Water resources assessment in the Minqin Basin: an arid inland river basin under intensive irrigation in northwest China

The Minqin Basin is at the lower reach of the Shiyang River of Gansu province in northwest China. Dramatic decline in groundwater level has resulted from over-abstraction of groundwater since the late 1950s to satisfy increasing irrigation and other demands. Severe water shortage led to environmental degradation. To better understand the spatial–temporal variation of groundwater levels and to evaluate the groundwater resources in the region, a three-dimensional regional groundwater flow model was built and calibrated under transient condition. The MODFLOW program was used and the research area was discretized as a square network with cell size of 400 × 400 m. The model showed that the aquifer was under destructive stress, with a groundwater resource deficit of 260 million cubic meters per year (Mm³/year) on average. Since the inflow of surface water from the upstream basin has declined to about 100–150 Mm³/year in recent decades, the irrigation return flow had become the main recharge and accounted for 60.6% of total recharge; meanwhile, abstraction by pumping wells took 99.2% from the total groundwater discharge.     

Groundwater recharge of carbonate aquifers of the Silesian-Cracow Triassic (southern Poland) under human impact

A Triassic carbonate unit has been intensively drained by zinc and lead ore mines and numerous borehole fields since the nineteenth century. Its groundwater recharge has increased due to: pumping of water from boreholes, mining activity, and urbanization. An approach to determine the amounts of the recharge at a variety of spatial scales is presented in the paper. Different methods were used to identify and quantify recharge components on a regional and local scale: mathematical modelling was performed for four aquifers included in an aquifer system, an analytical estimation based on the assumption that an average recharge is equal to the average discharge of the hydrogeological system—for six man-made drainage centres, and the method of water level fluctuation (WLF) was applied in one observation borehole. Results of modelling have been supplemented by observation of environmental tracers (δ¹⁸O, δ²H, ³H), noble gases temperatures, and ⁴He_exc in groundwater. The regional aquifer’s current recharge according to estimations performed by means of modelling varies from 39 to 101 mm/year on average. Depending on the aquifer site the average precipitation ranges from 779 to 864 mm/year. In the confined part of the aquifer average recharge ranges from 26 to 61 mm/year. Within outcrops average recharge varies from 96 to 370 mm/year. Current recharge estimated by the analytical method for man-made drainage centres varies from 158 up to 440 mm/year. High values are caused by different recharge sources like precipitation, induced leakage from shallow aquifers, and water losses from streams, water mains and sewer systems. Pumping of water, mining and municipal activities constitute additional factors accounting for the intensified recharge.     

An assessment of the potential and impacts of winter water banking in the Sokh aquifer, Central Asia

The dynamics of artificial recharge of winter surface flows coupled with increased summer groundwater use for irrigation in the Sokh aquifer (Central Asia) have been investigated. Water release patterns from the giant Toktogul reservoir have changed, as priority is now given to hydropower generation in winter in Kyrgyzstan. Winter flows have increased and summer releases have declined, but the Syr Darya River cannot pass these larger winter flows and the excess is diverted to a natural depression, creating a 40?×?10⁹m³ lake. A water balance study of all 18 aquifers feeding the Fergana Valley indicated the feasibility of winter groundwater recharge in storage created by summer abstraction. This modeling study examines the dynamics of the process in one aquifer over a 5-year period, with four scenarios: the current situation; increased groundwater abstraction of around 625 million (M) m³/year; groundwater abstraction with an artificial recharge of 144 Mm³/year, equivalent to the volume available in low flow years in the Sokh River; and with a larger artificial recharge of 268 Mm³/year, corresponding to high flow availability. Summer surface irrigation diversions can be reduced by up to 350 Mm³ and water table levels can be lowered.     

