PDBAW032

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SOMALI DEMOCRATIC REPUBLICMINISTRY OF MINERAL AND WATER RESOURCES

Water Development Agency

COMPREHENSIVE GROUNDWATER DEVELOPMENTProject 104

FINAL REPORTVOLUME 11

Hydrology

BERGER INTERNATIONAL, INC.MOSS COMPANY MARCH 1985

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VOLUMEII

TableofContents

1. GEOGRAPHY

1.1 Locaion and Physical -Features 1.2 Cultureand*Land Use

2. HYDROLOGY

2.1 Climate, 2.2. Evapotranspiration,Runoff, -Infiltration2.3 SurfaceWater 2.4 Water RequirementsandAvailability

3. GEOLOGY

3.1 BayRegion 3.2 CentralRangelandsArea

4. HYDROGEOLOGY,

4.1 BayRegion': 4.2 CentralRangelands 4.3 PumpingTests.

5. WATERQUALITY

5.1 WaterQuality in the BayRegion 5.2 WaterQuality in theCentralRangelands

6. GEOPHYSICS

6.1 SurfaceGeophysicalStudies .6.2 DownholeGeophysicalStudies

7. CONCLUSIONSANDRECOMMENDATIONS

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LISTOFTABLES

Table Title

211 RainfallData - Bay and'CentralRangelands

2.2 River Flows JubaandShabelli Rivers

3.1 Central Rangelands Formation Descriptionand AquiferCharacteristics

4.1 PumpingTest Data

5.1 ChemicalAnalyses ofNewCGDPDrilledWells

5.2 BacteriologicalTestsof DrilledWells inthe BayRegion

5.3 WaterQualityof Wars

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.LIST OF FIGURES

Figure Title

2.1 RainfallandEvapotranspiration - Somalia

3.1 Geology - BayRegion

3.2 Deleted

3.3 DiagrammaticGeologicalCrr'ss Section -Southern Somalia

3.4 GeologicalCross Section,Baidoa-QansaxOmane

3.5 GeologicalCross Section,RobayGaduud-DureiAllGalle

3.6 Generalizea GeologicMapofCentralRangelandsl

3.7 GeneralizedGeological Cross SectionoftheCentralBasin of Somalia - North-South

3.8 DrainagePattern BayArea

3.9 Surface andSubsurfaceDrainageofCentral.RangelandRegions

3.10 Groundwater MovementCentralSomalia

5.1 Wars inthe BayRegion

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1 GEOGRAPHY

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1.0 GEOGRAPHY

1.1 LocationandPhysicalFeatures

TheBayRegion andtheCentralRangelands ofSomaliahave

beentheareasof workandstudyfor theComprehensive

TheBay RegionisaGroundwater DevelopmentProject (CGDP).broadplain lying between theJubaandShabelliRivers in

southern Somalia. TheCentralRangelandsRegion includes

Hiran, GalgududandMudugh Provinces lying northwestof the

Bothareas comprise 189,000square kilometersShabelli River.between latitude3*-8*N and longitude42

0-490E. This isabout

28% of thetotal landarea of Somaliawhich is687,000 square

kilometers.

Thehydrogeolo~ical provinces locatedintheseareas as

identifiedinthe 1973 UNDP Report arethe MudughPlateau,the The MudughPlateau inOddur-BarderaPlateau,andtheBur Area.

theCentralRangelands isan undulatingplain occupyingthe centralportionof Somalia. There arewide shallowvalleys,

flat-tQpped broadhills, andadrainagesystemof shallow

emphemeralchannels that course southeastwardto thecoast.

TheOddur-Bardera Plateaucenters near thetown of Baidoa

and isreferred to inthis reportas the LimestonePlateauor

the BaidoaPlateau. It occupies the centralpartof the inter

basin areaof theJubaandShabelli Rivers as abroadplainof

moderatelyfractured andkarstifiedlimestone beds. TheBur

Area, lyingabout 100 kilometerswestof Mogadishu,isan

extensiveplain underlain by metamorphicand igneous rocksof

the basementrockcomplex. Erosionalprocesseshave reduced this basementcomplex to aplain withremnants that form

These hills arecalled "burs" andriseabruptlyinselbergs.from theplains with spectacular relief. The topographic sur

face iscut by shallowdrychannels thatcoursesouthward. The

soils arederived fromalluviumandtheweathering ofmeta

morphLcand igneous rocks. Muchof the areaisvegetatively

covered by Acaciathickets. The BayRegionof this report

includesallof the BurArea andthesoutheasternportionof

theOddur-BarderaPlateau.

1.2 CultureandLand Use

TheBay Region isthe principledry landfarming regionot

Somalia. Thedark clay soilsandrelativelyhighrainfall

allowsorghumandother crops to be grownextensively. The

1975 censusreported apopulationof 386,000peopleof which

70% wereengaged innomadicherding. Many familiesare engaged

in farmingwithsome familymembers assignedto herdingoften

at long distances fromtheir home. Theanimalpopulationis estimatedto be .87million.

TheCentral Rangelands ispopulatedwithan estimated

544,000inhabitants. Grazingof livestock isalmost exclusively

theprincipalsource of livelihood. Theanimal populationhas

beenestimatedat 9.95million for the CentralRangeland.

These figures includesheep, goats,camels andcattle.

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riABLE Z -

Rainfall Records for Bay and Central Rangelands Regions

Yearsof Annual

Region Station

Completed

Record Period

Mean Annual

Rainfall (m)

Rainfall

Range(mm)

Information

Source

M Baidoa 32 923-1940 585 315-1217 Idrotecneco

"BurAcaba 14 922-26;30, 516 247-1048

1,34,54-56,9-61

Dinsor 4 954-57 403 302-609

Bardera 37 L92 -39,43, 388 85-878

Average(Including87 482 85-1217

...."

Baidoa).

'IRAN Beled 39 926-76 248 44-553 -NR

Mataban 5 953-58 136 44-247

Average 44 235 44 -553

GADUD Cadaado 5 .953-58 123 28 -327 RMR

leelbur 28 .930-76 191 20-408

DhusaMareb 5 953-58* 126 15 -250

MareerGuur 4 .953-58* 109 58 -182

Average 42 167 15 -408

UGH BeyraGalinsor

56

L953-58*

953-58*

220

115

93 -373

21 -221

RMR

"

Galkacyo 15 933-58 154 33 -448 "

Hobyo(Coast) 15 954-76 224 81 -447

Average 41 182 21 -488

*FromdataIdrotecneco, 1976;R.M.Parsons, 1970; USAID,1979; andCGDPdocuments.

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2 HYDROLOGY

f

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TABLE 2.2

Mean Annual Flows of the Juba and Shabelli Rivers

River Site Years Mean Flow (mj/) Reference (Km)I

Juba Lugh Ganana 1951-78 192 0

Shabelli Belet Ven

Bulo Burti

Maladdei Ven

Balad

Afgoi

1951-79 68.3

66.4

58.8

46.9

46.1

161

349

477

547

(from FAO, 1979)

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Fig. 2.1

RAINFALL AND EVAPOTRANSPIRATION

SOMALIA

MEAN ANNUAL RAINFA'LL Cmni MEAN ANNUAL REFERENCE

EVAPOTRANSPIRATION mam)

*'(from, AID, Country Environmental Profile s Somalia, 1979)

b

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2.0 HYDROLOGY

2.1 Climate

SouthernSomalia has atropical,aridto semi-aridclimate

witharange of 100 mmof annualrainfall inthe northernpart

of the CentralRangelandsto 585 mm in theBay Regionat

Baidoa. The meandailymaximum temperature is 340Cand the

meandailyminimum temperature is 240Cinthesetwo regions

with lows andhighs of 180 and 410. The high temperatures

occur during FebruaryandMarch and low temperatures between

July andAugust. The rainfall is concentrated in two wet

seasons, the "Gu," April throughJune; and the "Der," October

through December. Table 2.1 lists rainfalldata fromthe study

areas and Figure 2.1 shows the.rainfall andevapotranspiration

isohyets.

2.2 Evapotranspiration, Runoff, Infiltration

By subtracting therainfall data fromthe meanannual

reference evapotranspiration data, it is foundthat apoten

tialannualwater deficit of no less than 1,500mm exists

throughout thearea. Annualevapotranspiration varies from

2,000 to 2,250mm.

Some researchers haveestimated thatas much as 5to 10%

of theannual raintall infiltrates the groundwater system, but

this estimatemay be high. Extensive thornbush cover indicates

that high evapotranspiration losses occur and limitdeep infil

trationof water over muchof the area. Groundwaterrecharge

must thereforeoccur mainlyby surface runoff into karst holes, tracture zones, andcoarse alluviumof wadi channels.

2.3 Surface Water

TheJuba and the ShabelliRiversare theonlytwo perennial

streams in Somalia. They run fromtheir headwaters in Ethiopia

throughSomaliaanddischarge into the Indian Oceannear

Kismayo. The JubaRiver flows southwardpassing to the westof

the BayRegion. TheShabelli flows almostparalleltothe

Juba, passing through the southernpartof theCentral Range

lands in the Hiran Province,and then turningsouthwest until

it joins the JubaRiver in anarea of swamps.

Themean annual flows of these rivers areshown in Table 2.2

for six sites. Adiscussionof the rivers impacton theground

water supply of the projectareas is treated in Section 4on groundwater movement.

Intermittent streams (wadis)arefound throughoutboth

areas. The wadis flow only during the rainyseason andconvey

water relativelyshortdistances before they become dry from

evaporation and infiltration into the alluvium.

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Wars, surfacewater reservoirs, aredesignedtocollectand store rainwater. Wars havetraditionally beenconstructed throughout Somaliaand serve effectively toprovidewaterduringthe rainyseasons. The watersupply generally does notlast through the dryseason due to heavy useandto the 2000-2250 mm

per year evapotranspiration rate. Modernwars, designed and constructedwithheavy equipment, have also beenconstructedin selected locations. Figure 4.1 shows the locationof modern wars built throughout the Bay Region.

2.4 Water RequirementsandAvailability

Approximations of the quantities of water necessaryto fulfill existing andfuture needs can bemadeusing estimates of thehumanpopulation, andthe numbers of camels, cattle,sheep,andgoats grazing in the two areas. These estimates place the human populationat 0.93million and the numberof animals at 10.77 mill.ofi.

The total water consumption requirement isobtainedbymultiplying the population figure times apotential improvedrateof 20 litersper day for humans, 35 litersper day forcamels andcattle, and 15 liters per day for sheep andgoats.Aweightedaverage consumption figure for animals for 20 litersper day was used. The calculated water demand for humans isthereforeabout 7M m3 and 78 M m 3 for animalson anannualbasis. This totals 85Mm 3of annualwater demand for theproject area.

Water consumption by rural inhabitants dependsprimarily

upon their proximity to thewater source. Consumptionincreases markedly ifthe distance traveled to obtain water is less thanone half kilometer, otherwise consumption is normallyless than 15 liters percapitaper day (lcd). This has been been shown to be true in water studies throughout the worldand has been confirmed by limited studies in Somalia (seeSociologyChapter).

One goal of the CGDP isto improve theaccessibility ot water to rural inhabitants and thus increase their consumption of water of improvedquality. Clearly, theonlyway to accomplish this goal isto place the wellas closeas possible

toas manypeopleas possible or, in some instances, expectthe people tomove to the newwater source. Since the occurrence of groundwater isdependent on thegeologic conditions, it is not alwayspossible to uniformly locatewellswhere populations are concentrated. Indeed, findinganypotable water has been shownto be most improbable in specific areaswithin theproject boundaries. For the abovereasons it isdifficult to determine waterrequirements based on potential water consumption.

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Completequantitativestudies havenot beenmadeof water production fromexistingwater point sources suchas drilled wells, handdugwells, springs, andwars. This will requirea comprehensiveone-year inventorybytwo full-time fieldsurvey teams. Suchasurveyhas been plannedas ajointUSAID-UN

effort usingUNvolunteers andWater DevelopmentAgency (WDA) personnel during theproposedproject extension. This survey isplannednot only for theproject area but for the restof Somalia as well.

Water availabilitywithin theprojectarea varies enormouslyfrom zero to reasonablyproductivewellsatspecific locations. Theactualquantity of water produceddependson thegeology,the well construction, thepump, andthe lengthof time that pumping isundertaken. Except for thegeology the other aspects of wellproduction on theCGDP have been sizedto fitthe demandof theprojectsite anddo not necessarily represent

themax:Lmum possibleproduction. Thus, pumpingdata fromexisting wells, were it available,wouldnotprovidea completepicture ofwater availability.

Potential aquifer recharge can be estimatedbyadopting a factor of 5%for deeppercolation of rainfall. This conservative value is basedon studies fromother areas of theworld butvaries considerably fromsite to site. It isnoted that averagepotential evapotranspiration is about 2,250mmannually andthat theaverage rainfall forthe CentralRangelands and the BayRegion isonlyabout 200mmannually. Assuminga5% rechargeof 200 mmof rainfallprovidesonlyone centimeterot groundwater recharge. However, this represents 1,900million cubicmeters of potentialaquiferreplenishment annuallyover the entireproject areawhich is more than 22 times the calculated demand (85 Mm3 ). While this indicates thattotalgroundwateravailability istheoretically sufficient to meet demand, it does notmean that it isdistributedevenlynorat the specificlocations where it ismost needed. It is evident thatmanymore wellswill be needed to obtain the figureof 20 lcd for rural dwellerswithinthe projectarea. Fieldobservations during ashortdrought in the springof 1984 indicated severe hardships for manyrural Somalis to theextent thatmany animals andafew humans diedasaresultof traveling long distances to obtainwater.

Thesecalculations do not consider the requirement for irrigatedagriculture. Presently, irrigation projectsexist mainly intheJuba andShabelliRiver valleys whereabout 200,000 hectaresare irrigated using riverwater. Onlymarginal amounts aresuppliedby supplemental groundwater. Large pump stationsalong therivers pump as muchas 80-100 cubic meters per hour during the croppingseasons.

