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BRARY

INTERNÂT~ÛNALPFF~R~NCËÖ~NTP~FOJ~COMMUNITY WATER SUPPLY ANDSANITATION (IRC)

Shallowwell construction

techniquesin Kibwezi, Kenya

M. Woodhouse

Environmental Health Unit

May 1990

212.5 9QSH

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AFRICAN MEDICAL AND RESEARCHFOUNDATIÖNP.O.Box 30125,NAIROBI, KENYA; TELEPHONE:501301;TELEX 23254AMREF KE; FAX: 506112

212. 5—9OSH--8382

IBRARY, NTERNATIONAL REFERENCECENWE F3P ~X)MMUNITYWATER SUPPLYAND SAt”flA~ION~RC)P.O. Box 93190, 2509 AD The Hagu.Tel. (070) 814911 ext. 141/142

RN: ($~J ~38~LO:al~ç ~

SHALLOW WELL CONSTRUCTION TECHNIQUES IN KJBWEZI, KENYA

Kenya

Mombasa

Kibwezi WaterProject

Fig. 1 Locationof project

Shallow well construction techniquesin Kibwezi, Kenya

M. Woodhouse,African Medical andResearchFoundation(AMREF)P.O.Box 30125,Nairobi, Kenya

IntroductionAMREF has assisteda self help waterprojectin Kibwezi Division, EastemProvince,Kenya since1983.The projectoperateson asmallscaleandon averagebasassistedten selfhelpgroupsayearto

constructshallowweils. The overall objectiveof the projecthasbeentotransferthe technologyfor construction,operationand maintenancetothe local people, an objective which is now being achieved.By March1990 over 70 groupshavebeenassistedand, as a result of this experi-ence and the collaborationof local people in well design, an almoststandarddesignbasbeen reached.This designis now being copied bylocal artisansindependentlyof the project—anindication of its appropri-atenessto the local conditions.The purposeof thispaperis to explainin

____________________ simpleterms the well constructiontechniquebeingadoptedby the proj-ectin Kibwezi.

Siting a wellSeitlementin Kibwezi Division is a recentevent, mainly at sites—a total of five—where peoplethemajor influx of peopleoccurredin the 1970s. had successfullydug for waterthemselves.Fur-Well constructionis stil a newtechnologyin the ther siteswere identified from a technicalpointarea.The first weils assistedby this projectwere of view basedupon local topography and sea-

SEPTAUG OCT NOV DECWELL CONSTRUCTIONSitingDiggingLiningCappingApronPump installation

Training courseFinishing off

F ACTORS

RainaDry season

Agriculture

I u T I

I APR~MAYI JUNI JULII , ,I I

I ~I - - I -~

L. I

I :~~lr~

I I I

JAN FEB~ NAR

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I I II I I II I I

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Fig. 2 Well constructioncalendar

1

SHALLOW WELL CONSTRUCTIONTECHNIQUESIN KIBWEZI, KENYA

sonal river courses.Limited geologicalinforma-lion for the area was also available.The geo-physicalmethodsavailablein the country at thattime hadbeentried in the areawith littie success.Thereforeattentionwas paid to naturalsigns toidentify suitablewell sites which would in thelong term constitutea community-basedmethodwithout relianceupon externalinput. At present,usingtopography,surfacegeology,andlocalvege-tation,a successrateabove70% is beingachievedby the local people(1). However, some14% ofthe weils have high salinities (above2500 p.S)and a detailedinvestigationis now beingcarriedout to try to identify andmappossiblesalineaqui.-fers. With the recentadvancementin electromag-netic geophysicaltechniques,thesenew methodsmayprove successfulin the area. Local groundwater is locatedin a discontinuousgneissaqui-fer. Although the gneissbandis some60 km longand some6 km wide, its local characteristicsarehighly variable. In general,at a goodsite thereisanoverburdenof some4 m of latentesoil, belowwbich,theremay be a thin layer of calcretefol-lowedby gneiss.The gneissbasbeenfound to bestili productive at a depthof 26 m; however,theaveragewell depthis 9.4 m. The gneissvariesinits quality as an aquiferbut generallyit is poor.