Modelling the response of an alluvial aquifer to anthropogenic and recharge stresses in the United States Southern Great Plains

This paper uses Visual MODFLOW to simulate potential impacts of anthropogenic pumping and recharge variability on an alluvial aquifer in semi-arid northwestern Oklahoma. Groundwater withdrawal from the aquifer is projected to increase by more than 50% (relative to 1990) by the year 2050. In contrast, climate projections indicate declining regional precipitation over the next several decades, creating a potential problem of demand and supply. The following scenarios were simulated: (1) projected groundwater withdrawal, (2) a severe drought, (3) a prolonged wet period, and (4) a human adjustment scenario, which assumes future improvements in water conservation measures. Results indicate that the combined impacts of anthropogenic pumping and droughts would create drawdown of greater than 12 m in the aquifer. Spatially, however, areas of severe drawdown will be localized around large-capacity well clusters. The worst impacts of both pumping and droughts will be on stream–aquifer interaction. For example, the projected aquifer pumpage would lead to a total streamflow loss of 40%, creating losing stream system regionally. Similarly, a severe drought would lead to a total streamflow loss of >80%. A post-audit of the model was also carried out to evaluate model performance. By simulating various stress scenarios on the alluvial aquifer, this study provides important information for evaluating management options for alluvial aquifers.     

Groundwater exploitation and recharge rate estimation of a quaternary sand aquifer in Dar-es-Salaam area,Tanzania

Dar-es-Salaam City gets water supply from surface water and groundwater. The groundwater is used to supplement surface water supply and has increasingly become a major source of water supply in the city. The study area comprises three major parts: the central coastal plain with quaternary fluvial–deltaic sediments, the deltaic Mio-Pliocene clay-bound sands and gravels in the northwest and southeast and the Lower Miocene fluviatile sandstones of Pugu Hills in the west of the study area. The main objective of this study was to quantify the integrated water balance. The major source of renewable groundwater in the aquifer is rainfall. Hence, the average recharge of 256.2 mm/year (for the year 2006) to the aquifer was estimated using the balance method of Thornthwaite and Mather, which is equal to 99.4 hm³/year for the whole alluvial aquifer. This value was balanced with total groundwater abstraction of 8.59 hm³/year, baseflow to rivers of 75.7 hm³/year and discharge into the sea (15.11 hm³/year).     

Determination of water balance equation components in irrigated agricultural watersheds using SWAT and MODFLOW models : A case study of Samalqan plain in Iran

Increasing water demands,especially in arid and semi-arid regions,continuously exacerbate groundwater as the only reliable water resources in these regions.Samalqan watershed,Iran,is a groundwater-based irrigation watershed,so that increased aquifer extraction,has caused serious groundwater depletion.So that the catchment consists of surface water,the management of these resources is essential in order to increase the groundwater recharge.Due to the existence of rivers,the low thickness of the alluvial sediments,groundwater level fluctuations and high uncertainty in the calculation of hydrodynamic coefficients in the watershed,the SWAT and MODFLOW models were used to assess the impact of irrigation return flow on groundwater recharge and the hydrological components of the basin.For this purpose,the irrigation operation tool in the SWAT model was utilized to determine the fixed amounts and time of irrigation for each HRU(Hydrological Response Unit)on the specified day.Since the study area has pressing challenges related to water deficit and sparsely gauged,therefore,this investigation looks actual for regional scale analysis.Model evaluation criteria,RMSE and NRMSE for the simulated groundwater level were 1.8 m and 1.1%respectively.Also,the simulation of surface water flow at the basin outlet,provided satisfactory prediction(R²=0.92,NSE=0.85).Results showed that,the irrigation has affected the surface and groundwater interactions in the watershed,where agriculture heavily depends on irrigation.Annually 11.64 Mm3 water entered to the aquifer by surface recharge(precipitation,irrigation),transmission loss from river and recharge wells 5.8 Mm3 and ground water boundary flow(annually 20.5 Mm³).Water output in the watershed included ground water extraction and groundwater return flow(annually 46.4 Mm³)and ground water boundary flow(annually 0.68 Mm³).Overally,the groundwater storage has decreased by 9.14 Mm3 annually in Samalqan aquifer.This method can be applied to simulate the effects of surface water fluxes to groundwater recharge and river-aquifer interaction for areas with stressed aquifers where interaction between surface and groundwater cannot be easily assessed.     

