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1.
Effectively estimating groundwater recharge is critical to manage water resources, especially in arid and semi-arid regions as impacted by intensive human activities and climate changes. Rare insights have been gained into groundwater recharge since direct observation is hard to carry out. Although several methods are currently available to estimate groundwater recharge, the estimated results may cover noticeable bias. The behaviours of different methods based on different conceptual frameworks and exhibiting different levels of complexity should be examined to estimate actual groundwater recharge. This study aims to assess the performance of four common methods to estimate groundwater recharge. For this end, large-scale lysimeters equipped with soil water content sensors and water table sensors were set up at a research site established in Guanzhong Basin of China. The data achieved by 1-year observation were employed to compare four estimation methods. As revealed from the results, the following findings are drawn. (a) Groundwater level fluctuation (GLF) method is simple, whereas its accuracy is determined by specific yield, and adopting a water balance method to estimate specific yield can considerably enhance the accuracy of GLF. (b) The calibrated numerical model can obtain the optimal result compared with the other methods, whereas long-term observation data are required for parameter calibration. (c) In the water balance method, the maximum entropy production (MEP) model and a practical method (estimating evaporation between two rainfall events) were used to calculate evaporation. As indicated by the results, water balance method combined with MEP is capable of obtaining more reliable results of groundwater recharge compared with the practical method. (d) With an analytical model based on linearized Richards' equation, accurate results can be achieved. What is more, the analytical model only needs the measurement of soil moisture near the surface. The limitation of this method is that it is difficult to determine the maximal water flux. The mentioned findings are of critical implications to the management and sustainable development of groundwater.  相似文献   

2.
A numerical experiment of flow in variably saturated porous media was performed in order to evaluate the spatial and temporal distribution of the groundwater recharge at the phreatic surface for a shallow aquifer as a function of the input rainfall process and soil heterogeneity. The study focused on the groundwater recharge which resulted from the percolation of the excess rainfall for a 90-days period of an actual precipitation record. Groundwater recharge was defined as the water flux across the moving phreatic surface. The observed spatial non-uniformity of the groundwater recharge was caused by soil heterogeneity and is particularly pronounced during the stage of recharge peak (substantial percolation stage). During that stage the recharge is associated with preferential flow paths defined as soil zones of locally higher hydraulic conductivity. For the periods of low percolation intensity the groundwater recharge was exhibiting more uniform spatial characteristics. The temporal distribution of the recharge was found to be a function of the frequency and intensity of the rainfall events. Application of sampling design demonstrates the joint influence of the spatial and temporal recharge variability on the cost-effective monitoring of groundwater potentiometric surfaces.  相似文献   

3.
Groundwater recharge and mounding of water‐table is a complex phenomenon involving time‐ and space‐dependent hydrologic processes. The effect of long‐term groundwater mounding in the aquifer depends on soil, aquifer geometry and the area contributing to recharge. In this paper, a GIS‐based spatio‐temporal algorithm has been developed for the groundwater mound dynamics to estimate the potential rise in the water‐table and groundwater volume balance residual in an unconfined aquifer. The recharge and mound dynamics as predicted using the methodology recommended here were compared with those using the Hantush equation, and the differences were quite significant. The significance of the study is to assess the effectiveness of the basin in terms of its hydrologic and hydraulic properties for sustainable management of groundwater recharge. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

4.
Groundwater catchment boundaries and their associated groundwater catchment areas are typically assumed to be fixed on a seasonal basis. We investigated whether this was true for a highly permeable carbonate aquifer in England, the Berkshire and Marlborough Downs Chalk aquifer, using both borehole hydrograph data and a physics‐based distributed regional groundwater model. Borehole hydrograph data time series were used to construct a monthly interpolated water table surface, from which was then derived a monthly groundwater catchment boundary. Results from field data showed that the mean annual variation in groundwater catchment area was about 20% of the mean groundwater catchment area, but interannual variation can be very large, with the largest estimated catchment size being approximately 80% greater than the smallest. The flow in the river was also dependent on the groundwater catchment area. Model results corroborated those based on field data. These findings have significant implications for issues such as definition of source protection zones, recharge estimates based on water balance calculations and integrated conceptual modelling of surface water and groundwater systems. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

