Declining Groundwater Levels Research Articles

Human-Induced Resource Scarcity in the Colorado River Basin and Its Implications for Water Supply and the Environment in the Mexicali Valley Transboundary Aquifer

The Colorado River delta is a sedimentary alluvial formation that embodies the Lower Colorado River transboundary aquifer. The Mexicali Valley overlies the Mexican part of the aquifer, and the Imperial Valley the aquifer’s portion north of the Mexico–U.S. border. Mexico receives an annual water allocation from the Colorado River stipulated by an international treaty between Mexico and the United States. The Colorado River water allocation to Mexico is shared by farmers in the Mexicali Valley and by several border cities, rural communities, and industries in the northern region of the State of Baja California. Farmers withdraw groundwater from the Mexicali Valley’s aquifer to make up for insufficient Colorado River water to grow their crops. Groundwater withdrawal has created overdraft of the Mexicali Valley aquifer with associated adverse impacts: sea water intrusion, declining groundwater levels, upwelling of brackish groundwater, land subsidence, degradation of groundwater-dependent ecosystems, and emigration of displaced farmers. This article reviews the natural and human histories in the Colorado River basin and the Mexicali Valley, and presents a methodology applying remote sensing, geographic information analysis, and hydrologic analysis to calculate the annual water deficit in the Mexicali Valley. Finally, this work evaluates the valley’s annual water deficit in reference to current agricultural and socioeconomic trends observed in the study region. Aquifer and related environmental degradation have adversely affected small-scale farming and exacerbated demographic instability.

Assessing Opportunities and Difficulties in Hydroponic Farming

Background: Hydroponics or water-culture-based agricultural systems are devoted to a reasonable prospect for future farming agriculture production. Especially in that region where the fertility of agricultural land is continuously going to there is a decline in groundwater level for irrigation. Hydroponics-based agriculture system realizes an admiring action towards an eco-friendly system and innovative technique to overcome challenges concerning food safety. Hydroponics is an advanced agriculture technique in which the plants grow without soil and without any pesticide use. It is used to grow plants, vegetables and shrubs on vertical as well as horizontal basis in the series and parallel. It could be applied via glass pots, clay pots, PVC pipes and useless plastic buckets and bottles. Methods: In the present study vegetables, flowering plants and shrubs were grown successfully by the use of mainly three techniques of hydroponics namely Kratky, Wick and DFT methods. This study was continued for two and half years (4th July 2020 to 21st March 2021 and December 2019 to April 2020) with controlled pH and TDS of the nutrient solution and conducted at different Indian climatic, weather and seasonal conditions at Markanda National College,Shahabad Markanda and at the researcher’s home. Several vegetables and plants were grown from Kratky, Wick and DFT hydroponics methods under continuous monitoring of pH and TDS of nutrient solutions. Result: During the conduction of this study of the growth of mustard, ladyfinger, spinach, marigold, daisy basil (Tulsi), cucumber, cauliflower, broccoli, tomatoes, peas, peppermint, coriander leaves plants in different sessions; some challenges and opportunities were discussed. The main objective of this research study is to spread awareness about novel types of advanced future agricultural techniques or farming among the farmers and masses, who have an interest in agriculture but cannot fulfill their ambitions towards agriculture farming due to scarcity of agricultural land. The results obtained from the growth of vegetable and plant through hydroponics methods province us to follow an idea to use of such agricultural techniques. We have grown several below said crops/vegetables two or three times and face several problems. It is an opportunity to overcome the world’s food scarcity at a large scale, if adopted by a large population all over the world.

Groundwater recharge estimation using in-situ and GRACE observations in the eastern region of the United Arab Emirates