Groundwater balance in the Khor Arbaat basin, Red Sea State, eastern Sudan

The Khor Arbaat basin is the main source of potable water supply for the more than 750,000 inhabitants of Port Sudan, eastern Sudan. The variation in hydraulic conductivity and storage capacity is due to the heterogeneity of the sediments, which range from clay and silt to gravely sand and boulders. The water table rises during the summer and winter rainy seasons; it reaches its lowest level in the dry season. The storage capacity of the Khor Arbaat aquifer is estimated to be 21.75?×?10⁶ m³. The annual recharge through the infiltration of flood water is about 1.93?×?10⁶ m³. The groundwater recharge, calculated as underground inflow at the ‘upper gate’, is 1.33?×?10⁵ m³/year. The total annual groundwater recharge is 2.06?×?10⁶ m³. The annual discharge through underground outflow at the ‘lower gate’ (through which groundwater flows onto the coastal plain) is 3.29?×?10⁵ m³/year. Groundwater discharge due to pumping from Khor Arbaat basin is 4.38?×?10⁶ m³/year on average. The total annual groundwater discharge is about 4.7?×?10⁶ m³. A deficit of 2.6?×?10⁶ m³/year is calculated. Although the total annual discharge is twice the estimated annual recharge, additional groundwater flow from the fractured basement probably balances the annual groundwater budget since no decline is observed in the piezometric levels.     

Combined hydrogeological and nitrate modelling to manage water resources of the Middle Soummam Aquifer,Northeast of Algeria

Water management is one of the most challenges in Algeria, a semi-arid Mediterranean country confronted to a serious water stress. The country will have to endure, beyond 2025, a situation of chronic water penury, adding an excessive pollution of the majority of groundwater reservoirs. The management of water resources by combined approach using hydrogeological model and nitrates evolution model was experimented in the Middle Soummam valley. The alluvial aquifer, offering good hydrodynamic and geometrical characteristics, is over-exploited, providing in drinking water Akbou and Tazmalt cities and irrigation perimeters. If exploitation continues at these steady paces, the depletion of the water resource and the hydrochemical imbalance will be inevitable. On the one hand, the results of hydrodynamic model, based on an increase of the water takings and simulated needs from 24.71 Mm³/year in 2015 into 39.69 Mm³/year in 2030, show a critical withdrawal. The aquifer budget expresses the inversion of flow between the wadi and the aquifer where the wadi feeds the groundwater reservoir. This hydrodynamic inversion was attributed to simulated pumping rates which increased and exceeded 100,000 m³/day, but the aquifer was partially relieved by the weight of the exploitation through Tichy Haf dam. The water management strategy adopted in this study was based on management measures promoting zones, which have been delimited between Tazmalt and Akbou, and containing important water quantities available in the axis of the valley. However, according to the depleted in isotopes of ¹⁸O and ²H, which could be explained by the influence of a paleoclimatic effect and suggested that the aquifer recharge would have largely been made under a colder climate, pumped groundwater could be old, and the implementation of new pumping sites has been studied minutely. On the other hand, the hydrogeochemical modelling allowed following nitrates concentrations in order to project their evolution. Four wells on 25 react in face to the imposed conditions in each scenario simulated until 2030, showing inertia of pollution, and confirmed after three series of tests. This inertia would be related to the hydraulic gradients and hydraulic conductivities, aquifer thickness and recharge. The low hydraulic gradients lead to a rather slow flow velocity and thus to an inertia in the dispersion of nitrates, with a mass transport weakened by the hydrodynamic conditions. It is also related to the aquifer thickness; when the aquifer is powerful (65–85 m), the stock of water would be important and allows a dilution process. The reverse is true for the simulated boreholes where the concentrations remain invariant; the aquifer is less powerful (32–37 m). Finally, the recharge effect through the rain was evoked; the aquifer is unconfined, and the rain water and pollution that reached the piezometric level can remain in position in slow hydrodynamic conditions. The methodology was demonstrated through a combination of monitoring and modelling for both water quantity and quality and the importance to use numerical models to support water resources management strategy in the Mediterranean aquifers.     

Groundwater optimization model for sustainable management of the Valley of Puebla aquifer, Mexico

The Valley of Puebla aquifer (VPA), at the central region of Mexico, is subject to intensive exploitation to satisfy the urban and industrial demand in the region. As a result of this increased exploitation, a number of state and federal agencies in charge of water management are concerned about the problems associated with the aquifer (decline of groundwater table, deterioration in water quality, poor well productivity and increased pumping and water treatment costs). This study presents a groundwater management model that combines “MODFLOW” simulation with optimization tools “MODRSP”. This simulation–optimization model for groundwater evaluates a complex range of management options to identify the strategies that best fit the objectives for allocating resources in the VPA. Four hypothetical scenarios were defined to analyze the response of the hydrogeological system for future pumping schemes. Based on the simulation of flow with the MODFLOW program, promising results for the implementation of the optimization of water quantity were found in scenarios 3 and 4. However, upon comparison and analysis of the feasibility of recovery of the piezometric level (considering the policy of gradual reductions of pumping), scenario 4 was selected for optimization purposes. The response functions of scenario 4 were then obtained and optimized, establishing an extraction rate of 204.92 millions of m³/year (Mm³/year). The reduction in groundwater extraction will be possible by substituting the volume removed by 35 wells (that should be discontinued) by the same volume of water from another source.     