5.
The anomalous entrance of water into groundwater systems can affect storage throughout long periods and normally relies on infrequent and irregular pulses of groundwater recharge defined by the term episodic recharge. Recently there was a groundwater recharge of large magnitude with unknown circumstances in the Caiuá aquifer. This unique event was explored in detail here and allowed to better understand the occurrence of such events in humid subtropical climates in South America. For this study, groundwater monitoring daily data from the Integrated Groundwater Monitoring Network was used combined with a specific yield obtained from geophysical wireline logging to obtain groundwater recharge rates. To improve the investigation, we also used a baseflow separation method to obtain the groundwater contribution into local rivers. The groundwater storage variations were also assessed by remote sensing with the GRACE data. Results showed the importance of high soil moisture storage on the occurrence of large episodic recharge events. We estimated that the groundwater recharger volumes derived from 1 year that included the unique episodic recharge observed (total of 866 mm for April 2015–March 2016) were comparable with the sum of 7 years of groundwater recharge (total of 867 mm). Atypical rainfall in winter periods were responsible for the increase in soil moisture that explained that unique event. GRACE-based GWS showed concordance detecting the occurrence of the unique episodic recharge. However, the variation in terms of volumes obtained by GRACE does not represent the behaviour observed in the aquifer by the WTF method. The results also indicated that changes in aquifer storage caused by episodic recharge events directly affect low flows in rivers over long periods. The main knowledge gap addressed here relates to exploring a unique episodic recharge event quite rare to observe with its long-term impacts on hydroclimatic variability over a humid subtropical portion of the Caiuá aquifer.  相似文献   

6.
《水文科学杂志》2013,58(5):961-973
Abstract

A study was carried out to investigate the use of the chloride profile method in conjunction with the water balance method to estimate the annual groundwater recharge in both natural and irrigation sites in Luanjing Irrigation Area, Inner Mongolia. Groundwater recharge from precipitation, estimated by the chloride profile method, is less than 0.1 mm year?1 which accounts for just 0.06% of the long-term average annual rainfall, indicating that rainfall presently plays a minor role in the groundwater recharge. It appears that recharge events only occurred after heavy rain or sustained rainfall events. In the cropped area, the chloride profile method indicated that the average annual recharge is 268 mm year?1 with an infiltration rate of 32.5%, which is reasonably consistent with the 33.1% obtained by the water balance method in 2007. The study shows that about one third of that water is discharged back to the groundwater.  相似文献   

7.
Groundwater recharge and discharge in the Akesu alluvial plain were estimated using a water balance method. The Akesu alluvial plain (4842 km2) is an oasis located in the hyperarid Tarim River basin of central Asia. The land along the Akesu River has a long history of agricultural development and the irrigation area is highly dependent on water withdrawals from the river. We present a water balance methodology to describe (a) surface water and groundwater interaction and (b) groundwater interaction between irrigated and non‐irrigated areas. Groundwater is recharged from the irrigation system and discharged in the non‐irrigated area. Uncultivated vegetation and wetlands are supplied from groundwater in the hyperarid environment. Results show that about 90% of groundwater recharge came from canal loss and field infiltration. The groundwater flow from irrigated to non‐irrigated areas was about 70% of non‐irrigated area recharge and acted as subsurface drainage for the irrigation area. This desalinated the irrigation area and supplied water to the non‐irrigated area. Salt moved to the non‐irrigation area following subsurface drainage. We conclude that the flooding of the Akesu River is a supplemental groundwater replenishment mechanism: the river desalinates the alluvial plain by recharging fresh water in summer and draining saline regeneration water in winter. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