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Large-scale irrigiitionprojects arenot feasible ineither theBay or the CentralRangelandRegions using groundwater resources that have been presently proven. Small irrigation venturesmight be possible, but would needto be developedona site-specific basis where local drillingand testing shows unu

sually largeamounts of water to be available. Mostwater has been found in fractureand fault zones of the limestones where karstic development has taken place. Somemodestamounts have been found in wadi gravels, alluvium,andweatheredbasement rock,.but never in aamount to support large irrigationprojects. Large,areally extensive aquifersystems havenot been identifiedat this time. In viewof theneed to overcomethe criticalwater deficit in the supplyfor humanandanimal needs it is consideredmoreappropriatetodrillwells for thispurpose andtodelay planning for irrigatedagricultureprojects.

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-3. GEOLOGY.

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3.0 GEOLOGY

TheCGDP conductedextensivegroundwater drillingoperations in the BayRegionwestof Mogadish" andlimiteddrilling operations in theCentral Rangelands. The geologyof the regions,asdetermined both through fieldoperations andprevious research, is described in the followingsections.

3.1 BayRegion

Thegeology of the BayRegion is conventionallydivided into twoareas. Precambrianmetamorphic rocks andtheir intrusions underlieabout two thirdsof theareaand is referred to as the "BasementComplex". The remainderconsists ofJurassic marine sediments and their weatheredproductsand is knownas the "LimestonePlateau."

Thecrystallinemetamorphicand intrusive complexis located in the central andeasternparts of the projectarea. Outcrops of bedrock and residualweathering productscoveringmost of the "BasementComplex"areof no significanthydrogeological importance. Awell-developed drainage system,however, directedsoutheastward,disappears under theyoungerfluviatile of the lower ShabelleRiver valley. Smallamounts of groundwater are stored in fine tocoarse-grainedchannel sedimentseven during extendeddryperiods.

The southern,western, and northern partsof theproject area consist of Jurassic limestone formingaplateauwithtypical karst drainage. This "LimestonePlateau"is separatedfrom theexposed BasementComplex, by amajor fault. Southeastof the fault interface, erodedremains of marinesedimentsoverlie thecrystalline basement,and this, bysome investigators, has been calledthe "LimestoneDepression" (Johnson,1977).

Theareal distributionof thecrystalline basementandthe Mesozoic sediments are shown in Figure 3.1.

3.1.1 Tectonics

Thegeologic structuresof the BayRegion,divided into the LimestonePlateau,Limestone Depression,andBasementComplex,

are described in the followingsections.

3.1.1.1 Limestone Plateau

In Jurassic timeatrenchopenedwest of thepresentlyexposedBasementComplex andwas filledfirstwith sandstones andshales, and later withmainly limestone. The sedimentation stopped duringthe Cretaceousperiod andthe sediments were upliftedabove presentsea level. The axis of the trench trends northeastward and iscalled the Luugh-Manderabasin (Beltrandiand Pyre, 1973).

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REGIONGEOLOGICAL MAP OF BAY

-4 :+ + 7

+ + +

++

"'4"-

+~

-3+

,+

+4-

)P+

+4

++

.

+

+

4,

+"

+

+

+/

.+

+ +

Bu Acb

+

+p +

t

4+"+

0 04 +

4-. t.

t++"

4m

+ur+

+

+p

+

+,

+

ssic i

grnt

t m l

;

0

• EGEND

20 40 60km

r9

F

'. ''J3 Jurassicnlimestone, morl,

N ,-op,l ,,,,,terar,.rouv . .alluvial sediments

pPrecambrian : gneiss crystalline sC istquarzile, granite '

From- UND I 1971

BiR

Fg:"- .

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Faultswith northwest strikes ontheLimestonePlateauare commonlywidened by karstification. Suchfaults providepathsfor groundwater movementandthusoffer good locations for sitingwells.

3.1.1.2 LimestoneDepression

Erodedremnants of marinesediments at thenorthernrimoftheLimestone Plateauoverliecrystallinebasement. Majorfaultsclearlyseparate these sediments from theLimestonePlateau. The escarpment zone, however, consists of tilted strata whichformaprominent cliff alongmost of thecontact(Johnson,1977). The sediments of theLimestone Depression aredeeplyweatheredanddo not show faultpatterns. Thearea iscoveredby athin layer of surficialmaterial, probably alluvium andcolluviumof the Limestone Plateau.

3.1.1.3 Basement Complex (Burarea)

The uplifted BasementComplex is detined by northeast trending lineaments on its south andnorth borders. The southwestern part of the area has anortheast trending tectonicpatternwith marine sediments extending over the basement areaandinliers of basement exposedwithin thesediment area. Thenortheastern interfaceot theBasement Complexand theLimestone Plateaushown an extension of the Baidoa Fault. The center of the BasementComplex does not showobvious fault patterns. Thepredominantdrainagechannel systemdirected southeastwarddoes not followmajor tectonic features, but rather follows the land surfacegradient.

3.1.3 Lithological Description

The lithology of the Bay Region is described in the following subsections for the LimestonePlateau andthe BasementComplex.

3.1.2.1 Limestone Plateau

In the northern Bay Regionstrata of AaleniantoOxfordian-Kimmoridgeage, the Iscia-Baidoa andAnole Formations,areexposed formingaplateau to thenorthandwestof theBasement Complex. Adescription

of themembers of these formations and their members is given in thesucceeding paragraphs.

Iscia Baidoa Formation

Uanei Member (JurassicAelenian)

The lowestpartof themarinesediments of the UaneiMember consist of green sandstones, darkmarls, limestone andvaricoloredshales depositedunconformablyover the BasementComplex.The upper parts are dark-red shalesseveral tensof metersthickwithalayer of limestone at the top. The total thicknessof the Uanei Member is about 90 meters, as logged

in borehole no. 11, Ministryof AgricultureHousingCompound,Baidoa.

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No outcrops of the UaneiMember have been foundas the interfaceof the Basementand LimestonePlateau is covered with limestonefrom the overlying strata. In borehole No. 45,drilled in theMinistry of AgricultureCompound in Baidoa, the Uanei Member was investigatedas apotential aquifer becauseofits sandstoneand limestonelayers. However, due

to the largeamountof marlsand shales as frequent inter-layers, the boreholeproducedonly smallamounts of groundwater.

BaidoaMember (JurassicAalenian)

Limestone layersoverlie conformablythe Uanei Member. The Baidoa Memberconsists mainlyof gray limestonewithafewinterlayers of blackmarlandshale. In thetown of Baidoa,it reachesathickness of about 90meters. Outcrops of its hard limestoneare frequent alongthe Baidoa escarpment. The limestone layers of theplateau aredeeplyweathered andkarstified,and formAgoodaquifer which has been tappedby local drilled

and handdug wells.

GplodaMember (JurassicCalloviantoOxfordian)

TheGolodaMember consists of lightgray crystallinelimestones, withoolitic beds andcoquina layers. Thin interlayers of the blackmarland shalearecommon. Regionally,dolomite beds, white to lightgray,arepresent.The uppermost bedsof theGolodaMember are resistant,forminghills in the area.

TheGolodaMember attainsathicknessof 650meters. As in the underlyingBaidoa Member,

theGolodaMember is deeplykarstifiedwithnumerous karstholesanddolines. It forms a goodaquifer with relatively highspecific yield. Mostkarstholes and dolines followajointpattern thathas anorthwesttrend.

Parts of themiddleof the GolodaMember, exposed in the Qansax Dheere area, have undergonemore intenseweatheringandshowa covering layer of caliche of severalmeters thickness,the top layer consisting of terra rossawith brown limonite concretions shaped likecoffee beans. This middle part of the GolodaMember isless karstifiedwith increasingdepthand yields less water to wells in theQansax Dheerearea.

Anole Formation (JurassicOxfordian to Kimmeridgian)

The Iscia Baidoa Formation is overlainconformablybythe Anole Formationof 30Umeters thickness. It consistsmainlyof blackmarl andshalewith interlayers of blue compact limestone.

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Thesofter marlandshale layersdo notoccuras outcrops as theyweather to light-brown clay. Thelimestone layersshow fewsignsof karstification, butsouth cf thevillageof Berdaletheyareweatheredto caliche.

ResidualSoils

Large parts of the IsciaBaidoa Formationare coveredbyresidualclaysoils, formingastrip fromBaidoa tothesouthwestalong theescarpment, and northof Awdiinletosouthwest of QansaxDheere.

The bedrocklimestone of the BaidoaandGolodaMembers decomposes to finegravel ofweatheredwhite limestone. An overlying dark brownsoil reachesathickness of upto 30 meters. After the firstrainfalls, theclay soil swells,closingall cracksandforming an imperviouscoverwith little

runoff butmanyrainwater-filled depressions.

Due to the low infiltrationrates of the underlyinglimestone there arefewer springsalong theescarpmentsouthof Baidoa. These springs inthe southyieldmore highlymineralized groundwater than the springs northof Baidoa. The weathered zonemay containsomegroundwater inthe lowerpartsconsistingof limestone fragments.

Basalts (CretaceousandTertiary)

Intheextremewestof theprojectarea, at the JubaRiver,

black basaltsareexposedfillinga300-meterwidejoint in limestonesof the AnoleFormation. Thesebasaltsextendfrom east of Luugh inthe north to Baardheere in thesouth. They are harderthan the surrounding rocksandprevent theJuba River frommeandering to theeast. These basaltsareof Cretaceous to Tertiaryage andweatherfromcoarse blocksto gravelsize. The basaltshouldbe investigatedmoreclosely for its capacityto storegroundwater, or to formimpervious barriers.

Figure 3.3 shows ageneralizedgeologicalcross sectionof the project area extendedfromthe IndianOcean in the'eastto theKenyan border in the west. Thecross sections inFigures 3.4 and 3.5 showthegeologicalprofileof theLimestone Plateau. Theprofile in Fig. 3.4runs fromBaidoa, in the east, to QansaxOmane inthewestandinFig. 3.5 fromRobayGaduud in theeast to Durei Ali Galle in thewest.

3.1.2.2 BasementComplex

In the interriver area, betweenthelowerJubato thewest and theShabelliRiver to the east,crystalline basementcovers about two-thirdsof the BayRegion.

17

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SW NE WNW

Road

Baildoa Luugh

0ansax Omone40- 15 WortaJof fc

*14

(TYPE 3-AB,C)

m,. 020J .

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--

NE WNW

Worta Jaf fay -.

*14

E .

ANOLE .FORMATION(TYPE 3-A,6,C)

10 5 2

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GEOLOGICAL CROSS

ESEw

Shabelle Dugsilo

*13

C201

:5 , ,

3o :,

400

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SECTION WARTA JAFFAY (QANSAX OMANE)- TUGEREW

SECTION A-A'

LIMESTONE PLATEAU

EWNW ESEWNW

Hareero Jufo

Sormaan Dheere *I?

*10

TYPE 4B - - -

- 7 BAIDOA MEMBER+ GOLODA MEMBER (?) - -

' ....B AIDOA - FORMATION

LEGEND

Sandstone Cloy/Shale Marl Limestone Cloy,!Gro

46 50 55

5A0 0 000 2000 3000 4000 Metres HORIZ.

5 0 50 100 150 200 Metres VERT.

99,

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(BAIDOA )

,A'

RoadBaidoo-Luugh

Ro(Baldoo-

(Type 2)Bonkay*2 us

I - WDA 4Residual soilI

°,i°,oo,,.. ........... w..

Sand Cl-y-Sil- -lay,C-lichea

Terra rosso-, '5 -O

65 70 75 80

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ESE

700

RoadBaidoo- Bur Akabo

USAID

WDA *1 LIMESTONE. DEFRESSION,

600

-1'-- Tugerew*4 400:,

- - -- . -- _.'-300"

. BASEMENT

'200

.. ..... .... ............. .. . .......... . .....

O'

80 90mkm

LBII/ RM

Fig. 3.4

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WSW

700M.

:ENE WNW

o

Dursi Ali Golle

20

E- iIi

.

Qansox Dheere

owrn

WOA*2

E

lOOm-

:0, ............ ..

2 m;

km5 0 10,

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GEOLOGICAL

ENE WIW .

Durei Ali Galle

*20

--

Qonsax

............... ..... - -

Dheere

W *2

,E-

[BAIDOA

Baidoa memlk

-FORM A-

Sandstone Clay/sha

15'

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GEOLOGICAL CROS S SECTION DUREI

SECTION B-B'

LIMESTONE PLATEAU

Godut

Baidoa memr + Golodo member (tipe4B) I 0

.... eimm nobt p---)4-- ...

*BAIDOA FORMATI ONI

LEGEND

I-I -j

Sandstone Cloy/shale Marl Umestone Cloy, sand Caliche andgravel Terra rossa

p

15 2O 25 30

ScalIe 1:100,000

I

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DUREI ALI GALLE ROBAY GADUUD

B-B'

AU

Robey Gaduud#*17aduudo Dhunte

*18

/Ri a _

sand Caliche andgravel Terra rossa

40 4530 35

1: 100,000

I

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ESE

•700m

600m

I 500mRobey Goduud

17 IRoad

Bokloa" diinsor 40 rn

II

I I

6o45 .5

,LBII/RM

Fig. 3.5 (3

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Exposedsince Jurassictime,itformsapeneplainwith

residualweathered igneous andmetamorphic rocks. Outcropsof

graniticandsyenitic intrusionsoccurabove theplain, forming

in theSomali language,inselberg hills that arecalled "burs,"

giving the name of "BurArea" to the entireBasementComplex.

ItalianandSomaliangeologists (Hilal,Pavan, &Robba,

1982) establishedthe followinggroups of rocks for theBur

Area; quartzites of Egherta,gneiss of Bur Mun,gneiss of Bur

Meldac,marbles of BuuloGasei,migmatitesof Lamma Lavet,and

granitesandsyenites of JacdumiandBur Sigirre. Theyoungest

metamorphic phasewith intrusions isdatedat 600millionyears

during theEarly Paleozoic.

The Bur area has awell-developeddrainagesystemdirected

southeastward. These channels arefilledwithcoarser alluvium

and formfiraquifers, collecting the runoff of thesurround

ingarea, :toring thewater inalluviumanddrainingtothe lowerShabelliRiver. Numerousshallowwells havebeen dug by

nomads inthese drainagechannels.

