Water Table Fluctuation Method Research Articles

New system for the assessment of annual groundwater recharge from rainfall in the United Arab Emirates

In this study, the first groundwater recharge map for United Arab Emirates (UAE) was developed using the recharge potential and water table fluctuation methods. Recharge potential estimates were made using information about infiltration rate, soil type, ground slope, geological and hydrogeological factors, and the availability of rainfall harvesting infrastructure and were validated by measurements of water table rise in alluvial aquifers in wadis. Based on this information, the total recharge in the UAE is estimated to be about 133 million cubic meters per year (MCM/year). Annual recharge rates are calculated to vary between 1 and 28% of precipitation in the different regions of UAE depending on several natural and manmade parameters including, among others, recharge enhancing infrastructure. Estimates from the two methods are 98% in agreement; which suggests that the recharge potential method is suitable for estimating aquifer’s recharge in UAE and arid regions. The water table fluctuation method was found to be more suitable for assessing recharge through gravel plains and wadis in mountainous areas.

Estimating groundwater recharge uncertainty from joint application of an aquifer test and the water-table fluctuation method

Specific yield and groundwater recharge of unconfined aquifers are both essential parameters for groundwater modeling and sustainable groundwater development, yet the collection of reliable estimates of these parameters remains challenging. Here, a joint approach combining an aquifer test with application of the water-table fluctuation (WTF) method is presented to estimate these parameters and quantify their uncertainty. The approach requires two wells: an observation well instrumented with a pressure probe for long-term monitoring and a pumping well, located in the vicinity, for the aquifer test. The derivative of observed drawdown levels highlights the necessity to represent delayed drainage from the unsaturated zone when interpreting the aquifer test results. Groundwater recharge is estimated with an event-based WTF method in order to minimize the transient effects of flow dynamics in the unsaturated zone. The uncertainty on groundwater recharge is obtained by the propagation of the uncertainties on specific yield (Bayesian inference) and groundwater recession dynamics (regression analysis) through the WTF equation. A major portion of the uncertainty on groundwater recharge originates from the uncertainty on the specific yield. The approach was applied to a site in Bordeaux (France). Groundwater recharge was estimated to be 335 mm with an associated uncertainty of 86.6 mm at 2σ. By the use of cost-effective instrumentation and parsimonious methods of interpretation, the replication of such a joint approach should be encouraged to provide reliable estimates of specific yield and groundwater recharge over a region of interest. This is necessary to reduce the predictive uncertainty of groundwater management models.

Métodos WTF e simulação numérica de fluxo para estimativa de recarga – exemplo Aquífero Rio Claro em Paulínia/SP

A estimativa do volume de recarga dos aquíferos é fundamental para o gerenciamento de recursos hídricos de subsuperfície. Parte da área de ocorrência do aquífero Rio Claro no munícipio de Paulínia/SP é marcada pela presença de hidrocarbonetos na fase residual e influência de poços de bombeamento dos sistemas de remediação em operação, além de incertezas associadas a heterogeneidades geológicas peculiares a essa unidade hidrogeológica. Esses fatores dificultam estimativas seguras de recarga. Para contornar o problema, foram realizadas simulações numéricas de fluxo, em regime transiente, utilizando dados de monitoramento levantados ao longo de 7 anos, para estimar a recarga do Aquífero Rio Claro nessa área. As variações de carga hidráulica da simulação são similares às variações do nível d’água em todos os poços monitorados, indicando que o modelo foi satisfatoriamente calibrado. A comparação entre as estimativas de recarga pelo método Water Table Fluctuation e os valores obtidos pelos modelos matemáticos revelam elevada discrepância entre ambos. Tal discrepância está associada à diferença nos valores do parâmetro Sy (produtividade específica) empregados nos diferentes métodos. Os valores de Sy podem promover taxas de recarga do aquífero superestimadas por não contemplar o efeito da histerese durante a flutuação do nível d’água.