The intensive agricultural expansion and rapid urban development in Abu Dhabi Emirate, United Arab Emirates (UAE) have resulted in a major decline in local and regional groundwater levels. By using the latest release (RL06) of Gravity Recovery and Climate Experiment (GRACE) satellite measurements and Global Land Data Assimilation System (GLDAS) products, the groundwater storage change was computed and compared with the time series of in-situ monitoring wells over the period of 2010–2016. The RL06 GRACE products from Jet Propulsion Laboratory (JPL), University of Texas Center for Space Research (CSR), German Research Center for Geosciences (GFZ), and JPL mass concentrations (MASCON) were assessed and have shown satisfactory agreements with the monitoring wells. The JPL MASCON reflected the in-situ groundwater storage change better than the other GRACE products (R = 0.5, lag =1 month, RMSE = 13 mm). The groundwater recharge is estimated for the study area and compared with the in-situ recharge method that considers multi recharge components from the rainfall, irrigation return flow and internal fluxes. The results show that the agreements between in-situ and GRACE-derived recharge estimates are highly agreeable (e.g., R2 = 0.91, RMSE = 1.5 Mm3 to 7.8 Mm3, and Nash-Sutcliff Efficiency = 0.7). Using the Mann-Kendall trend test and Sen's slope, the analyses of policies, number of wells, and farm areal expansion with groundwater time series derived from GRACE helped to validate GRACE and emphasize the importance of regulations for sustainable development of groundwater resources. The impacts of subsidy cuts after 2010 can be captured from the GRACE data in the eastern region of Abu Dhabi Emirate. The linear trend of groundwater storage anomaly obtained from GRACE over the period from 2003 to 2010 is −6.36 ± 0.6 mm/year while it showed a decline trend of −1.2 ± 0.6 mm/year after the subsidy cut. The proposed approach has a potential application for estimating groundwater recharge in other arid regions where in-situ monitoring wells are limited or absent.

Predicting Groundwater Level Using Climate Change Scenarios in the Southern Part of Mali

Groundwater is mainly demanded in all the activities for the population of the southern part especially in the Koda catchment, the studied area. These resources are affected by various factors especially climate change. Therefore, knowing the impact of projected climate change on groundwater recharge is an important issue for water resources management, especially for those responsible for the Koda catchment. In this work, the impact of climate change on groundwater resources in the study area in Mali, West Africa is investigated. The Hydrogeological modeling was performed using the Gardenia model, and the monthly precipitation and temperature data were used as the Baseline. These data considered the past 30-year period (1987-2016) and the projections for the next 30 years (2021-2050). Projected precipitation and air temperatures, extracted from the Rossby Centre regional Atmospheric climate model (RCA 4) statistically downscaled from the GCM-IHEC-EC-EARTH and the GCM-MPI-M-MPI-ESM-LR under the Representative Concentration Pathways RCP 4.5 and RCP 8.5 and corrected with the Multiscale Quantile Mapping bias correction method, were used as input data to the gardenia model. Potential evapotranspiration (PET) values estimated from Blaney Criddle method and groundwater levels measured in three piezometers were used to calibrate the Gardenia model. The outputs display the reduction of groundwater level in the three piezometers in the Koda catchment for all the two Regional Climate Models (RCMs) during the periods of rainy season from July to October. From the results of GCM IHEC-EC-EARTH, the projected decline in GWL reaches 1.09 m for the RCP 4.5 and it up to 1.26 m for the RCP 8.5 in the study area while the GCM MPI-M-MPI-ESM-LR presentes the decline in groundwater level (GWL) during winter season from about 0.62 m for the RCP 4.5 up to 1.93 m for the RCP 8:5. Both RCMs project a reduction trend of groundwater recharge over time. It is noticeable that this decline is greater in RCP8.5 for all the three piezometers. The results also show that the average groundwater recharge (90 mm) in the future (2021-2050) is lower (180 mm) than that of the current drought (1987-2016), which could lead to severe drought events. The projected impacts of climate change would have a significant impact on groundwater in the period of 2029-2039; this situation could have a negative impact the socioeconomic activities especially on agriculture, which depends on water resources. The results will help also to take some adaptation measures to climate change, the famers could have a possibility to know the period of groundwater recharge where they have more water infiltration therefore, where to seek crops that need less or more water. The study area presents numerous potential of groundwater, the results could be a tool for groundwater management and to determine the favorable sites to implant new boreholes.

