.4.2.4  Selection and method of calculation of drain spacing
iii5.5.       Drainability classes 5.5.1    Drainability  class 1 5.5.2    Drainability  Class 11
5.5.3    Drainabilily   Class III
5.5.4    Drainability   Class IV
5.5.5    Drainabilily   Class V
Description of Soil Profiles References
Maps
ft
6-1 to 6-8
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I B B 0< I
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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 Vjilley 
Project area is about 8 km to the west of Awash-Melle 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 north, 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
1-10.05  to  I  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  How by  diverting  the.  Awash  river  water  through  weir  al  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 of irrigation, water level &l its salinity have risen considerably in the project area Deptl<oi
1-2groundwater levels in Amibara under phase I, as reported by Halcrow & Partners, were within 300 cm below surface in an appreciable large area. Similarly in phase 11 areas, where  groundwater  level  is  within  300  cm  of  the  surface  have  been  included  in  the drainage programme which are contiguous to phase I 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 undertaken 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.
1-3
oCHAPTER 2
PLAN OF APPROACH AND METHODOLOGY FOR SOU. 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  determintlions. 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  1  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.
a
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
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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, sill 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
<5
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    1:2    soil-water suspension.   In   order   to   diagnose   the   salinity   occurrence   in   soil   profile.   EC   (1:2)   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-water 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  ot
carbonates  in soil is  distinguished by  nil, slight, strong or violent effervescence. HCI reaction with soil was tested at ail 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 particles. Magnitude and size of concretions were observed by feeling on crushing or rubbing soil. Whenever
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w-
coneretions noted were recorded in auger bore and profile sheets. In addition to above soil properties, other important parameters which are exceedingly important for drainage design such as
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a. depth 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  condutctivity  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 soiUdepth 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 difllection in multimeter indicator. This particular device functions accurately in field to provide an accurate measurement of water table depth. Using above data water level contours  were prepared at 100 cm. intervals and shown on maps no. 4 and 11 tor 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  &  1.5  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    1:2,    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   the  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.
2-7
32.2.2   Determining hydraulic properties in field - Hydraulic conductivity and
infiltration test
Hydraulic conductivity tests
As per TOR the hydraulic conductivity tests have been carried out at selected profile pits. 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 1 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  with  a  locally  prepared  scraper  by winding spirally, a piece of barbed wire on a wooden stick al 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.  Water  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 water 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
2-811 (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 (m3), rate of water flowing into hole, q, (m7min), and textural class  were used to compute hydraulic conductivity.
Hydraulic conductivity using pour-in method was carried out al eight selected profile sites. The results of K - values alongwith other associated parameters are presented in table 5.1.
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 waler 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
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    Tire 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    cylinder's remained projected above the ground level
b)     Initially   waler   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   the   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   tall   with   respect   to   time   were   continued   at   suitable   time intervals   until   stable   rate   was   achieved   which   was   generaly   obtained   in   S   to   o   hours duration.
2-10CHAPTER 3
DESCRIPTION OF SOIL TYPES IN PROJECT AREA
3.1 Introduction
