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JOURNAL OF THE EAST AFRICA NATURAL HISTORY SOCIETY AND NATIONAL MUSEUM June 1991 Volume 81 Number 197 , NATURAL INDICATORS OF SHALLOW GROUND WATER IN KIBWEZI DIVISION, KENYA MELVIN WOODHOUSE Environmental Health Unit African Medical andResearch Foundation, ABSTRACT Humanabilityto locatesourcesofground waterusingnaturalindicatorsisaskilldeveloped fromexperience whichimproveswithuse.Thisability,essentialinmanyenvironments forsurvival,hastobenurtured.This paperdescribestheuseofnaturalindicatorstodetectgroundwaterinKibweziDivision, Kenya.Theseskills havebeendevelopedandadaptedduringtheperiodofrecentsettlementofthe areaintheearly 1970s.The localpeoplehavebecomeself-reliantinsitingwellswithasuccessrateof70% inpartofthearea.The purposeofthispaperis torecordthesemethodsbeforetheybecomeredundant,replacedorforgotten. Already thereductionofnaturaltreecoverinKibwezihasreducedthevarietyofsignsavailable. INTRODUCTION Kibwezi Division, situated some200km south eastofNairobi (Fig. 1) haserratic rainfallaveraging 644 mm per year. The Divisioncoversanareaof8000km2andexperiencesdroughtsduring both rainy seasons in 60% ofyears (Fenner, 1982a). In thepast, theareawas covered with tangled scrub suchasAcaciamellifera (Vahl) Benth. andwashome forawide varietyofgame. Maasaipassed through theareaand the Akambapeople hunted there, although few made permanent settlementsin theareain thelastcentury. In 1891 theLovedale Mission wasestablished in Kibwezi near to thepresentsiteofthe railway station. Due toan earth tremor in 1896 (Younge, 1977) the Kibwezi river, then the main source of water, increased its flow. The Mtito Andei riverand the Masongaleni riverwere also important sourcesofwaterin the areaandconsequendy were stop-overpoints for Araband Akamba traders. Mackinnon’sroad reached Kibwezi in 1895, from where Sclater’sroad began as thecontinuation towardsUganda. With theestablishmentofaroad through thearea,enterprisingpersons ventured into the inhospitableenvironmentandattempted togrow rubber, to harvestSansevieria and, more success- fully, togrow sisal. Thisall required permanentsources ofwater, both foragricultureand human consumption. The mostreliableand readilyavailable sources were the rivers.Undoubtedly wells weredugatprime sites notfarfrom the visiblesurface watersources. Addressforcorrespondence: AMREF, P.O.Box30125, Nairobi, Kenya. MelvinWoodhouse • Natural indicatorsofgroundwaterinKibwezi 2 Therailway linewas built soon aftertheroadand watersources forthesteam engines, initially railedto thestations, were secured.'A numberofstationstotheeastofKibwezi were suppliedviaa pipeline from Umani spring in the nearby Chyulu Hills.Thewaterfrom this pipeline still supports a considerablenumberofinhabitants. In 1918 a secondmajorearth tremorreduced the flow ofthe Masongaleni riverconsiderably,butit was partiallyrestored in the 1930s. Itbecameobviousthat withoutadequateground waterany developmentin thearea wouldhave todepend totally on the rainsortherivers,ofwhichonly the Kibwezi appearedreliable, and ofgoodquality. There was thereforeconsiderable incentive toinvestigategroundwaterresources. Thegeological knowledgeofthearea was basedon anearly speculative, butperceptive,report (Brantwood Muff, 1908). Itwas not until 1954 thatamore thorough investigation was carriedout in astudy which establishedthebasisforthepresent-day understandingofthehydrogeology ofthe area (Temperley, 1955). Thecolonial administration wasactive during the 1930sdrilling boreholes, as was the Kenya Sisal Company at Dwa farm. A morerecentstudy hasserved toquantify the system suggestedby Temperley (British Geological Survey etal., 1988). The Chyulu Hills, which form the southernboundary ofthe Division, rise900 metres above the surroundingcountry. Benefitingfrom an averageannualrainfall above 1200mm, they form the focal pointofhydrogeological studies. TheChyulu Hillsareofrecentvolcanic origin andasa resultoftheirhighporosity there isnorainwaterrun off. Therainwaterpercolates down into the lavaand meetsan ArchaeanbasementoftheKasigauand Kurase series. Waterflows easton topof thebasementtoemergeat MzimaSprings, thesource ofMombasa’s water supply. Temperley (1955) estimated that80% oftherainfall on theChyulusreappearsatMzima Springsand thatthe remaining 20% feeds the springs ofthe local rivers, showingthatvery littleChyulu wateris recharging local aquifers. Thebasementsystem emerges from undertheChyulu lavaandgivesrise to the flat,red landscape characteristic ofthearea. Along theedge ofthe lava thereexistsamosaic ofgneisses which arepoorbutuseableaquifers. Itistheseaquiferswhich arenow being tapped by local people. Significantnumbersofpeoplebegan to settle in Kibwezi with the immigration ofAkamba in the late 1960s, thepreviousrestrictionson settlementnow only applying totheChyulu Hills. Theavailability ofdrinking waterbecameapriority and theGovernmentand non governmental organisations began todevelop waterresources in the area. With apresentpopulation ofabout 180,000peopleagreatdemandforwaterexists. In a 1985 survey, theaveragedistancepeople travelled toawatersource was4.4km, the averageamountofwaterobtained was eightlitresper headperday, anda singlejourney tookan averageround-triptimeof90minutesreturning with 20 litres ofwaterofdubiousquality (Fergusonetal., 1988). Efforts are continuing in the Division toimprove the water-supply situation viapipeline schemes, rainwater harvesting,boreholes andshallow wells. In thecaseofshallow wells, this is largely acommunity-basedactivity. The local people organize themselves into well groups, selecta suitable site todigand seekassistance with construction from agenciesactive in the area. Well-site selection usinggeophysicalequipmenthasnotbeenparticularly successful in thepast (Temperley, 1965) largelybecause noalternatives toresistivity techniques wereavailable in Kenya. Well groups usually haveonly theirownresources to call upon when siting anew welland consequentlydonot have theoption ofan elaborategeophysical survey. Asaresult, theyhaveused natural indicators to help them. As thepopulation ofthe Division increasesand more land is cleared for farming,indicatortrees, in particular,arebecomingscarce. Atthe same time,advances havebeen made in geophysical techniques whichareenablingcheaperand moreaccuratewell siting tobedone. The useofnatural indicators may wellbecomeredundant. J. EANHS &Nat. Mus. 81 (197)June 1991 3 MelvinWoodhouse • NaturalindicatorsofgroundwaterinKibwezi METHODS Overa six-yearperiodtheauthorbecame familiarwith the currentstateofscientific knowledge of waterresources in theKibweziarea. Localknowledge wasgathered informally through discussions with localWell groupmembersand leaders. The African Medical and Research Foundation (AMREF) has heldannual trainingworkshops forgroupsconstructing wells.There arenowover 80 suchgroups. The workshopswerea valuable forum fortheexchangeoflocal knowledge and served toconsolidate the information gainedthrough discussion. In particular, thecloseassociation between AMREFfield staffandtheWell groups theyhaveassisted has led toa deeper insightinto local methods forwell siting. RESULTS There is increasingreliance upon machinestoassist in locating ground water. In Zimbabwe in 1987, when using integrated geophysical techniques, a successrateof90% wasobtained for boreholes. When siteswereallocated“logistically” the successrate was 50% (White, 1987). These interpretations stillrequire humanjudgementtobe made,whethercomputerassistedornot. Incases wherepeopledonothaveaccess to modem technologies, they can only hope to use theirownjudgementtointerpret theirsensestofind ground water. In Kibwezi a success rate of 70% has been obtained forsiting wells inareas where natural indicators exist. Thecommunity is notreliant upon outside technical expertise and is in aposition tocontinue unaided to find well sites. Whereno alternatives existthere is littleneed toargue the merits ofsuch an approach and the methods shouldonly bejudgedby theirsuccess. Since theexploitation ofground wateris essential to sustain human life, itwouldbeexpected thatoursensesdogive indications ofthe locationof ground water. Natural indicators ofground water in Kibwezi The indicators identified in Kibwezi may notbe suitable foruse in otherareas. In fact in Kibwezi itselfthe indicators are notubiquitous. ThepeopleofKibwezi arecurrently making accurate