3.2 CentralRangelands Area

TheCentralRangelands extend northeastof theShabelli

River to the Nogal Valley innortheastern Somalia. Marine

sediments of mainly Tertiaryage andcontinental sediments of

sub-recent agecover the surface as part of alarge basin. The

basin extends through theOgadenanddown to theIndianOcean

parallel to the ShabelliValleyeastof Belet Uen to Jowhar.

The deepest partof the basin,theObbiaEmbayment, islocated

near Obbia on the coast of the IndianOceaneastof Gaalkacayo

(Barnes,1976). There have beenseveral transgressiveand

regressivephases of the seaover theHorn of Africa,andsedi

mentation thicknesses gene-ally decrease inland.

Theareal distributioncf thegeological formations inthe

CentralRangelands isshowninFigure 3.6 andexplainedin.

Table 3.1. Figure 3.7shows acrosssection of the project

areaandthe the northernpartof the basin near thecoastof

theGulfof Aden.

3.2.1 Lithological Descriptions

The lithology for theCentral Rangelands isdescribedin

the followingsubsections.

BeletUen Formation (CretaceousConiacian toCampanian)

TheBeletUen Formation, theoldest formation relatedto

the investigationof theCGDP project,reaches athicknessof

145-200meters. It isformedof alower partof interlayered

limestoneandgypsum beds, overlainby limestoneswith sandy

andmarly beds. The upperpart ofthe Belet Uen Formationcon

tainsalternating gypsiferous limestones,marls, sandstones,

andafewgypsum beds.

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Table3.

CentralRangeland

FormationDescriptionsandEstimatedDepthtoWater

Eluvialandcolluvial Deposit includingtheMudugh Beds, talus, dunes andbeachdeposits. Groundwater occurs inporespaces of soft unconsolidated formations.Sediments

of ephermeral streamsalso actas temporaryaquifers.

KarkarFormation limestone, marl,

calcareoussiltsoneandmudstone, some gypsiferous. Water occurs mainlyalong bedding planes and infissures. There appears tobe two separateaquifers

Taleh Formation - anhydrite,gypsum,

interlayersof dolomiteandmudstone,

commonlygypsiferous. Water circulationalong karst hollows ispredominant.

Auradu Limestone - massive limestone,

calcareous dolomite interbedded with siltstone. Water occurs inveins (withintectonic fractures), infissures, andalong bedding planes elsewhere.Inmanycases thereare twoidentifiableaquifers inthis series

YesommaFormation- sandstonewith

subordinate layersof consolidated clay. Groundwater occurs along bed

ding planesand infissures.

Uen Formation- limestone with

some sandstonegroundwater isfound alongbedding planes andinfissures

Mustehil Limestone- Thewater is found along bedding planes andinfissures.

GabraHarreGypsum - This formation

containskarst water

EstimatedThickness(meters)

30-40

80-230

350

15-20,.340-60

200

300

500

300

Estimated Depthtowater fromthe topof theFormation

Meters

5

150-180

20-80

40-60

50-70:

5-20

5-20

10-40.'

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Fig. -3.6

GENERALIZED GEOLOGICAL MAP OF CENTRAL RANGELAND

S LEGEND

colluvIal deos;ts;luvicl c

TC u,dun** abeach deposits "_"_-

3Tk Karkme Formation;liestone 15 conglomeratenTt ielefFrmationanhydrilegypsumshale/

V7 113 TOAuradu Limestone

.Z-' KTj YbsoUWI Formation,.

sandstone (kquartziteI[ .41 Belotwayn Formalionlimesone . Ib with some sandstone.,

sZ IayE kmMustehil Limestone

SKjg Garboharre Gypsum

"Hobpo

_' .Q Ag

I b

0 60 120 1801,

4W 4700Scale ; 1:3/:)0OO)0

490

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GENERALIZED GEOLOGICAL CROSI

South -CE N I

Shobelle river valley 'Duusamarreeb

ALLUVIUM MUDUGH PLi

"Mudug Beds"

-.

-

VvV

0. Its

V

v

Tat

Au

Not to scale

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CROSS SECTION : CENTRAL AND NORTHERN SOMALIA

,CENTRAL: RANGE LAND A RE:A

MUDUGH PLATEAU

Goolkocyo

"Mudug Beds'

OKpoh 09 ff11' 0

JURASSICLIMESTONE

v ., e

Tole h

v

formationV

f V, v~

-

OBBIA EMBAYMENT NOGAL VALLEY

UP LIFT

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North

Surud Add.

JURASSIC BASEMENT SOL PLATEAULIMESTONE

~Aden

00 Kokr frq o

v/o v t ,o.e

fm 0 1

IIWO " B aserme nt

NOGAL VALLEY

UP LIFT

LFI RN

Fi37t'l

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DRAINAGE FATTERN BAY REGION

Limestone plateau

" a aido -groundwater shedSupposed/ /

..'Li tone plateau Boldoa

- / e But okaba

sMnt complex

groundwot4/ Dlinsor

tld

Limestone area

Drainage towards

Juba River

--- Surface drainage

Subsurface drainage

Subsurface supposedNot to sc le

L B1I/RM

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YesommaFormation (CretaceousCompaniontoThanetian)

TheYesomma Formation consists of varicoloredquartzitic, poorlycemented,hardsandstone beds. Dominant colors are white,yellow, brown,anddarkred. Crossbeddingiscommonand interpreted to beof fluviatileorigin. Limestonelayersmay occur andthetopweatheredzone of uncementedsandstonecontains subsurfacecalcareous concretions.

Atthe villageof Yesomma, eastof Buulo Burti, theYesomma Formation has athickness of 300 to 400 meters andoverliesthe Belet Uen Formationunconformably. The unconformablecontact, however, isseldomseen as theYesomma sandstoneweathers deeplyandforms acover of severalmeters of loose sandover thefirstcemented layers. Sandwasheddown to thevalleyof thevalleyof theShabelliRiver covers large areas of the underlyingBelet UenFormation.

The Yesomma Formation intheHiran regionwith interlayered sandandsandstonebeds requires more testdrilling to determine ifit isapotential aquifer. Drilling i,difficult due

to thetendency of loosesandbeds tocaveinto theboreholes. Thesands, andalsofracturedsandstone beds,maycontain groundwater of goodqualityand showhightransmissivities in pumping tests (GTZwells III bandIV,Burco).

AuraduLimestone (TertiaryThanetian toPriabonian)

Afteratransgression, theAuraduLimestonewas deposited over the YesommaFormation. Outcrops are foundinaband extendingthrough thewesternpart of Galgududregion to the coast of the Indian Oceanvia DuusaMareebandCeelDheere.

The lower sections consist of dark-brown,fine, crystalline, compact,coarsely-banded limestone. Theupper sections showa finer andclearer bandingand lighter colors. TheAuradu Limestonereachesathickness of 400-500meters in thewestern parts of the areaand upto 2,000meters at theIndianOcean.

Outcropsmayshowsome karstification. The limestonebeds arecommonly fracturedandoffer agoodpotential for groundwater storageandyield. Wells in theAuradulimestone yields

goodquality water and frequentlyinlargequantities. If overlain by impervious layers, artesiangroundwater isfound such as in thesoutheastnear DuusaMareeb. Flowing artesian drilledwells exist intheCeelBur area.

TalehFormation (TertiaryPriabonian toLattorfian)

Theevaporitesediments of theTalehFormation weredeposited duringaregression of the seafromthe horn of Africa. TheTaleh Formationoverlies conformablymostof the central andnortheasternSomalia andconsists of gypsumanddolomites.

ij

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Alongthe coastof northeasternSomalia,the entireFormation isrepresented bydolomites, thus indicatingadeeper sedimentaryenvironment. TheTalehFormation reaches athicknessof 200 to 400 meters intheprojectarea,withamaximumof 450 meters intheNogal Valley. It often displays intense karsti

ficationwith large dolines andsinkholes whichtrapthe scarce rainfalls, andreduces the drainage systemto shortsegmentson gypsum-anhydrite plateaus. Groundwater isfound in fractured karstified zones, but isgenerallyof badquality.

Karkar Formation (TertiaryRupelian to Chattian)

The Karkar Formationoverlies conformablytheTalehFormation andconsists of limestones andmarlylimestonewithafew gypsumlenses similar to those found in theNogalValleyand in the northof the CentralRangelandsarea. Largeexposures mayconsist of weaklycemented coarsepebble conglomerates. The

Karkar reachesathickness of 200 to 400meters. Lateral changes infacies occur fromthe northeastof Somalia,whereit isrepresented by gypsiferousmarls, to ObbiaandMerka in the south,where shalesandsandstone beds were found inoilwell drilling attempts (Barnes,1976).

The Karkar Formation isthe uppermostmarinedepositon the centralSomalian Plateauanddoes not havemuch importanceas an aquifer inthe area. Springson both &ides of theNogalValley alongthe interfaceof the Karkar andTaleh Formations,however,may indicate thatan aquifer exisvs, even inthe absence of dug or drilledwells. Infiltrating rainwatermaybe

stored inthe Karkar Formation abovethe impervious beds ofthe TalehFormation.

Mudugh Beds (TertiaryMiocene)

Satellitephotographsof theCentralRangelands areashowa well developedregional fault patternwithstrikes ranging from NW-SEto NNW-SSE. IntheCentralRangelands lateTertiary streamscarvedshallowriver beds, drainingtheOgaden Plateau. Two distinct former drainageareas aredeveloped, theGhelinsor-DhusaMareb-Ceel Bur SystemandtheGaalkacayoSystemto the north. Into thesedrainageareas sediments of continental lacustrine conglomerates, fluvial sandstone, and clay andmarl weredepositedwhen the climate becamemore dry. Thesemiocene sediments contain uraniumminerals at Dhuusa Mareeband inthe area of Ceel Burwhere largedepositsof che sepiolites are mined for themagnesium-silicateclaymineral "meerschaum."

The surfacesof the Mudugh Beds are intenselykarstified with sinkholes, caves andlargedolines. Theystoregroundwater of lowquality, butof easy access, as groundwater is onlyafewmeters below thesurface. Towns and villages in the areaare supplied by dug or drilledwells intheMudughBeds.

Deeper drilling, however,may reachfractured zones of the AuraduLimestoneandencounter an artesianaquifer withgroundwaterof relatively lowmineralization.

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Basalts (CretaceousandTertiary)

Basaltsfrequentlyare encountered indeep drilledwells

northeast oftheShabelli river. Thesebasaltsmayserveas

aquiferswheretheyare fracturedor scoriaceous, andas con

fining layerswhere theyaredense and impermable. Artesian

water has beenstruckwhen deepening boreholes throughbasalts insomeareas.

Recent boreholes undertaken byGTZ encounteredolivine

basalts as asillinAuradulimestonenear DhuusaMareeb and

The basalt sill nearDhuusaMareebisimpervious.Ceel Bur.

Basaltswhichoutcropsouthwestof theShabelliRiver near

Bur Weyn needfurther investigation todeterminetheirpoten-,

tialas aquifers.

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. HYDROGEOLOGY

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4.0 HYDROGEOLOGY

As in theprevious section,the BayRegion andtheCentral Rangelands areaare describedseparately. Groundwater in the Bay Regionoccurs mainlyinlimestoneandin theCentral Rangelands in limestone,sandstone,and loose sand.

4.1 Bay Region

The LimestonePlateauwest of Baidoa istheeasternpartof amarineJurassic trench fill insouthwestSomaliaandnortheestKenya. Theplateaudips4degreeswest-southwlestand gruundwater drains inthe same direction towardthe JubaRiver. TheBasement Complex as wellas theerodedremainingareaof marinesediments on the westernandnorthern Baidoa fault interface, and springs alongthe escarpmentof the Limestone Plateau, drain southeastwardto the Shabelli Valley. The watersheds for groundwater andsurfacewateron the Limestone

Plateauarenot clearly def.ined. Faults thatmay drainpartsof theplateauare fewandvary inlength (Figure3.8). The different typesof aquifers describedbelowareranked according to their groundwaterpotential.

4.1.1 LimestonePlateau

TheLimestone Plateauwestof the Baidoaescarpmentis dividedhydrogeologically intoareas of exposedoutcrops, anda larger areawithathickcover of residual soils. Outcropsof karstified limestoneanddolomiteareencounteredwest, north,andnortheastof Baidoa. Karstholes arecommonandprovide

access forabundant groundwater recharge during the rainy seasons. Inboreholes, thekarstificationwas foundtooccur to depths of 30 to 50meters, but deeper karstifiedand fracturedzonesmayexistsuch as at thesite ofMartiMoog (wellNo. 55). Usually the uppermostaquifer has afreewater level, although rises of borehole fluidlevels frequentlywere recordedafter drillingpenetrated the karst zone immediatelybelowtheuppermost aquifer.

Wells inthese types of aquifers generallyyieldgroundwater having conductivitiesbelow2,500micromhos. Pumpingtests recorded specificcapacities of n.2 to 63.0m2/hour.Analyzed as aquifers inidealized unconsolidated

sediments,equivalenttransmissivities of 2.0 to 2021m2/daywere calculated. Apumping test inawellat the Ministryof Agriculture CompoundinBaidoa indicatedaspecificyieldof about 10 percent fromhighlykarstifiedlimestone, andan equivalent transmissivityof 487m2/day.

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Following thegentle surfacegradientof theLimestone Plateauand thedipof the ;trata, about 4degreesnorthwestward,togetherwithadecrease inaltitudeof theplateausouthward,themovement of groundwater istowardthe westand south. This isindicatedon thesketchof groundwater flow,

Figure 3.8. It remains unclear ifasinglewater tableaquiferwithregional extentwasencountered in the karstifiedzones, or ifsmall, independent systemswere developed. The latter wouldmean lessergroundwater storagecapabilityandgreater changes instatic water levelsover dryandwetperiods. Small karstifiedoutcropson the LimestonePlateauarefoundalongthe Baidoa escarpment.

