Estimation of groundwater recharge in Southern Ghana

Groundwater recharge concepts.- Groundwater recharge concepts.- An unexpected factor affecting recharge from ephemeral river flow in SWA/Namibia.- On the continuity of aquifer systems on the crystalline basement of Burkina Faso.- Groundwater recharge estimation (Part 1): physical/chemical methods.- A review of some of the physical, chemical and isotopic techniques available for estimating groundwater recharge.- Evaporation in arid and semi-arid regions.- Satellite remote sensing and energy balance modeling for water balance assessment in (semi-)arid regions.- A proposed study of recharge processes in fracture aquifers of semi-arid Botswana.- Estimation of natural groundwater recharge under Saudi Arabian arid climatic conditions.- Solute profile techniques for recharge estimation in semi-arid and arid terrain.- Recharge estimation from the depth-distribution of environmental chloride in the unsaturated zone - Western Australian examples.- Natural recharge measurements in the hard rock regions of semi-arid India using tritium injection - a review.- Comparison of recharge estimates from injected tritium technique and regional hydrological modelling in the case of a granitic basin in semi-arid India.- Studies on natural recharge to the groundwater by isotope techniques in arid Western Rajasthan, India.- Groundwater recharge estimation (Part 2): numerical modelling techniques.- Numerical and conceptual models for recharge estimation in arid and semi-arid zones.- Methods for estimation of natural groundwater recharge directly from precipitation - comparative studies in sandy till.- The principles of inverse modelling for estimation of recharge from hydraulic head.- Estimating natural recharge of ground water by moisture accounting and convolution.- Natural ground water recharge estimation methodologies in India.- BALSEQ - a model for the estimation of water balances, including aquifer recharges, requiring scarce hydrologic data.- Applications and case studies.- Quantification of groundwater recharge in arid regions: a practical view for resource development and management.- Groundwater recharge studies in semi-arid Botswana - a review.- Rainfall-runoff-recharge relationships in the basement rocks of Zimbabwe.- Recharge characteristics of aquifers of Jeddah-Makkah Taif region.- Groundwater recharge and subsurface flow in the Comodoro Rivadavia area, Chubut Province, Argentina. Isotopic and hydrochemical study.- Groundwater recharge over Western Saudi Arabia.- Natural recharge of karst aquifers in Western Taurus region (southwestern Turkey).- Estimation of recharge of sand aquifer of the Island of Mannar Sri Lanka.- Groundwater recharge from three cheap and independent methods in the small watersheds of the rainforest belt of Nigeria.- Quantitative estimation of ground-water recharge in dolomite.- Quantitative estimation of ground-water recharge in the Pretoria-Rietondale area.- Analysis of long-duration piezometric records from Burkina Faso used to determine aquifer recharge.- Humid zone recharge: a comparative analysis.- Humid and arid zone groundwater recharge - a comparative analysis.- List of participants.

This study presents an extension of the concept of “quasi‐saturation” to a quasi‐saturated layer, defined as the uppermost dynamic portion of the saturated zone subject to water table fluctuations. Entrapped air here may cause substantial reductions in the hydraulic conductivity (K) and fillable pore water. Air entrapment is caused by a rising water table, usually as a result of groundwater recharge. The most significant effects of entrapped air are recharge overestimation based on methods that use specific yield (S y), such as the water table fluctuation method (WTF), and reductions in K values. These effects impact estimation of fluid flow velocities and contaminant migration rates in groundwater. In order to quantify actual groundwater recharge rates and the effects of entrapped air, numerical simulations with the FEFLOW (Version 7.0) groundwater flow model were carried out using a quasi‐saturated layer for a pilot area in Rio Claro, Brazil. The calculated recharge rate represented 16% of the average precipitation over an 8‐year period, approximately half of estimates using the WTF method. Air entrapment amounted to a fillable porosity of 0.07, significant lower that the value of 0.17 obtained experimentally for S y. Numerical results showed that the entrapped air volume in the quasi‐saturated layer can be very significant (0.58 of the air fraction) and hence can significantly affect estimates of groundwater recharge and groundwater flow rates near the water table.

Groundwater, which is in aquifers below the surface of the Earth, is one of the most important natural resources. Due to the increased population, drought, improper irrigation practices, and pollution, depletion of groundwater takes place more rapidly. With the advent of remote sensing data and Geographical Information Systems (GIS) and integrating SWAT with MODFLOW model, estimation of groundwater recharge became much easier. The HRU’s in the SWAT model are exchanged with MODFLOW cells by using SWAT-MODFLOW interface to simulate the groundwater head distribution and groundwater recharge rates. The study is conducted in Chintalapudi village, which is located in West Godavari district, Andhra Pradesh. To estimate spatiotemporal distribution of groundwater recharge, it requires DEM, LULC map, Soil map, rainfall data, aquifer parameters such as aquifer thickness, hydraulic conductivity, and specific yield. Model results are shown by month and year to determine seasonal and decadal trends in groundwater recharge rates. The SWAT-MODFLOW was calibrated and validated using groundwater levels and streamflow data.