identifications ofthe indicatorsdiscussedbelow, andthis isreflected in the fact that many ofthe indicators have specific local names. Good knowledgeoftheenvironment hasalwaysbeen importantforsurvival in Kibwezi,a factstillevidentas well groups continue todeveloptheir skills in locating ground water. Forreasons ofclarity the indicatorsarehere put into six groups. Topography The flattopographyofKibwezi ispunctuated onlyby resistantinliers and seasonal riverchannels. The moreresistantbasementgeology has formed the watershedsofthearea. The land drains north intothe Athi river. As there is no run offfrom theChyuluHills,seasonal riversrise where the lava ends, which havingeroded linesofleastresistance havepreferentially cut intothe softergneisses, thus indicating their location. Thegneissesto theeastofthe main roadare less permeableand thereforepooreraquifers. The lackofdefinitive indicators ofground wateron theChyulu lava meant thatWell groups applied theirefforts away from the lavabeltand initially concentratedon the largerseasonal river beds. Theedges oflavaflows areeasily recognizableas they are several metresthick,endabruptly and havevery little soil cover. The lava isblack,often setagainstaredsoil, and supportsgreen vegetation formuch oftheyear. The mostproductive wells are located in riverbasinsgenerally not more than 2km from theedgeofthelava flow.Typical yieids from these wells ofdepthsbetween 6.5 and7.5 metres areabove 33 m perday. J. EANHS & Nat.Mus.81 (197)June 1991 MelvinWoodhouse • Natural indicatorsofgroundwaterinKibwezi 4 Withoutexception, theWell groupschoseto dig in low-lying places,locating theirwells in areasofsoftergneiss rockandaway from thebasementwatersheds. As more wells weredug, the peoplequickly realized thatthecloserthey were to the watersheds the deeperthey would haveto dig,and therewas the increased likelihoodofa low yield. Asexperience grew, initial siting of wellsbegan with ageneral survey torecognizethe location ofwatersheds. Generally, thedrainage channelsarewell definedand there was littledifficulty in excludingpotential basementsitesand the watersheds as they beardifferentsoils and vegetation. Some confusionoccurs whereseasonal watersourcesexistattheedgeofbasementoutcrops. These siteshave, withoutexception,failedtoprovidepermanentwater. Such sourcesareprobably fed from local rainfall recharge on theoutcrops, the waterbeing stored incracks.The storage volume is low and likely tobe subject toevaporation losses. Thereareanumberofoldearth dams in theareawhich wereexploredaspotential well sites. Thedams generally only store wateruntil Septemberandare thus useful but inadequateduring the dry season. As the damsdry outpeoplemake shallowexcavationsin thedam floorsandalong the walls thusgaining accurate information aboutthe locationofwater. Frequently, groups wenton to dig wells downstream ofthe dam walls. Presumably, thedams leak from thefloorthusrecharginga small areaoflocal aquifer. Diggingat the sidesand upstream ofthedams has so farproved un- successful. As mostofthe wells aredug along riverchannels, flood damage isarisk. Initially thisrisk was notaconsideration in sitingawell andcertainly previous experience with shallow holes in river beds hadresigned their users to the inevitableannual choreofre-excavation. With the location of good wellsoutside thechannels,betterpracticequicklycaughton. Sitescould stillbe improved by a more thorough consideration offlood levels, easilydoneby checking forpast flood debriscaught up in riverine trees. S—imilarly, wells could alsobe bettersitedafterconsiderationoftheerosion patternsofthe river wellsdugon the insideofmeandersare less likely tobedamaged in the future. Changingpatterns ofland usearealso increasing the run offcarriedby seasonal rivers. I.and clearance forfarming,resulting in lessretention ofrain water, is extending thedrainage systems. It is nowquite common to see drainage channels which haveencroached upon sitesofpreviously stable vegetation. Well groupsshouldbeparticularly wary when they choose to diga well neara riverwhere there are maturetreesbeing undercut in the middleofthechannel; this isclearsign of rapidly increasingerosion. Geology The Kibwezi areacan be divided