Net Recharge Research Articles

Governance and groundwater modelling: Hints to boost the implementation of the EU Nitrate Directive. The Lombardy Plain case, N Italy

The EU Nitrate Directive has been ruling for almost 30 years, nevertheless nitrate concentration in the Lombardy Plain did not decrease. Together with failures of management implementation, a possible cause for such field observations is that management actions were taken without adequately considering the actual hydrogeological dynamics. To consider this aspect, the paper presents a groundwater flow and transport numerical model of a specific area of the Lombardy Plain. The aim of this model is to demonstrate how modelling, as a management tool, can be useful in the governance process.The groundwater model, using well-known MODFLOW-MT3D codes, is based on existing hydrogeological information, while a nitrogen mass balance has been performed at municipal scale to determine the agricultural N surplus to the subsurface. The model adequately reproduces head levels and nitrate concentrations in observation wells for a 10-year simulation period, showing that 4.5% of the N annual input remains stored in the system. The model indicates the efficiency of rivers and springs to export N out from the system at an estimated rate of 77.5% of the annual N inputs.Back to governance, the model shows that management data at municipal level (e.g. irrigation rates, groundwater withdrawal, N net recharge) provide a satisfactory scale for successfully reproducing nitrate evolution. Hence those variables that can be object of debate during a governance process can be treated as input data to the numerical model. Therefore, backcasting exercises can be conducted to check whether the model outcome fits with the expected results of specific management actions. The model highlights how the N mass balance evolves, providing clues on which factors can be managed to reduce nitrate concentrations and meet the Directive's requirements. Numerical groundwater models, as an option to address water management issues, ultimately contribute to solve the information and capacity governance gaps.

Effect of hydrogeological conditions on groundwater nitrate pollution and human health risk assessment of nitrate in Jiaokou Irrigation District

Nitrate pollution in groundwater and related human health risk assessment are crucial to ensure groundwater quality safety. In this study, the grey water footprint (GWF), DRASTIC model, and human health risk assessment (HHRA) model were used to investigate the status of nitrate pollution, analyze the effect of hydrogeological conditions on groundwater nitrate pollution, and evaluate the human health risk of nitrate in the Jiaokou Irrigation District, China. The results show that the maximum and average NO3− concentrations in the Jiaokou Irrigation District were 895 and 170.73 mg/L and the over-standard rate (>20 mg/L) was over 80% (82.09%). High NO3− concentration was mainly distributed in the cultivated land. The GWF results indicate that the wastewater absorption was insufficient to bear actual pollution in this region, requiring freshwater between 0.1 × 108 m3 and 105.8 × 108 m3 to dilute the nitrate to a safe concentration. The aquifers with high vulnerability levels were observed in the central and eastern parts, which are mainly related to depth to water table (D), net recharge (R), soil media (S), impact of vadose zone (I), and hydraulic conductivity (C). High NO3− pollution in an area is generally caused by high aquifer vulnerability. Additionally, the human health risk assessment shows that the health risks for pregnant women and breastfeeding women were higher than the health risks for children in the 10–16 years age group and > 16 years of age. This research provides a basis for policy-makers to take appropriate measures for protecting groundwater from nitrate pollution.

Impact of climate change on groundwater resource in a region with a fast depletion rate: the Mississippi Embayment.

Mississippi Embayment (ME) is one of the fastest groundwater depletion regions around the world, while the impacts of climate change on groundwater resources in the region are complex and basically unknown. Using the U.S. Geological Survey’s Mississippi Embayment Regional Aquifer Study (MERAS) model, such a challenge was addressed through the base, wet, and dry simulation scenarios. Over the 137-year simulation period from 1870 to 2007, the cumulative aquifer storage depletions were 1.70 × 1011, 1.73 × 1011, and 1.67 × 1011 m3, respectively, for the base, dry, and wet scenarios. As compared with that of the base scenario, the aquifer storage depletions were only 1.76% more for the dry scenario and 1.8% less for the wet scenario. A multiple regression analysis showed that the aquifer storage depletion rate was controlled more by the groundwater pumping and stream leakage rates and less by the groundwater net recharge rate. Groundwater table variation in the forest land was much smaller than in the crop land. Results suggested that groundwater pumping rather than climate change was a key driving force of groundwater depletion in the ME. Our findings provide a useful reference to water resource managers, foresters, and farmers in the ME and around the world when developing their groundwater supply strategies.

