research article evaluation of groundwater recharge...

Research ArticleEvaluation of Groundwater Recharge Estimates in a PartiallyMetamorphosed Sedimentary Basin in a Tropical EnvironmentApplication of Natural Tracers

Felix Oteng Mensah1 Clement Alo1 and Sandow Mark Yidana2

1 Department of Earth and Environmental Studies Montclair State University Montclair NJ 07043 USA2Department of Earth Science University of Ghana Legon Accra Ghana

Correspondence should be addressed to Sandow Mark Yidana smyidanaugedugh

Received 1 December 2013 Accepted 29 January 2014 Published 19 March 2014

Academic Editors G-C Fang and K Nemeth

Copyright copy 2014 Felix Oteng Mensah et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

This study tests the representativeness of groundwater recharge estimates through the chloride mass balance (CMB) method in atropical environment The representativeness of recharge estimates using this methodology is tested using evaporation estimatesfrom isotope data the general spatial distribution of the potential field and the topographical variations in the area This studysuggests that annual groundwater recharge rates in the area ranges between 09 and 21 of annual precipitation These estimatesare consistent with evaporation rates computed from stable isotope data of groundwater and surface water in the Voltaian BasinMoreover estimates of groundwater recharge through numerical model calibration in other parts of the terrain appear to beconsistent with the current data in this study A spatial distribution of groundwater recharge in the area based on the estimated datatakes a pattern akin to the spatial pattern of distribution of the hydraulic head the local topography and geology of the terrainThis suggests that the estimates at least qualitatively predicts the local recharge and discharge locations in the terrain

1 Introduction

In regional hydrogeological studies and groundwater resour-ces assessments accurate estimates of groundwater rechargeare required to ensure proper water balance studies andevaluation of groundwater resources for productive usesRecharge is one of the uncertain parameters in model cali-bration and is regarded as one of the major parameters whichdetermine the accuracy and reliability of predictive ground-water flow models It is therefore apposite that this compo-nent of basin wide regional hydrogeological investigations isconstrained through a variety of methods Several methodshave been proposed in the literature for providing reliableestimates of groundwater recharge at both the regional andlocal scales They range from direct measurements throughmass balance techniques and Darcian method to the use oftracers [1 2] A wide variety of mass balance techniques areavailable and their utilities are often based on an assessmentof the validities of underlying assumptions in the areas where

such applications are sought Rorabaugh and Meyboom [3]developed methodologies that are based on baseflow reces-sion and assume amongst others that the baseflow componentof stream flow can be approximated to groundwater rechargein large basins especially where such a hydraulic connectioncan be established between stream flow and the underlyingaquifers Using thismethodology there is a high possibility ofoverestimating groundwater recharge rates especially wherethe catchment area of the stream is larger than the domainbeing examined The water table fluctuations method [4] hasalso been advanced and used in several areas to estimategroundwater recharge in unconfined aquifers The methodis based on the assumption that appreciation in groundwaterlevels between seasons is attributed to groundwater rechargewhich is proportional to the specific yield of the materialTherefore where the aquifer is confined or semiconfined themethodology is less appropriate and will lead to underes-timation or overestimation depending on the values of thespecific yield used Even where the aquifer is unconfined

Hindawi Publishing Corporatione Scientific World JournalVolume 2014 Article ID 419508 8 pageshttpdxdoiorg1011552014419508

2 The Scientific World Journal

the spatial variability in the specific yield field can lead tosignificant departures of recharge estimates from the realityon the ground The method is often used in places whereinitial estimates are required formuchmore detailed regionalhydrogeological studies Several tracer techniques have beenproposed in the literature and they range from the applicationof isotope techniques to the use of natural hydrochemicalconservative tracers such as the chloride ion [2] The use oftracers to explain groundwater recharge and flow processesis copiously documented in the literature [5] The chloridemass balance (CMB) technique is based on the assumptionthat the chloride ion behaves conservatively and is noteasily affected by reactions through the unsaturated zonethrough to the saturated zone If this assumption is validthen it follows that the ion can adequately trace groundwaterrecharge processes and can thus provide reasonable estimatesof groundwater recharge in the area Its reliability thereforehinges on the compatibility of the precipitation events thatrecharged the system under study and recent precipitationIt is also assumed that the main source of chloride ingroundwater is precipitation Therefore where it can bedetermined that a substantial proportion of the groundwaterchloride is generated frommineral dissolution processes themethod can lead to underestimation of recharge On theother hand where the groundwater chloride is negativelyaffected by a process which reduces its content compared tothat of precipitation groundwater recharge can potentiallybe underestimated The CMB methodology has been widelytested and regarded as one of the most reliable techniques forestimating groundwater recharge in regional hydrogeologicalstudies and basin wide groundwater resources assessments(eg [5ndash10])

The current study evaluates the performance of theCMBmethodology in a typical tropical climatic environmentwhere the availability of groundwater resources is critical tosocioeconomic conditions of populations and the survivalof ecosystems that depend on such groundwater resourcesfor sustenance Groundwater recharge estimates from theCMB method in this study are checked against estimatesof evaporation rates of percolating rainwater as estimatedfrom isotope techniques The spatial pattern of variation inthe resulting recharge estimates is then predicted using aspatial prediction method for the resource to be evaluatedThe novelty lies in the fact that the CMB method althoughnot new is rigorously evaluated using another conservativetracer