intotwodistinctgeologicalregions, the area underlain by basementsystem gneisses, and the volcanic region tothe southoftherailway (Saggerson, 1963). (Fig. 2) There are three main classesofrockofinteresttopotential well groups: lava, gneissand undifferentiated basementrocks. Theserocks have specific names in the Kambalanguageof Kibwezi; they are, respectively; kivuthi,ingee and nganza. Beingagriculturalists,the Akambawho moved into Kibwezi were well awareofthe potential of the varioussoil typesencounteredand hadagoodknowledgeoftherock types in thearea. Although thisknowledge is moregeneral than specific, itwasquickly appliedin the search for ground water. Experience gained from successful wells has enhancedcommon knowledgeandsoils and geology are now included amongstthenatural indicatorsofground waterin common use. The sitingofwells on lavaisaverydifficulttask for which thereis littlelocal expertise. Suit- ablegeophysical techniques have yettobe found,although some veryproductive wells havebeen dug in lava flows. Beinga haphazardprocess, fewgroups are willing to risk wasting theirenergies andresourcesdigging in lava. Itis important, however,toestablish wherealava-flow ends when sitinga new well. In following the coursesofoldrivers, which cutpreferentially intothe softer J. EANHS & Nat. Mus. 81 (197)June 1991 5 MelvinWoodhouse • Natural indicatorsofgroundwaterinKibwezi gneisses, lava flow boundariespointtowards the location ofsuitabledigging sites. The soils found neartheedge ofa lavaflow area hybridbetweenblackcotton soil and red laterite soil. These soils arerarely deeperthan five metresand thegneiss aquifersare found beneath them . Attheedgeofthe lavaflow, where watermay seep intogneissesfrom local recharge, many of the tree species which are indicatorsofwatermay be seen. Whenriverchannelsariseattheend ofalava flow, exposures oflimestone may be seen. These werelaiddown in places where watercollected overa long periodoftime,presumably showing historic drainage systems which cutintosofterrock. They indicate suitable sites for well digging. Goats arequick to identify these outcrops and use them as saltlicks. Riverchannels which exposegeology are surveyedby local Well groups. They look forthe darkerbiotite-richgneisses which are moreproductive aquifers. It is rare to find ahomogeneous gneiss more than four metres thick. Thegneiss hardens offand becomes less productiveat depth until itis impossible todigby hand. When banded with schists itcan still beproductive atdepths of upto26metres. Due to the very mixednatureofthese metamorphic rocks, local knowledge has not yetdeveloped to thepointatwhich accuratedetermination ofpossible well depth can bemade from surfacegeological information alone. Once digging has begun, and the gneiss reached, itscolour and hardness are interpretedtogive areasonably accurateprediction ofthe depth at which water maybe found. In somecases, bars ofgneiss can be seen cuttingacrossriverchannels where they form good sites forsanddams. As thesebars may havecut through productive gneiss, they help retain waterin theburied gneiss. Wells havebeen successful downstream ofthese bars wherepresumably leakage isoccurring and thebarsareacting as sub-surfacedams. Such areas are frequently exploredas seasonal water holes by the local people. Undifferentiatedbasementoutcrops forming inliersare notgood sites forwell construction. The soils in the vicinityoftheoutcropsaresandy,reddish andoften contain large quartz fragments. Such soils are good negative indicatorsofwaterpresenceeven when rock does notoutcrop. On theeastern sideofthe main Mombasaroad, theriverchannels areconsiderably larger; some havealmostpermanentbaseflows which areheld in the sandyriverbeds. The sands found in these locations are goodforconstruction workandcan be over 12 metres deep. Some productive wells havebeen sunk into these sands usingconcreterings. Caution is needed in such places since not only are flash floods a majorhazardbutalso theperformance oftheproposed well in the dry season mustfirstbe established. Therearegood murrainsbeneath the topsoil on the eastern sideoftheroad. When people have dugpits for latrines here they havefound that waterhasentered. These stony