복합 지하수위 변동법과 지하수 모델링에 의한 지하수 함양률 비교 분석: 여주시 강천유역을 중심으로

지하수 함양률은 지역 지하수계에서 지속가능한 산출량을 산정하기 위한 중요한 인자 중 하나이다. 본 연구에서는 경기도 여주시 강천유역을 대상으로 지하수 모델링과 복합 지하수위 변동법을 적용하여 지하수 함양률을 산정하고, 두 방법을 서로 비교·검토하였다. 지하수 모델링에 의한 강천유역(104.77 ㎢)의 지하수 함양률은 연평균 강수량의 18.13%로 산정되었다. 30년 평균 유효 강수량과 지하수위 자료 그리고 토양층의 입도분석 자료를 이용한 복합 지하수위 변동법에 의하면, 평균 지하수 함양률은 17.81%로 나타났다. 지하수 모델링에 의한 지하수 함양률은 연구지역 전체를 대표하지만 국지적인 지하수 함양률을 대변하지 못한다. 한편, 복합 지하수위 변동법으로 연구지역내 5개 지하수 관측공에서 산정한 지하수 함양률은 국지적인 지점을 대표할 수는 있으나, 연구지역 전체를 대표할 수 없다. 아울러서, 복합 지하수위 변동법은 강수에 따라 지하수 함양이 민감하게 일어나는 충적층 지역에 더 잘 적용되며, 지하수 함양률이 낮은 기반암이나 저 투수 지층에는 적용하는 것이 적절치 않다고 보인다.

A Modified Water-Table Fluctuation Method to Characterize Regional Groundwater Discharge

A modified Water-Table Fluctuation (WTF) method is developed to quantitatively characterize the regional groundwater discharge patterns in stressed aquifers caused by intensive agricultural pumping. Two new parameters are defined to express the secondary information in the observed data. One is infiltration efficiency and the other is discharge modulus (recurring head loss due to aquifer discharge). An optimization procedure is involved to estimate these parameters, based on continuous groundwater head measurements and precipitation records. Using the defined parameters and precipitation time series, water level changes are calculated for individual wells with fidelity. The estimated parameters are then used to further address the characterization of infiltration and to better quantify the discharge at the regional scale. The advantage of this method is that it considers recharge and discharge simultaneously, whereas the general WTF methods mostly focus on recharge. In the case study, the infiltration efficiency reveals that the infiltration is regionally controlled by the intrinsic characteristics of the aquifer, and locally distorted by engineered hydraulic structures that alter surface water-groundwater interactions. The seasonality of groundwater discharge is characterized by the monthly discharge modulus. These results from individual wells are clustered into groups that are consistent with the local land use pattern and cropping structures.

Avaliação de multiabordagem da distribuição espacial do rendimento específico: aplicação no aquífero da planície do Crau, França

Spatially distributed values of the specific yield, a fundamental parameter for transient groundwater mass balance calculations, were obtained by means of three independent methods for the Crau plain, France. In contrast to its traditional use to assess recharge based on a given specific yield, the water-table fluctuation (WTF) method, applied using major recharging events, gave a first set of reference values. Then, large infiltration processes recorded by monitored boreholes and caused by major precipitation events were interpreted in terms of specific yield by means of a one-dimensional vertical numerical model solving Richards’ equations within the unsaturated zone. Finally, two gravity field campaigns, at low and high piezometric levels, were carried out to assess the groundwater mass variation and thus alternative specific yield values. The range obtained by the WTF method for this aquifer made of alluvial detrital material was 2.9– 26%, in line with the scarce data available so far. The average spatial value of specific yield by the WTF method (9.1%) is consistent with the aquifer scale value from the hydro-gravimetric approach. In this investigation, an estimate of the hitherto unknown spatial distribution of the specific yield over the Crau plain was obtained using the most reliable method (the WTF method). A groundwater mass balance calculation over the domain using this distribution yielded similar results to an independent quantification based on a stable isotope-mixing model. This agreement reinforces the relevance of such estimates, which can be used to build a more accurate transient hydrogeological model.