2 The Study Area

The study area (Figure 1) is in the Northern Region of Ghanaand covers a total land area of about 17907 Km2 and itfalls within the White Volta Basin The agricultural sectoris the largest employer in the area employing about 97of the active populations [11] Most of the farmers dependon rain for food production and the typical crops growninclude yammaize rice groundnut cowpea and soya beansUnfortunately agricultural activities are constrained by unre-liable rainfall inadequate irrigation facilities and difficulty

in loan accessibility and lack of storage or processing unitsleading to postharvest losses [12] The area is generally flatwith gently undulating reliefs There are no high mountainsin the area except few hilly features observed in the southernpart with elevations generally ranging between 122 and 244mabove sea level however the north is low lying The areais mainly drained by the White Volta and its tributariesIt falls within the Sudan Savannah zone with an annualrainfall between 900 and 1200mm distributed on averageover 74 rainy days [13] The study area falls under theIntertropical Convergent Zone the interface where two airmasses tropical continental and tropical maritime overlapThe frontal activity and relative movement of the two airmasses control the amount and duration of rainfall Rainfallwhich is generally of short duration and high intensity andis often preceded by thunderstorms and line squalls startsintermittently between March and April through August toSeptember when it turns stable and very heavy The dryseasons are pronounced with temperature ranging between18 and 42∘C with mean value of approximately 30∘C [14]Relative humidity during wetrainy season is in the range40 and 70 and drops to about 15 during the rest of theyear [13]The observed lowhumidities and high temperatureshave led to high potential and actual evapotranspiration ratesin the basin

The area is underlain by consolidated Neoprotero-zoic sedimentary sequences of the Voltaian Super-Group(Figure 2) The rocks are mainly of the Middle Voltaian(Figure 3) which is the most extensive sedimentary for-mation in Ghana The Middle Voltaian comprises the Otiand the Obosum beds which are well consolidated andgenerally flat lying The beds are made up of interbeddedmudstonessiltstones sandstones arkoses and conglomer-ates [15] Details of geology and hydrogeology are docu-mented in detailed reports and articles on the basin [14 16ndash21] The rocks are largely impervious so that the occurrenceof groundwater is associated with the development of sec-ondary porosity through jointing shearing and fracturingand weathering Rock compaction and slight metamorphismis believed to have destroyed the primary porosity [16]leading to considerably reduced inherent primary permeabil-ities However where intense weathering occurs the rocksserve as better aquifers with significantly enhanced hydraulicand storage properties The nature aperture and degreeof interconnection between joints determine the hydroge-ological fortunes of the rocks [14 17ndash19] Drilling projectsand hydrological investigations reveal that shallow potentialaquifers capable of delivering water of sustainable quantitiesfor domestic and industrial use exist in the basin [20]

Peasant rain-fed agriculture is themain source of employ-ment in the basin However recent erratic patterns of rainfallin the area coupled with rising populations in the basinhave led to increased interests in developing the irrigationpotentials in the area This has heightened interests inassessing the potentials of developing the aquifers in the areafor commercial abstraction to support irrigation activities toenhance food security and reduce poverty since agriculture isthe mainstay of the communities there

The Scientific World Journal 3

10∘ 20998400 0

998400998400N

10∘ 0

998400 0998400998400

N9∘ 10998400 0

998400998400N

10∘ 20998400 0

998400998400N

10∘ 0

998400 0998400998400

N9∘ 10998400 0

998400998400N

0∘09984000998400998400W0∘209984000998400998400W

0∘09984000998400998400W0∘209984000998400998400W

EW

N

S

Location map

Study area

Community nameRiversRoad network

Study areaDistrict boundary

Figure 1 A map of the study area showing the major communities and settlements

3 Materials and Methods

A total of forty-two samples (19 groundwater 11 rainwaterand 12 surface water samples) were collected for the studyRainwater was taken in Tamale and analyzed for both

the chloride and isotopes (18O and 2H) Historical ground-water hydrochemical data from the basin were obtained fromthe Community Water and Sanitation Agency (CWSA) inthe Northern Region The surface water samples were takenfrom tributaries of the White Volta Strict adherence to


1∘10998400W 1∘0998400W 0∘50998400W 0∘40998400W 0∘30998400W

1∘10998400W 1∘0998400W 0∘50998400W 0∘40998400W 0∘30998400W

10∘ 0

998400 N9∘ 50998400 N

9∘ 40998400 N

9∘ 30998400 N

10∘ 0

998400 N9∘ 50998400 N

9∘ 40998400 N

9∘ 30998400 N

0 10 20 40 60 80

(km)

Sugu-Tampia

Ying

Ligba

Upper VoltaianMiddle Voltaian

Settlement

N

Figure 2 A geological map of the study area

minus100

minus80

minus60

minus40

minus20

0

20

40

60

minus15 minus10 minus5 0 5 10 15

GroundwaterRainwaterSurface water

Linear (groundwater)Linear (rainwater)Linear (surface water)

Surface water

R2 = 09651Groundwater

R2 = 08875

12057518O

1205752H

Rainwater

R2 = 0899

12057518O = minus45 1205752H = minus255

y = 53003x minus 22512

y = 51898x minus 16042

y = 74784x + 55345

Figure 3 Stable isotope signatures of rainwater surface water andgroundwater from parts of the White Volta Basin Ghana

sampling protocols was followed for collected water samplesboth in the field and the laboratory All the analyses werecarried out at the GhanaAtomic Energy Commissionrsquos chem-istry laboratory Chloride analysis was done using a DionexICS 90 ion chromatograph equipped with an AS14A-5120583mion pac column Stable isotope analysis of 12057518O was carriedout using VG Sira 10 mass spectrometry Delta deuteriummeasurements were done on a EuroVector elemental analyzer

(EA EuroPyrOH-3100) with a liquid autosampler (LAS EuroAS-300) coupled to aMicromass IsoPrime isotope ratio massspectrometer The isotope composition of water is reportedas the deviation of 2H1H or 18O16O ratio from that ofVienna Standard Mean Ocean Water (VSMOW) in parts perthousand (permil)