murram layers are usually not thicker than one metre, thus their storagecapacity is small. So farapermanentdry- season sourceofwaterhas notbeen found from these murrains. Thereare some claysand soils in thearea which actas impermeable layers preventing rainwater from percolating downwards. Wateris often taken from theseclay pan areas, but thepans are heavily influenced by evapotranspiration and rarely remain wet throughout the dry season. As more experience is gained from wellsthathavebeen dug, the richerthe understandingofthe relationshipbetween geology and ground waterbecomes. Obviously local knowledge ofgeology will notdevelop toa specialist level,nonetheless thepresentbasic understanding is a significant contribution to well siting. Trees Table 1 gives theEnglish,Kamba, Swahili and scientific names oftrees found in thearea. Longland (1952) refers to“Mkuju”,(FicussurForsk.) togetherwithAcacia tortilis (Forsk.) as indicators ofgroundwaterinTanzania. The useoftrees as indicators ofground wateris a very old practice, however, theusefulnessofsome species isprobably only applicabletocertain areas. For example, Longland’s (1952) observation thatground wateris found atadepth ofthree times the heightofthecrown ofA. tortilishas notbeen shown tobe the case in Kibwezi. It is importantto J. EANHS & Nat. Mus.81 (197)June 1991 MelvinWoodhouse • Natural indicatorsofgroundwaterinKibwezi 6 realizethattreesmay beassociatedwith acertain soil typeandenvironmentandnotdirectly with the ground watertable itself. Agoodgeneral descriptionofthe woodlandofKibwezi isgiven in Fenner(1982a). The Kambapeoplewere new to this area in the 1970sbutknew mostofthe treesthey came across. The names used locally for trees are notallofKambaorigin; many aresimilartoTaita names. Presumably thesenameswere imported by the Akamba settlers.They hadneverneededto look at these treesin relation to ground waterin thisareabefore; ratherthey hadtolearn from experience. As the numberofsuccessful wells has increased, ithas been possible tocompare local tree cover with the degree ofsuccess. Asaconsequence,confidenceandreliability have increasedand now, once a general site has been selected, the tree speciespresentare usedas theprincipal indicatoroftheexactsite todig. The mostsuccessful tree indicatorofgood-quality ground waterat shallow depth so far identified isAcacia robusta. (Taub.) Brenn (Figs. 3,4) Where this tree is foundand supportedby topographical indicators, ground waterofsalinitybelow 1500fiS1 can beobtained atdepthsofless than ten metres.TheappearanceofA. robustacan differgreatly depending upon its environment, and the anatomy ofits non-reproductiveparts isdiverse. Acacia gerrardii (Benth.),Acaciaxanthophloea (Benth.),andF. surareall useful indicatorsof ground waterat shallow depth and theirpresencein conjunction withA. robustaconfirms agood site. Hyphaene compressaGaeren isa very goodgroundwaterindicatorbutit isonly foundin Mangalete Sub-location ofKibwezi. Wherepresent,watercan beobtainedatdepths oflessthan seven metres. Grewia bicolor(Juss.) is frequently usedasaforked stickby dowsers3. Even though found nearrivervalleys, itspresence has notbeen associatedwith ground water. Table 1. Botanical names Generic/specific names English Kikamba Kiswahili Acaciagerrardii (Benth.) Gerrardsacacia Muthithiu - Acaciamellifera (Vahl) Benth Hook-thorn Muthia Kikwata Acacia robusta (Taub.) Brenan Munina - Acacia tortilis (Forsk.) Hayne Umbrellathorn Mulaa,Kilaa Mgunga Acaciaxanthophloea (Benth.) Fevertree Mulela Mukonge CyperuspapyrusL. Papyrus Ndoi Ndagomwitu Ficussur (Forsk.) Cape fig Mukuyu Mkuyu Grewiabicolor(Juss.) Mulawa Mkone Hyphaene compressa (Gaeren) Doum palm Malala Mkoma Newtonia hildebrandtii. (Vatke) Torre Mukami Sansevieria. spp. Bowstring hemp Mkonge Sphaeranthus cyathuloides. O. Hoffm. Musonzouwa Sterculiarhynchocarpa (K. Sch.) Kyusia '(iS ormicrosiemenis aunitoftheelectricalconductivity ofwaterandisproportionaltoits salinity. 