8.
Groundwater supplies a significant proportion of water use in the United States and is critical to the maintenance of healthy ecosystems and environmental processes, thus characterizing aquifer hydrology is important to managing and preserving these resources. While groundwater isotopes provide insight into hydrologic and ecologic processes, their application is limited to where measurements exist. To help overcome this limitation, we used the random forest algorithm to develop a predictive model for shallow groundwater isotopes in the conterminous United States. Our model uses environmental variables (e.g. temperature, elevation, precipitation isotopes) as predictors. We used our model to develop the first shallow groundwater isoscape of δ2H and δ18O for the conterminous United States. We describe the patterns in groundwater isotopes using both observations and our modelled isoscape. We find that throughout much of the Eastern United States, groundwater isotopes are close to annual amount weighted precipitation, while groundwater isotopes are significantly depleted relative precipitation across much of the High Plains and Western United States. Furthermore, we compare the observations compiled for this study to isotopes of precipitation, which allows us to determine the relative recharge efficiency (i.e. ratio of groundwater recharge to precipitation) between seasons and the proportion of annual recharge that occurs in a given season. Our findings suggest that winter recharge is generally more efficient than summer recharge; however, the dominant recharge season is more varied as it is the product of both seasonal recharge efficiency and the seasonal timing of precipitation. Parts of the central United States have summer dominant recharge, which is likely the result of heavy summer precipitation/nocturnal summer precipitation. Interestingly, parts of coastal California appear to have summer dominant recharge, which we suggest could be due to recharge from fog-drip. Our results summarize spatial patterns in groundwater isotopes across the conterminous United States, provide insight into the hydrologic processes affecting shallow groundwater, and are valuable information for future ecologic and hydrologic studies.  相似文献   

9.
The bomb tritium (3H) distribution patterns in the aquifer beneath an abandoned landfill at the Canadian Forces Base (CFB) Borden, Ontario, and in a sandy aquifer at Whiteshell Nuclear Research Establishments (WNRE) Pinawa, Manitoba, all in Canada, were delineated in great detail. A sampling and monitoring network of multilevel samplers and bundle piezometers were used. The directions of groundwater flow were established, and the boundary between the tritiated and non-tritiated zones of the two aquifers were closely demarcated. Using a cumulative mass balance method, the3H input mass into the aquifers was compared with the3H mass in groundwater storage to estimate the percentages of annual groundwater recharge from 1953 to 1978. Two recharge calculations for theeffective recharge zone and thetotal recharge area of the aquifers as established from the flownet analysis, and the distributions of dissolved geochemical constitutents showed that theeffective recharge zone calculations gave higher values of 30.6 cm/yr for CFB Borden and 20.1 cm/yr for WNRE while thetotal recharge areas gave lower values of 19.1 and 10.1 cm/yr for the Borden and WNRE aquifers respectively. The two recharge values provide possible minimum and maximum recharge estimates for the two study areas.  相似文献   

10.
The soil and water assessment tool (SWAT) has been widely used and thoroughly tested in many places in the world. The application of the SWAT model has pointed out that 2 of the major weaknesses of SWAT are related to the nonspatial reference of the hydrologic response unit concept and to the simplified groundwater concept, which contribute to its low performance in baseflow simulation and its inability to simulate regional groundwater flow. This study modified the groundwater module of SWAT to overcome the above limitations. The modified groundwater module has 2 aquifers. The local aquifer, which is the shallow aquifer in the original SWAT, represents a local groundwater flow system. The regional aquifer, which replaces the deep aquifer of the original SWAT, represents intermediate and regional groundwater flow systems. Groundwater recharge is partitioned into local and regional aquifer recharges. The regional aquifer is represented by a multicell aquifer (MCA) model. The regional aquifer is discretized into cells using the Thiessen polygon method, where centres of the cells are locations of groundwater observation wells. Groundwater flow between cells is modelled using Darcy's law. Return flow from cell to stream is conceptualized using a non‐linear storage–discharge relationship. The SWAT model with the modified aquifer module, the so‐called SWAT‐MCA, was tested in 2 basins (Wipperau and Neetze) with porous aquifers in a lowland area in Lower Saxony, Germany. Results from the Wipperau basin show that the SWAT‐MCA model is able (a) to simulate baseflow in a lowland area (where baseflow is a dominant source of streamflow) better than the original model and (b) to simulate regional groundwater flow, shown by the simulated groundwater levels in cells, quite well.  相似文献   