The CMB methodology is summarized in

Recharge =119862119901

119862gw119875 (1)

where 119862119901and 119862gw respectively represent chloride concen-

trations in precipitation and groundwater and 119875 representsthe average annual depth of precipitation in the area

Average chloride concentration in rainwaterwas obtainedfrom analyses of rainwater samples taken in Tamale theregional capital of the Northern Region as part of thisstudy Groundwater chloride concentration was obtainedfrom the historical hydrochemical data that had already beenprocured from the CWSA An average annual precipitationrate of 1100mmwas used in the estimation Ordinary Krigingwas then applied to the estimated recharge to achieve aregional distribution in the area Ordinary kriging is a linearestimation method which is based on [22]

119885 (119909) =

119899

sum

119894=1

120582119894119885 (119909119894) (2)

where120582119894refers to theweight assigned to a knownor estimated

value119885(119909119894) of the parameter and119885(119909) is the new value being

estimatedDifferent estimation methods use different criteria to

assign the weights to parameters but most of them arebased on the proximities of the known locations to thelocations being estimated [22] Where proximity is the soledeterminant the weights are assigned such that closer pointshave higher contributions to the estimates than farther pointsas is the case with inverse distance weighting [22] Theadvantage of ordinary kriging over the others is that it usesboth the proximity factor and the general pattern of spatialvariation of the parameter with distance A variogram ismodeled from the original data as part of the processes ofestimating the weighting factors or coefficients Such amodelcharacterizes the spatial dependence of the parameter in thedomain It is the fitted experimentalmodel which is then usedtogether with the proximity factor to estimate coefficients forall the data to be used in the estimation

In this study both the variography and ordinary krig-ing were performed from the R-platform An acceptablevariogram was carefully chosen and fitted to the computeddataset of the recharge estimatesThis was achieved by tryingthe various possible theoretical models available until themost appropriate model was achieved Ordinary krigingwas then performed from the variogram model chosenPrediction accuracy using ordinary kriging and any krigingmethodology partly hinges on how adequately the spatialdependence of the parameter was modeled This implies thatthe choice of an inappropriate model of spatial dependencecan potentially lead to inaccurate estimates or predictions


4 Results and Discussions

The sources and origin of groundwater recharge in the Volta-ian was assessed using stable isotope data of precipitation(rainfall) groundwater and surface water from parts of theVoltaian Historical stable isotope data (12057518O and 1205752H) forgroundwater surface water and rainfall were plotted on abiplot for the purposes of ascertaining the sources andorevolution of groundwater in the area Isotope tracers areamongst the most frequently used to trace the sources andorgenesis of water reservoirs and contaminants and have beennoted to provide useful insights to guide further detailedinvestigations The ratio of the rarer (and most often theheavier) isotope to the more abundant (often the lightest)isotope provides an indication of the relative enrichment ofthe two isotopes in the medium or the original source ofrecharge It is such a ratio that provides indications of theclimatic conditions prevailing at the period and location ofrecharge and can therefore be used qualitatively to infer theage of awater bodyThese ratios are expressed in relation to aninternational standard which provides some uniformity forcomparing environments or reservoirs on a global scale andis often expressed in the delta (120575) notation as indicated in

12057518O = (

(18O 16O)

sample

(18O 16O)

119881-SMOW

) times 1000

1205752H = (

(2H 1H)

sample

(2H 1H)

119881-SMOW

) times 1000

(3)

where the terms in the numerator and denominator respec-tively represent the ratio of the heavier to the lighter isotopein the sample and international standard respectively

The global meteoric water line (GMWL) was first pub-lished by Craig [23] and is a convenient reference forunderstanding and tracing water origin It is a linear relationin the form of

1205752H = 812057518O + 119889 (4)

where119889 the119910-intercept is the deuterium excess (or119889-excess)parameter when the slope = 8 [24] From Craigrsquos MWL119889 = 10 at this slope and is indicative of no evaporativeeffect during precipitation The underlying assumption [23]is that water with an isotopic composition that falls alongthe GMWL originates from the atmosphere and is relativelyunaffected by isotopic processes Isotopic signatures fromdifferent reservoirs are often discussed in relation to (4) Inthis study groundwater recharge in the area appears to beof meteoric origin as the groundwater data plots close tothe GMWL albeit with shallower slope and intercept whichsuggest some degree of enrichment of the heavier isotoperelative to the lighter ones (Figure 3) The observed patternis consistent with conditions of lower relative humidity than100 and high ambient temperatures as is common in thestudy area The shallower slope and 119889-excess values result

from evaporation of raindrops due to low relative humiditiesduring the course of the rains The average relative humidityin the area during the rainy season is about 70 [13] Verticalpercolation of precipitation down to the saturated zone isvariable in the space of the study area due to the variabilityin the clay content which limits the vertical hydraulic conduc-tivity of the material of the unsaturated zone Where the claycontent is high vertical percolation is significantly restrictedand the resulting recharged groundwater is significantlyenriched due to evaporative effects of high temperatures andlow humidities It is obvious that the surface water datafall exactly on the Global Meteoric Water Line GMWLwhereas both the rainwater and groundwater samples arerelatively enriched with shallower slopes and deuteriumexcess (119889-excess) values (Figure 3) The rainwater sampleswere taken during three events in the major rainy season andmay not adequately reflect the signature for the entire yearHowever studies conducted in the southern parts of the basinusing data mainly of the dry season precipitation suggestsignificant enrichment [25] A solution of the equation forthe Local Meteoric Water Line (LMWL) developed from theprecipitation data and the local Groundwater Line (LGWL)developed from the groundwater isotope data provides theisotopic signature of the most probable source precipitationof the groundwater in the areaThe intersection of the LGWLand LMWL in Figure 3 provides such a signature As isobviously presented in Figure 3 the isotopic signature atthe point of intersection of these two lines (12057518O = minus451205752H = minus255) suggests that the source of recharge is recent