Recharge estimation from discrete water-table datasets in a coastal shallow aquifer in a humid subtropical climate

A time-series approach to the estimation of recharge rate in unconfined aquifers of highly variable water level is proposed. The approach, which is based on the water-table fluctuation method (WTF), utilizes discrete water-level measurements. Other similar techniques require continuous measurements, which makes them impossible to apply in cases where no data from automatic loggers are available. The procedure is deployed at the Ressacada Farm site, southern Brazil, on a coastal shallow aquifer located in a humid subtropical climate where diurnal water-level variations of up to 1 m can follow a precipitation event. The effect of tidal fluctuations on the groundwater levels is analyzed using a harmonic component builder, while a time-variable drainage term is evaluated through an independent analysis and included in the assessment. The estimated recharge values are compared with those obtained from the continuous measurements showing a good agreement with the approaches for discrete dataset intervals of up to 15 days. Subsequently, the estimated recharge rates are incorporated into a transient groundwater-flow model and the water levels are compared showing a good match. Henceforth, the approach extends the applicability of WTF to noncontinuous water-level datasets in groundwater recharge studies.

Drip irrigation enhances shallow groundwater contribution to crop water consumption in an arid area

AbstractShallow groundwater plays a key role in agro‐hydrological processes of arid areas. Groundwater often supplies a necessary part of the water requirement of crops and surrounding native vegetation, such as groundwater‐dependent ecosystems. However, the impact of water‐saving irrigation on cropland water balance, such as the contribution of shallow groundwater to field evapotranspiration, requires further investigation. Increased understanding of quantitative evaluation of field‐scale water productivity under different irrigation methods aids policy and decision‐making. In this study, high‐resolution water table depth and soil water content in field maize were monitored under conditions of flood irrigation (FI) and drip irrigation (DI), respectively. Groundwater evapotranspiration (ETg) was estimated by the combination of the water table fluctuation method and an empirical groundwater–soil–atmosphere continuum model. The results indicate that daily ETg at different growth stages varies under the two irrigation methods. Between two consecutive irrigation events of the FI site, daily ETg rate increases from zero to greater than that of the DI site. Maize under DI steadily consumes more groundwater than FI, accounting for 16.4% and 14.5% of ETa, respectively. Overall, FI recharges groundwater, whereas DI extracts water from shallow groundwater. The yield under DI increases compared with that under FI, with less ETa (526 mm) compared with FI (578 mm), and irrigation water productivity improves from 3.51 kg m−3 (FI) to 4.58 kg m−3 (DI) through reducing deep drainage and soil evaporation by DI. These results highlight the critical role of irrigation method and groundwater on crop water consumption and productivity. This study provides important information to aid the development of agricultural irrigation schemes in arid areas with shallow groundwater.

Groundwater Storage Change Estimation Using Combination of Hydrogeophysical and Groundwater Table Fluctuation Methods in Hard Rock Aquifers

This study aims to estimate the groundwater storage change of hard rock aquifers in the face of change. For this, the approach developed consisted initially in the implementation of 5 Magnetic Resonance Soundings (MRS) around the observation wells realized and monitored from 2014 to 2015 in the Sanon experimental site. In a second step, we determined the storage change using the MRS data and the water table fluctuation method. The MRS data show that the water content varies spatially from 4.5 to 1.3%. The maximum value is recorded at the central valley where a piezometric dome is observed. The specific yield varies from 2.4% in the central valley to 1.3% at the outlet. The renewed water resource is estimated at 116 mm in the central valley and 32 mm at the outlet, which corresponds respectively to 13 and 3% of the annual rainfall. The renewed water resource is consistent with the annual recharge. Thus, the combination of the MRS geophysical approach and water table fluctuation method is an efficient, fast and cheaper (compared with long-term pumping test) tool for the estimation of groundwater storage changes.