11.
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12.
ABSTRACT

Groundwater is an important resource in semi-arid Chile to meet local social, economic and environmental water demands. Historical ground water level (GWL) data (1986–2014) in the Coquimbo Region were analysed to characterize short and long-term alluvial aquifer dynamics. Long-term trends were assessed using a seasonal Mann-Kendall trend test, which indicated that more than 80% of the time series exhibit a negative trend. Short-term analysis using cross-correlation provided information on recharge origin and its spatial pattern. Runoff and GWL are highly correlated depending on elevation, signifying that stream to aquifer flow is an important recharge process at higher altitudes. Long-term recharge behaviour was characterized using time-frequency wavelet power spectra. The results show significant amplitude of the 5-year recharge period for GWL, which is driven by a 5-year El Niño index periodicity. Such results provide key information of the spatiotemporal functioning of aquifers.  相似文献   

13.
ABSTRACT

Understanding recharge processes is fundamental to improve sustainable groundwater resource management. Shallow groundwater (SGW) is being developed for multiple purposes in Ethiopia without consideration of monitoring. We established a citizen science-based hydro-meteorological monitoring network, with a focus on SGW recharge estimation, in Eshito micro-watershed, Ethiopia. Citizen scientists collected rainfall, groundwater-level and stream water-level data. We characterized the shallow aquifer using pumping tests. The data were used to estimate SGW recharge using three methods: chloride mass balance, water-level fluctuation (WLF) and baseflow separation. Approximately 20% and 35% of annual rainfall amount contributes to recharge based on the chloride mass balance and WLF results, respectively. Baseflow separation showed recharge values for the watershed vary from 38% to 28% of annual rainfall at the upstream and downstream gauging stations, respectively. This study shows that the recharge in previously unmonitored micro-watersheds can be studied if citizens are involved in data generation.  相似文献   

14.
The present study examined groundwater recharge/discharge mechanisms in the regional Central Sudan Rift Basins (CSRB). Aquifers in CSRB constitute poorly sorted silisiclastics of sand, clay and gravels deposited in closed hydrologic systems of the Cretaceous–Pleistocene fluviolacustrine environments. CSRB are bounded to the north by the highlands of the Central African Shear Zone (CAZS) that represents the surface and groundwater divides. Sporadic recharge in the peripheries of the basins along the CASZ occurs subsequent to decadal and centennial storm events. Inflow from the Nile into the aquifers represents an additional source of recharge. Thus, groundwater resources cannot be labelled fossil nor can they be readily recharged. Closed hydrologic troughs located adjacent to the influent Nile system mark areas of main groundwater discharge characterized by lower hydraulic heads. This study has examined mechanisms that derive the discharge of the groundwater in these closed basins and concluded that only evapotranspirative discharge can provide a plausible explanation. Groundwater abstraction is mainly through deep‐rooted trees and effective evaporation. The increase of TDS along the flow indicates local recharge at the peripheries of basins and shows the influence of evaporation and rock/water interaction. The decline in groundwater level along a flow path was calculated using Darcy's law to estimate average recharge and evapotranspirative discharge, which are equal under natural equilibrium and make the only fluxes in CSRB. Steady‐state 2D flow modelling has demonstrated that an average recharge of 4–8 mm yr?1 and evapotranspirative discharge of 1–22 mm yr?1 will maintain natural equilibrium in CSRB. Sporadic storms provide recharge in the highlands to preserve the current hydraulic gradient and maintain aquifer dynamics. Simulated recharge from the Nile totals about 17·5 mm yr?1 and is therefore a significant contributor to the water balance. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