Characteristics of Groundwater Level in the Szarvas-Békésszentandrás Oxbow Subbasin

The shallow groundwater has a direct and indirect effect on natural vegetation and agricultural production. The decline in groundwater level (GWL) can have negative impacts. In many areas in Hungary decreasing GWL trends in the last decades were found by earlier studies. In our research we studied the characteristics of groundwater level focusing on our study area, the subbasin of Szarvas-Békésszentandrás Oxbow. We analysed 20 years daily data of groundwater level of eight monitoring wells. Annual course and long term tendencies of groundwater level were examined. In average of 16 years the GWL reaches its maximum in April and its deepest level in autumn (September, October and November depending on the station). Four typical groups of groundwater level courses could be distinguished based on the average depth and seasonal variations of GWL. The year to year GWL variability is larger in January and April compared to July and especially to October. The trends of the middle months of the seasons are almost the same in significance and slope compared to the trends based on yearly mean time series. The differences in trends can be found between stations rather than between the months used for calculations. The larger part of the subbasin can be characterised by decreasing trend in groundwater levels (2002-2020). The change exceeds 1 m at station Szarvas 2832 (144 cm) and Szarvas 2778 (122 cm). However, there is a station with no significant trend, GWL at Csabacsűd 2779 station shows relative stability in yearly average, which is valid for some areas in the eastern part of the subbasin.

Simulation of Groundwater Flow Dynamics under Different Stresses Using MODFLOW in Rechna Doab, Pakistan

Groundwater is a primary source of freshwater provisions all around the world. Due to its limited availability, water has become a precious entity nowadays. The future accessibility of groundwater is endangered due to its massive exploitation, particularly in the irrigation sector. Therefore, the current study was conducted to assess the declining groundwater levels in Rechna Doab, Punjab, Pakistan, where the aquifer has been reported to be highly stressed. A groundwater flow model was developed using the MODFLOW code of the USGS, and the steady-state model was calibrated for the year 2006, followed by a transient calibration for the years 2006–2010. Finally, the model was validated for 2011–2013, and a new scenario-based approach was used. Multiple future scenarios were developed to simulate the future response of the aquifer under changed recharge and pumping. The hydrodynamics of the groundwater flow was studied for two decades, i.e., up to 2033. The results under the business-as-usual scenario revealed a net gain in water levels in the upper parts of the study area. In contrast, a lowering of water levels was predicted in the central and lower parts. A maximum drop in the water level was anticipated to be 5.17 m, with a maximum gain of 5 m. For Scenario II, which followed the historical trend of pumping, an overall decline in water levels was observed, with a maximum expected drawdown of 15.68 m. However, the proposed water management Scenario III showed a general decrease in the upper study region, with the highest drop being 10.7 m, whereas an overall recovery of 6.87 m in the lower regions was observed. The simulations also suggested that the unconfined aquifer actively responded to the different scenario-based interventions. It was concluded that the region’s aquifer needs immediate action regarding pumping and recharge patterns to avoid a potential increase in pumping costs and to preserve the sustainability of endangered groundwater resources. Moreover, proper groundwater pumping and its policy legislation for its management should be implemented in order to protect this precious resource.

Improving the pit wall seepage resistance at the V. Grib diamond deposit

Introduction. V. Grib deposit development includes complex dewatering operations, all water-bearing rocks overlying the mining floor are drained. The open pit is mainly flooded by the Padunsky aquifer system. At present, the open pit is being drained by surface dewatering wells together with mine drainage. In total about 7–8 thousand m3 /h of drainage water is pumped out. Setting of the problem. Uncovering a multilayer water-bearing strata characterized by different filtration characteristics of rocks contributes to the formation of pit walls in the Padunsky strata that have not been dewatered. The height of groundwater seepage on pit walls reaches 50 m due to the low conductivity of the Padunsky strata bottom. It is suggested that the Padunsky strata bottom should be dewatered using lateral drain holes built from the pit to the wall benches in areas with no dewatering wells. Methods of research. For pit wall stability improvement, the developed multilayer numerical model of geofiltration is applied to study the use of lateral drain holes built from the pit. The finite difference method in the GMS MODFLOW package was applied for modelling. Research results. It has been found that the operation of 12 lateral drain holes during 1 year reduces the height of groundwater seepage on pit walls by 15–20 m, contributes to the groundwater level decline of the Padunsky aquifer system by 5–10 m on the drainage contour of dewatering wells; water inflow to lateral drain holes will be 810–850 m3 /h. Conclusions. The feasibility of lateral drain holes for the Padunsky strata dewatering intensification in the adjacent rock mass has been established using the method of numerical modeling.