Discrepancy and estimates of groundwater recharge under different land use types on the Loess Plateau

The reliable estimation of groundwater recharge is fundamental to the appropriate use of groundwater resources. Shallow groundwater resource quantification for irrigation in highland regions remains challenging. Specifically, in the humid Ethiopian highlands, only limited research has been done on groundwater recharge estimation. Despite the various techniques used to determine recharge, the objective of this study was to better understand natural groundwater recharge using water table fluctuation (WTF) and empirical methods in the sub-humid Ethiopian highlands. The Ene-Chilala watershed was selected for this study. Precipitation, infiltration rate, and piezometric water levels were measured. Precipitation was measured over a 4-year period (2013–2016), whereas infiltration and the groundwater table were measured over a 1-year period (2014). Recharge rates using WTF were determined from the three slope positions and the median of all piezometers for the whole watershed. Infiltration rates on the upslope were greater compared to the mid- and downslopes. The rainfall intensity exceeded the infiltration rate in all slope positions, so the excess rainfall recharged the perched upslope aquifer and eventually drained as interflow to recharge the mid- and downslopes. The estimated groundwater recharge from WTF was less compared to the average of empirical estimations. Surprisingly, from the nine selected empirical equations, the modified Chaturvedi formula had a similar estimation to the WTF method. In conclusion, it is challenging to find long-term seasonal and spatial groundwater-level data. Long-term groundwater data should, therefore, be available in order to arrive at a reliable recharge estimate and for effective groundwater management practices.

Since groundwater is an integral component of natural hydrologic systems, an estimation of groundwater recharge is required to understand the changes in the temporal water budget and groundwater flow system. The rate of groundwater recharge varies widely in space and time particularly in arid to semiarid regions, and it is rather difficult to measure recharge directly. The aim of this study was to assess the natural groundwater recharge in Al Zerba catchment and the interaction between the surface and groundwater. The catchment is classified as an arid to semiarid climate with an aridity index of 0.25 to 0.3 and long-term average annual precipitation ranging from 300 to 350 mm. Delineation of the catchment boundary was carried out using spatial interpolation of elevation data extracted from the digital elevation model. The effects of vegetation and abstraction from pumping wells on the groundwater table were investigated. Furthermore, groundwater recharge was estimated based on water budget, water table fluctuation analysis by using rainfall infiltration breakthrough, and soil water balance using hydrologic evaluation of landfill performance model (HELP3). The results show that groundwater pumping leads negative impact to long-term decrease in groundwater levels, particularly in the dry season, while no significant effects of vegetation on groundwater were observed. Moreover, the result showed an average annual groundwater recharge ranging from 20 to 35 mm/a (about 10 to 15 % of the precipitation period 2001–2010), concentrated in the north and southwestern regions (outcrops of permeable/coarse-grained limestone and a major fault zone).

Groundwater flow modeling and recharge estimation of heterogeneous aquifer: Applied to Matmata aquifer, southeastern, Tunisia

Groundwater recharge is an important metric for sustainable water management, particularly in semi-arid regions. Hard-rock aquifers underlie two-thirds of India and appropriate techniques for estimating groundwater recharge are needed, but the accuracy of such values is highly uncertain. The chloride mass balance (CMB) method was employed to estimate annual groundwater recharge rates in a monsoon-dependent area of Jaisamand Lake basin in Rajasthan, which contains the Gangeshwar watershed. A monitoring program was established within the watershed during summer 2009, with local participation for the collection of rainfall and groundwater samples. Groundwater recharge was estimated spatially over a 3-year period with pre-monsoon and post-monsoon datasets. Recharge rates estimated using the CMB method were then compared to those estimated using the water-table fluctuation (WTF) method. Specific yield was 0.63 % and assumed to be homogenous across the watershed. The average recharge rate derived from the WTF method (31 mm/year) was higher than that derived from the CMB method (24.3 mm/year). CMB recharge rates were also applied to obtain a water balance for the watershed. CMB recharge rates were used to estimate annual groundwater replenishment and were compared with estimates of groundwater withdrawal using Landsat imagery. Over the 2009–2011 study period, groundwater demand was about seven times greater than the estimated groundwater renewal of 5.6 million cubic meters. This analysis highlights the challenges associated with estimating groundwater recharge in fractured hard-rock aquifers, and how renewable groundwater-resource estimates can be used as a metric to promote sustainable water use.