3waterdiviner J. EANHS & Nat. Mus. 81 (197)June 1991 7 MelvinWoodhouse • Natural indicatorsofgroundwaterinKibwezi Some tree species havealso been found tobe useful negative indicatorsofground waterthus enablingan areatobeexcludedfrom asurvey.Acaciamellifera(Vahl) Benth. and Sterculia rhynchocarpa (K. Sch.)generally existwhere there isvery littlechanceoffinding shallow water. Thus, byelimination, themargins ofaquiferscan be inferred. Even so,S. rhynchocarpa can beseen growingclose toseasonal riverbeds. Thechangein treecoverabovedifferentgeological systems isreadily observable.Newtonia hildebrandtii(Vatke) is a very useful indicatorofwater, butdue to the high valueofits timberforcarvingandcharcoal it isnowrarely found in the settled areas. Mature specimensofN. hildebrandtiican beseen near tothe springsanddamsprotectedon Dwa sisal estate. Aroughestimateofthenumberofwells in Kibwezi with tree indicators in theirimmediate vicinity is 30%. As more landisclearedforagriculture itcan beexpected thatin thenot toodistant future the natural treecoveroftheareawill havebeenremoved. Herbaceousplants No herbaceousplantshavebeenrecognized in Kibwezi as reliablegroundwaterindicators. Those which wereconsidered were mainly wet-areaplants and includedmarsh grasses, rushes and CyperuspapyrusL. andSphaeranthus cyathuloides(O. Hoffm.) whichcanbe found nearmostof the wells in therainy season. Thelatterspeciesappearstoenjoy the moistfreshwaterenvironment resulting from retainedrun-off. Presumably it is forthesamereasons that itis foundgrowing near tograniteinliers. Even so, S. cyathuloidesdoesnotthrivein areasofstagnantwaterand thus may indicate goodquality localrecharge, although this has notbeen confirmedby theauthor. Areas which retain somegreen coverduring thedry season are likely well sites. The obvious exception ison lava flows where moisturecanberetained in pocketsofblack soiland support somegreen coverformostofthe year. Fauna In thepast,theareasupportedabundantwildlifeand manyoftheearliersettlers rememberplaces whereanimalscouldbe seen drinking water. Somepeople insistthatElephant(Loxodonta africana) (Blumenbach),Warthog (Phacochoerus aethiopicus) (Pallas) andZebra(Equus (Hippotigris)burchelli) Gray,areall able to detect shallow ground waterand dig forit. Even though somepeoplesay thattheir wells weresited where theseanimals used todrink, there islittle consensusofopinionastowhetherthisis atruerelationshipornot. Bees(Hymenoptera: Apidae) areundoubtedly fond ofwetareasandare very common around wells. Local bee-keeperssay thatbees will notoccupy ahive ifthe nearestsourceofopen water is more than 1.5 kmaway. However,beesarenotregardedasadefinitiveindicatorofground water. Itis also wellknown thattermitesdonotbuild mounds inplaces whichare wet. Thiscan be seen particularly when trying todeterminewherespring linesexistwhen springs are non-emergent. The termitemound marginon theuphill side ofaswampyareawould normally mark the limitfor attemptedexcavations. Perception by the localpeople Therearenumerous dowsers in theareaand somehaveagood reputation having sited good wells. Many ofthem utilizenatural indicators togetherwith aforkedstick (Fig. 5). Sticks ofG. bicolor arecommonly used. Thedowsersusea simple technique. They havenotbeen seen tomake multiplepassesovera specific site,butsometimesdo giveclients an indication ofdepth and yield butnotofquality. Therearealsoanumberofvery poordowsers in thearea. Asconsiderableamounts ofmoney canbe made from dowsing, this is notsurprising. Atsomeparticularly poorsitesadowsermay specify aconsiderable depth to water, through arockwhich cannotbe dug by hand, thus maintain- ing hisreputation, since thedepth specifiedcan neverbereached. Thedowsersencountered by the J. EANHS & Nat.Mus.81 (197)June 1991 MelvinWoodhouse • Natural indicatorsofgroundwaterinKibwezi 8 authorhaveall been men. It wouldbe useful tostudy theabilitiesofthe local dowsersin detail and to introduce them totheapproachesandexperiencesofestablisheddowsing societies. Ata few wellspeoplehave said thata furtherreason forchoosing thesite was a sensationof warmth orcold when walkingpastthe siteatnight.This may be linkedtoamicroclimatic effect resulting from groundwaterorfrom the factthatthe site was inalow-lyingenclosedarea. Itisnot disputed thatsuch sensations exist. Table 2. Summary ofnatural indicators fordetecting shallow ground waterin Kibwezi Highly likely Nearseasonal/permanentriverbeds. Within 2km oftheedgeofthe