Water quality and interaction between groundwater and surface water impacted by agricultural activities in an oasis-desert region

A comprehensive understanding of groundwater dynamics and its interaction with surface water under the influence of agricultural activities is essential for local agriculture, ecology and resident in arid regions, which is poorly understood in arid oasis-desert region. In our study, with emphasis on a comparison of hydrogeochemical characteristics between the oasis (irrigated) and desert (non-irrigated) areas, the water quality and groundwater-surface water interaction of a typical oasis-desert system with a rapid irrigation agriculture development were examined to clarify the effects of agricultural activities on groundwater level and quality using stable isotopic and hydrochemical data of 83 water samples. Results showed that cultivated land area increased by 121.8 % (732.4 km2) during 2000 to 2020, mainly transferring from grassland and bare land. Groundwater EC ranged from 786 to 49,400 μS/cm, with weakly alkaline. Shallow groundwater had a much higher EC than other water components. Stable isotopic and EC values of shallow groundwater in the non-irrigation areas were much greater than those in the irrigation areas, whereas middle groundwater isotopic values were more depleted in the desert than in the oasis. Shallow groundwater EC value was lower in summer, middle groundwater had higher EC in summer. Streamflow and confined water in the study area are suitable for agricultural irrigation, but phreatic water in the oasis is generally not suitable for irrigation at present. The groundwater chemistry was mainly controlled by strong evaporation, dilution, mixing, water-rock interaction and agricultural drainage. Groundwater in the irrigation areas was recharged by ephemeral runoff seepage, irrigation return flow and subsurface lateral inflow. Long-term development of irrigation agriculture (large-scale land reclamation, irrigation and groundwater pumping) in arid region has caused groundwater level decline and salinization, with a strong interaction between phreatic water and surface water. Hence, decreasing irrigation area and groundwater exploitation, carrying out gradual ecological restoration, improving water-saving efficiency and agricultural drainage system would be the viable method to restore groundwater and maintain the oasis-desert ecosystem coexistence in arid regions in the context of climate change.

The vulnerability of springs and phreatophyte communities to groundwater level declines in Oregon and Nevada, 2002–2021

Increased groundwater demand is causing aquifer declines that impact viability of groundwater-dependent ecosystems (GDEs) like springs and phreatophyte communities. To understand which springs and phreatophyte communities may be stressed by groundwater level declines in Oregon and Nevada, we assessed groundwater level trends in nearby monitoring wells. Very few springs and phreatophyte communities were near monitoring wells with adequate data. Less than 1% of >50,000 springs in Nevada and Oregon were within 800 m of analyzed wells, and only 52 springs were near a shallow (<30 m below ground surface) well. Among springs near analyzed wells, 56% in Nevada and 29% in Oregon were near wells with declining groundwater level trends, and percentages were similar among springs that were within 800 m of analyzed shallow wells. Less than 22% of all phreatophyte communities in Nevada and Oregon were near analyzed wells, and only 9.6% were within 800 m of a shallow well. Of phreatophyte communities near analyzed wells, 48% and 57% were near wells with declining trends in Nevada and Oregon, respectively. Differences among GDE types could reflect more groundwater development where phreatophytes exist. Differences between states in proportion of springs near wells with declining trends could be due to more surface water capture in Oregon or increased pressure for groundwater development in Nevada. State-specific policies and administration of groundwater rights and monitoring affect data availability and trends observed in the two states. More groundwater level data are essential for understanding impacts of groundwater withdrawals to GDEs.

Factoring Impacts to Water Supply Well Operations into Groundwater Management Planning.

Groundwater management planning requires balancing the interests of different stakeholder groups because (1) water supply development causes changes to groundwater systems that include declines in groundwater levels and (2) benefits and costs from pumping the common-pool resource often do not occur such that they are shared proportionate to use. Quantifying impacts from declining groundwater levels among user groups can be useful for evaluating management strategies. In California, considering impacts to supply well operations is proving important for acceptance of management plans that have been required by law. A case study is presented to illustrate the types of results that may contribute to the planning process. The results indicate that significant differences in impact may occur between groundwater pumpers. Suggestions are provided for using this information to mitigate impacts to the most vulnerable stakeholders.