15.
This paper proposes an approach to estimate groundwater recharge using an optimization‐based water‐table fluctuation method combined with a groundwater balance model in an arid hardrock‐alluvium region, located at the Oman–United Arab Emirates border. We introduce an “effective hardrock thickness” term to identify the percentage of the considered hardrock thickness in which effective groundwater flow takes place. The proposed method is based upon a Thiessen polygon zoning approach. The method includes subpolygons to represent specific geologic units and to enhance the confidence of the estimated groundwater recharge. Two linear and 1 nonlinear submodels were developed to evaluate the model components for the calibration (October 1996 to September 2008) and validation (October 2008 to September 2013) periods. Long‐term annual groundwater recharge from rainfall and return flow over the model domain are estimated as 24.62 and 5.71 Mm3, respectively, while the effective groundwater flow circulation is found to occur in the upper 7% of the known hardrock thickness (42 m), confirming conclusions of previous field studies. Considering a total difference in groundwater levels between eastern and western points of the study area of the order of 220 m and a 12‐year monthly calibration period, a weighted root mean squared error in predicted groundwater elevation of 2.75 m is considered quite reasonable for the study area characterized by remarkable geological and hydrogeological diversity. The proposed approach provides an efficient and robust method to estimate groundwater recharge in regions with a complex geological setting in which interaction between fractured and porous media cannot be easily assessed.  相似文献   

16.
Rapid urbanization in the Jakarta area has become a severe subsurface environmental issue as it entails groundwater level decline and land subsidence caused by excessive groundwater pumping. In this study, apparent groundwater age rejuvenation in the deep aquifer under DKI Jakarta was found by comparing 14C activities between 1985 and 2008. We discussed the use of a numerical groundwater flow model to evaluate the rejuvenation process in this urbanized area. When considering the deep aquifer in the DKI Jakarta area, we can assume six direction fluxes toward the aquifer: two vertical fluxes (downward and upward flux) and four horizontal fluxes (northern, southern, western, and eastern flux). Results of model calculations show that the greatest groundwater flux among six flux directions became ‘vertical downward flux’, which means that shallower groundwater intrudes into the deep one because of excessive groundwater pumping from the mid‐1980s. This flux grows about 50% during the 2000s. This result is consistent with the detection of CFC‐12 and SF6, which functions as an indicator of young groundwater even in the deep groundwater. The rejuvenation ratio ‘R’ was determined using 14C activity in the groundwater; R increases with the CFC‐12 concentration and both show good correlation. Furthermore, we estimated the ‘vertical downward flux’ at each well's screen depth using model estimation. Results show that this flux is greater in the urban groundwater depression area and especially at shallower parts of the deep aquifer, and that it affects the magnitude of the shallow groundwater intrusion. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

17.
Stream–aquifer interaction plays a vital role in the water cycle, and a proper study of this interaction is needed for understanding groundwater recharge, contaminants migration, and for managing surface water and groundwater resources. A model‐based investigation of a field experiment in a riparian zone of the Schwarzbach river, a tributary of the Rhine River in Germany, was conducted to understand stream–aquifer interaction under alternative gaining and losing streamflow conditions. An equivalent streambed permeability, estimated by inverting aquifer responses to flood waves, shows that streambed permeability increased during infiltration of stream water to aquifer and decreased during exfiltration. Aquifer permeability realizations generated by multiple‐point geostatistics exhibit a high degree of heterogeneity and anisotropy. A coupled surface water groundwater flow model was developed incorporating the time‐varying streambed permeability and heterogeneous aquifer permeability realizations. The model was able to reproduce varying pressure heads at two observation wells near the stream over a period of 55 days. A Monte Carlo analysis was also carried out to simulate groundwater flow, its age distribution, and the release of a hypothetical wastewater plume into the aquifer from the stream. Results of this uncertainty analysis suggest (a) stream–aquifer exchange flux during the infiltration periods was constrained by aquifer permeability; (b) during exfiltration, this flux was constrained by the reduced streambed permeability; (c) the effect of temporally variable streambed permeability and aquifer heterogeneity were found important to improve the accurate capture of the uncertainty; and (d) probabilistic infiltration paths in the aquifer reveal that such pathways and the associated prediction of the extent of the contaminant plume are highly dependent on aquifer heterogeneity.  相似文献   