meteoric water or a mixture of precipitation types whichare of recent origin The local surface water line (LSWL) issimilar to the groundwater line in terms of slope and intercept(Deuterium excess) and suggests that both have a similarsource and may have been affected by similar processes overtime A recent assessment of the isotope characteristics of theentire Voltaian indicated a similar isotopic signature of thesource water of groundwater recharge in the basin [26] andindicated that the processes of infiltration and percolationof precipitation water may be variably slow in the terraindue to the variability in the nature of the overburden evenwithin short distances Yidana [26] estimated the rates ofevaporation of precipitation water in transit down the unsat-urated zone to the saturated zone and reports evaporativelosses of 198ndash706 for the Voltaian sedimentary basin inGhana This contrasts with significantly higher evaporationrates estimated for surface water bodies in the area (295ndash847) and highlights the fact that surface water in view ofits continuous exposure to the atmosphere endures higherimpacts of higher ambient temperatures and low humiditiesthan infiltrating water In both cases however the estimatesare most likely the average conditions over a long period oftime since the waters sampled are most likely mixed watersfrom different events These estimates do not include theeffects of transpiration as the impacts of transpiration onisotopic signature of water are difficult to estimate Howevertranspiration contributes significantly to water loss especiallyin the unsaturated zone Therefore if included the rate ofwater loss due to the combined effects of evaporation and


precipitation in the entire terrain and in the study area willbe significantly higher

Estimated groundwater recharge from the CMB suggestsannual recharge in the range of 09ndash21 of the total annualprecipitation This is consistent with the observation of highevaporation rates estimated for the entire basin and suggeststhat much more water may have been lost to transpirationHowever this much of groundwater recharge suggests highfortunes in terms of commercial groundwater resourcesdevelopment in the area if a significant proportion of it isavailable for abstractionThewide range in the estimated dataand the high standard deviation suggests significant spatialvariation in groundwater recharge rates in the study areaThis may be related to the nature of the unsaturated zonematerial and its variability in the space of the domain ofthis study The average rate of about 55 is significant andcompares favorably estimates in other parts of the terrain Forinstance Attandoh et al [11] estimated groundwater rechargein the range of 03ndash41 of total annual precipitation in thearea through model calibration in the same terrain Earlierestimates of Yidana [27] in the south of theVoltaian suggestedsimilar rates through model calibration

Ordinary kriging was employed to predict the spatialpattern of variation in groundwater recharge in the studyarea Figure 4 presents the variogram that was fitted tothe original estimated groundwater recharge rates from theCMB methodology A spherical variogram was adjudgedappropriate for the distribution and was accordingly chosenfor the estimation stage of ordinary kriging This ensuredthat the prediction is as accurate as possible The resultingpredicted surface for the spatial variation in recharge inthe domain is presented in Figure 5 A significant spatialpattern of variability in groundwater recharge is suggested inFigure 5

There is an apparently high variability in direct ground-water recharge from precipitation in the area and muchof the Voltaian basin This observation is consistent withthe nature of the material in the unsaturated zone whichvaries in space in terms of the clay content Where the claycontent is considerably high vertical percolation of rainwateris much reduced leading to reduced vertical recharge Infil-trating rainwater experiencing such restricted vertical flowtherefore undergoes significant evaporation such that a highpercentage is lost to the atmosphere Yidana [26] suggeststhat on the basis of the analyses of stable isotope data ofprecipitation rainwater and groundwater from parts of theentire basin evaporation of infiltrating rainwater is in therange of 198 and 706 of the total annual precipitationin the basin This is quite consistent with the observedlow humidities and high annual temperatures and explainswhy surface impoundments have not been successful assustainable sources of irrigation water in the region

The estimated groundwater recharge distribution appearsto be consistent with configuration of the groundwater flowpattern suggested by the groundwater table map (Figure 6)and the surface topographical map (Figure 7) of the areaThehighest recharge areas (Figure 5) are generally in the easternparts of the area which coincide with the local recharge areassuggested by the potentiometric map (Figure 5)

Sem

ivar

ianc

e

Distance005 010 015 020

0004

0003

0002

0001

Figure 4 Semivariogram for estimated groundwater recharge in thestudy area

91

92

93

94

95

96

97

98

99

0010020030040050060070080090101101201301401501601701801902021022023024Wawani

Nanton

Pong Tamale

(m)

minus09 minus08 minus07Longitude (deg)

Latit

ude (

deg)

006

006

006

011

011

016

Figure 5 Spatial distribution of estimated groundwater recharge inSavelugu and surrounding subcatchments of the White Volta Basin

Some of the areas of low recharge in the north andsouth of the study area (Figure 5) also coincide with locationsof the lowest hydraulic head (Figure 6) and suggests thatthe groundwater recharge rates from the CMB methodol-ogy accurately accounts for the observed groundwater flowgeometry in the area Groundwater recharge estimates fromthe CMB methodology is largely accurate when applied inarid to semiarid areas where local surface runoff is negligible[28] Yidana and Koffie [29] applied the same methodologyto similar aquifers in the north of the area and suggestedgroundwater recharge in the range of 18 and 32 of thetotal annual rainfall in the area These variable recharge ratespredicted in their study are consistent with the nature of thematerial in the unsaturated zone as suggested by some welllogs in the area