Evaluation of Potential Seawater Intrusion in the Coastal Aquifers System of Benin and Effect of Countermeasures Considering Future Sea Level Rise

In the present study, a three-dimensional SEAWAT model was developed to generally simulate the impact of climate change and anthropogenic activities on seawater intrusion (SWI) in the coastal region of Benin by the end of 2050. The model was calibrated and validated from 2015 to 2020, considering groundwater head and salt concentration measured in 30 wells. After calibration, a sensitivity analysis was performed with the model parameters (hydraulic conductivity, recharge, storage coefficient and boundary conditions). For the calibration, model computed and observed values displayed good correlation, approximatively 0.82 with a root mean square error (RMSE) of 0.97 m and 13.38 mg/L for groundwater head and salt concentration, respectively. The simulation results indicate that freshwater head had declined by 1.65 m from 2015 to 2020 (taking reference from the average groundwater head in 2015: 27.08 m), while the seawater intrusion area increased in the same period by an average of 1.92 km2 (taking reference from the seawater intrusion area in 2015: 20.03 km2). The model is therefore used to predict groundwater level decline and seawater intrusion area increase by the end of 2050, considering the predicted sea level rise (SLR) and estimated groundwater pumping rate. Furthermore, the interface fresh groundwater–saltwater change was studied using the SHARP interface developed by USGS in 1990. The interface variation was found to be influenced by the distance from shoreline, sea level, groundwater level and geological formation hydraulic conductivity. Finally, the 3D model was used to simulate the effect of a managed aquifer recharge system on reducing SWI rate in the study region.

Hydrodynamic Behaviors and Geochemical Evolution of Groundwater for Irrigation in Yaoba Oasis, China

The Yaoba Oasis is an irrigated cropland entirely dependent on groundwater; previous investigations (1980–2015) revealed an over-abstraction of groundwater and deteriorating groundwater quality. For further exploring the hydrodynamic behaviors and geochemical processes of groundwater during the irrigation season, groundwater samples were collected and analyzed using different techniques including classical statistics, correlation analysis, Piper diagrams, and Gibbs diagrams. The results indicated that Na+, K+, SO42− and Cl− were the main ions in groundwater, which were significantly correlated with TDS. The water–rock interaction is manifested by the precipitation of calcite and dolomite and the dissolution of rock salt and gypsum as an increase in TDS related to evaporation. In addition, the increasing complexity of hydrochemical type is caused by the rapid variation of hydrodynamic regime, irrigation and evaporation, which are subjected to the constraints of salty water intrusion from the desert salty lake and infiltration of irrigation return flow. Existing wells should limit overexploitation to halt the decline in groundwater levels and cut down irrigation water to reduce the risk of groundwater contamination and restore ecological balance in desert oasis.

Use of meta-heuristic approach in the estimation of aquifer's response to climate change under shared socioeconomic pathways

Climate change is one of the main sources of stress on the aquifers. However, few studies have appraised its impact on groundwater systems, especially in Iran with unprecedented groundwater depletion rates. Not influenced by anthropogenic influences, Pali aquifer, southwest Iran, has climate data scarcity. To determine the response of the aquifer, one approach is to utilize a pre-downscaled data set. To this end, WorldClim data set under shared socioeconomic pathways (SSPs), i.e. SSP245 and SSP585, was considered. Furthermore, nonlinear autoregressive exogenous (NARX) and artificial neural networks (ANNs) along with support vector regression (SVR) combined with the meta-heuristic algorithms of wavelet (WSVR) and innovative gunner (AIG-SVR) were applied, regarding 1970–2000 as the base time span, and 2021–2040 and 2041–2060 as the future time periods. Among observational data (2007–2018), 80 and 20% were considered for the network's training and testing, respectively. An increase in temperature, between +1.93 and + 3.7 °C, would occur in the future with the most increment in summer 2041–2060 under SSP585. Additionally, precipitation fluctuate from −0.43 to +1.17 mm/month with a probable rise in fall and most decline in winter 2041–2060 under SSP585. As regards the groundwater modeling, considering that NARX and ANNs were not able to simulate the aquifer altogether, the meta-heuristic approaches demonstrated high proficiencies. With R = 0.995, R2 = 0.989, mean absolute error (MAE) = 0.249 m and Nash-Sutcliffe efficiency (NSE) = 0.982 for the test data, WSVR illustrated the greatest efficacy, which disclosed that the groundwater level would face the utmost reduction from −5.4 to −10.9 m in observation wells, especially in spring 2041–2060. Indeed, this decline in groundwater level is exclusively induced by climate change, emphasizing on proposing groundwater adaptation strategies to address the groundwater issues, like land subsidence, in Iran. Moreover, it is proposed that different modeling approaches be evaluated, such that the outputs of the best model be considered.