Contribution of rainfall and agricultural returns to groundwater recharge in arid areas

Recharge estimation in arid and semi-arid areas is very challenging. The chloride mass balance method applied in western
\nSouth Africa fails to provide reliable recharge estimates near coastal areas. A relationship between rainfall events and water
\nlevel fluctuations (WLF) on a monthly basis was proposed in the rainfall infiltration breakthrough (RIB) model for the
\npurpose of groundwater recharge estimation. In this paper, the physical meaning of parameters in the CRD and previous
\nRIB models is clarified, and the RIB model is reviewed with the algorithm improved to accommodate various time scales,
\nnamely, daily, monthly and annual scales. Recharge estimates on a daily and monthly basis using the revised RIB approach
\nin 2 study areas, one in a sandy alluvial aquifer (Riverlands) and the other in the Table Mountain Group (TMG) shallow
\nunconfined aquifer (Oudebosch), are presented, followed by sensitivity analysis. Correlation analysis between rainfall
\nand observed WLF data at daily scale and monthly scale, together with recharge estimates obtained from other methods,
\ndemonstrates that the RIB results using monthly data are more realistic than those for daily data, when using long time
\nseries. Scenarios using the data from Oudebosch with different rainfall and groundwater abstraction inputs are simulated to
\nexplore individual effects on water levels as well as recharge rate estimated on a daily basis. The sensitivity analysis showed
\nthat the recharge rate by the RIB model is specifically sensitive to the parameter of specific yield; therefore, the accurate
\nrepresentative specific yield of the aquifer needs to be selected with caution. The RIB model demonstrated in these two cases
\ncan be used to estimate groundwater recharge with sufficiently long time series of groundwater level and rainfall available in
\nsimilar regions. In summary, the RIB model is best suited for shallow unconfined aquifers with relatively lower transmissiv
\n-
\nity; the utility of the RIB model for application in different climatic areas under different hydrogeological conditions needs
\nto be further explored.

First posted February 14, 2020 For additional information, contact: Director, Upper Midwest Water Science Center U.S. Geological Survey5840 Enterprise Drive Lansing, MI 48911 Subsurface drainage is used to efficiently drain saturated soils to support productive agriculture in poorly drained terrains. Although subsurface drainage alters the water balance for agricultural fields, its effect on groundwater resources and groundwater recharge is poorly understood. In Minnesota, subsurface drainage has begun to increase in southeastern Minnesota, even though this part of the State is underlain by permeable karstic bedrock aquifers with only a thin layer of glacial sediments separating these aquifers from land surface.To gain a better understanding of groundwater recharge effects from subsurface drainage, the U.S. Geological Survey (USGS), in cooperation with the Legislative-Citizen Commission on Minnesota Resources, led a 2-year hydrologic study to investigate this connection for two agricultural fields in southeastern Minnesota with subsurface drainage. A total of three monitoring plots were used between the two agricultural fields: two monitoring plots that included an actively drained area with peripheral, undrained areas, and a third monitoring plot without any subsurface drainage. Multiple piezometer transects were set up across the three monitoring plots to characterize the unsaturated zone and shallow water-table flow using pressure transducers and soil moisture probes. From these piezometers, groundwater recharge rates were derived using two different methods: the RISE Water-Table Fluctuation (WTF) method and the DRAINMOD model. In addition to these two methods, the USGS Soil-Water-Balance (SWB) model was used to estimate potential recharge rates for three different monitoring plots.In addition to deriving groundwater recharge rates, the hydrologic budget was analyzed to interpret the water-table surface elevation and soil volumetric water content time series. At one of the two drained plots, the transects exhibited varying water-table surface elevation patterns. Frequent backflow from the adjacent ditch caused subsurface drainage flow to slow down or stop drainage through the main collector drain and cause pipe pressurization, so the closest transect appeared to be mostly controlled by the drain pressurization, whereas the farthest transect was more efficiently drained. Both of the drained monitoring plots had an elevation gradient parallel to the pattern tiles, sloping downward towards the collector drain that aggregated the parallel lines into a single drain. Because the transects were set at different gradients in the field, some of the water-table surface elevation differences were also attributed to lateral flow towards the lowest parts of the field.Three methods were used to derive potential groundwater recharge rates: the RISE WTF method, the USGS SWB model, and DRAINMOD-derived deep seepage rates. Potential groundwater recharge rates, using the RISE WTF method, across all piezometers were 1.55 and 1.94 inches per year, respectively, for water years 2017 and 2018. More differentiation of potential recharge rates between different piezometer types occurred for water year 2018. Although the difference was slightly more than 1 inch between the drained and nondrained piezometers for water year 2018, this difference was statistically significant based on a t-test with a p-value of 0.036 (α=0.05). When looking at recharge based on distance from the drain, the subsurface drain did not affect potential recharge, although other factors such as variability in screen depths, well construction, and specific yield variability cannot be eliminated. The SWB model was also used to estimate potential recharge rates for water years 2017–18, with rates between 2.44 and 5.92 inches per year for the two drained sites, generally higher than the RISE WTF estimates. DRAINMOD-derived potential recharge rates were generally the highest of the three methods, with potential recharge rates varying from 2.07 to 9.49 inches per year.Overall, there was a lack of agreement between the three methods. These results were not remarkable, considering the fundamental differences in the methodology for each method. However, all methods did show a fundamental difference between piezometers within the drained area and piezometers outside the drained area, including the third undrained monitoring plot. The drained areas show a lower overall potential groundwater recharge compared to the nondrained areas for all three estimates. The difference for the 2018 recharge estimates was slightly higher than 1 inch for the RISE WTF method, the difference was almost double for the nine sites for the DRAINMOD model, and the difference between the drain and undrained plots was even more significant for the SWB model.