Vulnerability assessment, transport modeling and simulation of nitrate in groundwater using SI method and modflow-MT3DMS software: case of Sminja aquifer, Tunisia

Like most North African countries, Tunisia is characterized by a harsh arid and semi-arid climate with scarce water resources and poor water quality on most of its territory. The quality of groundwater is not immune to pollution. Sminja aquifer, located in Zaghouan district in Northeastern Tunisia, has been used to meet Zaghouan agglomeration needs for drinking purposes and irrigation uses. On the other hand, the region has suffered from inefficient usage and mismanagement of water resource due to appropriate legal, political, and economic frameworks to take into consideration the regional vulnerability to climate change and population growth. The application of the Susceptibility Index (SI) makes it possible to evaluate the impact of agricultural activities on the water quality in Sminja aquifer, using five parameters [depth of water (D), net recharge (R), aquifer media (A), topography (T) and Land use (LU)]. Modular three-dimensional multispecies transport model was used to assess, simulate and predict pollution transport of nitrate. The vulnerability index's spatial distribution shows that the most vulnerable area was found in the extreme north of the Sminja aquifer. It shows that a high vulnerability characterizes 21% of the study area (70 < SI < 60). The moderate to high vulnerability areas to pollution occupied 12% of the aquifer and the moderate to low vulnerability zones occupied 67% of the total area. The outputs of the SI reflect a good correlation with the measured nitrate concentrations. After calibration completion, the MT3DMS transport model results showed a good correlation between measured and simulated nitrate concentrations. The predict scenarios show that the nitrate propagates in all the aquifer, from the irrigated area to the non-irrigated area.

Evolution of a hybrid approach for groundwater vulnerability assessment using hierarchical fuzzy-DRASTIC models in the Cuddalore Region, India

Uncertainty in the supply and demand and a lack of available freshwater resources require a better management plan for sustainable development in agriculturally dependent communities. Therefore, scarce freshwater resources are protected and monitored to prevent contamination. Groundwater is the largest freshwater reservoir, and groundwater zones prone to contamination need to be identified. A precise model that enables the simplification and validation of the assessment process was developed by applying a fuzzy logic technique. A hierarchical fuzzy inference model (HFIM) was developed to better handle the input. The application of the developed model was then compared with the conventional index-based DRASTIC model in the Cuddalore District. The parameters that were found to influence the degree of vulnerability, including the depth of the water table (D), net recharge to the aquifer (R), aquifer media (A), soil properties (S), topography of the area (T), impact of the vadose zone (I), and hydraulic conductivity of the aquifer (C), were considered in the model development. A geographical information system (GIS) framework was utilized to synthesize the DRASTIC model and MATLAB was employed to develop the hierarchical fuzzy inference model. The results obtained from the GIS-DRASTIC model and HFIM were classified into five and seven categories based on their index values, respectively. The models were validated using nitrate concentration (mg/l) data obtained from 40 sampling points in and around the study area. A sensitivity analysis was performed on the models by varying the input from their minimum to maximum values for a selected hydrogeological setting. The results revealed that the HFIM was better at determining groundwater vulnerability levels in the Cuddalore District. It could cope with the uncertainty and nonlinearity of the datasets; the output showed a continuous response to modifications of the input data, which contrasts the DRASTIC model.

ANFIS-MOA models for the assessment of groundwater contamination vulnerability in a nitrate contaminated area