Largeareas of the bedrock limestone inthezoneof Awdiinleto Qansa Dheere,are coveredwithcalicheandterra rossa. Cavities inthe bedrockwereencounteredinsome boreholes, andprovethat karstificationexists-evenifsurface

evidence, such as karstholes, isabsent. Wells inthe area vary considerably inregard to theiryield andchemicalquality of water.

Closelyspaceddrilledwellsof approximatelyequaldepth mayshowlarge difterences inchemicalquality as exemplifiedby two WDAwells supplying the townof QansaxDheere. WDAwell No. 7yields water having aconductivityof 2,000 umhos andWDA No. 8haswater of 4,000 umhos.

Wells inthecaliche zonedrilledunder theCGDPareTaflow No. 16, Durei Ali Galle No. 20 andBuuloFuur No. 42with

equivalenttransmissivitiesof 20.45and 36.03m2

/day forwells No. 20 andNo. 42 respectively.

Large areas of the LimestonePlateauarecoveredby residual clayeysoils. Clay swellingafter thefirstrainfall creates an impervious layer causing ponding insmalldepressions on theplateau. Theseponds are frequentlysites for the construction of wars. Groundwater rechargefromtheseclaysoilareas, along the escarpmentand fromBerdale toQansax Dheere inthesouthwest, remainsquestionable. WDAwellspreviously drillednear Baidoa,yieldingwater fromlowerpartsof the residual soilcover or upperweathered bedrock,were not

functioningduring the projectperiod.

Drainage fromthe part of theLimestonePlateauimmediately west of the escarpment toward theBasementComples feeds through anetworkof faults into numerous springs at the baseof the escarpment. The larger fault systemsare thosewest andnorth of Baidoaandthe Baidoasprings: the fault attheManas Springsand the fault near RobayGaduudand the Dimer Spring.Smaller faults are developednorthof Baiaoa. The springssouth of Baidoa, with the rechargearea below the residual soils, yieldmineralizedgroundwater withhigh chloridecontent. Springs northof Baidoa,originating frombedrockout

crops, yieldwater of lowmineralization. Baidoaissuppliedwater fromfour drilledwells thatyieldwater with highchloridevalues indryseasons andlowvalues after rain periods.

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In addition to the upper water tableaquifers, oneor severaldeeper aquifers of highmineralizationexist. Confined groundwater withapressureheadof about120meterswas encounteredinproject boreholesNos. 2,3,and 50 in the Bonkayfarmarea. Awater sampletaken fromwell No. 50 showed amineral content similar to samples collectedfrom theManaas Springs, suggesting an extensive lower aquifer withafew dischargepoints at wells along the escarpmentunconnectedto the near surface karsticaquifer.

Inthewells westof the Bay Regiongroundwaterwithhigh degreesof mineralizationwereencountered ininterlayered marls, shales,andlimestone of theAnole Formation. Thesewere not transformedinto productionwells due to thepoorwater qualityof thegroundwaterwhichhas conductivitieshigher than 20,000micromhos. Single, thick limestone beds, withcalichetype weathering, formsmall-scalegroundwateraquifersserving as sourcesof water for handdugwellssouthandsouthwestof

Berdaale.

4.1.2 Limestone Depression

Thearea eastandnortheastof the Baidoaescarpment and southof Dolondole to Bur Heibi iscoveredwithdeeply weatheredremnants ofmarinesediments. On falsecolor satellite imagery the areaisshownto havearelatively dense cover of vegetation. This has leadto theassumptionthata groundwater systemmay be present. Previous studies by the WorldBankformulatedplans for intensive use of thearea by assuming the existenceof groundwater reserves.

Of eightproject boreholes inthis area, however,only boreholeNo. 4atTugerewcouldbe transformed intoaslightlyyieldingproduction well; itwas equippedwithahandpump. Theextensive vegetationseen on the satellite imagerymaybe suppliedwater by thenumerous smallspringsalong the baseof theescarpment that drain theLimestone Plateau. In thearea of Dolondole,astreamlet fed by karstsprings flows downthe escarpmentanddisappears inaquicksandarea. It isconcluded that the LimestoneDepressionmay beexcluded fromfurtber investigationas an exploitablegroundwater resource.

4.1.3 BasementComplex

TheBasementComplex consists of impervious crystalline metamorphicandplutonic rocks. Groundwater storageandcirculation isonlypossibleunder specific circumstances. Groundwaterpotentiallyoccurs either near outcropsof granite(burs), withindeep residual soils, or inephemeral stream beds. Burs, or outcrops of graniticplutonics,overliethe BasementArea andhave been exposedsinceJurassictimeto weathering. These inselbergsmay reachan altitudeof 250 metersabove the surrounding plain. Faultor joint traces are

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frequentlycovered by vegetation, indicatingthepresenceof groundwater. Afewsprings, or wells, are known to be fedby this typeof aquifer, suchas the spring supplyingthevillage of Bur Heibi. Therearemanyhanddug wells inthealluvium aroundthese outcrops,suchas at Bur Akaba andKananax,yield

ing freshwater. Faults or joints ingranitecovered byathin layer of residualsoil or talus also may store groundwater, as are foundinthe springsalong the roadnorth of Bur Heibi.

The residualsoils of the BasementComplex consistmainly

of clayey material fromdecomposed feldsparandmica, as well as other silicates, withmuchquartz sandandweathered feldspars. Thesesoils covermost of the Basement Area,. Wells in these soils all yield highlymineralizedwater of morethan 20,000micromhos. CGDP wells drilled intheareahad tobe abandoned,as this typeof groundwater cannot be usedfor human or animal consumption.

The BasementArea has awell developeddrainagesystem directedsoutheastward. These drainagechannelsmayreach up to four kilometers inwidthandcontain 20 to 30 meters in thicknessof sand,gravel, andfiner alluvium. Numeroushand dug wells instreamabeds supply nomadsandvillagers withsmall amounts of groundwater of acceptablequality.

AtYaaq Brave,avillagelocatednearadrainagechannel, theaquiferhas been developedinadifferentway. Thedrainagechannel isfilledwithcoarse sandandcrossed byanatural damconsistingof agrantic dike. Innormal yearstheimper

viousdike forces groundwater to cometo thesurface,and flow over the dikeas asteamlet. Dug wells builton residualsoils inthevillagereach groundwater sevenmeters belowsurface, thus deeper than the static groundwater level inthe wadi,only tens ofmeters away. Thewellwater isof highmineralization, about 3,000 micromhos, andispollutedby animals.

4.2 CentralRangelands

TheCentralRangelands area fromthe ShabelliRiver inthe southwest to theNogal Valleyinthe northeastconsistsmainly of aquifers insandstone, limestone, andgypsum-anhydrite.

Aquifers inunconsolidatedmaterialareof local significance, as inthe dunebelt along thecoastof the IndianOcean and alluviumindry river beds.

Noperennialsurface drainageoccurs northeastof the

Shabelli River. Numerous wadis (dryriver beds), however, show thatthe Central Rangelands areaispartof adrainagesystem withadirectedsouth eastward. Largerwadis commonlyhave vegetationgrowing instrips across thedrychannels, the "broussetigree."

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The lowprecipitationof the area,withannual rainfall

rangingbetween 100millimeters inthe north andabout 200

millimeters inthe south,maypartially infiltratethe karstified limestoneandgypsumanhydrites. Groundwater flow near the surface followsasoutheast direction. Adeeper

large-scale regionalgroundwater flowoccurs fromrecharge areas inthe Ogaden northwestof Somalia. This confined aquifer has staticwater levelsof 100 to 150meters belowthe surface along the border ofEthiopiaandSomalia,andispresumedto bepresent inthearea southeastof CeelBur.

Theupperwater-table aquifer systems showadirectrelation to thechemical composition of theoutcrops andarehighly mineralized. Groundwater fromthe deeper aquifer,probably

consistingof the AuraduLimestone, isof lowermineralization andischaracteristically undersaturatedinsulfates. The coastaldune belt has groundwater of highsodiumcontentwhich

rapidlydiminishes inconcentration inland.

Adescription of groundwater conditions in the Central Rangelands isgiven in the followingsections. Theprincipal zones, as indicated in Figure 3.6, arediscussed includingthe

Coastal DuneBelt, Belet Uen andYessommaFormations, Auradu Limestone,Taleh Formation, andMudughBeds. Table 3.1 summarizes the formation descriptions.

4.2.1 Coastal DuneBelt

Lenses of fresh groundwater in dunesof fineunconsolidated

whiteto yellowish-brown sandare rechargedbyrainfallalong thecoast and, incertainareas, by groundwater flowfromthe inlandthatproduces acoastal freshwater-saltwater interface. Townsandvillagesalong the coastare suppliedby hand dug wells. Thegroundwater isgenerally high insodiumand chloride.

Coastaldunes aquifersmay be locally important butrequire

detailedstudies ifplans aremadeto use themfor wells. For example,atestwell inthe dunes nearMerka, 100 kilometers south ofMogadishu, yielded 20m3/hover 24 hours withaminor drawdown. Waterwas of relatively lowmineralizationwith

values rangingbetween 2000-3000micromhos. An analysis for tritiumcontent to determinetheageof thegroundwater showed nonepresent as the water isveryoldandhas insignificant recharge (GKWGroundwater Program,1978).

4.2.2 Belet Uen andYesommaFormations

Bothformations haveaminor importaac6as aquifers because of their lithologicalcomposition. TheBelct UenFormation in thevalleyof the ShabelliRiverconsists of limestonewith

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interlayers of gypsumwhichreducesthequalityoftheground

water. The formationmaybe apartof thegroundwatersystem

related to theShabelli River with infiltrationsofriverwater

into the aquiferrather thanhaving groundwater flowfromthe

formation to the river. TheBelet Uen Formation has asmall

rechargearea. Surface andnear-surfacegroundwater flow, however,mayoccur fromtheYesommaFormation intothe Belet

Uen Formation andto theShabelliRiver duringandafterrainy

periods (Figure3.9).

4.2.3 AuraduLimestone

In theCentral Rangelands area,outcrops of theAuradu

Limestoneareexposed in astrip parallelto the Shabelli River. The karstified limestonecollectsred lateriticsoils indolines, giving the Somali nameof "Galgudud" (reddepres

sion) to the area. TheAuraduLimestoneregionally has large

scale karstificationwithkarst-widened joints that storeand transmitgroundwater,making itan excellentaquifer. Numerous

drilledandhanddugwells yieldwater of relatively low

mineralization having conductivitiesof around 2500micromhos.

Theentire formationdips gently north-northeastwardand is

found indeepdrilledwells under evaporitesof the Taleh

Formation. Wells penetrating the AuraduFormation,northeast

of the outcrops,yield confinedgroundwater containing sulfa

tes. This suggeststhat theremaybe asemi-permeable boundary between theAuraduLimestoneand theoverlaying evaporites,or that groundwater flows fromtwodifferent aquifer systems are

present.

The deepergroundwater flowmay be related to recharge

areas inthewesternOgaden andthe extremewestof Somaliaand havingadischargearea onthe coastof the IndianOcean. A dischargearea for this artesianaquifer,west of Somaliaand

havingadischargearea on the coastof the IndianOcean. A dischargearea for this artesian aquifer,west of the fault

parallel to tha coast, exists inthe areasoutheast of Ceel

Bur. More detailedhydrogeological investigations arerecom

mendedto verifythe significanceof this area.

Theoutcropsof theAuraduLimestone intheprojectarea receives annual rainfallof about 200millimeters withestimated infiltrationrates of 5to 10 percent. Small-scale isolated near-surface karst systems, suchas occur on theBaidoa

LimestonePlateau,are inferredrather thanacontinuous shallowgroundwater flow tothecoast (Figures3.9and 3.10).

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Fig. 3.9

SURFACE AND SUBSURFACE DRAINAGE NEAR THE SHASELLE RIVER

CENTRAL RANGELAND REGION

ammt Sketcha Detrital sand washed from

yesomma plateau

00/

River valley "a 0 ~ 0

.0 0

OffA

0

a 0ul 0a

Shabelle o

River

BELET UEN * -

FORMATION

YESOMMAFORMATION AURADU

LIMESTONE

Bdsg CoastalBed dunes

Bur -Rivr'-:Tash Formati• - Not to scl

Aurodu Limes onev _ 0 C/_

LIMESTONE

Formtion Surface drainageSuburfcedrainage

Dip Subsurface drainageassume d

Direction of strike

and dip of stratasee f igu re-N N I t o 9 a a

LBII/RM

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4.2.4 TalehFormation

Outcrops of the Taleh Formationoccupyabout two-thirdsof the CentralRangelands projectarea. Consistingmainlyof anhydrite, itdecomposes togypsumon thesurface. Gypsum crystal aggregates of large sizes (0.5cubicmeter) mayoccur,

andsurface layers aredeeply karstifiedwithkarstholesand dolines thatcollect thescarce rainfall. Northof thetownof Gaalkacyo, alarge dolinewithadiameterof approximately 30-50 meters andadepth to themud-filled bottomof 15-20meters, showedno change of water levelduring theyear (1983)from almost full to completelydry. Thepondlevel paralleledthe changesof staticwater levels inthe near-surfacekarst Oystem. An increaseof the annualaverageprecipitation of 100 to 200 millimeters per year could leadto an overflowof this shallowsystemandthe reactivationof the surfacedrainage systemdown to the IndianOcean, nowconsisting of dryriver beds filledwith calcreteandgypcretecrusts (MudughBeds).

Deepgroundwater systems maybe developedwith interlayers of marl andshale (somebituminous). Bothtypesof systems, theshallowone inintenselykarstified top layers, andthe lower systems, drainto the coast of the IndianOcean. They are probablynot interconnected. Thegroundwater inshallow and deeper drilledwells issaturatedwithsulfates thatraise the conductivities to as muchas 3,500micromhos.

4.2.5 MudughBeds

Mudugh Bedsarecontinental, fluviatileandlagoonalsedi

ments depositedindrainagechannelscrossing theMudughplateau. Thesebeds are of relativelyyoungage (Miocene)and consistof crusts of limestone,gypsumandsandstones. Locally, minerals suchas carnotite (uranium,thorium)andsepiolite (meerschaum)mayoccur.