Estimating one of the key hydrogeological parameters isbased on a proper understanding of estimates of other uncer-tain parameters in the terrain in hydrogeological modelingIn the study of Attandoh et al [11] the key parameters ofaquifer hydraulic conductivity and recharge were estimated


115

115

115

140

91

92

93

94

95

96

97

98

99

9095100105110115120125130135140145150155160

(m)

Local discharge areas

Local recharge areas

Pong Tamale

Nanton

Wawani


Latit

ude (

deg)

Figure 6 Potentiometric map of the study area showing localrecharge and discharge areas

through model calibration Previous researchers [24 30]criticized the estimation of key parameters of groundwaterflow in this pattern contending that a wide range of valuescould produce the same level of calibration leading to thelack of uniqueness in such estimates The range of estimatesobtained from the current study provides a wider range andprobably accounts for the marked variability in the natureof the material in the unsaturated zone which regulatesgroundwater recharge In addition as suggested in the studyof Attandoh et al [11] much of the recharge was computedthrough the general head boundary In effect when all thecomponents of recharge estimated from the model are puttogether the range is compatible with those computed withthe CMB methodology in this study This suggests that inspite of the criticisms of nonuniqueness in parameter esti-mates through model calibration the methodology providesquite reliable estimates if carefully executed

5 Conclusion

Results of this study suggest that the chloride mass balance(CMB) approach performs well in a tropical setting inproviding fairly accurate estimates of groundwater rechargefor groundwater resources evaluation Estimates in this studycompare well with estimates from numerical model calibra-tion and analyses of evaporation rates of infiltrating rainwaterEstimated groundwater recharge from the CMB indicatesthat 09 to over 21 of annual precipitation recharges theshallow aquifer system in the areaThismuch of groundwaterrecharge suggests high fortunes in terms of commercialgroundwater resources development in the area The studyalso indicates that the source of groundwater recharge inthe terrain is recent meteoric water which may have beenisotopically enriched in the heavier isotopes of the elementsof the water molecule during the process of recharge It issuggested in this study that whenever the CMBmethodology

125

125

125

150

minus09 minus08 minus07

91

92

93

94

95

96

97

98

99

100105110115120125130135140145150155160165170175

Wawani

Pong Tamale

Nanton (m)

Longitude (deg)

Latit

ude (

deg)

Figure 7 Local topographical map of the study area

must be used in groundwater recharge estimation othertracers must be used to check the validity of the results asindicated in this study

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] C-S Ting T Kerh and C-J Liao ldquoEstimation of groundwaterrecharge using the chloride mass-balance method PingtungPlain TaiwanrdquoHydrogeology Journal vol 6 no 2 pp 282ndash2921998

[2] D N Lerner A S Issar and I SimmersGroundwater RechargeA Guide to understanding and Estimating Natural RechargeUNESCO International Hydrogeological Program Interna-tional Association of Hydrogeologists Hannover Germany

[3] W C Fetter Applied Hydrogeology Prentice Hall Upper SaddleRiver NJ USA 4th edition 2000

[4] R W Healy and P G Cook ldquoUsing groundwater levels toestimate rechargerdquo Hydrogeology Journal vol 10 no 1 pp 91ndash109 2002

[5] A Horst J Mahlknecht B J Merkel R Aravena and YR Ramos-Arroyo ldquoEvaluation of the recharge processes andimpacts of irrigation on groundwater using CFCs and radio-genic isotopes in the Silao-Romita basinMexicordquoHydrogeologyJournal vol 16 no 8 pp 1601ndash1614 2008

[6] L Dassi ldquoUse of chloride mass balance and tritium data forestimation of groundwater recharge and renewal rate in anunconfined aquifer from North Africa a case study fromTunisiardquo Environmental Earth Sciences vol 60 no 4 pp 861ndash871 2010

[7] AM Subyani ldquoUse of chloride-mass balance and environmen-tal isotopes for evaluation of groundwater recharge in the allu-vial aquiferWadiTharadwestern SaudiArabiardquoEnvironmentalGeology vol 46 no 6-7 pp 741ndash749 2004


[8] A S Bazuhair and W W Wood ldquoChloride mass-balancemethod for estimating ground water recharge in arid areasexamples fromwestern Saudi Arabiardquo Journal of Hydrology vol186 no 1-4 pp 153ndash159 1996

[9] S W West and W L Broadhurst ldquoSummary appraisals ofNationrsquos ground-water resourcesmdashRio Grande regionrdquo USGe-ological Survey Professional Paper 813 D

[10] WWWood andW E Sanford ldquoChemical and isotopicmethodfor quantifying groundmdashwater recharge in a regional semiaridenvironmentrdquo Ground Water vol 33 no 3 pp 456ndash486 1995

[11] N Attandoh S M Yidana A Abdul-Samed P A SakyiB Banoeng-Yakubo and P Nude ldquoConceptualization of thehydrogeological system of some sedimentary aquifers inSavelugu-Nanton and surrounding areas Northern GhanardquoHydrological Processes vol 27 pp 1664ndash1676 2013

[12] F A Armah D O Yawson G T Yengoh J Odoi and E KA Afrifa ldquoImpact of floods on livehoods and vulnerability ofnatural resource dependent communities in Northern GhanardquoWater vol 2 no 2 pp 120ndash139 2010

[13] K Dickson and G Benneh A New Geography of Ghana Long-mans Group Limited London UK 5th edition 2004

[14] S Y Acheampong and J W Hess ldquoOrigin of the shallowgroundwater system in the southern Voltaian SedimentaryBasin ofGhana an isotopic approachrdquo Journal of Hydrology vol233 no 1-4 pp 37ndash53 2000