The soils  of lhe project area were studied and classified through conducting field soil surveys in identified area of phase 11. 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 al 400m x 400m grid in order of 1 per 16 ha Some ten per cent of lhe observations were studied by  excavating profile pits  of dimensions  2 x  15x2 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 al selected locations were studied In addition 28 observations oCauger
holes and profile pits studied by previous cosuitants including lial consult, 1969,7), Sir William Halcrow Ai Partners, 1981 A: 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  properties  which include colour, texture, consistence, electrical conductivity, soil reaction (pH), mottling & presence of 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  rs 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, HC1 reaction, porosity, mottling and other site characteristics  os  depth to relatively impermeable layer, groundwater depth, EC and pH Detailed description of soif profiles examined in Amibara and Melka Sadi areas  are presented in profile description sheets The field soil survey  studies  including determining hydraulic  conductivity  and in&tration tests were carried out between October 10th. 199$ to February 7th, 1996 in project area located at Arnibara and Melka Sadi cotton state farms adjacent io Melka Wafer and Melka Sadi towns  in the Middle Awash Valley  about S km to the west of ail weather Awasb- mille highway at about 260 km cast of Addis Ababa
The comprehensive data ot detailed auger hole studies, profile examination, laboratorx analysis, and hydiaulic  conductivity  tests  were used to classify  soils  of project area into different soil types  and to provide salient information for drainage inve^Ugaiton. Ihciclorc, in ordci to generate valueablc  datj base for drainage investigation parucuLuty lor sub-surtacc design these data were analysed and interpreted Following self cxplanuuy maps were prcpaicd
i)          Map no     I  • Soil classifyalioii ofAmibaaa
ii)         Map no    2  - Sod textural groups of Anubara
iii)        Map no    3  • Sod saluuly of Anubara
iv)        Map no    4  - Depth to groundwater ol Anubara
v)         Map no   5  * Groundwater saluuly of Am.bara
vi)        Map no o - Depth to relatively impermeable layer of Anubara 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 - Ground water 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 foundamental and permanent characteristics  that has  direct bearing on pore-geometry  which determines  the water transminssion behaviour of soil. Infact, texture provides  the open spaces  in soil mass  used for retaining and draining of water alongwilh 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,
3-3particularly, for drainability  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 proportion 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
V-
b)
c)
Coarse : Silt loam, silt, sandy loam or coarser.
Mixed : About equal thickness of fine and coarse textured layers.
ii)
Relativ
e thickness of clay or silty clay layers in the conrol section;
iii)
Relativ
e thcikness of sand and loamy sand in control section.
Based on above.criteria, in present study, following types of textural profiles have been classified:
1) Clay :                    Profiles which have at least 200 cm of clay or silty clay at surface
A maximum of 20 cm of coarser textured soil may be present in this surface layer.
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 wit
h 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 n’o.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 sill loam, sandy loam or coarser texture.
The  extreme  southern  part  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 northern part 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 part extending from south to north 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 arc  widespread About 65 per cent area is  composed of fine textured soil profiles  with clay and silty clay dominant texture with mote than 20 per cent clay or silty clay in control section. Mixed profiles with more or less equal thickness of fine and coarse textured layers occupy  about 25 per cent area Coarser textured soils  with silt loam, sandy  loam or coarser layers occupy only about 10 per cent area Intact 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 part 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
9.0
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 of about 300 cm. Occasionally  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 silt 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 struerture 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 underpressure in such areas. In Melka Sadi area these soils also occur in extreme eastern part.
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. AJongwith 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 ol 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 resembleness with the alluvial soils.
3-103.3.4     C : Relatively coarse textured soils (332 lia)