Shallowwells, whichdependonsmaller near-surfacesystems,

vary in water qualityaccording tovariations inthechemical character of the aquifer. However,wells withsulfate saturatedwatermaydrawwater fromthe underlyingTaleh Formation.

Thesystem,of Mudugh Beds fromGaalkacyosoutheastward, terminates inaformer lake,nowdry, locatedwestof thefault runningparallel to the IndianOcean (Figure3.10). This system requires further hydrogeological investigationto determ.ne thequantityandquality of groundwater. Thereareeroded remnantsof MudughBeds isolatedfromthe twomainaccumulations. Furtherexamination of the areasoutheast ofCeelBur, the supposeddischargearea of the Ghelinsor-CeelBur System, isneeded.

Ji

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4.3 Pumping Tests

Thepumping test programfocusedon themeasurementof

aquifer characteristics suchasmaximumyield,specificcapa

city, andtransmissivity; andontheestablishment of the

properpumpingequipment. Pumpingtestswere completedfor 19

wells withthe results listedinTable 4.1 anddiscussedbelow.

Thepumping test dataare included intheAppendix.

4.3.1 Description of PumpingTests

Pumping testswithsustainedyields werecompletedat

twelve locations. Stepdrawdowntestswereconductedbefore

handwhenever feasibleto determine theoptimumpumping rate

for 24-hour tests. This data fromthe 24-hourtests allowed

the calculationof specificcapacityandof transmissivity.

Theyields of wells inthe limestoneareasvariedprimarily

according to thenumber of fractures inthe rockandto the

degree of fracturewidth through karst solutionprocesses. Since

otherparts of the limestonearesolidandgenerally impervious,

groundwater will flow inbedding planes, joints, fracturesand

cavitiesto thewell. The aquifersare nothomogeneouswith

isotropicaquifer conditions inall directions. Since transmis

sivity formulaswere originally developedfor unconsolidated

isotropicaquifers, the values listedinTable 4.1 provideonly

acomparison withwells drilledundersimilar conditions.

Astandardmethodologywas employed incalculating equiva

lent transmissivity. The recordedvalues of drawdownata constantpumpingrateandof thewater level recovery, atpump

ingcompletion, wereplottedon semilogpaper (seeAppendix).

Thedrawdown isshownon the linear verticalscale in meters

andthetime in minutes on the horizontal logarithmicscale.

For the recoverycurve onthe logarithmic horizontalscale the

quotient t/tl represents the total timeof thepumping test

drawdown andrecovery,divided by thetimeof recovery. When

the points for drawdownandrecovery formlines, thedifference

inwater levelover one logarithmic cycle can be readfrom the

graph andused intheequation:

T= 0.183x Qm3/hr

(S2 - Sl)m

T = Transmissivity inm2/hr

Q = Average dischargeby pumpingm3/hr

= Water levelat beginningof test,m1

S2= Water level atendof test,m

8/13/2019 PDBAW032


Table4.1

PumpingTestData

WellNo. Location

10 Sarman Dheere

11 Min.Agric CMPJBaidoa

12 HareeroJiffo

16 Taflow

17 Robay Gaduud

18 GaduudoDhunte

20 Durei Ali Galle

21 Min. Agric CMP Baidoa

42 Buulo Fuur

45 Min Agric CMP Baidoa

46 QansaxDheereRodwell

47 Awshiini

50 Bonkay SeedFarm

51 Mintaan

52 Maleel

54 Isgeed

55 MartiMoog

57 Hagarka

59 Shawka

63 Bonkay SeedFarm

Transmiss-ivitym2/day

2,021.

487.

1.9

20:,45

-

10.12

36.03

-

10.51

22.32

23.67

294.

7.06

11.21

-

-

-

SpecificCapacity(m2/hr)

63.4

6.4

0.22

1.69

0.20

0.90

0.34

1.72

0.20

0.71

0.20

0.68

23.77

0.77

0.83

0.23

0.23

0.10

Pumping Test Rate Length (m3/hr) (hrs)

26.6 24.

13.3 11.

11.4 5.

15.6 24.

11.4 0.67

11.4 24.

11.4 0.33

24.

11.4 °24.

10.9 .,0.42

11.4 24

11.4 24.

11.4 0.33

15.6 12.

25.2 11.5

17.0 i24.,

22.7 24.

11.4 0.18

11.4 0.17

9.1 1.33

gR

8/13/2019 PDBAW032


During drawdown,conditions suchas dewateringof theaquifer andequilibrium ofpumpingwithflowofgroundwater to thewell become apparentwithachangeinlineslopeon thegraph.Ifthe slope flattens, as occurred inthe drawdownfor well No. 54, the well has reachedastate of semi-equilibrium.theslope steepensabruptly, as

inwell No. 51, theaquifer

If

is of limitedextent and rapiddewateringoccurs. Thegraph lineslopes for recoveryanddrawdown datashouldbe similar although recoverydata aremoreaccuratesincewater level measurements can bemadewithout interference frompump vibration andwithout beingaffected by intermittentvariations in pumping rates.

The theoretical final positionof the recoverycurve should be throughthe initial water level. However, an interceptabovethis isevidenceof rechargeto theaquiferandalesserintercept iscaused by areduction in specificyield. Anincomplete recovery

isdue to limitedextent of theaquifer.The reliability of the transmissivityvalueswas enhancedwhenanother methodof analysisonalog-logplotgave comparableresults.

4.3.2 Well Yields

As indicated inTable 4.1, well #10, at Sarman Dheereisbyfar the mostproductivewelldrilled to dateby theCGDP inthe BayRegion. It appearsthat the siteislocatedonafaultwithanorthweststrike onwhich numeroussinkholesare found. The specific capacityand transmissivityaregreater than any

of theother wells tested. Wells Nos. 11 and52 have comparativelyhightransmissivi

ties andspecificcapacities andappear to be goodproducers,althoughtheywere notpumped for 24 hours.

Thewells drilledat Taflow,GaduudoDhunte,Buulo Fuur,Qans Dheere, Awshinini, MintaanandMartiMoog (Nos.16, 18,42, 47, 51 and 55) respectively appear to beabove-averagewells for theLimestone Plateau. Well Nos. 16, 18, 46 and55reachedasemi-equilibrium state duringpumpingandalthoughthe specific capacities arelow, they willsustain long pumping

periods.

The wellat BuuloFuur, No. 42, isalsoaboveaveragealthough the breakdowncurve never flattenedor reachedastate of semi-equilibrium. However,the results for wells No. 47 and51 arequestionable inspiteof the fact that the transmissivities are higher than someof thewells describedabove. Bothdrawdown slopes steepenbefore the testcompletion andthe well at Mintaan,No. 51, was onlypumped for The12-hourperiod.pumping level inthis well should bemonitoredclosely after the installation of amotorpump.

8/13/2019 PDBAW032


The transmissivities ofwells No. 12 and54 areexceptionally lowalthoughNo. 54at Isgeedwasableto sustainapumpingrateof 17m /hr fora24-hourperiodwhile reachinga stateof semi-equilibrium. Thewell atHareoroJiffo,No. 12,had considerabledrawdownandwas onlytestedfor5hours. A motorpump has been installedat thissite, but thepumpingrate isset for less than 11.4m3/hour andthe villagers have been instructedto limit the daily useof thepump. Water levelsshould be monitoredclosely at this site.

Thosewells listed inTable 4.1with no transmissivityvalues wereable to sustainyieldsof 9.1m3/hr to 11.4mi/hr(40 to 49 gpm)forshortperiods of time. Althoughthespecific capacity for wellNo. 63was very lowthe wellrecovered quickly as didthewellat RobayGaduud,No. 17.

4.3.3 Pump Redommendations

Indetermining themost suitablepumps to be usedin permanent well installationsseveral criteriawere considered.recognition that thewellsare intendedfor villageandstock-

In

water use andoften located inremoteareas, the singlemost importantcriteriaisreliability. Apumpthat issimple,efficient,requires lowmaintenance andcapable of delivering3.2 liters per second (11.4m3/hr, 50 gpm)at 150metersof headwas required.

In meetingthesecriteriaapositivedisplacement, helical rotor,monopump was recommended. Thepumpisdrivenvia lineshaft, by asingle-cylinder air-cooleddiesel Bngine. In order to meetrequirementsandalso in anattempt to standardizewith someexisting pumps inSomaliamonopumps drivenby Lister engineswerepurchased. The problemofstandardization isimpossibleto resolvebecause there areabout 20models fromdifferentmanufacturerscurrently inuse inSomalia. However,therearemanymonopumps inoperation andtheequipment uniformityestablished by theCGDP should helpto improve themaintenance and spareparts situation.

For those locations where thewell yieldor water, demands do not warrant the use of amotorizedpump,handpumps havebeen installed. Helical rotor typepumps

known aSMoynopumps,wereprocured fromthe RobbinsandMeyers Company. TheMoynopump has passedcomparative tests underconditions similar torural Somaliaand isratedat approximately 2m3/hr (0.3liter/sec, 4.4 gpm) up to depths of 90meters.

It isbelieved thatwindmills offer potentialadvantagesandtwo testwindmills have beenordered but have notyet been placedinproduction. Windconditions aregenerallymarginalwithin theCGDPareas duringpartof theyear but specificsitesmayproveeffective.

8/13/2019 PDBAW032


,5. QUALITYWATER

8/13/2019 PDBAW032


5. WATERQUALITY

Thequalityof groundwater in Somalia has beenaconcern of theCGDPsince the inceptionof theproject. Groundwater in theprojectareas isgenerally veryhigh indissolvedsolids. Salinityhas been found to bealimiting factor in manywellsdrilledunder theCGDP. This has necessitated theadoptionof water qualitystandards by theWDAwhichallowsacompromisebetweenthe World HealthOrganization (WHO)recommendedinternationalstandards andtherealities of water conditions in Somalia. The water qualityconditions for the BayRegionand Central Rangelands, respectively, arepresented inthe followingsubsections.

5.1 Water Qualityinthe BayRegion

Theassessment of thewater qualityinthe BayRegionis basedon analysesof water samplescollected by theCGDF from

1982-1984; UNTechnical ReportNo. 3,1971; and resultspublished by Idrotecneco (IDT), 1976. Thewater samplescollectedby theCGDP areprimarily fromdeepwells intheLimestone Plateau. Mostof the samples inthe IDTand UNDP reportsarefrom handdugwells inthe BasementComplex. Theanalyticalresults from the threeorganizations have been consolidatedand are provided intheAppendix, (TableA5.1). Thegeographicallocations of these water sourcesare showninPlate 4inthe Appendix. Table 5.1providesthe chemicalanalyses of theCGDP wells inthe BayRegion.

5.1.1 MineralContent

Themineralcontentof water isexpressedas total dissolvedsolids (TDS)or electrical conductivity (EC). TDS andECaregenerallywell correlated (FigureA5.1,Appendix) as well as the sumof cation andthe sumof anions to theEC(FigureA5.2ab). Thevariationsof theEC inthreeareasof theBayRegion areshown inFigure A4.8.

There are threemainsourcesof highlymineralizedwater. These areas are:

1. Karsticchannelscontaining water of highconductivities intheLimestonePlateau. Thedirectionsof the channelscoincidewiththedirectionof faults.

2. Along part of theedge of theLimestonePlateaubetween

Baidoa and Dinsor.

3. TheAnole Formation.

5.1.1.1 Chlorides

The variations of thechlorideconcentration inwellsofthe BayRegionis shown in FigureA5.9. The figureshows -:he

8/13/2019 PDBAW032


m z5.1

cheical Analysis ofNew GP DrilledWells

eo No.

d-tea

.

NO. zocatinSaNpl&ngDate IOM lat p

x106(mnzds)

DS(mg/1)

HardnessasCaC03

(Ca Mg Na K(w/1) (mg/1) mgI) (Mg/)

c:OwJ/)

SO4(M/) /)

F(mg/i)