Analysis of groundwater mining in two carbonate aquifers in Sierra de Estepa (SE Spain) based on hydrodynamic and hydrochemical data

The carbonate aquifers of Lora and Mingo form part of the hydrogeological unit of Sierra de Estepa (SE Spain). By means of time series analysis and a 1D numerical groundwater model, groundwater exploitation was quantified and the mean annual recharge in both systems was estimated (2001–2004). During this period, the Lora and Mingo aquifers received an average groundwater recharge of 0.29 × 10⁶ m³/year and 0.14 × 10⁶ m³/year, respectively, whereas an average of 0.34 × 10⁶ m³/year and 0.21 × 10⁶ m³/year, respectively, was extracted. These conditions led to a conspicuous lowering of the water table in both systems. In addition, the analysis of the evolution of the main hydrogeochemical parameters of the groundwater showed that the increased pumping rates produced an increase in total dissolved solids, and chloride and sodium ions in both aquifers. In the case of the Lora aquifer, the only ion that presented decreased levels was nitrate. The results show that groundwater pumping in both aquifers should not exceed the mean annual recharge of 0.29 × 10⁶ m³/year and 0.14 × 10⁶ m³/year in the Lora and Mingo aquifers, respectively. Nevertheless, it would be advisable to reduce pumping rates to below these values in order to restore piezometric levels and improve groundwater quality for different uses in the future.     

Hydrogeology and groundwater management in a coastal granitic area with steep slopes in Galicia (Spain)

Groundwater availability, management and protection are great challenges for the sustainability of groundwater resources in the scattered rural areas of the Atlantic regions of Europe where groundwater is the only option for water supply. This report presents a hydrogeological study of the coastal granitic area of Oia in northwestern Spain, which has unique geomorphological and hydrogeological features with steep slopes favoring the erosion of the weathered granite. The hydrogeological conceptual model of the study area includes: (1) the regolith layer, which is present only in the flat summit of the mountains; (2) the slope debris and the colluvial deposits, which are present in the intermediate and lowest parts of the hillside; (3) the marine terrace; and (4) the underlying fractured granite. Groundwater recharge from rainfall infiltration varies spatially due to variations in terrain slope, geology and land use. The mean annual recharge estimated with a hydrological water balance model ranges from 75 mm in the steepest zone to 135 mm in the lowest flat areas. Groundwater flows mostly through the regolith and the detrital formations, which have the largest hydraulic conductivities. Groundwater discharges in seepage areas, springs, along the main creeks and into the sea. The conceptual hydrogeological model has been implemented in a groundwater flow model, which later has been used to select the best pumping scenario. Model results show that the future water needs for domestic and tourist water supply can be safely provided with eight pumping wells with a maximum pumping rate of 700 m³/day.

     

Groundwater flow modeling of Quaternary aquifer Ras Sudr,Egypt

Recently, Ras Sudr (the delta of Wadi Sudr) area received a great amount of attention due to different development expansion activities directed towards this area. Although Quaternary aquifer is the most prospective aquifer in Ras Sudr area, it has not yet completely evaluated. The present work deals with the simulation of the Quaternary groundwater system using a three-dimensional groundwater flow model. MODFLOW code was applied for designing the model of the Ras Sudr area. This is to recognize the groundwater potential as well as exploitation plan of the most prospective aquifer in the area. The objectives were to determine the hydraulic parameters of the Quaternary aquifer, to estimate the recharge amount to the aquifer, and to determine the hydrochemistry of groundwater in the aquifer. During this work, available data has been collected and some field investigation has been carried out. Groundwater flow model has been simulated using pilot points’ method. SEAWAT has been also applied to simulate the variable-density flow and sea water intrusion from the west. It can be concluded that: (1) the direction of groundwater flow is from the east to the west, (2) the aquifer system attains a small range of log-transformed hydraulic conductivity. It ranges between 3.05 and 3.35 m/day, (3) groundwater would be exploited by about 6.4 × 10⁶ m³/year, (4) the estimated recharge accounts for 3 × 10⁶ m³/year, (5) an estimated subsurface flow from the east accounts for 2.7 × 10⁶ m³/year, (6) the increase of total dissolved solids (TDS) most likely due to dilution of salts along the movement way of groundwater from recharge area to discharge area in addition to a contribution of sea water intrusion from the west. Moreover, it is worth to note that a part of TDS increase might be through up coning from underlying more saline Miocene sediments. It is recommended that: (1) any plan for increasing groundwater abstraction is unaffordable, (2) reliable estimates of groundwater abstraction should be done and (3) automatic well control system should be made.     