[15] G O Kesse The Mineral and Rock Resources of Ghana A ABalkema Rotterdam The Netherlands 1985

[16] S Dapaah-Siakwan and P Gyau-Boakye ldquoHydrogeologicframework and borehole yields in Ghanardquo Hydrogeology Jour-nal vol 8 no 4 pp 405ndash416 2000

[17] N R Junner and H Service ldquoGeological notes on Volta RiverDistrict and Togoland under British mandaterdquo Annual Reporton the Geological Survey by the Director 1935

[18] N R Junner and T HirstThe Geology and Hydrogeology of theVolta Basin vol 8 of Memoir Gold Coast Geological SurveyThe Gold Coast Australia 1946

[19] S M Yidana D Ophori and B Banoeng-Yakubo ldquoHydro-geological and hydrochemical characterization of the VoltaianBasin the Afram Plains area Ghanardquo Environmental Geologyvol 53 no 6 pp 1213ndash1223 2008

[20] B Banoeng-Yakubo S Yidana J Ajayi Y Loh and D AsieduldquoHydrogeology and groundwater resources of ghana a reviewof the hydrogeological zonation inGhanardquo in PotableWater andSanitation J M McMann Ed Nova Science 2010

[21] S Y Achcampong and J W Hess ldquoHydrogeologic and hydro-chemical framework of the shallow groundwater system in thesouthern Voltaian Sedimentary Basin Ghanardquo HydrogeologyJournal vol 6 no 4 pp 527ndash537 1998

[22] E H Isaaks and R M Srivastava Applied Geostatistics OxfordUniversity Press Oxford UK 1989

[23] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702ndash1703 1961

[24] L F Konikow and J D Bredehoeft ldquoGround-water modelscannot be validatedrdquo Advances in Water Resources vol 15 no1 pp 75ndash83 1992


[26] S M Yidana ldquoStable isotope characteristics of groundwater inthe voltaian basin an evaluation of the role ofmeteoric recharge

in the basinrdquo Journal of Hydrogeology ampHydrologic Engineeringvol 2 no 2 pp 1ndash10 2013

[27] S M Yidana ldquoGroundwater flow modeling and particle track-ing for chemical transport in the southern Voltaian aquifersrdquoEnvironment Earth Science vol 63 pp 709ndash721 2013

[28] N L Nyagwambo Groundwater recharge estimation and waterresources assessment in a tropical crystalline basement aquifer[PhD dissertation] UNESCO-IHE Institute for Water Educa-tion Delft The Netherlands 2006

[29] S Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks an application of natural environmental tracersrdquo Hydro-logical Processes vol 28 no 7 pp 3104ndash3117 2013

[30] C R Jackson ldquoHillslope infiltration and lateral downslope un-saturated flowrdquo Water Resources Research vol 28 no 9 pp2533ndash2539 1992

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Advances in


MineralogyInternational Journal of


MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Geological ResearchJournal of


Geology Advances in


the spatial variability in the specific yield field can lead tosignificant departures of recharge estimates from the realityon the ground The method is often used in places whereinitial estimates are required formuchmore detailed regionalhydrogeological studies Several tracer techniques have beenproposed in the literature and they range from the applicationof isotope techniques to the use of natural hydrochemicalconservative tracers such as the chloride ion [2] The use oftracers to explain groundwater recharge and flow processesis copiously documented in the literature [5] The chloridemass balance (CMB) technique is based on the assumptionthat the chloride ion behaves conservatively and is noteasily affected by reactions through the unsaturated zonethrough to the saturated zone If this assumption is validthen it follows that the ion can adequately trace groundwaterrecharge processes and can thus provide reasonable estimatesof groundwater recharge in the area Its reliability thereforehinges on the compatibility of the precipitation events thatrecharged the system under study and recent precipitationIt is also assumed that the main source of chloride ingroundwater is precipitation Therefore where it can bedetermined that a substantial proportion of the groundwaterchloride is generated frommineral dissolution processes themethod can lead to underestimation of recharge On theother hand where the groundwater chloride is negativelyaffected by a process which reduces its content compared tothat of precipitation groundwater recharge can potentiallybe underestimated The CMB methodology has been widelytested and regarded as one of the most reliable techniques forestimating groundwater recharge in regional hydrogeologicalstudies and basin wide groundwater resources assessments(eg [5ndash10])

The current study evaluates the performance of theCMBmethodology in a typical tropical climatic environmentwhere the availability of groundwater resources is critical tosocioeconomic conditions of populations and the survivalof ecosystems that depend on such groundwater resourcesfor sustenance Groundwater recharge estimates from theCMB method in this study are checked against estimatesof evaporation rates of percolating rainwater as estimatedfrom isotope techniques The spatial pattern of variation inthe resulting recharge estimates is then predicted using aspatial prediction method for the resource to be evaluatedThe novelty lies in the fact that the CMB method althoughnot new is rigorously evaluated using another conservativetracer

2 The Study Area

The study area (Figure 1) is in the Northern Region of Ghanaand covers a total land area of about 17907 Km2 and itfalls within the White Volta Basin The agricultural sectoris the largest employer in the area employing about 97of the active populations [11] Most of the farmers dependon rain for food production and the typical crops growninclude yammaize rice groundnut cowpea and soya beansUnfortunately agricultural activities are constrained by unre-liable rainfall inadequate irrigation facilities and difficulty

in loan accessibility and lack of storage or processing unitsleading to postharvest losses [12] The area is generally flatwith gently undulating reliefs There are no high mountainsin the area except few hilly features observed in the southernpart with elevations generally ranging between 122 and 244mabove sea level however the north is low lying The areais mainly drained by the White Volta and its tributariesIt falls within the Sudan Savannah zone with an annualrainfall between 900 and 1200mm distributed on averageover 74 rainy days [13] The study area falls under theIntertropical Convergent Zone the interface where two airmasses tropical continental and tropical maritime overlapThe frontal activity and relative movement of the two airmasses control the amount and duration of rainfall Rainfallwhich is generally of short duration and high intensity andis often preceded by thunderstorms and line squalls startsintermittently between March and April through August toSeptember when it turns stable and very heavy The dryseasons are pronounced with temperature ranging between18 and 42∘C with mean value of approximately 30∘C [14]Relative humidity during wetrainy season is in the range40 and 70 and drops to about 15 during the rest of theyear [13]The observed lowhumidities and high temperatureshave led to high potential and actual evapotranspiration ratesin the basin