Soils  of this  unit are characterised by  the 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. 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 md-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 part of Amibara. Generally soil consistence is friable and effervescence ofHCI 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 (1:2
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 silt 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 md-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 oi 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 of 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 I ha-m, up to 2.1 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 water 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. Il is attributed to 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.
\
4-14.2       Criteria for 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 of saturation of soil exchange conmplex with Na+ and may be calculated using following relation.
Exchangeable Na+ (ineqJH)Og of soil)
Calion Exchange capacity (ineq./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+ activity. It is also used to distinguish the salt affected soils. The criteria for classifying salt affected soils is given in Table 4.1.
Table 4.1. Criteria for classifying salt affected soils
Property
normal
Saline
Sodic
Saliiit^Sodic
ECe (dSin-1)
<4
>4
<4
>4
SAR
< 13
< 13
> 13
> 13
PH
7.0
7.0-8.5
8.5-10.0
8.5-10.0
4-24.3 
Saline Soils
Salin
e  soils  are  often  recognized  by  the
presence
of  a  white  c
rust  on  the  surface.
The
abse
nce  of  a  white  crust,  however,  does
not  precl
ude  the  existe
nce  of  a  saline  soil.
The
SAR
value  of  less  than  13  reflects  relat
ively  low
level  of  adsor
bed  sodium,  whereas
the
high
salt concentration gives a saturation
extract of
ECe value of
greater then 4 dSm-
1.
The
soil  pH  is  less  than  8.5.  The  Cl'
and  SO^
“  “  ions  are
the  principal  anions,
with
smaller  amount  of  HCCh  .  The  principal  cations  are  Ca2+  and  Mg2+  with  lesser  amount
of Na+ ion. The presence of compounds  with soils  as  gypsum (CaSO4.2H2O) and calcium carbonate (CaCOa) 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 tends  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 CCh to form Naz CCh. Under these conditions the pH of sodic soil may increase to 10. At these high pH values, calcium and magnesium ions are precipitated as carbonats because of relatively  high concentration of CCh ions. The prominent cation is  Na+, with some Ca2+, Mg?+ 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+ on the exchange complex
b)  The hydraulic conductivity increases
c)  The sodium salts are leachd from the system
The source of Ca2+ 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+ 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-l The presence of the excess  salt maintaining the soil permeability  as  a high level and acts  io 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 field
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.
%
w
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 filteralion 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(l: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.
4-54.7       Determining 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.4,1.  The correlation  was  similar  to  that  of  Master  Plan  Study.  The  equivalent  EC  1:2  and  ECe values for the standard USBR (1954) salinity classes is shown in following Table 4.2.
4-6
ILEGE HO
Phese H EC values Hester plan EC values
z
VERY HIGH
0
1
EC (Saturation Extract dSn )
Fig.4.1 Relationship between electrical conductivity of 1.2 foil wafer suspension & saturation extract-
WAPCOS (II Ltd, / eb-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
3.00-5.00
> 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.
4-7Tabic 4.3 - Soil salinity distribution in study area
Soil Salinity Classes
Area in Amibara
(ha)
Area in Melka Sadi (ha)
Total area
(ha)
fercentage
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
6
1
Moderate
207
98
305
8
High & Very High
120
25-
145
3.7
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 site, fairly large part of Amibara area, about 72 per cent, is  non-saline with very  low (VL) salinity values  < 0.75 dsm-l (1:2 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 part are generally non - saline. Soils in this area are coarse textured and ground 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 dSm-1.
About 16 per cent area is  occupied by  low salinity  (0.75 - 1.5 dSm-1) 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-1). 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-1. 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-1. Soil profiles in these areas are dominated by fine texture including silty clay loam, silty 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-1.
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 appearance.
t
!CHAPTER S
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)      Particle- size distribution
iii)     Chemical properties