Hydrology of the coastal sabkhas of Abu Dhabi, United Arab Emirates

Water fluxes were estimated and a water budget developed for the land surface and a surficial 10-m-deep section of the coastal sabkhas that extend from the city of Abu Dhabi, United Arab Emirates, west to the border with Saudi Arabia. The fluxes were estimated on the basis of water levels and hydraulic conductivities measured in wells and evaporation rates measured with a humidity chamber. In contrast with conceptual models proposed in earlier studies, groundwater inflow is estimated to be small, whereas the largest components of the water budget are recharge from rainfall and evaporation from the water table. Estimates within a rectilinear volume of sabkha, defined as 1 m wide by 10 km long by 10 m deep, indicate that about 1 m³/year of water enters and exits by lateral groundwater flow; 40–50 m³/year enters by upward leakage; and 640 m³/year enters by recharge from rainfall. Based on the water and solute fluxes estimated for the upward leakage into the sabkha, 7–8 pore volumes of brine have entered the sabkha from below since the time the sabkha became saturated (7,000 years ago) as a result of the last global sea-level rise.

Hydrogeology and sustainable future groundwater abstraction from the Agua Verde aquifer in the Atacama Desert,northern Chile

The hyper-arid conditions prevailing in Agua Verde aquifer in northern Chile make this system the most important water source for nearby towns and mining industries. Due to the growing demand for water in this region, recharge is investigated along with the impact of intense pumping activity in this aquifer. A conceptual model of the hydrogeological system is developed and implemented into a two-dimensional groundwater-flow numerical model. To assess the impact of climate change and groundwater extraction, several scenarios are simulated considering variations in both aquifer recharge and withdrawals. The estimated average groundwater lateral recharge from Precordillera (pre-mountain range) is about 4,482 m³/day. The scenarios that consider an increase of water withdrawal show a non-sustainable groundwater consumption leading to an over-exploitation of the resource, because the outflows surpasses inflows, causing storage depletion. The greater the depletion, the larger the impact of recharge reduction caused by the considered future climate change. This result indicates that the combined effects of such factors may have a severe impact on groundwater availability as found in other groundwater-dependent regions located in arid environments. Furthermore, the scenarios that consider a reduction of the extraction flow rate show that it may be possible to partially alleviate the damage already caused to the aquifer by the continuous extractions since 1974, and it can partially counteract climate change impacts on future groundwater availability caused by a decrease in precipitation (and so in recharge), if the desalination plant in Taltal increases its capacity.     

Groundwater resource sustainability in the Wadi Watir delta, Gulf of Aqaba, Sinai, Egypt

The Wadi Watir delta, in the arid Sinai Peninsula, Egypt, contains an alluvial aquifer underlain by impermeable Precambrian basement rock. The scarcity of rainfall during the last decade, combined with high pumping rates, resulted in degradation of water quality in the main supply wells along the mountain front, which has resulted in reduced groundwater pumping. Additionally, seawater intrusion along the coast has increased salinity in some wells. A three-dimensional (3D) groundwater flow model (MODFLOW) was calibrated using groundwater-level changes and pumping rates from 1982 to 2009; the groundwater recharge rate was estimated to be 1.58?×?10⁶ m³/year. A variable-density flow model (SEAWAT) was used to evaluate seawater intrusion for different pumping rates and well-field locations. Water chemistry and stable isotope data were used to calculate seawater mixing with groundwater along the coast. Geochemical modeling (NETPATH) determined the sources and mixing of different groundwaters from the mountainous recharge areas and within the delta aquifers; results showed that the groundwater salinity is controlled by dissolution of minerals and salts in the aquifers along flow paths and mixing of chemically different waters, including upwelling of saline groundwater and seawater intrusion. Future groundwater pumping must be closely monitored to limit these effects.     