Irrigation return flows in a mediterranean aquifer inferred from combined chloride and stable isotopes mass balances

The supply of irrigation water often overcomes crop evapotranspiration, and the resulting return flow may infiltrate and significantly contribute to an aquifer water budget. Despite its crucial importance for water resource management, the proportion of irrigation water that contributes to groundwater recharge, namely the return flow coefficient, often remains difficult to assess. Here, a chloride mass balance is combined with an isotopic mixing model (δ18O and δD) to quantify return flow coefficients, in the Crau alluvial-type aquifer (Southern France), characterized by a long-term traditional practice of flood irrigation. Local groundwater compositions are interpreted in terms of average recharge along different flow paths. The high isotopic contrast between irrigation water and regional precipitation allows the partitioning of recharge between rainfall infiltration and irrigation return flows. Isotopic mixing proportions are then used to decipher the chloride concentration of groundwater purely recharged by return flow. This allows an original application of the chloride mass balance approach to estimate return flow coefficients, which doesn't rely on any atmospheric chloride survey. Values around 0.53 ± 0.16 were found for well defined stream lines averaging the functioning of the upstream aquifer, which leads to a return flow rate of 1190 ± 140 mm yr−1. These results are consistent with a local daily time series of recharge fluxes derived from the water-table fluctuation method over the 2003-2009 period, and in line with the spatial average previously quantified over the whole aquifer. This study confirms the ability of geochemical tracers to provide recharge rates fully independent from flux measurements. They can be further used to assess the irrigation efficiency in other similar systems, or to monitor the variations of irrigation return flow, which will result from the future modifications of land use, irrigation practices and climate.

Groundwater storage changes and estimation of stream lateral seepage to groundwater in desert riparian forest region

Abstract Field experiments were conducted in the lower reaches of the Heihe River basin in the northwest of China to determine relationships between stream and groundwater and to quantify stream lateral seepage. The water table fluctuation, water balance and statistical analysis methods were used to analyze long-term experimental data. Results showed that the groundwater depth along the experimental section responded strongly to the streamflow of the East River in the basin. The streamflow of the East River in all periods significantly influenced the amplitude of groundwater depth within the range of 300 m from the riverbank; the stream lateral seepage was mainly controlled by the streamflow and its durations. The evapotranspiration of riparian forest had used larger proportions of groundwater storage in summer, close to approximating 60%. This study quantified stream lateral seepage to groundwater for different water conveyance and provides support for regional water resources management in an arid inland river basin.

Comparison of groundwater recharge estimation techniques in an alluvial aquifer system with an intermittent/ephemeral stream (Queensland, Australia)

This study demonstrates the importance of the conceptual hydrogeological model for the estimation of groundwater recharge rates in an alluvial system interconnected with an ephemeral or intermittent stream in south-east Queensland, Australia. The losing/gaining condition of these streams is typically subject to temporal and spatial variability, and knowledge of these hydrological processes is critical for the interpretation of recharge estimates. Recharge rate estimates of 76–182 mm/year were determined using the water budget method. The water budget method provides useful broad approximations of recharge and discharge fluxes. The chloride mass balance (CMB) method and the tritium method were used on 17 and 13 sites respectively, yielding recharge rates of 1–43 mm/year (CMB) and 4–553 mm/year (tritium method). However, the conceptual hydrogeological model confirms that the results from the CMB method at some sites are not applicable in this setting because of overland flow and channel leakage. The tritium method was appropriate here and could be applied to other alluvial systems, provided that channel leakage and diffuse infiltration of rainfall can be accurately estimated. The water-table fluctuation (WTF) method was also applied to data from 16 bores; recharge estimates ranged from 0 to 721 mm/year. The WTF method was not suitable where bank storage processes occurred.

Estimativa de recarga do sistema aquífero guarani por meio da aplicação do método da variação da superfície livre na bacia do Rio Ibicuí-RS

A estimativa da recarga subterrânea é determinante para a gestão sustentável das águas subterrâneas. A recarga pode ser estimada usando diferentes métodos que variam de acordo com as características da área estudada, as escalas temporais e espaciais adotadas e a disponibilidade de dados. O objetivo é estimar a recarga de unidades hidroestratigráficas pertencentes ao Sistema Aquífero Guarani (SAG), localizado na bacia do rio Ibicuí, com base na aplicação do método Variação dos Níveis d'Água (VNA). Os dados de nível d'água foram obtidos a partir de cinco poços de monitoramento pertencentes à rede RIMAS (Rede Integrada de Monitoramento de Águas Subterrâneas) da CPRM/Serviço Geológico do Brasil, instalados na bacia. O método foi aplicado para a média mensal dos níveis de água em cada poço de monitoramento, em períodos que variaram entre 24 e 39 meses. A recarga mensal foi estimada entre 417 mm e 730,7 mm, e as porcentagens de recarga em relação à precipitação variaram entre 11% e 18%, com média de 13,82%. Na região noroeste da bacia foram encontrados valores mais altos em contraposição à região sul. O método apresentou resultados compatíveis com outros estudos realizados na mesma região.