2

3

4

8

8

Bonkay1I

Brmy 11I

Tugerew

TLz-erew

Tugerew

SanhanDheere1

Sanmn Dheere 2

12/4/82

10/9/83

4/8/82

2/2/84

6/2/84

29/6/82

29/6/82

43:39.00

43:39.00

43*:42.45

43°:41.66

43*:41.66

43*:21.38

430:21.38

3:07.00

30:07.00

3:07.06

30:06.86

30:06.86

3°:16.62

3*:16.62

7.8

7.0

7.3

7.4

7.0

7.1

7.3

2,300

3,100

1,100

1,700

1,400

2,400

2,300

-

2,216

868

1,348

1,352

3,004

2,912

353

716

472

729

564

1,071

1,080

77

229

138

218

157

269

256

39

35

31

45

42

97

107

260

135

58

98

96

102

105

16

3

5

2

6

8

5

229

5:3

243

461

461

649

632

648

12

3i

55

59

47

47

"397

427

489

536

536

509

489

pre-mipetin iMple-PCSP;s

PCs

h pump

hand pump

pump test

pump t

10

10

11

12

12

12

13

14

15

16

16

17

17

17

18

18

18

18

42

42

42

42

42

20

20

20

20

21

-

SarwanDheere3

SarmnDheere

WSAID Oopound

HareeroJiffo

HareetoJiffo

BareeroJiffo

SubelleDugsi-

WartaJaffay

gansaxOware

Taflow

Tafl

PdmayGaduud

RobayGaduud

1tjayGaduud

Gaduudo Dhunte

GaduuloDhunte

Gaduudo unte

GaduudoDhunte

Binulo FuurII

Buxo FuurII

Bui'io FuurIIBuUloFuurII

Buulo Fnwe II

DurelAllGal1e

DurelAliGalle

DurelAliGalle

DureiAllGalle

USAIDCopound

29/6/82

18/1/84

15/1/83

10/9/83

10/1/84

26/1/84

26/6/82

10/9/83

16/6/82

10/9/83

25/2/84

27/3/84

27/3/84

4/4/84

13/3/84

13/3/84

13/3/84

21/3/84

10/9/83

16/4/84

16/4/8416/4/84

7/5/34

30/6/83

7/3/84

29/4/84

29/4/84

15/1/83

43*:21.38

43*:21.38

43*:38.93

43*:25.16

43*:25.16

43*:25.16

430:13.00

43*:08.47

43°:02.36

430:1i.42

43*:11.42

43:18.75

430:18.75

430:18.75

430:15.75

430:15.75

430:15.75

430:15.75

43*:05.00

430:05.00

43*:05.0043o:05.00

43*:05.00

42*:55.85

42*:55.85

420:55.85

42*:55.85

43*:39.65

3°:16.62

3*:16.62

30:7.29

3*:13.95

3*:13.95

3:13.95

3*:17.15

3*:19.03

3*:19.92

30:03.88

3*:03.88

2*:46.25

20:46.25

2*:46,25

20:47.50

20:47.50

2:47.50

20:47.50

2*:53.75

2*:53.75

2*:53.752*:53.75

2*:53.75

2*:49.85

2°:49.85

2*:49.85

2*:49.85

3*:07.40

7.1

7.6

7.5

7.8

7.6

7.8

6.8

7.1

8.0

7.6

7.5

8.2

8.2

7.8

7.7

7.9

8.2

7.8

7.6

7.6

7.77.7

7.2

6.8

8.4

7.5

7.5

2,300

3,300

3,000

2,800

2,500

3,900

24,000

10,000

24,000

1,480

1,650

1,600

1,220

1,280

1,900

3,800

3,800

3,400

2,300

1,950

2,0001,950

2,150

3,000

1,800

2,200

2,000

2,300

2,888

2,964

1,868

--

3,554

19,772

9,188

16,436

1,528

1,452

1,408

1,060

1,024

1,796

3,380

1,932

2,812

1,800

2,024

1,8362,024

1,340

-1,584

1,964

1,816

1,928

1,046

1,321

729

888

1,463

1,262

12,211

3,065

5,462

420

854

325

1,408

362

894

1,161

1,186

1,068

984

766

831903

1,008

940

617

878

825

601

272

308

170

192

205

311

2,761

599

670

35

205

99

93

122

167

234

231

228

221

208

183192

247

208

87

35

159

183

89

134

74

99

231

185

1,291

381

920

81

83

19

19

14

116

140

148

121

105

60

91103

95

107

97

192

104

35

100

165

77

180

110

230

250

750

250

100

100

125

113

138

114

250

240

194

100

106

106106

105

121

125

120

115

8

53

0,6

14

7

3

34

23

105

13

11

1

2

3

1

2

2

2

8

7

66

11

17

5

6

7

0,1

632

1,063

305

454

638

1,382

9,618

3,024

8,740

265

391

355

319

355

567

1,148

1,148

1,008

214

336

308420

336

789

496

448

448

341

53

118

105

92

217

257

284

105

362

130

123

76

73

89

99

102

204

79

314

267

258249

369

58

109

203

100

64

484

625

388

610

482

373

351

445

1,193

232

631

104

79

186

388

210

115

163

592

367

378420

420

488

252

472

430

243

pump testhandpump

PCs

pump test

handpump

PCs

PCs

PCS

1'CS

handpump

pump test#1

pumptest02

hau pup

pumptest#1

pimptest#2

pumptest#3

motorpump

FM

pump test#1

pimptest#2pump test#3

handpwmp

PCS

had pump

pumptest, firstsal3a

pumptest,lastsample

motorpump

8/13/2019 PDBAW032


iWZ5.1,(coatinud)

MM. umW. 1&o- M&tee M. IUcatixsarlin

Date Irog Lt

I IL

!106

DsmrOs) (Mg/1)

'Ibtal

thardnessasCCa3

C(mg/)

azs.) (sq/i)

K01g/)

clOAg/) )

F) (M,/I) amarks

23 KM n 24/1/83 42=:51.25 2:28.95 7.. 900 - 311 80 327 54 6 187 28 244 PCs23

25

25

26

Kuzman

DodoeDodole

ShidaalowI

29/2/84

19/1/83

30/3/84

20/1/83

42:51.25

43Y:33.93

43:33.93

44*:16.12

2o:28.95

2*:18.32

2:18.32

2:53.57

7.6

7.2

8.0

6.8

2,400

900

595

33,000

1,868

660

744

32,092

824

318

262

20,800

144

96

77

1,910

113

19

17

3,900

167

45

56

815

8

0.4

14

1

756

52

84

10,000

132

26

68

1:,250

251

384

344

284

bandpump

PCs

handpusp

PCs27 Sgdaa1II 10/9/83 44*:16.12 2":53.57 6.7 1,600 1,288 456 99 50 112 54 210 12D 317 Ps31 B AcabaIV 25/i/83 44*:05.10 2':47.45 7.7 34,000 33,3763232

32

41

ar abeaBur ba VBr AcabaV

Doloodole

10/9/8329/3/84

7/5/84

10/9/83

44*:05.10

440:05.10

44*:05.10

2*:47.45

2':47.45

2*:47.45

7.9

8.2

7.8

7.9

800

1,060

1,140

1,040

624

836

916

564

12

202

240

508

3258

58

135

11

14

23

42

92

125

70

29

86

81

179

20

48

224

168

71

8085

81

72

232

136

304

634

PKs

handpup

hand pump

PCS45 USAID mpou 14/9/83 43*:38.93 3:7.29 7.9 - 1,340 460 102 52 221 25 338 452 38446 habey 15/5/83 42:57.32 2:55.45 7.1 1,600 - 912 240 76 83 6 386 82 323 PM46

46

47

habey

Aabey

hm ShlLaL

19/10/83

16/5/84

10/9/83

42:57.32

42*:57.32

43*:23.52

2*:55.45

2':55.45

3*:12.19

7.1

7.3

7.5

2,000

1,550

3,200

-

1,376

2,704

774

577

1,016

196

58

199

69

105

126

89

80

250

1.5

4

11

390

308

601

70

63

189

592

378

592

pumptest

pump test

PCs47

47

4750

50

51

51

52

A SheinL

WSheinL

ShiniocaySeedF.

EBokaySeedF.

Mintaan

Mintaan

Maleal

10/4/84

10/4/84

11/4/8417/8/83

20/11/83

20/1W.83

20/11/83

20/11/83

43*:23.52

43*:23.52

43*:23.5243*:36.58

43*:36.58

43°:33.16

43*:33.16

43*:35.20

3:12.19

3°:12.19

3*:12.193*:U.84

3':Ui.84

3*:20.75

3°:20.75

3*:26.20

7.7

8.0

8.07.2

7.0

7.1

6.8

7.5

3,100

2,800

3,0002,900

11,400

1,440

1,400

1,000

2,740

2,604

2,280-

8,290

756

1,164

595

%7

799

887672

3,705

689

666

512

202

218

192109

1,055

192

196

90

113

62

9997

260

51

43

70

257

257

250200

738

116

57

43

11

13

u15

7

2

12

3

851

815

840263

4,000

213

248

106

371

300

251699

222

55

40

40

294

241

199366

478

584

676

531

pu p test#1pumptest#2

pump test#3pumptest

pup test

bandpump

hand pup

PKs

52

54

54

54

54

54

54

Maleel

Isgeed

Isgend

Isgeed

Isgeed

lageed

logeed

1/3/84

28/1/84

28/1/84

28/1/84

28/1/84

28/1/84

1/3/84

43*:35.20

43*:33.16

43:33.16

43*:33.16

43:33.16

43:33.16

42:33.16

3*:26.20

3*:26.84

3:26.84

3*:26.84

3*:26.84

3*:26.84

3:26.84

8.0

7.6

7.8

7.5

7.6

7.6

7.7

670

1,200

1,350

1,500

1,300

1,400

1,525

608

1,064

992

1,076

1,008

1,008

1,448

349

671

808

792

703

776

905

44

147

109

182

186

179

125

58

74

130

82

58

0

144

10

57

57

73

57

60

94

5

2

2

2

2

2

3

112

266

283

237

248

284

448

67

53

40

52

55

40

63

294

606

652

536

723

629

252

handpip

pump test04.10A4pumptest09.50A4

pumptest04.10A4

pumptest10.10AK

ptup test10.00PM

55

55

55

mart1mHag

MartLMoog

N argL

22/2/84

22/2/84

22/2/84

43:28.80

43:28.80

43*:28.80

3:34.01

3*:34.01

3:34.01

7.1

7.0

7.0

1,150

1,150

1,150

1,064

960

964

589

672

579

170

170

166

40

60

40

38

39

36

2

2

2

178

178

142

21

18

21

631

631

573

pumptest#1

pumptest#24wV test#3

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-.robability ofdifferent cniLoriae concentrations ' Theprobabilities ofobtaining chloride-withconcentrations less than the value indicatedare:

Probabilities inPercent

50% 77% 93%

BasementComplex 500 1500 4000 mg/iCi

LimestonePlateau 500 1000 4000 mg/1C1

KarsticSprings i00 200 250 mg/1C1

Thereareonly small differences inthechlorideconcentrations betweenwells inthe LimestonePlateauand intheBasementComplex. In these two areas thereisa60 percentprobability of finding

water withachloride concentration below the recommendedWDAwater standards of 800mg/l. Thechlorideconcentrations of the karstic springsareall below 800mg/l.

Theregionalvariations inthechloride ionconcentration aresimilar to the variationsof theEC (Plate9). Therearehigh (>1000mg/1) chlorideconcentration inthewells from the Anole Formationand at bothsides of the fault between theLimestonePlateauand theBasementComplex. In the karstic zone there arelowchlorideconcentrations (<3U0 mg/1). IntheBaidoa Formationand inthe southernpartof the Basement

Complex,the chlorideconcentrationsare slightly higher(300-1000mg/1).

Chloridewaters dominante in75 percent of thewells inthe BasementComplex and in65 percent of thewells intheLimestonePlateau (TableA5.2, Appendix). In the BasementComplex thechlorides are associatedwithsodium,intheLimestonePlateauwith calciumandmagnesium.

5.1.1.2 Sulfates

Thesulfateconcentrations inthe Bay Regionareoften

below the highestconcentrationrecommended byWDA (FigureA5.10). Theprobability of obtaining sulfateswithconcentrations less than thevalue indicatedare:

Probabilities in Percent

50% 77% 93%

BasementComplex 90 100000 mg/1SO4

LimestonePlateau 60 250 700 mg/l S04

Karstic Springs 10 50 100 mg/1S04

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Only5%of thewells intheBayRegioncan be considered to have sulfatewaters. Thefewwells withsulfatewatersare scatteredoverthe entirearea, thus indicating thattheymaybe dueto local pockets ofgypsum.

5.1.1.3 Bicarbonates

Theconcentrationsof bicarbonates intheBay Regionare high. Thereisa50 percentprobabilityof findingabicarbonate concentration between 500 and1000mg/i in theBayRegion (FigureA5.11). Bicarbonate concentrations aresimilarthroughout theregion althoughthe dominantanions differ. Bicarbonatewaters areprimarily foundamong the karsticsprings and inwells west of these springs. These areas coincide withtheareas of lowchlorideconcentration (<300mg/lCl)(Figure A5.9). It isapparentthat the limestonewestofthe springsare inkarstified limestone. Outsidethis zone,the limestone ismorecompactandcoveredwithaclay layerwhich decreases the amount of infiltrationandminimizes karsticdevelopment. The absence ofkarstification inother parts of the LimestonePlateauresults inwaters of highermineralcontent.

5.1.1.4 Hardness

On the LimestonePlateauthere isa25 percentprobabilityof findingahardness belowthe WHOrecommended not-to-beexceededvalueof 500mg/lCaCO 3 (WHO,1982). The hardnessof water isless inthe BasementComplexandthe karsticsprings.In theseareas thereisa50 to 60 percentprobability

offindingwater withahardness belowtheWHOrecommended level (SeeA4.12).

5.1.1.5 Fluorides andNitrates

Thirty-sevensamples have beenanalyzed for fluoridein the BayRegion (TableA4.1, Appendix). The rangewas 0.07to 3.0mg/lF,with two of the samplesexceeding 1.5 mg/lF,thehighest allowable level (WHO,1982; 1970). Due tothe lowconsumptionofwaterper capitaandthe lowconcentrationoffluoride, health hazards dueto fluoridewater intakeareunlikely.

Thirteensamples were analyzedfor nitrates,mostof them from drilledwells. The rangewas 3to 40mg/l N03- N. Nine of the samples had concentrationsabove themaximumrecommended by the WHO (10mg/l). High concentrations of nitrates are often associatedwith fecalcontamination. Examplesof other parameters indicating fecal pollutionarephosphate andammonium. Spot tests of ammoniumandphosphateallgave low values. Since thedrilled wells arerather deep, itisbelieved that phosphate isabsorbedby the limestoneandsoil,ammonium isnitrified,and nitrateeasily transporteddownto

43

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thewater level. The highnitrate concentrationswouldthen indicatepollutionfromcattle. Fecal contaminationof theold drilledwells has beenverified inbacteriological tests.

5.1.2.6 Organic PollutionofWells

Thecontrol ofpollution isespecially important inthe LimestonePlateau,whereanetwork of cracksand fissuresallow thetransport of contaminatedwater over rather longdistances. Mostof the drilledwells intheLimestone Plateauare usedas cattlewateringpoints, and defecation by animals aroundthe water points often contaminates the wells. Precautions have been takenwithCGDPwells to avoidcontamination by arrangingthe wateringpointat some distancefrom thewell headand by constructingbrush fencesaround thewell. Althoughmoderate contaminationfrom thecattle isnotgenerally believedto bea seriousproblem, its presence suggeststhat the watercould potentially be infectedby humanexcreta.

Ifthe wellis located insideavillage, thenumerousdug septic pitsarea potential source for human fecal contamination of thewell water.

Bitcterial contaminationofwater ismeasured by total coliforms, fecal coliforms and fecal streptococci. Allthese types aie found inthe intestinesofwarm-blooded animals. Theyare thus frequent infeces inhigh amountsandare usedas indicators of fecal contamination. These bacteriaarenot pathogenic, but their presence indrinkingwater indicates that epidemics might be transmitted viadrinkingwater. The ratio betweenfecal coliforms (FC)and fecal

streptococci (FS) is usedto indicate theoriginof the fecal contamination. Ratios above 4.0 indicate humanorigin andbelow 0.7animalorigin.According to WHO (WHO,1970, 1982) thenumber of fecal coliforms per 100 ml indrinkingwater shouldbe zero. Thesamplefrequency shouldbe one sample permonthwhen thepopulation is below 5,000.