Response of groundwater quality to river-aquifer interactions during managed aquifer recharge: A reactive transport modeling analysis

Managed aquifer recharge (MAR) has been applied for groundwater restoration as an effective strategy in many overdraft regions. In Jinan, China, MAR through river infiltration was conducted regularly in recent years because of the most famous spring groups’ drying up due to continuous decline of groundwater level caused by extensive pumping. A substantial rise of water table (∼20 m) has been observed near the river, however, the potential change in groundwater quality and geochemistry during MAR process remains unknown. In this study, a flow and multi-component reactive transport model was developed to evaluate the impact of MAR on chemical reaction processes and the response of groundwater quality to the interaction of river water and groundwater. The geochemical conditions of the river water and groundwater are significantly different, as river water contained more dissolved organic carbon (DOC) and less nitrate than groundwater did in the study area with intensive agricultural activity. This study revealed that nitrate dilution rather than denitrification was the main process responsible for observed groundwater quality change during MAR. Preferential flow occurring in the aquifer resulted in strong spatial variability of nitrate concentrations in the groundwater. River water DOC, aquifer hydraulic conductivity distribution, and river-aquifer hydrodynamic conditions can all affect the redox condition in the riparian zone by changing either reaction rate or residence time. The results from this study indicate that groundwater geochemistry can be significantly altered during MAR, suggesting the importance of regular monitoring plan to assess the changes in groundwater quality, especially in the area where river sediments are rich in organic carbon. Such monitoring and reactive transport modeling analysis is critical to ensuring that the adverse impact on groundwater quality by potential MAR operations be kept to a minimum.

Sustainability of fresh groundwater resources in fifteen major deltas around the world

Population growth, urbanization and intensification of irrigated agriculture in the world’s deltas boost the demand for fresh water, with extensive groundwater extraction as a result. This, in turn, leads to salt water intrusion and upconing, which poses a threat to freshwater and food security. Managing fresh groundwater resources in deltas requires accurate knowledge about the current status and behaviour of their fresh groundwater resources. However, this knowledge is scarcely present, especially for groundwater at larger depths. Here, we use three-dimensional variable-density groundwater model simulations over the last 125 ka to estimate the volume of fresh groundwater resources for 15 major deltas around the world. We estimate current volumes of onshore fresh groundwater resources for individual deltas to vary between 1010 m3 and 1012 m3. Offshore, the estimated volumes of fresh groundwater are generally smaller, though with a considerably higher variability. In 9 out of 15 simulated deltas, fresh groundwater volumes developed over thousands of years. Based on current groundwater extraction and recharge rates, we estimate the time until in-situ fresh groundwater resources are completely exhausted, partly leading to groundwater level decline and mostly replacement with river water or saline groundwater. This straightforward analysis shows that 4 out of 15 deltas risk complete exhaustion of fresh groundwater resources within 300 m depth in 200 years. These deltas also suffer from saline surface water which means their groundwater resources will progressively salinize. With a fourfold increase in extraction rates, seven deltas risk a complete exhaustion within 200 years. Of these seven deltas, six suffer from saline surface water. We stress that the groundwater of these six vulnerable deltas should be carefully managed, to avoid non-renewable groundwater use. The progressive exhaustion of fresh groundwater resources in these deltas will hamper their ability to withstand periods of water scarcity.