Alluvial groundwater recharge estimation in semi-arid environment using remotely sensed data

Data limitations on groundwater (GW) recharge over large areas are still a challenge for efficient water resource management, especially in semi-arid regions. Thus, this study seeks to integrate hydrological cycle variables from satellite imagery to estimate the spatial distribution of GW recharge in the Ipanema river basin (IRB), which is located in the State of Pernambuco in Northeast Brazil. Remote sensing data, including monthly maps (2011–2012) of rainfall, runoff and evapotranspiration, are used as input for the water balance method within Geographic Information Systems (GIS). Rainfall data are derived from the TRMM Multi-satellite Precipitation Analysis (TMPA) Version 7 (3B43V7) product and present the same monthly average temporal distributions from 15 rain gauges that are distributed over the study area (r=0.93 and MAE=12.7mm), with annual average estimates of 894.3 (2011) and 300.7mm (2012). The runoff from the Natural Resources Conservation Service (NRCS) method, which is based on regional soil information and Thematic Mapper (TM) sensor image, represents 29% of the TMPA rainfall that was observed across two years of study. Actual evapotranspiration data, which were provided by the SEBAL application of MODIS images, present annual averages of 1213 (2011) and 1067 (2012)mm. The water balance results reveal a large inter-annual difference in the IRB GW recharge, which is characterized by different rainfall regimes, with averages of 30.4 (2011) and 4.7 (2012)mmyear−1. These recharges were mainly observed between January and July in regions with alluvial sediments and highly permeable soils. The GW recharge approach with remote sensing is compared to the WTF (Water Table Fluctuation) method, which is used in an area of alluvium in the IRB. The estimates from these two methods exhibit reliable annual agreement, with average values of 154.6 (WTF) and 124.6 (water balance) mm in 2011. These values correspond to 14.89 and 13.53% of the rainfall that was recorded at the rain gauges and the TMPA, respectively. Only the WTF method indicates a very low recharge of 15.9mm for the second year. The values in this paper provide reliable insight regarding the use of remotely sensed data to evaluate the rates of alluvial GW recharge in regions where the potential runoff cannot be disregarded from WB equation and must be calculated spatially.

Quantification of peatland water storage capacity using the water table fluctuation method

AbstractPeat specific yield (SY) is an important parameter involved in many peatland hydrological functions such as flood attenuation, baseflow contribution to rivers, and maintaining groundwater levels in surficial aquifers. However, general knowledge on peatland water storage capacity is still very limited, due in part to the technical difficulties related to in situ measurements. The objectives of this study were to quantify vertical SY variations of water tables in peatlands using the water table fluctuation (WTF) method and to better understand the factors controlling peatland water storage capacity. The method was tested in five ombrotrophic peatlands located in the St. Lawrence Lowlands (southern Québec, Canada). In each peatland, water table wells were installed at three locations (up‐gradient, mid‐gradient, and down‐gradient). Near each well, a 1‐m long peat core (8 cm × 8 cm) was sampled, and subsamples were used to determine SY with standard gravitational drainage method. A larger peat sample (25 cm × 60 cm × 40 cm) was also collected in one peatland to estimate SY using a laboratory drainage method. In all sites, the mean water table depth ranged from 9 to 49 cm below the peat surface, with annual fluctuations varying between 15 and 29 cm for all locations. The WTF method produced similar results to the gravitational drainage experiments, with values ranging between 0.13 and 0.99 for the WTF method and between 0.01 and 0.95 for the gravitational drainage experiments. SY was found to rapidly decrease with depth within 20 cm, independently of the within‐site location and the mean annual water table depth. Dominant factors explaining SY variations were identified using analysis of variance. The most important factor was peatland site, followed by peat depth and seasonality. Variations in storage capacity considering site and seasonality followed regional effective growing degree days and evapotranspiration patterns. This work provides new data on spatial variations of peatland water storage capacity using an easily implemented method that requires only water table measurements and precipitation data.