The area is underlain by consolidated Neoprotero-zoic sedimentary sequences of the Voltaian Super-Group(Figure 2) The rocks are mainly of the Middle Voltaian(Figure 3) which is the most extensive sedimentary for-mation in Ghana The Middle Voltaian comprises the Otiand the Obosum beds which are well consolidated andgenerally flat lying The beds are made up of interbeddedmudstonessiltstones sandstones arkoses and conglomer-ates [15] Details of geology and hydrogeology are docu-mented in detailed reports and articles on the basin [14 16ndash21] The rocks are largely impervious so that the occurrenceof groundwater is associated with the development of sec-ondary porosity through jointing shearing and fracturingand weathering Rock compaction and slight metamorphismis believed to have destroyed the primary porosity [16]leading to considerably reduced inherent primary permeabil-ities However where intense weathering occurs the rocksserve as better aquifers with significantly enhanced hydraulicand storage properties The nature aperture and degreeof interconnection between joints determine the hydroge-ological fortunes of the rocks [14 17ndash19] Drilling projectsand hydrological investigations reveal that shallow potentialaquifers capable of delivering water of sustainable quantitiesfor domestic and industrial use exist in the basin [20]

Peasant rain-fed agriculture is themain source of employ-ment in the basin However recent erratic patterns of rainfallin the area coupled with rising populations in the basinhave led to increased interests in developing the irrigationpotentials in the area This has heightened interests inassessing the potentials of developing the aquifers in the areafor commercial abstraction to support irrigation activities toenhance food security and reduce poverty since agriculture isthe mainstay of the communities there


10∘ 20998400 0

998400998400N

10∘ 0

998400 0998400998400

N9∘ 10998400 0

998400998400N

10∘ 20998400 0

998400998400N

10∘ 0

998400 0998400998400

N9∘ 10998400 0

998400998400N

0∘09984000998400998400W0∘209984000998400998400W

0∘09984000998400998400W0∘209984000998400998400W

EW

N

S

Location map

Study area








1∘10998400W 1∘0998400W 0∘50998400W 0∘40998400W 0∘30998400W

1∘10998400W 1∘0998400W 0∘50998400W 0∘40998400W 0∘30998400W

10∘ 0

998400 N9∘ 50998400 N

9∘ 40998400 N

9∘ 30998400 N

10∘ 0

998400 N9∘ 50998400 N

9∘ 40998400 N

9∘ 30998400 N

0 10 20 40 60 80

(km)

Sugu-Tampia

Ying

Ligba


Settlement

N


minus100

minus80

minus60

minus40

minus20

0

20

40

60




Surface water


R2 = 08875

12057518O

1205752H

Rainwater

R2 = 0899

12057518O = minus45 1205752H = minus255

y = 53003x minus 22512

y = 51898x minus 16042

y = 74784x + 55345





Recharge =119862119901

119862gw119875 (1)




119885 (119909) =

119899

sum

119894=1

120582119894119885 (119909119894) (2)









12057518O = (

(18O 16O)

sample

(18O 16O)

119881-SMOW

) times 1000

1205752H = (

(2H 1H)

sample

(2H 1H)

119881-SMOW

) times 1000

(3)



1205752H = 812057518O + 119889 (4)










Sem

ivar

ianc

e

Distance005 010 015 020

0004

0003

0002

0001


91

92

93

94

95

96

97

98

99

0010020030040050060070080090101101201301401501601701801902021022023024Wawani

Nanton

Pong Tamale

(m)


Latit

ude (

deg)

006

006

006

011

011

016





115

115

115

140

91

92

93

94

95

96

97

98

99

9095100105110115120125130135140145150155160

(m)



Pong Tamale

Nanton

Wawani


Latit

ude (

deg)



5 Conclusion


125

125

125

150


91

92

93

94

95

96

97

98

99

100105110115120125130135140145150155160165170175

Wawani

Pong Tamale

Nanton (m)

Longitude (deg)

Latit

ude (

deg)





References










































Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in


10∘ 20998400 0

998400998400N

10∘ 0

998400 0998400998400

N9∘ 10998400 0

998400998400N

10∘ 20998400 0

998400998400N

10∘ 0

998400 0998400998400

N9∘ 10998400 0

998400998400N

0∘09984000998400998400W0∘209984000998400998400W

0∘09984000998400998400W0∘209984000998400998400W

EW

N

S

Location map

Study area








1∘10998400W 1∘0998400W 0∘50998400W 0∘40998400W 0∘30998400W

1∘10998400W 1∘0998400W 0∘50998400W 0∘40998400W 0∘30998400W

10∘ 0

998400 N9∘ 50998400 N

9∘ 40998400 N

9∘ 30998400 N

10∘ 0

998400 N9∘ 50998400 N

9∘ 40998400 N

9∘ 30998400 N

0 10 20 40 60 80

(km)