Sustainability Indicators of Groundwater Withdrawal in a Heavily Stressed System: The Case of the Acque Albule Basin (Rome, Italy)

Groundwater sustainable yield is a concept widely treated theoretically in the literature. Moving from theoretical concepts to the definition of practical measures for groundwater management is not easy due to site-specific characteristics of the system. This study is aimed at identifying which factors influence the sustainable yield of the plain of Tivoli (Central Italy), where thermal springs with considerable flow (over 2 m3/s) emerge (or rather emerged) and supply a thermal plant. In the same plain, another profitable economic activity concerns the extraction of travertine; it caused a progressive decline in groundwater levels and in the discharge of the thermal springs. The hydrogeological history of the site and the data available in the literature and in new focused surveys are encapsulated in a simple flow model addressed to compare the pre- with the under-development conditions. The withdrawal of groundwater from the quarry area determined a significant impact on the water balance of the system. An increase in inflow from surrounding aquifers and a decrease in storage and in natural discharge of the travertine aquifer result in under-development conditions. Residual discharges towards the springs and river are very sensitive to the pumping flow rate of quarries, according to an inverse linear relationship; this hydrogeological feature may be adopted as an indicator of the sustainability of groundwater withdrawals from the plain. The residual discharge is most affected by the position of the pumping center in the groundwater flow net and its distance from boundaries to be captured, as well as on the depth and extent of the quarries. This lays the basis for developing sustainable management models of groundwater considering the economic and environmental aspects of the issue.

Spatial Estimation of Soil Loss and Planning of Suitable Soil and Water Conservation Interventions for Environmental Sustainability in Northern Karnataka in India Using Geospatial Techniques

The selected study area lies in Karnataka State of Southern India and is frequently subjected to prolonged dry spells, high soil erosion, declining groundwater levels, and reductions in crop yield. In order to make this region sustainable, estimation of soil loss, selection and prioritization of suitable interventions, and its adoption are very important. In this study, spatial soil loss estimation models were developed sub-district-wise using the Revised universal soil loss equation (RUSLE) and GIS for a period of 70 years (1951 to 2020). The observed soil loss data for the period of 2011 to 2015 were used for validation of the model (R2 = 0.89) and were found satisfactory. The average annual rainfall ranged spatially from 420 to 3700 mm, erosivity (R) ranged from 2606 to >15,000 MJ mm ha−1 h−1 year−1, and average annual soil loss varied from <2.0 to >15.0 t ha−1 y−1 in the northern dry zone of Karnataka. Most of the study area had an average annual rainfall of 550 to 800 mm and the soil loss was <10.0 t ha−1 y−1. A higher erosivity and soil loss occurred in the western part of the selected area where high rainfall is predominant. A considerable variability in rainfall, erosivity, and soil loss was found in high, medium, and low-rainfall regions from 1951 to 2020. The spatial soil loss was estimated catchment-wise and prioritized to determine the vulnerable areas. It was found that 7.69% of the area with soil loss ≥ 15.0 t ha−1 y−1 needs top priority for planning interventions (Priority 1) followed by 10.49% of the area with soil loss ranging from 10.0 to 15.0 t ha−1 y−1 (Priority 2) and 42.7% of the area under 5.0 to 10.0 t ha−1 y−1 (Priority 3), and the remaining area has lower priority. In order to make Northern Karnataka more sustainable, suitable site-specific moisture conservation practices and water-harvesting/groundwater recharge structures were planned using geospatial techniques. Among the selected moisture conservation interventions, conservation furrow and contour cultivation are very suitable for all the nine districts followed by compartmental bunding and semi-circular bunds. Out of the total area, conservation furrow was found suitable for 45.3% of the area, contour cultivation for 24.3% of the area, and compartmental bunding and semi-circular bunds for 16.8 and 16.9% of the areas, respectively. The study indicated that a considerable amount of topsoil is lost as erosion and, hence, planning and adoption of suitable in situ soil and water conservation practices and water-harvesting/groundwater recharge structures are the need of the hour for the sustainable management of this region. The identified locations were validated using visual interpretations, ground truth, and recorded data.