Groundwater recharge and salinization in the arid coastal plain aquifer of the Wadi Watir delta,Sinai, Egypt

The Quaternary coastal plain aquifer down gradient of the Wadi Watir catchment is the main source of potable groundwater in the arid region of south Sinai, Egypt. The scarcity of rainfall over the last decade, combined with high groundwater pumping rates, have resulted in water-quality degradation in the main well field and in wells along the coast. Understanding the sources of groundwater salinization and amount of average annual recharge is critical for developing sustainable groundwater management strategies for the long-term prevention of groundwater quality deterioration. A combination of geochemistry, conservative ions (Cl and Br), and isotopic tracers (^87/86Sr, δ⁸¹Br, δ³⁷Cl), in conjunction with groundwater modeling, is an effective method to assess and manage groundwater resources in the Wadi Watir delta aquifers. High groundwater salinity, including high Cl and Br concentrations, is recorded inland in the deep drilled wells located in the main well field and in wells along the coast. The range of Cl/Br ratios for shallow and deep groundwaters in the delta (∼50–97) fall between the end member values of the recharge water that comes from the up gradient watershed, and evaporated seawater of marine origin, which is significantly different than the ratio in modern seawater (228). The ^87/86Sr and δ⁸¹Br isotopic values were higher in the recharge water (0.70,723 < ^87/86Sr < 0.70,894, +0.94 < δ⁸¹Br < +1.28‰), and lower in the deep groundwater (0.70,698 < ^87/86Sr < 0.70,705, +0.22‰ < δ⁸¹Br < +0.41‰). The δ³⁷Cl isotopic values were lower in the recharge water (−0.48 < δ³⁷Cl < −0.06‰) and higher in the deep groundwater (−0.01 < δ³⁷Cl < +0.22‰). The isotopic values of strontium, chloride, and bromide in groundwater from the Wadi Watir delta aquifers indicate that the main groundwater recharge source comes from the up gradient catchment along the main stream channel entering the delta. The solute-weighted mass balance mixing models show that groundwater in the main well field contains 4–10% deep saline groundwater, and groundwater in some wells along the coast contain 2–6% seawater and 18–29% deep saline groundwater.A three-dimensional, variable-density, flow-and-transport SEAWAT model was developed using groundwater isotopes (⁸⁷Sr/⁸⁶Sr, δ³⁷Cl and δ⁸¹Br) and calibrated using historical records of groundwater level and salinity. δ¹⁸O was used to normalize the evaporative effect on shallow groundwater salinity for model calibration. The model shows how groundwater salinity and hydrologic data can be used in SEAWAT to understand recharge mechanisms, estimate groundwater recharge rates, and simulate the upwelling of deep saline groundwater and seawater intrusion. The model indicates that most of the groundwater recharge occurs near the outlet of the main channel. Average annual recharge to delta alluvial aquifers for 1982 to 2009 is estimated to be 2.16 × 10⁶ m³/yr. The main factors that control groundwater salinity are overpumping and recharge availability.     

The effect of the variation of river water levels on the estimation of groundwater recharge in the Hsinhuwei River,Taiwan

Land subsidence is a serious problem in Taiwan’s Yunlin area due to groundwater overpumping. There are safety risks in the high-speed railway structures in the areas of Siluo, Huwei, Tuku, and Yuanchang towns that run from north to south in the Yunlin area. Therefore, it is important to increase the groundwater recharge and to remedy the land subsidence in this area. The purpose of this study is to use the stream-flow estimation model (SF) and the groundwater flow numerical software MODFLOW (MF) to estimate the stream infiltration with consideration to the variation of the river water level in the Hsinhuwei River. The Ferris analytical model (FA) and MF are used to estimate the increased stream infiltration after the water level of the river rises. The hydraulic parameters required for each model are obtained from field observations and laboratory experiments. The results indicate that the assessment of the stream infiltration obtained through the SF and MF models are 264.2 × 10⁴ and 170.9 × 10⁴ m³/year, respectively. When the river water level increases by about 2.5 m, the annual stream infiltration obtained through the FA and MF models significantly increases by 31.6 × 10⁴ and 26.4 × 10⁴ m³/year, respectively. Taken together, the stream storages estimated using these two models indicate that an increasing efficiency of groundwater recharge is within the range of 10.0–18.5%.     