Well diggingThe weils areall handdug. With only oneexcep-tion the weils weredug first andlined later. Theexceptionwas a well caissonedinto sand in ariver bed. Due to the poor quality of the aquiferand its low productivity, a large storage capacityis requiredbelowground.This, togetherwith poorsoil stability in the rainy season,led people tomakeenormousexcavationsof 100 m3 or moreto reachwater at 9 m. The practicewas soonmodifiedby startingto dig at the endof the rainsand,eventhoughfood is scarceas the dry seasoncontinues,people put in considerableeffort todig as deepas possible.Once the well is yield-ing, work on lining canbegin so thatthe lining isabove ground before the rains come. By usingthis techniquethe localpeoplesoonbeganto digmuch smaller holes whcn exploring for water,and as soonas water is found the upper section

of the holecanbewidenedto enablethe lining tobe built. 1f time allows in the dry season,thelower sectioncan be deepenedand widenedbe-low the restwater level to createmore storage.Now the averagediameterfor the exploratoryshaftfor a well is 1.5m. The techniquewas successfulwhenthe well was lined beforethe rains becausetherewas an enormousreductionin the amountof work required.

No hard and fast ruleshaveeverbeenappliedto theconstructiontechniquesfor the projectsinceultimately, what the people like will succeed.Thus, early in the project—somegroups dugsquareweils, probably becausethey were morefamiliar with the shape—andsome squarewellswere completed.However, as more groups be-cameinvolved, andas moremasons were trained,the people themselves asked the project staff topromoteonly roundweils.This was becausetheyfound that round weils use less lining materials,hence theycostIessand arc much quicker to build.There is also the other technicaladvantagethat around lining is bettersuitedto resistthe compres-sion forcesfrom the overburden.

Safety in digging is takenseriously althoughh is often difficult to ensure that advice is fol-lowed. Even so, protectivehaLs and good ropesare always given to groups.Advice is given onsafetyproceduresand a brief resuméon the sub-ject is provided (2).

Digging is done using 4-lb and 10-lb sledgehammerswith cold chisels.Good chiselsare es-sential but very difficult to obtain. In somc casescrow bars andpick axescan be used in soft gneiss.Spoil is raised from the well by rope anda metalbucket and is dumpedon the uphill side of thewell to preventany ram wash entering.Tnpodsandpulleys have been used to raise spoil but wereabandoned as peoplewerenot panticularly happyusing them and pulleys were expensive. From asafety point of view only li-litre buckets are usedto raise spoil.

Dewatening is carried out manually, which ispossible if the group is large and active, but of-ten, however, assistance is given by the ban of amodified hand pump or a centrifugal pelrol pump.In fact, the centrifugalpump is usedduringearlyconstruction stages to keep water levels bebow

2

SHALLOW WELL CONSTRUCTION TECHNIQUESIN KJBWEZI, KENYA

the level of freshconcreteand motar. It is alsousefulwhencleaningprior to capping.This prac-tice alsoservespartly to developthewell.

At somesites the overburdenis black cottonsoil. In the dry seasonit generallyremainsstableonce dug and a vertical face of 3 to 4 m willremain stable for over 12 weeks. However, if thisface is exposedto water h becomestreacherousand this situation is avoided as far as possible. Inthe rare caseof a face still beingexposedin thewet season,woedenforms are used to supportthe face whilst the wel lining is completed.

Efficienily organizedgroups generallycom-pletedigging in threemonthsof part timework.

Well liningA vaniety of materials have been tnied out to linewells including concrete well rings, lava rock and

of constructionmaterial is thereforelocal bumt

brick. The bricks are4” x 6” x 12” (10 x 15 x

30 cm) and are of varying quality, thus carehasto be takenin selection.Thebricksarecommonlyavailable but much work could lx done to im-

prove their quality.The lining is built on top of the gneiss on a

concrete foundation. A level surface of gneisshasto beprepared2.5 brickswide. In somecasesit is easierto build up with brick to the levelof aparticularly hard rock ratherthanattempt to re-move the rock. Once the level is caught a ringbeamcanbe cast.In exposingasufficientareaofgneissit maybenecessatyto dressbackthe wallof overburden.Oncea suitableflat surfaceis pre-pared, a circular ring beam of 1:2:4 concrete10 cm thick, 1.5 bricks wide and containingtwohoopsof 8-mm round iron bar is cast and curedin situ.