The enhanced assessment of groundwater contamination vulnerability is necessary for the management and conservation of groundwater resources because groundwater contamination has been much increased continuously in the world by anthropogenic origin. The purpose of this study is to determine the best model among three ANFIS-MOA models (the adaptive neuro-fuzzy inference system (ANFIS) combined with metaheuristic optimization algorithms (MOAs) such as genetic algorithm (GA), differential evolution algorithm (DE) and particle swarm optimization (PSO)) in assessing groundwater contamination vulnerability at a nitrate contaminated area. The Miryang City of South Korea was selected as the study area because the nitrate contamination was widespread in the city with two functions of urban and rural activities. Eight parameters (depth to water, net recharge, topographic slope, aquifer type, impact to vadose zone, hydraulic conductivity and landuse) were classified into the numerical ratings on basis of modified DRASTIC method (MDM) for the input variables of ANFIS-MOA models. The Original ANFIS, and 3 combined models of ANFIS-PSO, ANFIS-DE and, ANFIS-GA used 95 adjusted vulnerability indices (AVI) as the target data of training (70% data) and testing (30% data) processing. The performance of 4 models was evaluated by mean absolute errors (MAE), root mean square errors (RMSE), correlation coefficients (R), ROC/AUC curves and predicted AVI (PAVI) maps. The statistical results, spatial vulnerability maps and correlation coefficients between PAVIs and nitrate concentrations revealed that the order of model excellence was ANFIS-PSO, ANFIS-DE, ANFIS-GA, and Original ANFIS, and that ANFIS-PSO showed the highest performance in training and testing processing. The performance rates of ANFIS-MOA models were also compared with 10 recent popular worldwide models using the correlation coefficients between PVI and nitrate concentrations, and they were superior to other recent popular models. ANFIS-MOA models were also useful for resolving the subjectivity of physical and hydrogeological parameters in original DRASTIC method (ODM) and MDM. It is expected that ANFIS-PSO models will produce the excellent results in assessing groundwater contamination vulnerability and that they can greatly contribute to the groundwater security in other areas of the world as well as Miryang City of South Korea.

Forest regeneration can positively contribute to local hydrological ecosystem services: Implications for forest landscape restoration

Abstract Governments are increasingly committing to significant forest restoration. While carbon sequestration is a major objective, the case for restoration often includes benefits to local communities. However, the impacts of forest restoration on local hydrological services (e.g. flood and erosion risk, stream flow during dry periods) are surprisingly poorly understood. Particularly limited information is available on the impacts of passive tropical forest restoration following shifting cultivation. The outcome depends on the trade‐off between the improved soil infiltration capacity (reducing overland flow and increasing soil and groundwater recharge) and greater evapotranspiration (diminishing local water availability). Using measurements from highly instrumented plots under three vegetation types in the shifting cultivation cycle in Madagascar's eastern rainforests (forest, tree fallow and degraded abandoned agricultural land), and infiltration measurements for the same vegetation types across the landscape, we explore the impacts of forest regeneration on the ecohydrological processes that underpin locally important ecosystem services. Overland flow was minimal for the tree fallow (similar to the forest) and much lower than for the degraded land, likely leading to a lower risk of erosion and flooding compared to the degraded land. Conversely, evapotranspiration losses were lower for the tree fallow than the forest, leading to a higher net recharge, likely resulting in more streamflow between rainfall events. These results demonstrate that young regenerating tropical forest vegetation can positively contribute to locally important hydrological ecosystem services. Allowing tree fallows to recover further is unlikely to further reduce the risk of overland flow but may, at least temporarily, result in less streamflow. Synthesis and applications. Encouraging natural regeneration is increasingly seen as a cost‐effective way to deliver forest landscape restoration. Our data suggest that increasing the abundance of young secondary forest in the tropics, by increasing fallow lengths in the shifting cultivation cycle, could make a positive contribution to locally important hydrological ecosystem services (specifically reducing overland flow and therefore erosion and flooding, while maintaining streamflows). Such empirical understanding is needed to inform the models used for planning forest landscape restoration to maximize benefits to local communities.

Predictions of groundwater vulnerability and sustainability by an integrated index-overlay method and physical-based numerical model

This study presents a new concept that integrates the index-overlay method and a physical-based numerical model for predicting groundwater sustainability under various climate conditions and anthropogenic activities. The index-overlay DRASTIC method was modified with an analytical hierarchy process theory and employed to create groundwater vulnerability maps for the Pingtung plain groundwater basin in southern Taiwan. The physical-based MODFLOW model was used for predicting the dynamics of a basin-scale groundwater system. Solutions and calibrated hydrogeological parameters in the MODFLOW model provide feedback to the factors in the modified DRASTIC method which enables predicting groundwater vulnerability. In this study, different climate conditions were considered in the numerical model to obtain the changes in depth of water and net recharge for predicting future groundwater vulnerability and for evaluating the current state of the sustainability indicators. Results show that the depth of water and net recharge obtained from the groundwater model improve the accuracy of the groundwater vulnerability prediction. The variations of future climate conditions have less influence on the variations of groundwater vulnerability because of the dense river network that controls the shallow groundwater levels in the Pingtung plain groundwater basin. Therefore, the influence of climate conditions on the risk of groundwater contamination is also relatively low. Based on the analysis of the sustainability indicators, we found that the groundwater resource system in the Pingtung plain groundwater basin is in a critical condition of high vulnerability.