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.
5-1Different 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 water table at
mid point of drain spacings and steep fall of hydraulic head adjacent to drains,
w
%
w
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 water 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 5.1 and 5.2 respectively.
5-2TABLE 5.1 HYDRAULIC CONDUCTIVITY DETERMINED USING POUR - IN METHOD
Profile
No.
Field No.
Location
Test
Depth
(m)
Radius of hole,
* >(m)
Depth of W.T. or
Tmpenlous Strata
front surface of
water maintained
In hole. Tu (m)
Water
maintai
ned In
hole, h
(nt)
h
Tu
h
r
Condition
1 Tu > Jh
Condition II
3h>Tu >h
Total quantity of water flown In hole (m3)
Rate  of  flow, q (m3 mln-1)
K-value (md-l)
SoilTetfural
daises
P-l
F5AI0
Amibara
0-1
0.05
I.J5
040
0.52
16
N.A
Applicable
0.027
0000010
Oil
ZCLZL
1-2
0.05
0.55
0 50
0.91
10
-
-
0.087
0.000015
0.15
ZLCL
P-2
F5B 11A
Amibara
0-1
0.05
1.85
0.80
0.43
16
•
•
0014
0.000078
0.08
ZC.ZCL
1-2
0.05
0.35
0 50
060
10
•
■
0.053
0.000090
0.27
ZCLZL ZC
r-j
FSB 14
Amibara
0-1
0.05
1.55
0 80
050
16
•
•
0013
0.000020
0.020
ZCL
1-2
0.05
0.75
0 50
066
12.5
•
0018
0.000015
0.045
ZCL
P-4
F6/I7
Amibara
0-1
0.05
2.80
0 80
0.28
16
Applicable
NA
0.014
0 000021
0 018
ZC
1-2
005
1.80
0 80
0.44
16
N.A
Applicable
0052
0.000100
0.10
ZCL
P-5
F9JI7O
Amibara
0-1
0.05
2.40
OSO
033
16
Applicable
N.A
0.034
0.000060
0.06
ZLZC
1-2
0.05
1.40
0.80
057
16
NA
Applicable
0.086
0.000170
025
ZL
P-6
F5B20B
Amibara
0-1
0.05
1.47
0 80
0.54
16
•
Applicable
0.017
0.000032
0021
ZCLZL
1-2
0.05
0.50
0.50
100
10
Applicable
NA
0.047
0.000100
035
ZLZ.SL
P-7
Fl 28.47
Melka Sadi
0-1
0.05
2 40
OSO
0.33
16
Applicable
N.A
0.056
0.00011 0
0.13
ZC. ZL.ZCL
1-2
0 05
1.40
0.80
0.57
16
N.A
Applicable
0.024
0.000035
0.032
C. ZC
P-8
Fi'j.h
Melka Sadi
0-1
005
2.20
0.80
0 36
16
•
Applicable
0.065
0.000169
0018
ZCLZC. SCL
1-2
0.05
1.20
0.80
0.67
16
•
Applicable
0.145
0 000200
030
ZC.FSL
NA. Nut Applicable, Z : Silt. ZL : Silt Loam. ZC : Silty Clay. ZCL : Silly Clay Loam. C:Clay SCL : Sandy Clay Loam. FSL : Fine Sandy Loam. CL : Clay Loam. SL : Sandy LeantTabic 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
6.25
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 : Silty 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  of  water  also  contributes  to  the  radial  movement  of  water causing more rapid flow of water 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  gel  cleaned  by  removal  of  silt  panicles  through  repeated  bailing-out  of  waler from hole.
5-4On the contrary, the hydraulic  conductivity  tests  using pour-in method were carried out in top 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 vertic  characters  which generally exhibit swelling and shrinking properties. During tests, when waler 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 particles  may  also tend to block  very  fine pores  in the soil, thus  further 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
0.01
Hard   clay,   hard   silty   clay,   hard   clay   loam, hard sandy clay loam
0.08
Clay,   silty   clay,   silty   clay   loam,   clay   loam, sandy clay loam, sandy clay
0.30
•
Silt loam, silt, loam, very fine sandy loam
1.00
Loamy   sand,   sand,   sandy   loam,   fine   sandy loam
2.00
Coarse sand, loamy coarse sand
6.00
5-5On comparing the the K - values obtained in present study by determining in Geld and
above standard values following inference was drawn
During field survey  the observed K - values  as  obtained trom 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  w'ere as  0.10 and 0.020 md-l 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, tor designing the field laterals  spacing and classifying the soil dnuiubility. the standard values  of hydraulic  conductivity  of Table 5 3 were used in the present studs  as the same were also adopted in ADI* 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 draiiu and below 1.25 cm up to the depth of relatively impermeable layer aie 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 corttour 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 al 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 pan of Amibara
relatively impermeable layers occur at shallower depths i.e. from 200 to 300 cm below groundsurface and in northern part 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 machinary, equipment, excavation (earth work) cost, etc.
iv)     Satisfactory  outfalls  conditions,  taking  into  consideration  complete  drainage  system originating from field through secondary and main drains,etc. up to outfall in the river. 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 1.8 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 1 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 drain 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
1
Silt     loam,     sandy loam or coarser
Cs
2.0
II
Other             profiles except ones with
>  2.0  m  of  clay  or silty clay
C, M, M+,F+
1.4
111