Accurate estimates of infiltration and groundwater recharge are critical for many hydrologic, agricultural and environmental applications. Anticipated climate change in many regions of the world, especially in tropical areas, is expected to increase the frequency of high-intensity, short-duration precipitation events, which in turn will affect the groundwater recharge rate. Estimates of recharge are often obtained using monthly or even annually averaged meteorological time series data. In this study we employed the HYDRUS-1D software package to assess the sensitivity of groundwater recharge calculations to using meteorological time series of different temporal resolutions (i.e., hourly, daily, weekly, monthly and yearly averaged precipitation and potential evaporation rates). Calculations were applied to three sites in Brazil having different climatological conditions: a tropical savanna (the Cerrado), a humid subtropical area (the temperate southern part of Brazil), and a very wet tropical area (Amazonia). To simplify our current analysis, we did not consider any land use effects by ignoring root water uptake. Temporal averaging of meteorological data was found to lead to significant bias in predictions of groundwater recharge, with much greater estimated recharge rates in case of very uneven temporal rainfall distributions during the year involving distinct wet and dry seasons. For example, at the Cerrado site, using daily averaged data produced recharge rates of up to 9 times greater than using yearly averaged data. In all cases, an increase in the time of averaging of meteorological data led to lower estimates of groundwater recharge, especially at sites having coarse-textured soils. Our results show that temporal averaging limits the ability of simulations to predict deep penetration of moisture in response to precipitation, so that water remains in the upper part of the vadose zone subject to upward flow and evaporation.

This paper used three methods namely: water-table fluctuation (WTF), soil moisture balance (SMB), and chloride mass balance (CMB) to estimate groundwater recharge in a degraded Kahe catchment located on the southern slope of Mt. Kilimanjaro, Tanzania. Three methods yielded different groundwater recharge rates. Results of the WTF method showed that recharge in the catchment was about 248.4 million m3/year, whereas those of CMB and SMB methods were 156.0 and 132.1 million m3/year, respectively. The estimated recharge rates ranged between 132.1 and 248.4 million m3/year with an average of 191.34 ± 27.80 million m3/year. Differences in the estimated rates can be attributed to the scales of measurements, assumptions in each method, and the quality of the data used. Satellite images taken in between 2000 and 2017 were used to estimate the land-use changes and their impacts on groundwater recharge in the study catchment. Analyzed satellite images showed that over the 17-year period, natural forests and bushes and shrubs decreased by 3.6 and 4.1%, while agricultural land and built-up area increased by 12.8 and 0.8%, respectively. Using SMB method, we found that these land-use changes have contributed to a decrease in groundwater recharge of about 42% between 2000 and 2017 (i.e., from 227.8 to 132.1 million m3/year). The findings from this study are useful for assessing the potential impacts of land-use change on water resources in the catchment.

Estimation of shallow groundwater recharge in central Qinghai-Tibet Plateau by combining unsaturated zone simulation and improved water table fluctuation method

Reliable estimation of groundwater recharge rate is crucial for the assessment of groundwater resource potential in Africa. In this study, we reviewed existing studies on groundwater recharge, especially in the semi-arid and humid regions of Africa. After the assessment of the main advantages and disadvantages of each method, we strongly agree that among the distinct existing methods, Water-Table Fluctuations (WTF), Recession-Curve Displacement, and Chloride Methods can be used with a better certainty of improved estimation of groundwater recharge in these regions. In addition, the features of existing studies on groundwater recharge are outlined. The major challenge of these regions on recharge study is the lack of basic data. Therefore, this paper suggests methods for dealing with this limitation and also the future outlook using recently developed technologies such as Remote Sensing (RS) and Geographical Information System (GIS). Watershed hydrologic modeling, which is a robust method for recharge estimation that is widely applied around the world, should also be applied for future perspective by solving the problems of its use and data requirements to find a better result. Strictly speaking, the key to the successful estimation of groundwater recharge lies in the utilization of a variety of independent methods. Therefore, by bringing together the advantages, limitations, and cost of each method, the study of the recharge estimation in different climatic environments of African regions can enter a new era.