Balanço hídrico e modelagem computacional visando estimar recarga subterrânea

As águas subterrâneas são a principal fonte hídrica em diversos países e regiões na América do Sul e Brasil. Entretanto, os volumes extraídos desses mananciais já ultrapassam a capacidade de reposição, resultando na diminuição dos níveis dos aquíferos. Assim, a garantia de disponibilidade futura depende do correto gerenciamento desses recursos hídricos. Para isso, é necessário conhecer as taxas de recarga e o fluxo subterrâneo que ocorrem nos aquíferos. Neste trabalho, avalia-se a recarga subterrânea para diferentes usos agrícolas com base no balanço hídrico da zona não saturada do solo. A avaliação foi feita, primeiramente, por meio da comparação com estimativas obtidas pelo método da Flutuação da Superfície Livre (WTF - Water Table Fluctuation). Em seguida, as taxas computadas foram usadas como entradas num modelo transiente de fluxo com intuito de verificar sua consistência por meio da comparação com dados de níveis medidos em campo. Os resultados indicam que o método aplicado apresentou desempenho satisfatório e, apesar de limitações inerentes, evidenciam a vantagem de sua utilização em relação a outras técnicas por requerer dados de maior facilidade de obtenção.

Assessing the recharge of a coastal aquifer using physical observations, tritium, groundwater chemistry and modelling

Assessing recharge is critical to understanding groundwater and preventing pollution. Here, we investigate recharge in an Australian coastal aquifer using a combination of physical, modelling and geochemical techniques. We assess whether recharge may occur through a pervasive layer of floodplain muds that was initially hypothesized to be impermeable. At least 59% of the precipitation volume could be accounted for in the shallow aquifer using the water table fluctuation method during four significant recharge events. Precipitation events <20mm did not produce detectable aquifer recharge. The highest recharge rates were estimated in the area underneath the floodplain clay layer rather than in the sandy area. A steady-state chloride method implied recharge rates of at least 200mm/year (>14% of annual precipitation). Tritium dating revealed long term net vertical recharge rates ranging from 27 to 114mm/year (average 58mm/year) which were interpreted as minimum net long term recharge. Borehole experiments revealed more permeable conditions and heterogeneous infiltration rates when the floodplain soils were dry. Wet conditions apparently expand floodplain clays, closing macropores and cracks that act as conduits for groundwater recharge. Modelled groundwater flow paths were consistent with tritium dating and provided independent evidence that the clay layer does not prevent local recharge. Overall, all lines of evidence demonstrated that the coastal floodplain muds do not prevent the infiltration of rainwater into the underlying sand aquifer, and that local recharge across the muds was widespread. Therefore, assuming fine-grained floodplain soils prevent recharge and protect underlying aquifers from pollution may not be reasonable.

Groundwater uptake of forest and agricultural land covers in regions of recharge and discharge

Groundwater uptake of vegetation in discharge regions is known to play an important role, e.g., in the Hungarian Great Plain. Nevertheless, only little detailed monitoring of water table fluctuations and groundwater uptake (ETgw) were reported under varying hydrologic conditions and vegetation cover. In this study, results of water table monitoring under forest plantations and adjacent corn plots in discharge and recharge regions were analyzed to gain better understanding of the relation of vegetation cover to groundwater uptake. A poplar (Populus tremula) plantation and adjacent corn field plot were surveyed in a local discharge area, while a black locust (Robinia pseudoacacia) plantation and adjacent corn field plot were analyzed in a recharge area. The water table under the poplar plantation displayed a night-time recovery in the discharge region, indicating significant groundwater supply. In this case an empirical version of the water table fluctuation method was used for calculating the ETgw that included the groundwater supply. The mean ETgw of the poplar plantation was 3.6 mm day-1, whereas no water table fluctuation was observed at the nearby corn plot. Naturally, the root system of the poplar was able to tap the groundwater in depths of 3.0-3.3 m while the shallower roots of the corn did not reach the groundwater reservoir in depths of 2.7-2.8 m. In the recharge zone the water table under the black locust plantation showed step-like changes referring to the lack of groundwater supply. The mean ETgw was 0.7 mm day-1 (groundwater depths of 3.0-3.2 m) and similarly no ETgw was detected at the adjacent corn plot with groundwater depths between 3.2 and 3.4 m. The low ETgw of the young black locust plantation was due to the lack of groundwater supply in recharge area, but also the shallow root system might have played a role. Our results suggest that considerations should be given to local estimations of ETgw from water table measurements that could assist to better understanding of groundwater use of varying vegetation types in recharge and discharge zones.