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 to varying textural layers (highly stratified soil profiles, in which even up to as many as 15 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 I 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 behaviour of layers just in the vicinity of the drains. Neat
5-9.he   drains,   flow   converses   and   there   is   increased   rare   of   head   loss.   Keeping   in   view   .he 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   ?   in above and 0.5 m 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 ot 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 1 Considering the laterals
5-104
■
•»
are   placed   1.8   m   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   m   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.
iii)        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  ol the relatively impermeable layer below drain level play important roles in determining the
I
After   computing   the   drain   spacings   based   on   above   mentioned   criteria   four   values   ot 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 flow equation as BKdh                       4KIU
or S  =
z
( 8Kdh + 4Khz )
----------------------- --------------------------------------- 2 q
where : q =                   discharge rate per unit surface area. In present study 
q = 2.5 mm/day.
K =           Representative weighted hydraulic conductivity md-1
*
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 wetted perimeter of drain U.
5-12The equivalent depth'd' upto impervious layer
Do
d = ----------------------------------
8Do         Do
------- Ln---------- + 1
KS          U
The symbols used in above equations are given in following Fig. 5.1
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 Table no. 5.5
Table 5.5 Drainability classes and drain spacing alongwitb dominant soil texture in study area
Drain
ability
class
Drain
spacing
(in)
Amibara area
Melka Sadi area
Total for $rud> area
Domi
nant soil
texture
Area
(ha)
Percent
age
Area
(ha)
Percent age
Area
(ha)
Percent
age
claxs
l
30
576
19
2S4
32
Soo
V. F*
11
45
317
ll
243
27
560
14
F, M-
111
60
1632
54
301
33
1925
49
M
IV
75
393
13
20
2
408
11
C..M
V
100
109
3
55
6
105
4
CD
Total
3027
903
39305.5.1 Drainability Class I ( 866 ha)
Drainability  class  1 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 part of Melka Sadi.
5.5.2     Drainability Class U ( 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     Drainabiity 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 central part, extending from south to north 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 lia)
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 patches in central part 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 m. This class occupies only 4 per cent area. The profiles of this class have more proportion 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.
5-16DESCRIPTION
OF
SOIL PROFILESExplanatory Notes
Boundary:
a :      abrupt
s :
c :
clear
w :
g :
gradual
i :
d :
diffuse
b :
smooth wavy
irregular broken
Colour            Colour in Munsell notation Mottling:        Quantity
vf :      very few
f :       few
c :       common
m :      many
Colour    RB :       reddish brown
Size
f •:      fine
m :      medium
m :      medium
YB: yellowish brown
Structure Form: Size:
sbk :   subangular blocky abk :   angular blocky
pr :    prismatic
cl :    columnar
pi •    platy
m         maassive
sg :    single grain Pores:                Quantity: as mottling Texture:
f :
m :
fine
medium
c :
coarse
vc :
very coarse
grade 1 :
weak
2
moderate
3 :
strong
size
as mottling
C:
clay
sc :
sandy clay
ZCL:
silty clay loam
ZC :
silty clay
scl:
sandy clay loam
ZL :
silt loam
cl :
clay loam
SL :
sandy loam
z
silt
L
: loam
ls :
loamy sand
s
sand
(F - fine; VF: very fine; C: coarse)Explanatory Notes (Continued)
Consistence:
Dry 
Moist
1:     loose
l: loose
s:     soft
vfr: very friable
sh:      slightly hard
fr: friable
h:      hard
fi: firm
vh:      very hard
vfi: 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 : Electrical conductivity in deci Siemen per m. (dSm-1)
Reaction to HCI:            eo :     nil
e :     slight
es :      strong
ev :      violent
2. -J
Amibara Drainage Project Phase II, Soil Profile Characteristics
1. Profile No.
2.  Field No.
3. .Area
: P - 1 
: F5A/I0 
: Amibara cotton state farm
5. Groundwater Depth (cm)
: 175 
8. Date
6. Groundwater EC (dSm-1)
: 0.82 
9. Author
: 18.10.95 
. Dr. Dhan Pal
4.  Site Description
. Fairly good cotton growth, even plant density , plant height varies about 80-100 cm picking
7. Groundwater pH
: 7.49 * 
10. Depth to Rel. Impermeable Layer (cm) : 440
stage, free from local weeds, profile site 30m east of inrigtion field canal.
lloozou
L oiour
matrix
Texture
Structure
Bourxlirx
ConJilrun
EC(I:2)
dim-1
Concretions
Mottling
Remark
I
4
<
b
0-25
22-70
70-110
110-120
120-1 J5
IJ5-I50
reaction      Quantity       Size         Quantity          Size          Quantity        Size
Fexv fine rooU
Present up to
100cm
Deep Aufcnng
7
IfO-250
290-120
320-440
Ven few fine
Im
440-460
4*>O-526
concretions of
CaCoJ
it
ZC intemtived
with S <fc Z
6-1Amibara Drainage Project Phase II, Soil Profile Characteristics
1. Profile No.