lavabelt. PresenceofA. robusta,A. gerrardii,A. xanthophloea Absenceoftermitemounds, S. rhynchocarpaandA. mellifera Likely Absence ofbasementoutcrops. Neartoadam. ? Green coverin thedry season. In alow-lying area. Surface outcropsofmafic schist. Approvedby areputable dowser. Humid/cool sensation in still weather. Poor Presenceofmurram. On high ground. Neargraniteoutcrops. Sandy/quartz soils. Waterquality Itis important, when promoting themethods mentioned,thatasfaraspossible good-quality water is identified. This isdue totheneed fordrinking waterandbecausediggingawellby handisa major undertaking. Theaverage salinityofthe wellsdug so faris 1900pS. This is high because 17% ofthewells had asalinity above 3000pS. Waterisoftenpotable up to2500pS, whilstinternational standards may be setas low as400 pS. Atpresentan investigation isbeingcarried outtorelate salinity to soil typeand vegetation anditisapparentthatthe high-salinity wells arerestricted toa small geographical area. It is hoped that, shouldarelationshipbe identified,then the vegetationofthe “saltaquifer” areascould beusedasanegative indicatortopreventpeople from digging where such an aquiferexists. Itisamajorconcern thatthechange in land use, which isresulting in theremovalofnatural bushcover, will increaseevapotranspiration lossesfrom the soil. This in turn may increase the salinityofthe well water. Theresultantincrease inrunoffalsorepresents the lossofa valuable resource as well as athreattothe stabilityofrivermorphology. There isaconsiderable wealthoflocalknowledgeandawarenessoftheenvironmentin Kibwezi. This may changeas landpressure increases andnew technologiesare introduced. In such a fragileecosystem theinhabitants representthemostpowerful forcetoconserve ordestroy the environment.Fortunately,thepeople ofKibwezi havean intimateawarenessoftheirenvironment and itisencouraging to see thepresenttrendofcommunity-basedconservation strategies emerge. The harnessingoftheknowledgeandattitudesofpeople in Kibwezi could tipthebalancein favour ofsuccessful conservation ofthearea. J. EANHS & Nat.Mus.81 (197)June 1991 9 MelvinWoodhouse • NaturalindicatorsofgroundwaterinKibwezi ACKNOWLEDGEMENTS I thank the followingpeople for theirinterestandkeenobservation which havecontributed tothis paper: Costas Emmanuel,John Kavali,Tom Konana, Samson MutukuandGeorgeWambua. Special thanks toGerry Dekker forpersevering with identifying theAcacia speciesand to Anne Bimie whoprovided very useful commentson thepaperand produced the illustrations of A. robusta. REFERENCES Brantwood Muff, H. (1908) Reportrelating to thegeology oftheEast Africa Protectorate. ColonialReportsmisc. no.45. HMSO. BritishGeologicalSurvey, (1988) Ministry ofWater Development, InstituteofHydrology (U.K), Ministry ofEnvironmentandNatural Resources. TheChyulu HillsWaterResource Study. WD/88/5C . Fenner, M. (1982a) Aspectsoftheecology ofAcacia-Commiphora woodland nearKibwezi. JournalEastAfricaNaturalHistorySocietyandNationalMuseum, no. 175, 1-12. (1982b) Featuresoftherainfall atKibwezi, Kenya.Journalofthe .EastAfrican AgricultureandForestryResearch Organisation. 45 (1) 83-91. Ferguson, A., Absolom, E., Kogi, W. & Omambia, D.(1985) Kibwezi Integrated Survey. African Medical andResearchFoundation, Nairobi. Longland, F. (1952)FieldEngineering. Dares Salaam. HMSO. Saggerson, E.P. (1963) Geology ofthe Simba-Kibweziarea. Geological Survey ofKenya,Nairobi. Temperley, B.N. (1965) The locationofground waterin areasofArchaean gneiss in which depth probesgiveresistivitycurvesofconstantgradient.ProceedingsoftheInternational African Conferenceon Hydrology. CCIA. Nairobi. (1955) A study ofthe movementofground waterin lavacoveredcountry. Ministry ofEnvironment & NaturalResources, Kenya, (unpublished). White, C. (1987) Borehole siting usinggeophysics.In:Developing World Water. (Ed.) J. Pickford. pp 106-113 Hong Kong: GrosvenorPress. Younge, B. (1977) The Ugandaroad. KenyaPastandPresent, no. 8. Kenya Museum Society. Editor: C. F. Dewhurst Publishedby: The EastAfricaNatural HistorySociety •TypesettingbyThe PrintShop• Printedby AMREF J. EANHS & Nat. Mus. 81 (197)June 1991 MelvinWoodhouse • NaturalindicatorsofgroundwaterinKibwezi 10 J. EANHS &Nat.Mus. 81 (197)June 1991