Sustainable groundwater management on the small island of Manukan,Malaysia

Numerical models are capable of simulating various groundwater scenarios and relate it towards groundwater management. This paper focuses on numerical modeling and water balance approaches in the search for a sustainable management plan in Manukan Island. The impacts of pumping and recharge rates represented by groundwater scenarios were investigated by means of hydraulic heads, chloride concentrations and water balance components. Overpumping and inconsistency in recharge rate are the stresses shown in Scenario A. Scenario B involved with reduction pumping rate by 25% has shown an increase in groundwater levels, chloride concentration and groundwater storage. Scenario C showed the most promising finding compared with Scenarios A and B. Highest hydraulic heads, lowest chloride concentration (1,552.2 mg/L) and positive groundwater storage (254.3 m³/day) were obtained in Scenario C. Chloride concentration in pumping wells still exceeds World Health Organization International Standard limit in Scenario C which illustrates an additional water treatment is needed. Nevertheless, in view of a compromise groundwater management plan in study area, Scenario C is the best plan so far to protect the groundwater resources in the study area. More understanding of the artificial recharge method (percolation tank) and study site by means of modeling studies is needed. Additionally, further progress is needed in obtaining the water usage data from each part to determine the best pumping rate. A sustainable groundwater management plan is crucial to maintain the natural resources and social benefits as well as to protect the ecological balance of Manukan Island.     

Environmental impact assessment of risk associated with groundwater overdraft remediation in cone of depression,Jining, China

In this paper, a simple scenario and probabilistic approach is used to assess the potential groundwater risk due to proposed overdraft remedial actions in cone of depression, Jining City, China. Focusing on the concentrations of Chloride ions (Cl⁻) and total hardness (TH), the impact of artificial recharge and reduced pumping on groundwater quality and quantity is analysed by using the three-dimensional finite difference groundwater flow and transport model, Visual MODFLOW, to simulate groundwater flow and transport within the study area based on scenarios, and utilizes SURFER software to map risk levels. Although 5, 10 or 15% reduced pumping with artificial recharge leads to more decrease in Cl⁻ and TH concentrations than the 25%, less volume increase is achieved for the remediation of land subsidence and other environmental problems in the cone of depression. The Cl⁻ concentrations in recovered groundwater are within the desired concentration of 200 mg/l; however, TH in some cases are above the maximum permissible limit of 500 mg/l, with an exceedence probability of about 0.67 for recharge and recharge with reduced pumping at 25%. The presence of fractures and hydrogeological complexity greatly determines impacts of remediation, and the 22% reduced pumping with artificial recharge offers an optimum strategy for overdraft remediation in the Jining cone of depression.     

Hydrochemical and isotopic evidence of recharge,apparent age,and flow direction of groundwater in Mayo Tsanaga River Basin,Cameroon: bearings on contamination

Unplanned exploitation of groundwater constitutes emerging water-related threats to MayoTsanaga River Basin. Shallow groundwater from crystalline and detrital sediment aquifers, together with rain, dams, springs, and rivers were chemically and isotopically investigated to appraise its evolution, recharge source and mechanisms, flow direction, and age which were used to evaluate the groundwater susceptibility to contamination and the basin’s stage of salinization. The groundwater which is Ca–Na–HCO₃ type is a chemically evolved equivalent of surface waters and rain water with Ca–Mg–Cl–SO₄ chemistry. The monsoon rain recharged the groundwater preferentially at an average rate of 74 mm/year, while surface waters recharge upon evaporation. Altitude effect of rain and springs show a similar variation of −0.4‰ for δ¹⁸O/100 m, but the springs which were recharged at 452, 679, and 773 m asl show enrichment of δ¹⁸O through evaporation by 0.8‰ corresponding to 3% of water loss during recharge. The groundwater which shows both local and regional flow regimes gets older towards the basins` margin with coeval enrichment in F⁻ and depletion in NO₃ ⁻. Incidentally, younger groundwaters are susceptible to anthropogenic contamination and older groundwaters are sinks of lithologenic fluoride. The basins salinization is still at an early stage.