2. Field No
3. Area
4 Site Description
: P - 2 
: F5B/11A
5.   Ground water Depth (cm) 6.     Groundwater EC (dSm-l)
: Amibara cotton state farm          7. Groundwater Ph 
: 205
: 1.75
: 7.43
8. Date              : 1.11.95
9. Author          : Dr. Dhan Pal
10 Depth to Rel. Impermeable Layer (cm): 320
:  Medium  cotton  growth,  plant  height  varies  from  80-100  cm.,  first  picking completed, free from local weeds..
No.
Horizon
Depth
Boundary
Condition
Colour
Texture
Consistence
Structure
ECe
PH
Pores
Concretions
Mottling
Dey
Moist
Dry
Moist
Wet
Form
Size
Grade
EC(1:2)
dS<n-l
HCL
reaction
Quantity
Size
Quantity
Size
Quan lity
Size
Remark I
1
0-60
B-*
I0VR
32
ZC
sh
li
s
P
sbk
nt
3
1.54
7.31
eo
c
f
Soil crack 1 continue | up to 50 I cm depth |
2
60-70
8-’
I0YR
43
ZCL
vfr
ss
ps
sbk
nt
2
131
7.49
eo
e
nt
1
3
70-85
83
I0YR
42
ZL
fr
ss
E*
abk
in
2
0 46
781
es
c
ni
1
4
85-150
I0YR
3/2
ZC
fr
s
E
sbk
in
1
0 44
7.61
co
c
f
-
Dee
i Augering
-
1
5
150-210
10 YR
33
ZCL-ZL
fr
ss
ps
e
1
6
210-250
I0YR
3/2
LS
Its
c
7
250-320
I0YR
3/3
ISL
____
ns
np
e
1
8
320-390
I0YR
32
ZC
l*i
s
P‘
e
1
c
tardness 1 at* lax er I inther 1 ugering I
not      1
ctvjible J■U bJ
Amibara Drainage Projecl Phase 17 , Soil Profile Characteristics
1. Profile No.
2. Field No. 
.Area
. Site Description
:P-3
.F5B/14
: Amibara cotton state farm
5. Groundwater Depth (cm)
6. Groundwater EC (dSm-1)
7. Groundwater pH
- /rr-\m
Medium cotton growth, cotton at picking stage, fairly good
from field canal in cotton field.
■—    — - ■*"  ■ •
: 175
: 1.24. 
. 8.10. 
germination, surface soil
8. Date 9. Author
. 13.1195
: Dr. Dhan Pal
10. Depth to Rel. Impermeable Layer (cm) dry with slight crack, location about 10m. west
350Amibara Drainage Project Phase II , Soil Profile Characteristics
1. Profile No.
2. Field No.
3. Area
4.  Site Description
P-4 F6/17
5. Groundwater Depth (cm)
6. Groundwater EC (dSm-1)
: 240
: 1.07 : 7.80
8. Date
9 Author
. 4. 12.95
: Dr. Dhan Pal
Amibara cotton state farm          7. Groundwater pH
10. Depth to Rel. Impermeable Layer (cm): 250
: Poor cotton growth, and plenty of local weeds, uneven plant density, gaps in germination, patchy area with out plants, profile excavated 
in patchy area, all pickings are complete.
No.
Horizon
Depth
Boundary
Conduit
Colour
Texture
Consistence
Structure
EC(1:2)
dSm-1
ECe
PH
HCL                        Pores
Concretions                  Monlint:
Dry
Moist
Dry
Moist
Wet
Form
Size
Grade
reaction 1 Quan 1 Size
tity
Quan      1 Siz<          Quan
Size          Remark
9
tity
tity
1
0-60
I0YR
3'2
ZC
h
fi
s
Pi
sbk
r
3
0.55
7.55
e                  1c
f
Surface soil
1 dry to 60
1 cmsduelo
1 surface
| cracking
2
60-113
fr*
10YR
33
ZC
fr
s
sbk
f
3
0.55
7.55
c                  1c
r
| More
I compact
1 horizon
3
113-200
10YR
33
ZCL
fr
IS
pi
sbk
m
2
0.76
7.05
e                  1c
1c
fp
I Brown
/ colour 1
| mottles
Deep Augcnng
1
4
200-230
I0YR
37
LS
l-vfr
ns
np
co
5
230-250
10 YR
3'2
S
1
ns
np
eo
6
250-320
10YR
37
ZC
fr-fi
s
P
eo                i
J
7
320-350
10YR
33
z
KS
rs
eo
1—1
8
350-390
I0YR
32
LS
ns
"P
e
11
9
390-430
10 YR
32
S
1
ns
np
e
1 fine               |
I concretions I
I  fCaCo3 I
o
10
430-470
10YR
33
FSL
if.
c
r
11
470-520
10YR
33
Z
ss
J2
J
------- —
s
-E
1
6-41. Profile No.
2. Field No.
3 Area
4. Site Description
. P-5
: F9/3/17B
. Amibara maize filed
Amibara Drainage Project Phase II, Soil Profile Characteristics
5. Groundwater Depth (cm)
6. Groundwater EC (dSm-1)
7. Groundwater pH
; 260 : 6.31 
7.93 
8. Date 9. Author
. 11 12. 95 
: Dr. Dhan Pal
. Ver}' poor maize growth, intensly infested by local tall grass growth, used for grazing, 
in the maize field.
-
10. Depth to Re) Impermeable Layer (cm) : - maize cobs hervested, profile excavated well with
6-5
iCM m
Amibara Drainage Project Phase II, Soil Profile Characteristics
1. Profile No. 
. Field No. 
. Area
4. Site Description
. P -6
: F5A /20B
5. Ground water Depth (cm)
6. Ground water EC (dSm-L)
: 167 : 1.21
: 7.45
8. Date 9. Author
: Amibara cotton state farm           7. Groundwater pH
: 14. 12/95 
: Dr. Dhan Pat
10. Depth to Ret. Impermeable Layer (cm): 360
. Poor cotton growth, few local weeds, uneven plant density, picking is over, surface soil powdery with medium size cracks.
No.
Horizon
Depth
Boundary Conduit
Colour
Texture
Consistence
Structure
ECe
Dr\
Moist
Dry
Pores
Moist
Concretions
Mudline
Wet
Fom
Size
Grade
EC(l:2)
dSni-1
pH
HCL
rvactio
n
h
Quan tity
Size
Size
Size
Remark
1
0-30
d,b
I0VR
3/3
zc
fi
s
P
Quan tity
Quan tity
sbk
f
3
4.5
7.97
c
m
f
Few fine grass 1 and local
needs roots
2
30-90
8.'
I0YR
3/3
ZCL
fl
s
abk
in
2
2.47
7.55
eo
c
m
J
3
90-1 10
c,s
I0YR
3/3
ZL
fr
_____
ss
ps
Pl
m
2
0.55
7 60
es
c
m
c
m
4
110-130
c.s
I0YR
3/4
FSL
vfr
ns
np
C
I
0.63
7.21
cs
c
c
f
m
monies  black  1
in colour,           1
horizon  v  en  1
moist
5
130-150
g,w
I0YR
3/3
ZL
fr
ss
ps
ci
111
2
0.56       ’
7.45
ev
c
m
f
f
c
c’
1
6
150-160
I0YR
3/2
SL
fr
ss
_____
e
I
0.60
7.30
ev
c
c
r
f
m
c
J
J
Deep Aug   enng
7
160-170
I0YR
3/3
Z
I'r
ss
E2
es
3
170-200
I0YR
3/3
ZL
fr
ss
p*
es
few fine ohKK i
monies J
9
200-270
I0YR
33
ZCL
fr
ss
co
_____________
10
270-360
I0YR
J3
SL
vii
_____
ss
E2