Bacterialtests undertakenonCGDP drilledwells with motor driven pumpsareall uncontaminated, while someof the newly drilledwells with handpumps arecontaminated (Table5.2).Mostof the handpumpswere temporarily installedas emergencywatering points during the severe

drought inthe spring of 1984. Pumps will eventually be changedtomotor driven pumps andthe surface sealingsof the wells will be improved. As acomparison, bacterial tests were performedon someof the earlier drilledwellsoperatedby WDA (Table5.1). Most of thesewells were found to be contaminated. Due to thedifficulties of operating testingequipment inthe field, (testproceduresrequire an incubation temperatureof 35*C but ambientair temperaturesusually exceeded this) tests for fecal streptococci couldonly be completedafewtimes. The results indicated that the wellsarecontaminated bothfromhumanandcattle feces.

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TABLE 5.2

Bacteriological Tests of Drilled Wells in the Bay Region

WDA New Fecalo. e WellellO. LEI Dt-Colforms FecalNo Date Location Source Streptococusper 100 ml per 100 ml _C/FS

2 27/2/84 Dusta Tap2Dusta- Pump house 7 27/2/84- Wabdore4 Tap27/2/84 Xawalbarbar 110 -Tap _4 5-...27/2/84 Xawalbarbar

6 27/2/84 LowraarPumphouse 6.Tap7 31/10/83 Oansadhere Tap 53

- 2 0 7 31/10/83 Qansadhere Pumphouse7 11/5/83 Qansadhere0 10 -Tap7 11/5/83 Qansadhere 0 14 -Pump house 16 9 1.8

11/5/83 Qansadhere47 10/5/83 Watercontainerwdiinle 500 300ap 1.714 9410/5/83 Awdiinle 37 2.5Pumphouse4 14210/5/83 Awdiinle 59 2.4Watercontainer14 9631/10/83 Awdiinle 809 0.6Tap18 1/11/83 GofGaduud Buuray19 12 1.6

18 Tap1/11/83 GofGaduud Buuray

40 30 1.3Pumphouse18 31/5/83 GofGaduud Buuray25 8 3.1Tap18 31/5/83 GofGaduud Buuray74 247 0.3Pump house19 1531/5/83 Barbaray 210 0.1

Tap19 31/5/83 Barbaray 129 11 11.7Pumphouse19 4121/11/83 Barbaray 25 16.5Tap19 281/11/83 Barbaray 40 0.7Pump23 1930/6/93 Daymunay 42 0.5Tap1 26/2/84 0 0ofGaduud Shabelow Tap

1 4328/6/83 GofGaduud Shabelow Tap 0- _

8 27/3/84 Tugerow 0 -Tap

10 12/3/84 Sarman Dheere15 - _

-11- 20/3/84Tap 2Sarman Dheere Tap-11- 20/3/84 Sarman Dheere 2Pump house11,21,45 02/11/83 USAID Compound Tap "

11,21,45 30/6/83 30 10 3.0,SAID Compound Tap11,21,45 07/3/84 USAIDCompound Tap 00

16 13/3/84 Taflow0 .-

Tap17 16/4/84 Robey Gaduud'0

Tap18 16/4/84 Guduudo Dhunte Pump house

00

23 19/3/84 Kurmann Tap25 25/4/84 Dodole 0

Tap32 25/4/84 BurAcaba 0Tap 01 19/3/84 Mintaan Tap52 19/3/84 Maleel

7 Pump house

54 19/3/84 Isgeed Tap2

55 19/3/84 Marti Hog2

Tap57 26/4/84 Xagarka 0-Tap12 13/3/84 Hareero Jifo 0Tap 0,47 6/5/84 Awshiini Tap 042 7/5/84 Buulo Fuur Tap 0

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Allof thenewlydrilledCGDPwells weretestedwhenthe

pumps were installed. Thewells have,to date, been usedonly forashort period,mainlyduring the dryseason. When the cattle start togather aroundthesewatering points and the

rains begin, thesenewlydrilledwellsmaybecome contaminated

dependingon the localgeology. The highfrequencyof pollu

tionamong theearlier drilledwells givessupport for suchan assumption. Regularmonitoring forpollutionwill confirm these conditions.

5.1.3 Water Qualityof theWars

Wars, or surface reservoirs, areutilizedextensively in

theBayRegion, andmustbe consideredinananalysisof water quality. Since wars aremore numerousandthereforemore

accessible,somewells incurreducedoperationschedules during

therainyseason. Fewwars containwater all yeararoundand

people, duringdryperiods, mustrelyondeepwellwater sour

ces. There areafew technically designedandengineeredwars inthe BayRegionoperatedby theNationalRangeAgency. These

wars are sealedwithplastic sheets to minimizeseepageandare

surrounded withbarbedwirefences topreventanimaland human intrusion. Thewater ispumped outsidethewar to concrete basins. Figure 5.1 shows the distributionof thewars inthe Bay Region.

Samples were obtainedfromeight selectedwars. The

variation inwater qualitywas considerableandfound to be dependentupon the relativeamountof water inthewar at the

timeof sample collection (Table5.3). Immediatelyafter the

rainyseason thewars are full and themineralcontent islow.

In additionto consumption,thereareseepage andevaporation losses. Evaporation causes an increase inmineral contentof the remaindingwateras the seasonprogresses.

5.1.4 Summary

Highconcentrations of dissolvedsolids,whichare

generallypresent throughout Somali, havenecessitatedthe

introductionof relaxedwater qualitystandards. Basedon

electrical conductivity, wells exce.eding 3,500micromonos

(umhos)have not been completedfir humanuse. Wells designatedonly for animal use havealimitof 10,000 umhos.

Recommended internationalstandards of water quality, ifthey

were implemented, wouldcondemn over 60% of existingwells.

Poor waterquality isfoundalong the escarpment, in suspected faultareas of the LimestonePlateau, intheAnole Formation,andindeeper wells of the Basement Complex. Except

for those wells inthe karstic limestonenorthof Baidoa which haveconcentrations of calciumcarbonate,mostof the-wells

aredominated by chlorides.

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EEC WAR LOCATIONS IN THE

Luuqe BAY REGION

Wajid Xuddur e

0

oo

11o0 0 I

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9 2p 4p 6 ep lkm

0 War LBII/RM

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Vter Quality of -rs

I~octin Sawple SanpleM~e Pos tion CxToa

Lotion o

-rta wabadey B14

EARSynilow B 515

CaliMwmin B516

AriisUAR B517

TcogalHoosle B518

Gorisane 519

nteS

28/6/82 R

28/6/82 V R

28/6/82 VAR

7/7/82 vaR

12/7/82 mR

29/6/82 VAR

Long at 106

43°37'30* 3 "16'30 700

43030'00' 3*17'001 , 270

43 °30'00* °58130:,100

43*20'30" 2*53'00 3,700

4303'30* 2*31'00" 550

43*25'00" 2059'00 500

p11

7.5

7.4

7..

7.7

7.2

as

385

233

440

1,733

140

+aOX

32

22.5

77.5

250

45

K

14

6

8

9

5

++

90

29

125

577

48

Mg

39

39

31

71

5

C'

34

17

43

85

52

5-S 0

193

9

508

2,305

143

H003

205

188

113

76

157

TM

584

312

1,124

3,700

460

Rema -ks

Almosteipty

Fullofwater

Almostenpty

Almosteapty

Halffull

aUmloBarakay B520 29/6/82 MR 43022'00" 2*591000 430Halffull

Safarnoolays B 521 28/6/82 MRa 43010'00 2-41100 170Fullofwater

Ftdlofwater

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5.2 WaterQuality in theCentral Rangelands

Theassessmentof thewaterquality in theCentral Rangelands isbasedon results published in the UNTechnical Report No. 3(1973)anddata obtained from five fieldtrips conducted in May, 1982; February, September, andOctober,1983;

andFebruary, 1984. Thedata are compiled in theAppendix (TableA5.3).

5.2.1 Mineral Content

The total mineral content of water isrelatedto Electrical Conductivity (EC)and theTotal DissolvedSolids (TDS). Therelation betweenECand the total mineral content depends on the kinds of ions in the sample. Achloridewater with the same mineral content as asulfate water has ahigher EC. However, this isonly of importancewhen thewaters are highly mineralized. Inthe Central Rangelands themajority of

wells contain water having highconcentrationof sulfate or chloride. Theserelationships areshown in FigureA5.1. Because of these relationships, the total mineral content in the Central Rangelands isdiscussedas afunction of TDS, even though the TDS analyses have ahigher riskof analytical errors.

Themineral content of drinking watershould, according to the provisional standards adoptedby the WDA,not exceedanEC of 3,500 umhos. This correspondsto TDS of about 2,500 mg/l. In Plate 14 areas are indicatedwhere wells have TDS less than 2,500 mg/l. Thereare only three small areas thatmeetWDA standards in theproject area. Possibleexplanations for this

pattern are discussed inthe following subsections.

5.2.1.1 Chlorides

Chlorides inwater giveasalty taste. The levelwhere people perceive thesalty taste varies between individuals, the lowest level being around 120 mg/land the highest around 1,200 mg/l (Train,EPA). In 1970, WHO stated that for concentrations above 200 mg/l Cl, potability problems may ariseand innocircumstances should thechloride concentrationsexceed600 mg/l (WHO,1970). In 1982, WHO included thechlorides among the aesthetic parameters and ga':e aguidelinevalueof 250mg/l Cl.

The initial fear about the health hazards of chloride intake via drinking water isapparently not given the same importance as earlier.

In some areas of Somaliapeople are drinkingwater containing 2,000 mg/iCl. It has been observedthat in suchareas people add salt to tea water ifthemineral content is low. The WDAhas adoptedan upper limit of 800mg/l C1as asuitable compromise between the extremes of acceptance.

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In Plate 12 the regionalvariationof chlorides is presented. The chlorideconcentrations of the wells decreasewith thedistance from thesea. The high concentrations of chlorides (>1,000mg/1) the coast areprobably notall due to sea water intrusion, however, sincethe widthof this coastal stripisas broad as 30 to 50 km. The chloride isolines in the high rangeare

rathersteep,which indicate the influence of geologicmaterials. The geology of theCentral Rangelandscan be seen in Figure 3.6. The coastal stripconsistsof recent geologic deposits (Plioceneto recent age), mainly sanddunes and coral reefs. Amodifiedpiperdiagramof the analyses from the coastal strip (areaTQcon the geologicalmap) ispresentedin Figure A5.5. Thesewells have mainly sodium (magnesium)chloridewatar eue to the influenceof the recentmarine deposits and from seawater intrusion into thewells nearest the coast.

5.2.1.2 Sulfates

Sulfatesgive abitter taste to water. Thetaste threshold value isinthe range of 200 to 500mg/l. Highsulfate concentrations indrinking waterhave alaxative effect andthe effect isstronger in combination withmagnesium.Magnesium sulfate is awell-known purgative. Astudy done intheUSA showed that 62 percent of apopulation drinkingwater containing 1,000 to 1,500mg/l sultate reportedgastrointestional disturbances. In the rangeof 200 to 500mg/l only25 percent of respondents reported difficulties (Train,EPA).In 1970, WHO recommendedthat aconcentrationof 250mg/i of sulfate should not be exceeded. In 1982 theorganizationgave400mg/i as aguideline value,mainly basedon taste considerations. Theprovisional standards adoptedby WDA for

sulfate not to be exceeded is600 mg/l.

The sulfateconcentrations of thewells in the Central Rangelands increase Northwest Ward (Plate13). The central partof the area isdominated by deposits of gypsum and anhydrite. The thir:.ess of the deposits variesfrom 200 to 400 meters and increases northward (Hilal et. al, 1977), wherethe highest sulfate concentrationsare found (1,500to 3,000mg/i). At theedgesof these deposits the sulfateconcentrations are lower, which is believedto be due to the thinner layers of gypsum-anhydrite,and to theeffects of underlying limestone formations. Along thecoastal strip,sulfate concentrationsof wellwater are low.

In FigureA5.6 amodified Piper diagramshows thewater types found ingypsum/anhydritearea. The wellsyieldmainlycalcium (sodium)sulfatewater.

5.2.1.3 Bicarbonates

The bicarbonatesconcentrationof thewells are rather evenlydistributed in the rangeof up to 1,000mg/i; one third

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in the rangeof up to 250mg/i; one third in therange of 250 to 500 mg, andthe finalone-third in the rangeof 500 to1,000 mg/l.

Only about 10 percentof thewells havebicarbonateconcentrationshigher than 500 mg/l. All of thesewells dominated by

bicarbonates are of goodwaterqualitywith TDS less than 2,500 mg/l. The bicarbonate wells are found in the limestone formationwest of the Shabelli River and in the zones between the gypsum/anhydrite deposits. Thereare, however,other water types in these areas, but the locations of the bicarbonate waters support the conclusion thatat the thinner edgesof the maingypsumdeposit, limestone formations influence thewater quality.

5.2.1.4 Calcium andMagnesium

Calciumandmagnesiumare the dominatingcations in the gypsum-anhydrite areas, andsodium isthe dominating cation in other areas. The calciumconcentration in the gypsumareas are aresult of the solubilityof gypsumwhich isaffected by the ion-pair formationof calcium sulfate,and by its ionic strength. This phenomenon isdemonstrated inFigure A5.7,where the logarithms of the true ion concentrationsof calcium andsultate, calculated by taking into consideration the ionpair formation and the ionic strengths,areplottedagainsteachother. The two straight lines in the figure represent the equilibrium between gypsum andwater at two different ionic strengths. The data points between the lines are in equilibriumwithgypsum, the datapoints above the upper line are oversatirated,and the points below undersaturated. In Figure

A5.7most of the samples in the gypsumareas havewater in equilibrium withcalciumsulfate but 38percent are undersaturated. This indicates that thecontact time betweengypsumandwater has been rather long and there is rechargefromthe surface.