18.
Groundwater discharge flux into rivers (riverine groundwater discharge or RGD) is essential information for the conservation and management of aquatic ecosystems and resources. One way to estimate area-integrated groundwater discharge into surface water bodies is to measure the concentration of a groundwater tracer within the water body. We assessed groundwater discharge using 222Rn, a tracer common in many surface water studies, through field measurements, surface water 222Rn mass balance model, and groundwater flow simulation, for the seldom studied but ubiquitous setting of a flooding river corridor. The investigation was conducted at the dam-regulated Lower Colorado River (LCR) in Austin, Texas, USA. We found that 222Rn in both the river water and groundwater in the river bank changed synchronously over a 12-hour flood cycle. A 222Rn mass balance model allowed for estimation of groundwater discharge into a 500-m long reach of the LCR over the flood. The groundwater discharge ranged between negative values (indicating recharge) to 1570 m3/h; groundwater discharge from groundwater flow simulations corroborated these estimates. However, for the dynamic groundwater discharge estimated by the 222Rn box model, assuming whether the groundwater 222Rn endmember was constant or dynamic led to notably different results. The resultant groundwater discharge estimates are also highly sensitive to river 222Rn values. We thus recommend that when using this approach to accurately characterize dynamic groundwater discharge, the 222Rn in near-stream groundwater should be monitored at the same frequency as river 222Rn. If this is not possible, the 222Rn method can still provide reasonable but approximate groundwater discharge given background information on surface water-groundwater exchange time scales.  相似文献   

19.
Artificial recharge of groundwater is an increasingly important method for augmenting groundwater supply and can have a positive or negative influence on the quality of water resources. We instrumented a managed aquifer recharge (MAR) pond in central coastal California to assess how patterns of infiltration and recharge affect the load of nitrate delivered to the underlying aquifer. The concentration of nitrate in infiltrating water consistently decreased during passage through the first metre of subsurface soils. Enrichment of 18O and 15 N in the residual nitrate in infiltrating water proceeded in a ratio of 1:2, indicating that denitrification plays a significant role in the quantitative reduction of nutrients exported during infiltration through shallow soils. The extent and rate of nitrate removal was spatially and temporally variable across the bottom of the recharge pond, with 30% to 60% of the nitrate load being removed over the first 6 weeks of managed aquifer recharge operation. During the period of highest N loading to the system, when the average infiltration rate was > 1 m/day, the recharge pond achieved a load reduction efficiency of 7 kg NO3?‐N/day/ha, which compares favourably to nitrate load reductions achieved by treatment wetlands. Groundwater mounding and water composition below the recharge pond suggest that recharge and subsequent lateral transport occur heterogeneously in the underlying aquifer. Nitrate concentrations in the aquifer following infiltration were lowered primarily by dilution, with little evidence for additional denitrification occurring in the aquifer in comparison to high rates documented during shallow infiltration. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

20.
Groundwater flow modelling of the Kwa Ibo River watershed in Abia State of Nigeria is presented in this paper with the aim of assessing the degree of interaction between the Kwa Ibo River and the groundwater regime of the thick sandy aquifer. The local geology of the area comprises the Quaternary to recent Benin Formation. Potential aquifer zones that were delineated earlier using geoelectrical resistivity soundings and borehole data for the area formed the basis for groundwater flow modelling. The watershed has been modelled with a grid of 65 rows by 43 columns and with two layers. Lateral inflow from the north has been simulated with constant heads at the Government College, Umuahia, and outflow at Usaka Elegu in the south. The Kwa Ibo River traverses the middle of the watershed from north to south. The river‐stage data at Umudike, Amawom, Ntalakwu and Usaka Elegu have been used for assigning surface water levels and riverbed elevations in the model. Permeability distribution was found to vary from 3 to 14·5 m day?1. Natural recharge due to rainfall formed the main input to the aquifer system, and abstraction from wells was the main output. A steady‐state groundwater flow simulation was carried out and calibrated against the May 1980 water levels using 26 observation wells. The model computations have converged after 123 iterations. Under the transient‐state calibration, the highest rainfall (and hence groundwater recharge) over the 10‐year study period was recorded in 1996, whereas the lowest was recorded in 1991. The computed groundwater balance of 55 274 m3 day?1 was comparable to that estimated from field investigations. Results from the modelling show that abstraction is much less than groundwater recharge. Hence there is the possibility for additional groundwater exploitation in the watershed through drilling of boreholes. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

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