co
___ J
1I
360-4X0
10 YR
J3
zc
ti
s
P
eo
—
12
4X0-520
I0YR
J3
Z
fr
ss
J2
co
L
----------------------
1
6-6Amibara Drainage Project Phase fl , Soil Profile Characteristics
1 Profile No
2.  Field No.
3. Area
A. Site Description
:P-7
: Fl/28/47
Melka Sadi cotton state farm
5. Groundwater Depth (cm)
6. Groundwater EC (dSm-1)
7. Groundwater pH
8 Date 9. Author
: 26. 12. 95 
: Dr. Dhan Pal
Fairly good cotton growth, all pickings are over, plant height about 100cm, 
: 260
: 1.23
: 7.44
10. Depth to Rel. Impermeable Layer (cm) . 150, 380
the cropped field
» no cracking of surface soil. Profile excavated is well with in
1 No.
1 Horizon
Depth I n<n
Boundary Conduit
1     c
J Dry
olour
Moist
Texture
Dry
Cons isle
Moist
nee Wet
ECc
" pH
I Fonn
Structi Size
i1 i
ire
Grade
EC(L2)
dSm-1
1 1ICL react io
n
p
Quan tify
xes
Si2e
Cone
Quan tity
retion Size
Mot
Quan-
ilinr.
Size
Remark
i 1
ZC
h
33
I *bk
f
3
1.12
7.98
eo
c
f
tLi
wide and
vertical
L
s
3'4
I ZCA "7<
Q"
10^ R
34
10^ R
33
10\ R
34
as
-n
| iW.
m
2
I.OI
7.96
co
c
m
1
.
ZCL
fr
SS
P
1 abk
in
2
0.45
7.99
eo
c
nt
c
m
I4
i 75-90
Kb
ZL
fr
ss
p
pbR
in
2
0.42
7.99
cs
c
c
ni
m
15
1&
1/
90-120
120-140
H1UJi-fIi/J1*
L
black and
reddish
brown mottles
1 vfr
ss
p
'"d
m
nt
0.62
7.84
eo
c
ni
f
nt
CS
10>  R 22
c
fine tools
arc
observed
tf»
nt
f
3
0.50
7.92
eo
c
f
nt
c
fi
I
33
s
p
sbk
r
3
0.45
7.87
co
f
f
Deep
.Augerin
£
1 
1 1
175-330
ICH R
33
SL
ns np I
e»
-------------- -
feu fine
black
mottles
1 9
380-520                |
10^ R 33
ZC
fr-fi
co
ztAmibara Drainage Project Phase II, Soil Profile Characteristics
1. Profile No.
2. Field No.
3. Area
4.  Site Description
: P - 8 
: F1/3/3 3 
: Melka Sadi cotton state farm
5. Groundwater Depth (cm) 6. Ground water EC (dSin-1) 7. Groundwater pH
: 240         8. Date
: 192  9. Author
: 29. 12. 95 
: Dr. Dhan Pal
: Poor cotton  growth,  uneven  germination,  all pickings are complete, 
plants in field are used for grazing.
: 7.65         10. Depth to Rel. Impermeable Layer (cm) : - profile is excavated in patchy area affected by salinity, dry cotton
No.
1 lorizon
Depth
0 10
Boundary Conduit
Colour
Texture
Consistence
Structure
ECe
PH
Pores
Concretion
Mottling
Dry mx'D
Moist
Dry
Moist
Wet
Fonn
Size
Grade
EC(I:2)
dSm-l
I
-
7Cf
HCL
reactio
n
Quan tity
1 Size
Quan-
Size
Z.\ L
Sil
ss np
abk
in
10.51
Quan tit
Size
~l Remark
y
34
7.58
co
c
ni
highly saline I
2
lu-J)
3<-55
a.s
10'l R
3/4
i0\ R
3/3
!0\ R
3/4
ZCL
fir
ss rip
abk
in
2
1.44
7.70
co
c
m
3
U.S
SCL
fr
ss np
sbk
in
2
1.33
7.64
co
f
c
•
j
< S.MS
F
•»
<
L
fr
S3 pS
cl
m
2
1.58
766
co
c
Q < IK O J-l J J
ni
f
f
j
IO i K 3/3
ZCL
li
sips
sbk
F
f
3
140
7.73
co
ni
f
f
6
135-200
5\
3/2
FSL
1
ns np
c
1
0.94
"»0l
co
c
c
ni
nt
c
De ep Auger ing
distinct lawr ol 1 tine sand
1
7
200-250
IO\ K
34
ZL
fr
co
J
8
250-300
l0\   R 32
ZCL
ir
co
J
9
300-320
R
32
IS
ns up
co
—
L
J
Sand slip* Ff')ni I
auger, fiirtlmr 1
juecmig is not 1
Mythic j
6-SREFERENCES
All India Soil and Land Use Survey Organization
FAO FAO FAO
1970 Soil Survey Manual, I.A.R.I., New Delhi
FAO
ILR1
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 Develope- 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.
Sir M MacDobnald &. Partners Ltd.
Sir W Halcrow
& Partners
United States Department of Agriculture
Winger, R.J.
1989   Amibara  Drainage  Project  1,  Drainage  Specialist Filed Visit Report. WRDA, Addis Ababa
1985 Master Drainage Plan for Melka Sadi and Amibara Areas. Final Report, Vol. 3, Annex Al: Soils and Drainability Classes, WRDA, Addis Ababa
1964 Diagnosis and Improvement of Saline and Alkali Soils. Agricultural Handbook No 60 (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.LIST OF MAPS
Map no. I - Soil classification of Amibara
Map no. 2 - Soil textural groups of Amibara
Map no. 3 - Soil salinity of Amibara
Map no. 4 - Depth to groundwater of Amibara
Map no. 5 - Ground water salinity of Amibara'
Map no. 6 - Depth to relatively impermeable layer of Amibara
Map no . 7 - Soil drainability & drain spacing of Amibara
Map no. 8 - Soil classification of Melka Sadi
Map no. 9 - Soil textural groups of Melka Sadi
Map no. 10 - Soil salinity of Melka Sadi
Map no. 11- Depth to groundwater of Melka Sadi
Map no. 12- Ground water salinity of Melka Sadi
Map no. 13 - Depth to relatively impermeable layer of Melka Sadi Map no. 14 - Soil drainability and drain spacing of Melka SadiVlllogaI
0 rPi V
\
AM^S
rj
SOIL TEXTURAL GROUPS AMIBARA
I-Iiuuiuu
\?\
y a l qlETA '
\____ S
SOIL SALINITY
AMIBARA .H 49      3-LJj v\
vr7
s*>
5 \
^m7/^T. T±«.
DEPTH TO GROUND WATER AMIBARA
re 4TGI r L  i *      ’*       ( / ]a!
■i« /
5^'
\ A CV7\ ’ \
V°6 mX>\
\W\W J-&             X
VsooAV-71
depth to relatively impermeable layer
AMI BARA\
. Main Drain
’■?
VE.HnMon
\
V
\
\
\
\
•V
GCM7WO.T OF ETHOPIA MWSTfW Of WATER RESOURCES
AIASARA CRANAGE .'TOJECT PHASE -II
SOIL ORAINABILITY CLASSES 4 DRAIN SPACINGS
AMIBARAGnrtl Rood
LEGEND TOR SOIL SALINITY
Vlllop
SOIL SALINITY MELKA SADI AREA
i . roooo               V—/
«***’**’ ’OMCa ln Lnt “n
-.■a*  ----------------- :----------------
-•
’■DEPTH TO GROUNDWATER
MELKA SADI
wew^aj^"' —M*lko So*
groundwater salinity
MELKA SADIJ&LWL.■LE5ENP-
FXIST1NG WORKS