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Fig. 3 A hoeder bondedWell

local burnt brick. Well rings were not liked bythe peopleas the intemal diameterof the rings islimited and in a well lined only with rings it isvery difficult to deepenor widen the well. Lavarock is a good building material but requiresagreat deal of cementin building and plastering(37%mortarby volume in building alone)and isnot alwayslocally available.The preferredchoice

In caseswhere the quality of brick is goedand the overburdenstable, bricks are laid instretcherbond,byt in difficult cases,headerbondis used.The first coursesof brick are laid with 6-mm roundiron barhoopseveryfive courses.Theinitial diameterof the lining at this point variesgreaüy from well to well and is almost impos-sible to standardize.However,as diggersareget-

3Continuedonpage6

SHALLOW WELL CONSTRUCTIONTECHNIQUESIN KJBWEZI, KENYA

Fig. 4 Drawingshowingsectionthrougha typical well in Kibwezi

4

SHALLOW WELL CONSTRUCTION TECHNIQUESIN KIBWEZI, KENYA

DETA IL 0F WELL HEAD

OPTIO’IAL S~&J~’IT

~‘ILLWAY — S..Œ~E 1 IN 10

DETAIL OF DELIVERY PIPE

AMREF ~W MAR ‘90EF~NI ROF’,VIAENTAL I-EALTH UNITKI~WEZIWATER PROJECT

TYPICAL WELL PLAN

Fig. 5 Drawingshowingtypicalplanof well in Kibwezi

~ER5Oan

DCTE1~C~oa. iv~’PIPE

PIPESA~ 1.5 0.1.

NOTcIED 1 OUTLETTO P~VENrAIR SEAL

~PRONDRA I I~A~SA1~OD~’N~ LLWAY

5

SHALLOW WELL CONSTRUCTIONTECHNIQUESIN KJBWEZI, KENYA

ting moreexperiencedthediametersarenow, withfew exceptions,less than2 m. In an attempt toreducethe time andcostto build thelining, localmasonswereshownhowto corbelthe brickworkin until the internaidiameteris reducedto 1.2 m.1f donegraduallyit presentsno problemsin sta-bility or when climbing into the well and is ac-ceptedby the well groups.Ladder rungsarebentfrom lengthsof 12-mm twisted squareiron barand arecementedbetweenbrick coursesat suit-ablespacings.Thelining is extendedat least1.3mabove ground level to ensurean adequatefinallevel above the reinstatedspoil. On average,lo-cal masonsare using 3.7 litres of 1:4 mortar tocementeachbrick in place,which is highdue tothe poor shapeof the bricks. A numberof meth-ods havedevelopedto assistthe work atthisstage.Strongpalesareplacedacrossthe well andbuild-ing continuesabovethem.The poles are usedtostandon like scaffoids(putlogs).Whenthe polesare later removedtheholes in the wall are filledwith concrete. Some groupshave built woodencradiles which can lx raised and lowered insidethe well. Somemethodshavebeenusedto checkth~centring of the brick work, include usingafull length of waterpipe to mark the centreandto fix a wire to it to check mdii. Also, circieformscut from wood andboardhavebeenused,but in generala good masonwith plumb line,tapeand spirit level is ableto do thejob satisfac-tonly.

The insideof the lining is plasteredto a depthof atleast3 m belowgroundlevel.

Once sections of the lining become firm,backflhling behindthelining cango ahead.Thereareno suitablelocal claysfor thisjob andusuallyspoil is used.As the backflll takesa long time toconsolidate,careshouldlx takento placeit care-fully andto tampit down evenly, backfllling onlya smallamountat a time.

Usually by the time this stageis reachedtherains arenearand groupsare eagerto return totheir agriculturalwork. Wherepossible,well cov-ers are eastand pumpsfitted at this time sa thatgroupscari get the benefitfrom their work imme-diately. Duning the peakof the rainy season(De-cember)projectstaff takeleaveand local peopleare busy weeding their fields. The backfill usu-

ally requiresaperiodof 2 to 3 monthsto consoli-datebefore an aproncanlx built on it. Consoli-dation usually occurs during the rainy seasonwhenthe groundis wet.