Sugu-Tampia

Ying

Ligba


Settlement

N


minus100

minus80

minus60

minus40

minus20

0

20

40

60




Surface water


R2 = 08875

12057518O

1205752H

Rainwater

R2 = 0899

12057518O = minus45 1205752H = minus255

y = 53003x minus 22512

y = 51898x minus 16042

y = 74784x + 55345





Recharge =119862119901

119862gw119875 (1)




119885 (119909) =

119899

sum

119894=1

120582119894119885 (119909119894) (2)









12057518O = (

(18O 16O)

sample

(18O 16O)

119881-SMOW

) times 1000

1205752H = (

(2H 1H)

sample

(2H 1H)

119881-SMOW

) times 1000

(3)



1205752H = 812057518O + 119889 (4)










Sem

ivar

ianc

e

Distance005 010 015 020

0004

0003

0002

0001


91

92

93

94

95

96

97

98

99

0010020030040050060070080090101101201301401501601701801902021022023024Wawani

Nanton

Pong Tamale

(m)


Latit

ude (

deg)

006

006

006

011

011

016





115

115

115

140

91

92

93

94

95

96

97

98

99

9095100105110115120125130135140145150155160

(m)



Pong Tamale

Nanton

Wawani


Latit

ude (

deg)



5 Conclusion


125

125

125

150


91

92

93

94

95

96

97

98

99

100105110115120125130135140145150155160165170175

Wawani

Pong Tamale

Nanton (m)

Longitude (deg)

Latit

ude (

deg)





References










































Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in


1∘10998400W 1∘0998400W 0∘50998400W 0∘40998400W 0∘30998400W

1∘10998400W 1∘0998400W 0∘50998400W 0∘40998400W 0∘30998400W

10∘ 0

998400 N9∘ 50998400 N

9∘ 40998400 N

9∘ 30998400 N

10∘ 0

998400 N9∘ 50998400 N

9∘ 40998400 N

9∘ 30998400 N

0 10 20 40 60 80

(km)

Sugu-Tampia

Ying

Ligba


Settlement

N


minus100

minus80

minus60

minus40

minus20

0

20

40

60




Surface water


R2 = 08875

12057518O

1205752H

Rainwater

R2 = 0899

12057518O = minus45 1205752H = minus255

y = 53003x minus 22512

y = 51898x minus 16042

y = 74784x + 55345





Recharge =119862119901

119862gw119875 (1)




119885 (119909) =

119899

sum

119894=1

120582119894119885 (119909119894) (2)









12057518O = (

(18O 16O)

sample

(18O 16O)

119881-SMOW

) times 1000

1205752H = (

(2H 1H)

sample

(2H 1H)

119881-SMOW

) times 1000

(3)



1205752H = 812057518O + 119889 (4)










Sem

ivar

ianc

e

Distance005 010 015 020

0004

0003

0002

0001


91

92

93

94

95

96

97

98

99

0010020030040050060070080090101101201301401501601701801902021022023024Wawani

Nanton

Pong Tamale

(m)


Latit

ude (

deg)

006

006

006

011

011

016





115

115

115

140

91

92

93

94

95

96

97

98

99

9095100105110115120125130135140145150155160

(m)



Pong Tamale

Nanton

Wawani


Latit

ude (

deg)



5 Conclusion


125

125

125

150


91

92

93

94

95

96

97

98

99

100105110115120125130135140145150155160165170175

Wawani

Pong Tamale

Nanton (m)

Longitude (deg)

Latit

ude (

deg)





References










































Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in




12057518O = (

(18O 16O)

sample

(18O 16O)

119881-SMOW

) times 1000

1205752H = (

(2H 1H)

sample

(2H 1H)

119881-SMOW

) times 1000

(3)



1205752H = 812057518O + 119889 (4)










Sem

ivar

ianc

e

Distance005 010 015 020

0004

0003

0002

0001


91

92

93

94

95

96

97

98

99

0010020030040050060070080090101101201301401501601701801902021022023024Wawani

Nanton

Pong Tamale

(m)


Latit

ude (

deg)

006

006

006

011

011

016





115

115

115

140

91

92

93

94

95

96

97

98

99

9095100105110115120125130135140145150155160

(m)



Pong Tamale

Nanton

Wawani


Latit

ude (

deg)



5 Conclusion


125

125

125

150


91

92

93

94

95

96

97

98

99

100105110115120125130135140145150155160165170175

Wawani

Pong Tamale

Nanton (m)

Longitude (deg)

Latit

ude (

deg)





References










































Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in







Sem

ivar

ianc

e

Distance005 010 015 020

0004

0003

0002

0001


91

92

93

94

95

96

97

98

99

0010020030040050060070080090101101201301401501601701801902021022023024Wawani

Nanton

Pong Tamale

(m)


Latit

ude (

deg)

006

006

006

011

011

016





115

115

115

140

91

92

93

94

95

96

97

98

99

9095100105110115120125130135140145150155160

(m)



Pong Tamale

Nanton

Wawani


Latit

ude (

deg)



5 Conclusion


125

125

125

150


91

92

93

94

95

96

97

98

99

100105110115120125130135140145150155160165170175

Wawani

Pong Tamale

Nanton (m)

Longitude (deg)

Latit

ude (

deg)





References










































Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in


115

115

115

140

91

92

93

94

95

96

97

98

99

9095100105110115120125130135140145150155160

(m)



Pong Tamale

Nanton

Wawani


Latit

ude (

deg)



5 Conclusion


125

125

125

150


91

92

93

94

95

96

97

98

99

100105110115120125130135140145150155160165170175

Wawani

Pong Tamale

Nanton (m)

Longitude (deg)

Latit

ude (

deg)





References










































Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in



































Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in

research article evaluation of groundwater recharge...

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