Assessing future climate trends and their impact on different fractured rock aquifers in Northern Togo

Abstract Water resources in the West African Sudan Savannah are concentrated in fractured crystalline and sedimentary rock aquifers. Due to their low storage, these aquifers are vulnerable to changes in climate. This study assesses future temperature and precipitation trends in the Koumfab watershed of northern Togo. The impact of these future climate trends on surface water and the two types of fractured rock aquifers is also investigated. A fully integrated hydrologic model of the Koumfab watershed in Northern Togo is used to study the impact of climate change on water resources. Bias-corrected temperature and precipitation from four regional climate models (RCMs) and two greenhouse emissions scenarios are used as climate forcings for the integrated model. Climate projections from the four RCMs indicate a rise (1.4 −5.5 °C) in average temperature, from the control (1971–2000) to the future period (2031–2060). Projected precipitation follows two contrasting trends with some RCMs predicting an increase (by up to 14%) in mean annual precipitation, while others predict a decline (by up to −14%). These changes in precipitation and temperature will have a noticeable effect on groundwater levels and stream flow. The hydrologic model indicates a decline in groundwater levels for all future climate projections by 1.4−5.7 m. The decline in groundwater levels is not uniformly distributed in the two types of aquifers. The decline in the fractured sandstone aquifer will be four times greater than that of the fractured granodiorite/migmatite aquifer. Projected stream flow at the watershed outlet shows increasing (59 -332%) and decreasing trends (−39 −100%).

Identification of Suitable Recharge Sites by Integrated Hydrogeophysical Approach for Augmenting Groundwater in Reodar Block, District Sirohi, Rajasthan

Abstract The dependence of human beings on groundwater and ever-increasing demands of growing population, agriculture and industries, has resulted in its over-exploitation. This has led to the decline of groundwater levels and its shortage especially in lean season. The study area, Reodar block of Sirohi district, Rajasthan, is an over-exploited block with the stage of groundwater extraction at 159% and has an average declining water level trend at the rate of 0.24 m/year. Artificial recharge was proposed in the study area through the construction of recharge shafts and injection wells, after delineating the weathered thickness in the submergence area of existing ponds and check dams of the study area by carrying out vertical electrical sounding (VES). In all, VES were conducted at 178 sites and recharge structures were constructed at 76 out of 109 scientifically selected sites with suitable weathered thickness and attempt was made to establish their impact on water levels through pre-monsoon water level monitoring. The comparison of pre-monsoon water level observations spanning over four decades reveals its spatio-temporal decline in the study area. The construction of these recharge structures has resulted in significant increase in area from 38% to 68%, under 0 to 20 m below ground level water level range. This study demonstrates the importance of resistivity surveys in scientifically selecting the suitable sites for construction of recharge structures and significance of long-term water level monitoring in assessing the groundwater scenario and impact assessment, in poorly characterized hydrogeological areas.

An ensemble approach for predicting future groundwater levels in the Zagreb aquifer impacted by both local recharge and upstream river flow

This paper presents the first study assessing the climate change impact on groundwater levels of the Zagreb alluvial aquifer in Croatia by coupling climate projections under RCP8.5 for the period 2040–2070 with local scale groundwater flow modelling. As a novelty in groundwater modelling of climate change impacts, this study utilizes an ensemble of five climate models and two land surface models for providing projections of relevant boundary conditions to the groundwater model. The groundwater model is used for predicting climate driven changes in groundwater levels in the aquifer system influenced by both changes in local groundwater recharge and changes in river-flow. Both boundary conditions are obtained from the land surface models. In addition, the uncertainty contributions to groundwater levels from both climate models and land surface models were quantified using variance decomposition. The results revealed that the spatial pattern of changes in groundwater levels can be related to different processes influencing groundwater dynamics. In areas dominated by a strong groundwater-surface water interaction, close to the Sava river, the multi-model ensemble mean change in groundwater levels is negligible for low and average water levels. However, for high water levels, an increase was identified. In contrast, a decline in groundwater levels prevails in all areas where aquifer recharge is largely driven by rainfall infiltration. For the variance decomposition analysis, climate models were identified as the main source of uncertainty for groundwater levels. However, the uncertainty contribution of the choice of land surface model to the impact simulations was found to be more important in the area affected by a strong groundwater–surface water interaction and for periods of high groundwater levels. Also, specific local issues related to low and high groundwater levels that are associated with extreme hydrological regimes were found to exacerbate under climate projections.