Capping the wellWell covers are cast in excavatedmoulds, theyare 10 cm thick 1:2:4 concretewith adoublelayerof BRC 610 reinforcingmeshinside. After tryingseveraldesigns,peoplesaid that they prefer notto have manholecovers on the well head butwould ratherhave a cover which splits in halfenablingawholehalf to lx removed.The reasonsfor this arethat it would takea group decisiontoremovea well cover, that manholesare difficultto manoeuvrein and out of, and that removinghalf thecoverlets in more light when deepeningthe well.

Thereforethe coversare madeas two halves.At the junctionthey arerebatedto allow aweak,removable plaster seal to key. One half cover.canesthe anchorbols for the pump and a plinth5 cm high is cast as part of the slab upon whichthe pump base-platewill sit. Keeping the pumpbaseabovetheslablevel is one way of prevent-ing spilled water from getting suckedback intothe well. The formerusedto makethe hole forthe pumpstring is usually asuitabletin canor apieceof PVC pipe.The anchorbobtsfor the pumparewelded into a frame to ensurecorrectalign-mentin casting.

The apronThe apronarounda well is often overlookedas aminordetail whereas,in fact, it is the place\vhereall usersstandwhendrawing water; it thereforehasavery significantsanitaryfunction.An apronshould provide a stable surfaceupon which tostandwhendrawingwater, it shouldlie designedto remaincleanwith a minimumof attentionandh can also act as a physical bamerto preventlood waterfrom damagingor enteringthe well.

Severaldesignshavebeentried out in Kibweziandthe final versionis stili evolving. At present,an apronof width 1.2 m (outsidethe well lining)is built by building a brick wall aroundthe well

6

SHALLOW WELL CONflUCUON TECHNIQUESIN KIBWEZI, KENYA

and backfilling with rock and spoil. The wall isusually 50 cm high. Once backfllled, a slab ofconcrete,reinforcedwith one layerof BRC 610,is poured on top to the approximateslope re-quired.In the presentdesign,drainageis directedin towards the well lining and down towardsaspillway. This methodof drainingwatertowardsthe well doesnot require a perimeterwall to bebuilt aroundthe apronto catch spil, but it doesmeanthat the seal betweenthe apronandlininghasto be goodor elsespill watercould penetratethe lining. The apron is then plastered,takingcareto catchthe correctleveLs for drainage.Theapronis not given acementnil coatingas suchasurfacewouldbe slipperywhenwet.

The spillway is built in a similar way on arubble foundationfrom brick. Siting the line forthe spifiway is done with care to ensurethat itwill not be damagedby any stream fiows andthat the groundbeyondthe spillway continuestoslope away, otherwisespilt water could form apond.Wherepossiblethe spillwayshouldbe 6 mlong with a slope of 1 in 10. It should be wideenoughto be sweptclean and should be plas-tered. In caseswherethe spill water is not di-rectedawayfor anotherpurposeasoakpit is dugattheendandfilled with rock.

The size of theseapronsmay seemextrava-gantbut in usetheyappearto remainclean,evenwhennot well maintained,andtheykeepthe areaaroundthe well stable.The visual impressionisgood.Peopleappreciatethis and cometo expectcleanlinessaroundtheirwells.

Someseriousproblemswith crackingof apronshavebeenobservedand correctiveactionshavebeentaken. Thesehave included reducing thewidth from 1.5 to 1.2 m and introducing rein-forcemeiit into the slab.However,themaincauseof major crackingis when the apronis built onan unconsolidatedbackflll. Thus adequatetime.of at least two months througha rainy seasonmust be allowed before building. Minor crackscan result from poor plastermixes or poor cur-ing, both of which can be easily correctedbyadequatesupervision.

Pump installationThe pumps usedin this project are Dutch SWN80s, now made in Kenya. Three-inchcylindersareusedas standard.Themostimportantconsld-erationtakenin installationjs to ensurea water-tight sealbetweenthebase-plateandtheconcreteplinth. At presentthis is achievedusingbitumenapplied with a building trowel. One drawbackwith this methodis thatsubsequentpumpremovalafterthebitumaihasdriedout canbedifficult. Infutureit ishopedto cutmatsfrom nibbersheettoform the seal.