According to WHO (1970)magnesiumshouldnot exceed30mg/l ifthereare 25Umg of sulfateper liter. If there is less sulfate, amagnesiumconcentration of 125 mg/lmay be allowed. The level at whichmagnesium-sulfate in water has a laxative effect for an adult isabout 1,000mg/l (about200 mg/lMg and 800 mg/l S04). In 1982, WHOdidnot recommendanyguidelines specifically for magnesium, however, aguideline

value for hardnessof 500 mg/l as CaC03 was givenas an aesthetic level. Only 15 percentof the samples analyzedfromwells inthe Central Rangelands haveahardness of less than 500mg/i as CaC0 3.

In the following table the distribution of themagnesiumconcentrations ispresented. The ranges are based at levels given by WHO in 1970 andthe level for the laxative effectof magnesium sulfate. The gypsumarea, shown as Tt (TalehFormation) inFigure 3.6, has been treated separately because sulfate concentrations are high,above 800 mg/l, inthis area.

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PercentageofWells in theCentral Rangelands with Varying MagnesiumConcentrations

Mg<30mg/l Mg<125 mg/l Mg<200 mg/1

All CentralRangeArea 18% 59% 77%

TalehFormationOnly 20% 60% 88%

Themagnesiumconcentrations arenot extremelyhigh despite the reported presenceof dolomite in thecentralareas. It is thus concludedthat the healthaspects inmagnesiumof drinkingwater in theCentral Rangelands are of minor importance.

5.2.1.5 Nitrates and Fluorides

According toWHO (1970)moderateconcentrationsof fluoride in drinkingwater cause mottlingof the teeth. The effect has been reportedoccasionally at levelsabove 1.5mg/i F. At levelsabove 3mg/l skeletal fluorisismayoccur, andat levels above 10 mg/l crippling fluorisis may occur. WHOrecommendsalevel below 1.5 mg/lF.

Only afew samples have beenanalyzed for fluoride in the

Central Rangelands; 19 by LBI fromApril, 1982andFebruary, 1983, and19 by GTZ from February, 1982 (TableA5.6). Eighteen (50%)of the samples hadconcentrationsbelow1.5 mg/iFandone sample had aconcentrationof above 3mg/l F. Sincethe rural population of Somalia hasalowdailyconsumptionof water, higher fluori' concentrationsthan recommended byWHOmightbe acceptable. The results reported inTableA5.6 are toofewto draw any firm conclusions, but theydo not indicateany serious fluorideproblems.

Highconcentrations of nitrates in drinking watermay causemethemoglobinemia (bluebabies) in bottle-•.dinfants and canceramong adults. WHO (1970, 1982) recommends that 10 mg/l N03-Nshould not be exceeded in drinkingwater.Althoughprocedures for nitrateanalyses have notyet beenestablishedatthe MMWR laboratory, 29 samples have been analyzed fromtheCentral Rangelands (TableA5.6). Sevenof the samples hadanitrate

nitrogenconcentration above10 mg/l. There are no indications that highnitrate concentrations areaproblem in thearea but amore extensive review isnecessary before firmconclusions can be drawn.

5.2.2 Summary

Areas wherewaterof goodquality have been identified in theCentral Rangelandsandare shown in Plate 14. There is a

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6 GEOPHYSICS

/j.

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6. GEOPHYSICS

6.1' SurfaceGeophysical Studies

Theprocedure for selectingdrillingsites involvedseveral

steps including, in some instances, the useof geophysical surveys. Initially, alist of villages needing ruralwater supply wereprepared by the BayRegion Agricultural DevelopmentProject (BRADP)or the Central RangelandsProject (CRP)and presented to the CGDP. The villages were locatedon maps anda studywas madeof aerial photographs and the satellite imageryavailable. Acomplete set of satellite images for Somalia is storedat the WDA, Hydrogeological Department,with blackand white images in bands 4and 5and falsecolor images in band 7. Black andwhite aerial photographs are availableatWDAand detailedsingle photographs for the areas arestored in the Ministryof Mineral andWater Resources. Satellite imageryand aerial photographsallowpossible interpretationof faulttra

ces and drainagepatterns, as vegetal cover does not obscure most areasof Somalia.

Thestudy of photographswas followedby field surveys, to identifysinkholes anddolines in the LimestoneArea, andpossible faults anddrainage channels inthe BasementComplex. This was often done in conjunctionwith the villagemeetingprocesswhich isdescribed in the Sociologychapter of Volume I.

In addition, acrewof WDAassistantswas trainedto run geophysical traverse lines in order to indicatewhere the best well sitesmight be located. Hammer seismicandgeoelectric

testswere utilized.

6.1.1 Hammer Seismic Tests

The available test equipment (Sciltest, Inc.) allowed Seismicdepth penetrationmanually by hammer of 10-15meters. Numerous trouerseswere pertormednear Baidoa, on the Limestone Plateau, the crystalline BasementComplex, andovertheir interface. Themeasurementswereprocessed andplotted bythe WDAcrewand discussedwith theLBI hydrogeologist and thickness of the top layers of overburdenwerecalculated. Rocks in the limestoneand basementareas andtheir overburden of loose residual soils wereclassifiedaccordingto their

characteristic transmission of shockwaves.

The hammer seismicmethod isintended to be utilizedwhen investigatingthe drainage channelsof the BasementComplexfor well sites by measuring the thickness of the overburdenandthe depth of the static water levels.

6.1.2 ElectricalResistivity Test

AWDAcrew was also trainedtoconduct direct-current electricalwithresistivity testwith the "Soiltest"equipmentandprocess the dataobtained. In using thisequipment tosite

75

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As another example,BuuloHawo, Borehole #66, was originallydrilled toatotal depthof 133m. Anelectric logwas then run. From themeasurements of theresistivity log,complementedby the recordof sample drill cuttings, themain compositionof the formations below 85 meters were foundto be calcareous shalewith poor waterquality. Toprevent these

formations fromdegrading thewaterof goodqualityobtainable from shallower depths, the boreholewas backfilledto 85 meters andplugged at that depthwithcement.

6.2.k Spontaneous Potential

The SP log is arecord of thenatural electricalpotentialbetween thegeologic formation and the fluid in an incased borehole. The SP measurement requires the use of aborehole fluidwithadifferent electricalconductivitythan the formation water. The Ingersoll RanaTH-60rigs use air only, or air withwater and foam injection, for drilling in karstareas to reduce theproblemof lost circulation that results

when drilling withmud. Drillingwithout muddoes notallow useof aSP log.

There wereonly afewholes drilledwithmud during the project andthesewere in the Central Rangelands Region. An idealSP log will allow interpretation salt-water formations, fresh-water formations, and interbeddedclay/shale layers. The quality of the formation watermaybe determined fromobservingthe deflectionof the SP log. InSP logs obtainedfrommuddrilled boreholes in theCentral Rangelands, interpretation was notpossible because borehole fluidswere notof uniform conducitivy,probably due to unevenmixtures with formation

water.

6.2.3 GammaRay

Thegamma ray log isarecordof radioactivityemittedbyradioactiveminerals or the differences in the backgroundradioactivities of differentgeologicmaterials. Clay, for example,has greater background radioactivity than sandstone or limestone. Granites of theBasement Complex haveahigherradioactivity than limestoneand quartz sandstone becausethey aremore denseand because granite contains small amounts of a radioactivepotassium isotope in potassiumfeldspar.

Together with the resistivitylog, thegamma ray log identifies boreholesections composedof granite in the basement areaandclay shalesections inthesedimentarycover, aswell as marly rocksections containingclay materials. The amount of gamma radiation is measured in counts per second (CPS). In the sedimentary layers of theproject area, limestoneandsand show values below 10 CPS. Marly rock sections are indicatedbyvalues around10 CPS. Clay shalesections are indicated by values of 30-40 CPS.

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In basement rock,values ranged between 30-50 CPS andmore. In contrast to sedimentaryuover, basementrock has bothhigh gamma ray outputandhigh electrical resistivity. This allowsa clear distinction between sedimentaryclay andshale layers and basementrock sections.

6.2.4 Caliper

Thecaliper log isarecordof the borehole diamoter versus depth. This log iseasy to interpret,and in uncasedholes indicates depths at which the boreholes wallsare swelling, have collapsed, )rhave passed through large fractures. In cased holes, acaliper log can indicate total depthof the casing, casing joints, casing joints whichhave separated,and casing sixes. The caliper log has beenused frequently in all of the above-mentionedcircumstances.

6.2.5 Flowmeter

The flowmeter log is arecordof relative fluidflow within the borehole. The fluid flowmayoccurnaturally,as between two aquifers, or in an artesian well. Fluid flowmay also be caused by pumping. The flowmeter isusually positioned at the point of maximum fluid flow in the borehole and logged. The tool isthenmoved to other depths inthe borehole, held stationaryand the relative fluid flowat this new point recordei. Alternatively, the flowmetermay be raisedor lowered at aconstant rate through the borehole for acontinuous curve of relative fluid flow. Interpretationof a flowmeter log will indicate borehole sectionswheregroundwater isenteringor leaving thewell.

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. CONCLUSIONS AND RECOMMENDATIONS

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7. CONCLUSIONS ANDRECOMMENDATIONS

In Somalia, semi-aridconditionsof lowrainfall, highevapotranspirationrates, areally limitedaquifers andpoor qualitywater, particularly in the BasementComplex andthe

CentralRangelands areas, have createdconditionsot limited groundwaterresources. Surfacewater resources arealsominimal withonlytwo perennial rivers existing in Somalia, the Juba and theSnabelli.

Somalia willneedacontinuous effort to develop themeager water resources to their fullestpotential by drillingwells, diggingwells, constructingwars, developingsprings, harvesting rainfall in sisterns, and re-cyclingwaterwhere feasible.

Fromresults of this project it isevident that existing groiundwater reserves are insufficient for large-scaleagri

cultural development in the areas studied. Village water supplies for people and animals will continue to be primary goals for development. The recommendations for continued drilling for futuregroundwater supplies are basedon the69 boreholes drilled during this Project andon data fromearlier research and fromother developmentprojects

The chances of success in finding usablewater ataspecific sitevaries fromarea to area, andcontains elementsof risk. Basedon drilling results to dateprobabilitiesof futuresuccess can beprojected. In the LimestonePlateauarea of the BayRegion the number of successfulwellsdrilledwas 74%; in the Basement Complex, 15%; inthe LimestoneDepression,

12%; and in the Central Rangelands, 29%. Asummary of these areas basedonascaleof good,moderate,and lowprobability of finding usablewater during developmentdrilling is as follows:

7.1 High Probability,LimestonePlateau

This areacomprises the Iscia Baidoa Formation limestones west of the Baidoa escarpment and east of the first outcrops of theAnole Formation. The best conditions for boreholewells are encountered inkarstified limestones. Well sites are located throughanalyses of satelliteand aerial photographs

that allowsmain fracture zones and faults, enlarged by karstic chemical solution processes, to be traced. Theremote sensinghas to be combinedwith fieldsurveys, assisted by information obtained from the local farmers or herders whoare familiar with thearea. in areas coveredby acaliche layer of several meters of thickness or by residual clay soil, remote sensingand field surveys may not reveal faults and fractures. Several

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Incontrastto the limestone areas, the BasementComplexhas awell-developed drainagesystembeginning attheLimestonePlateau in the Northwestand disappearingas abraidedchannelsinyoung alluvialsediments intheSoutheast. This indicatesarateof high surface-water runoff. Zonesof coarser alluviumalternatewith zoneshavingagreaterclaycontent,reducingthealluvium's permeabilityandfrequently storingsalinegroundwaterwith specificconductivity valuesup to 48,000micromhos.

The groundwater level isgenerally shallowand in dryseasonsgroundwaterqualitymay be degradedduetoevaporationof groundwater risingby capillarity to near landsurface.Electrical conductivityvaluesmayrange from i,000 to5,000micromhos according to the season andcapillaryconductivityofthe alluvium.

As an alternative todrillingshallowwells inthis zone,largediameter handdugwells offer some advantagesover drilledwells.

7.3 LowProbability,Exposed BasementRock andthe Anole Formation

The exposedbasement and its residual coverconsistingmainly of clay, can be expected to haveonly slightyields, andgroundwater with highelectrical conductivities. InDiinsor,water of 22,000micrcmhos wasmeasuredandinYaaq Braawe,35,000micromhos. Theoutcrops of basement (burs)sometimesfacilitate thecollectionof water inthe alluvialmaterial

attheir base.

TheAnole Formation,overlying the Iscia Baidoa Formationwest of acontact running through the villageof Berdaalewithanortheast trend,iscomposedupof shales,marls, andclayscontaining groundwater withelectrical conductivitiesrangingfrom 10,000 to 20,000micromhos. Overlying soilsand alluviumalso bear groundwater of unacceptablequality. Singlelayersof limestone,deeply weatheredandformingacaliche surfacemaycontaingroundwater of acceptablequality, butthe wells inthis material have lowyields.

Some additional exploratorydrilling shouldbeconductedinthe Diinsorarea. The limestonearea southwestof Diinsoriscoveredwith residualclaysoils whichallows farming. Thedrilling resultscollected inthis areaunder theCGDP do notagree with older reports which assume sedimentary cover of onlyseveral tensof meters over impervious basement. Thedrillingsite atBuulo Gaddudencountered 190mof limestonesandshalesthatcould notbe correlatedwith basalmembers in the IsciaBaidoa Formation. Numerous shallowwells inthe areawith

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groundwater of acceptablequality, but highinchlorides, leadsto theprobability thatone ormoreaquifersmay be developedthere. Before drilling operations arecontinued, asurveyofsatellite arid aerial photographs of theDinsoor areaisrecommended as thegroundwater recharge areamay be toosmalltoallow exploitation ofgroundwater ofsignificant quantity. 7.4 Central Rangelands

The Central Rangelands isalargeareaandtheGCDP hasundertaken an insufficientnumber of wells to makeanyfirmrecommendations as to probability of success. The fewwellsdrilledinthe southernpart of theCentral Rangelandswereprimarilyunsuccessful. Adrilling programinthe Hobbiodistricthas been recentlybegunwithasuccessful first well.Researchwill be continuedat sites selectedby theCRP.

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