Estimating aquifer properties and distributed groundwater recharge in a hard-rock catchment of Udaipur, India

The present study determined aquifer parameters in hard-rock aquifer system of Ahar River catchment, Udaipur, India by conducting 19 pumping tests in large-diameter wells. Spreadsheet programs were developed for analyzing pumping test data, and their accuracy was evaluated by root mean square error (RMSE) and correlation coefficient (R). Histograms and Shapiro–Wilk test indicated non-normality (p value <0.01) of pre- and post-monsoon groundwater levels at 50 sites for years 2006–2008, and hence, logarithmic transformations were done. Furthermore, recharge was estimated using GIS-based water table fluctuation method. The groundwater levels were found to be influenced by the topography, presence of structural hills, density of pumping wells, and seasonal recharge. The results of the pumping tests revealed that the transmissivity (T) ranges from 68–2239 m2/day, and the specific yield (Sy) varies from 0.211 to 0.51 × 10−5. The T and Sy values were found reasonable for the hard-rock formations in the area, and the spreadsheet programs were found reliable (RMSE ~0.017–0.339 m; R > 0.95). Distribution of the aquifer parameters and recharge indicated that the northern portion with high ground elevations (575–700 m MSL), and high Sy (0.08–0.25) and T (>600 m2/day) values may act as recharge zone. The T and Sy values revealed significant spatial variability, which suggests strong heterogeneity of the hard-rock aquifer system. Overall, the findings of this study are useful to formulate appropriate strategies for managing water resources in the area. Also, the developed spreadsheet programs may be used to analyze the pumping test data of large-diameter wells in other hard-rock regions of the world.

English

The shapes and forms of piezometric hydrographs arising from the recharging and discharging of unconfined aquifers offer a hydrological tool for the classifications of inland valley bottoms in Ghana for crop production. A two-year measured water table fluctuations at Besease wetlands were plotted on a reference scale of time in months on the x-axis and hydraulic head on the y-axis. The water table fluctuation method was used to evaluate the seasonal and annual variations in the water level rise and to estimate the groundwater recharge. The monthly slopes segment of the water table fluctuations were used as a base for the classification of the heads. Results from the study showed that the estimated recharge for the study area ranged from 133 to 467 mm for the fourteen (14) piezometers, representing 9 to 31% of 2009 annual rainfall and 47.6 to 427.9 mm in 2010 representing 4 to 34% of the annual rainfall. The Results also showed that most of the piezometers had their monthly slopes dominated by the acute segment followed by the obtuse segment, flat segment and right-angled segment in that order. It can be inferred that most of the piezometric areas dominated by acute forms become relatively dry during the dry season; however, these areas may still have some water to support crops. The hydrograph representation of the monthly slopes were employed to classify the studied Inland Valley Bottoms into three hydrological regimes as a management tool for developing wetlands for crop production. The regimes were Water table fluctuation (WTF) Class I - acute slopes segment varying from 0 to 30%, WTF Class II - acute slopes segment varying from 30 to 45% &nbsp;and WTF Class III - acute slope segment &gt; 45%. It is concluded that a controlled water table offers a distinguishing criterion for the development of Inland Valley Bottoms for year round crop production in Ghana. &nbsp; Key words: Water table fluctuation, hydrological regimes, inland valley bottoms, slope segments, crop production.