< <

Summery

Project: Amibara Drainage Project Phase-II
Location: Right bank of Awash River, 260 km east of Addis Ababa
Study Area: ~4,000 ha in Amibara and Melka Sadi state farms
Conducted by: Water and Power Consultancy Services (India) Ltd.
Survey Period: October 1995 - February 1996

1. Study Area Characteristics

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

2. Soil Classification

Soil Type	Description	Area (ha)	Percentage
V	Deep clay soils (>200cm clay/silty clay)	465	12.7%
M+	Soils with ≥20% clay/silty clay in control section	1,790	48.8%
M	Medium/mixed texture with <20% clay	533	14.5%
C	Coarse textured soils	332	9.0%
CD	Coarse soils with >5% sand/loamy sand	537	14.6%
R	Rock outcrop	13	0.4%

3. Soil Salinity Distribution

Salinity Class	ECe (dS/m)	Area (ha)	Percentage
Very Low	0-2	2,141	58%
Low	2-4	506	14%
Moderate	4-8	305	8%
High/Very High	>8	145	3.7%

4. Drainage Recommendations

Drainability Class	Drain Spacing (m)	Area (ha)	Percentage	Characteristics
I	30	866	22%	Clay and fine textured soils with poor drainage
II	45	566	14%	Fine textured soils with moderate drainage
III	60	1,925	49%	Mixed texture soils with good drainage
IV	75	408	11%	Coarse textured soils with very good drainage
V	100	165	4%	Highly permeable sandy soils

        Key Findings:
        Most soils (58%) have very low salinity, but 11.7% show moderate to high salinity issues
Nearly half the area (48.8%) has soils with significant clay content (≥20%)
Recommended drain depths: 1.8m below ground level
Drain spacing varies from 30-100m depending on soil characteristics
Hydraulic conductivity tests showed wide variation (0.01-6.25 m/day)

    

5. Maps Included in Report

Soil classification maps (Amibara & Melka Sadi)
Soil textural group maps
Soil salinity maps
Depth to groundwater maps
Groundwater salinity maps
Depth to relatively impermeable layer maps
Soil drainability & drain spacing maps