FinishingoffThe well is chlorinatedwhen the pump is in-stalled.Due to the difficulties of on-sitedetermi-nationof the amountof chiorine required,atrialand error method is used. Chloride of lime ismadeinto solution in abucket and poured intothe well. The well is pumped.If chlorine cannotbe smeltin the outfiow, more solutionis added.This methodalso ensuresthat the pump is chlo-rinated. Once a discemiblelevel of chiorifie isreachedthe well is left for 6 hours and thenpumpedto remove any excess.When a suitablechiorine level is reachedthe remainingcover isput in placeand sealedwith a weakplaster, thussealingoff the well head.

Fencesfrom living localtreesareusuallybuiltaround the well during constructionto preventaccidents.After completion,thesefences arere-inforced with barbedwim to protect the treeswhilst they establishthemselves.

Adviceis given to encouragepathsto the wellto be aligned in such a way that they wjll notdirectstormwaterto thewell in future.

A guaranteeis issuedon the woit for oneyearafterthe dateof pumpinstallation.Thisprac-tice enablesgroupsto begin a savingsfund forfuture repairsand,duringthat year,two n’oembersfrom eachgroupattenda training course.to teamhowto maintaintheir well.

7

SHALLOW WELL CONSTRUÇI1ONTECHNIQUESIN KIBWEZI, KENYA

CommentsThe techniques used have been developedspecifically in Kibwezi and shouldbe usedwithcautionin other areas.The techniquesappeartohavebeenacceptedby the local people. In a re-cent survey (3) of bacterialcontamination,20%of weils were found to contain more than ten

faecal coliforrns per 100 ml of water. Possiblereasonsfor each specific well were visible, forexample,an unsealedwell cover, but, by corn-parisonwith otherweils, this rate of occurrenceis quite low.

The autilor welcomescommentsandquestionsonthisarticle.

Fig. 6 A completedwell beirigchiorinated

References(1) WOODHOUSE, M. 1990. NaturalSigns of Groundwater in Kibwezi Division Kenya. AMREF in

press.

(2) WOODHOUSE,M. 1988.Safetyin Well Construction.RNCBulletin No 4. AMREF

(3) WOODHOUSE,M. 1990.ConsumerInvolvementin BacteriologicalTestingof Well Waterin Kibwezi.Waterlinesin press.

8

SHALLOW WELL CONSTRUC11ONTECHNIQUES IN KJBWEZI, KENYA

Glossaryof terms

Caissoning Sinking a well by digginginsidethelining. The lining sinksas diggingcontinuesandthelining is extendedatthetop.

Calcrete Gravelswhich have beennaturally cementedtogetherby calcium carbonate.

Corbel Laying bricksnot directly on top ofeachother to widen a wall or to reducethe diameterofacircularwall.

Gneiss A generalnamefor banded metamorphic rocks.

Putlog A horizontal scaffold to support boards used to stand on when building.

Fig.7 Bill of quantities

BILL OF BIJANTITIES FOR A 9.5 M NELL IN KIBWEZI (JULY 1989)

ITEM UNIT UNIT COST NO. TOTAL CUTI US $KSHs KSHs (IUS$~20K

80 3 240 12150 1 150 7.5210 I 210 10.5

70 2 140 795 1 95 4.75

7 15 105 5.2560 2 120 6

110 3 330 16.5

15 20 300 1598 30 2940 14720 12 240 1280 B 640 32

TOOISbucket PC

hauer 41b PChauer Bib pchard bat pcpick axe pcropelé.. Mshovel pcstone chisei pc

CONSTRUCTIONbrc 610 .esh .2ce.ent baground bar 12 I• C

round bar 6 ii pc

ENGINEERIN6barbed cire rollbituien kgchain 3/16 I

iiscellaneous *

padlock pcpipe fittingspipe 91 1.5 I

ptfe tape roi)

PUNTsen 80 co.pI.te PCpuep spanners pcpu.p tuaIs PC

SERVICESchiorination

3803030

45

i012

380 1930 1.5

2.5 75 3.75500 25

45 2.25100 5

2 20 II 12 0.6

I 12000 6002 250 12.52 120 6

training course peopleguarantee

TOTAL

120 62 3000 150

1500 75

23662 1183.1

AMREPS Environmental Health Unit houses the East Af rican Regional Network Centre for Water andSanftatlon, whlch forms part of the International Training Network.

9

) 1

Printedin Kenyaby theAfrican MedicalandResearchFoundationP.O. Box 30125,WilsonAirport, Nairobi