Estimation of groundwater recharge using simulation-optimization model and cascade forward ANN at East Nile Delta aquifer, Egypt

Study regionThe Quaternary Aquifer at the Eastern Nile Delta (QAEND), Egypt. Study focusA novel model is studied to build relationships between the available geomorphological and hydrogeological data, and the unknown time-dependent recharge rates. This is useful in performing inexpensive sustainable simulation and management of the proposed aquifer. Recharge rates in the year 2005 are calibrated using the observed hydraulic heads. The unstructured grid version of MODFLOW (MFUSG) coupled with the Particle Swarm Optimization (PSO) algorithm is used to solve the calibration problem. Then, a multilayer Cascade Forward Artificial Neural Network (CFNN) is trained using the calibrated recharge rates to conclude the required relationships between available data and unknown recharge rates, for any subsequent year. Four different training methods are adopted for CFNN: 1) PSO, 2) Levenberg Marquart (LM), 3) LM in combination with the Bayesian Regularization (BR), and 4) hybrid algorithm between LM - BR and PSO, which is used for the first time in training the CFNN to predict the net recharge rates and is found to be the best one. New hydrological insights for the regionThe trained CFNN is used to provide the groundwater flow model, MFUSG, with necessary recharge rates during the transient simulation of the groundwater between 2005 and 2015. Good matching between simulated and observed hydraulic heads is validating the model in forcasting future recgharge rates.

Application of DRASTIC and Modified DRASTIC Models for Modeling Groundwater Vulnerability of Malda District in West Bengal

Groundwater is one of the most important freshwater resources in our daily life. Under the background of global climate change, untreated rate of urbanization, human interferences and policy variations affect the change of global and local groundwater quality which is very common in developing countries like India. Hence, protecting groundwater from different types of contamination is the most accurate and appropriate measures of groundwater conservation. The main objectives of this work are to assess the groundwater vulnerability of Malda district using DRASTIC and modified DRASTIC methods. Seven influencing factors groundwater depth, net recharge, aquifer material, soil media, topography, the impact of vadose zone and hydraulic conductivity were used to complete DRASTIC method, agricultural DRASTIC, land use DRASTIC and AHP land use DRASTIC methods. The multi-model approach has been used to identify the best vulnerability model. For modeling Land use DRASTIC and AHP Land use DRASTIC, the land use layer was added with other layers. The groundwater vulnerability zone has been divided into three categories like high, moderate and low. High-vulnerability zones were found in the northern and southern parts, moderate zones were found in the middle part of the district, and the low-vulnerability zones in the eastern part of the district. The vulnerability model was validated using the ROC curve and Friedman test. The AHP land use DRASTIC shows better performance compared to other vulnerability models.

Development of potential map for groundwater abstraction in the northwest region of Bangladesh using RS-GIS-based weighted overlay analysis and water-table-fluctuation technique.

The increasing trend of population growth along with the rapid groundwater-based agricultural expansion and decreasing trend of mean annual rainfall in the Northwest region of Bangladesh has been exacerbating the declination of groundwater for further expansion. Therefore, the present study attempts to demarcate the potential groundwater abstraction zones from the assessment of potential recharge and available recharge. Potential recharge was obtained with commonly used geospatial-based weighted linear combination (WLC) technique. Here, WLC analysis was based on eight factors related to physiographic (e.g. drainage density, lineament density, slope), geomorphologic (e.g. geomorphology, lithology, soil), land use and land cover (LULC) and hydrology (i.e. rainfall). Available net recharge was assessed for the period 1993-2017 by employing the water table fluctuation method. Finally, the resultant map on potential abstraction was characterized into five different classes, viz. 'very low', 'low', 'moderate', 'high' and 'very high'. The derived map reveals that 'very high' potential zone is distributed along the Teesta river floodplain, especially the northeastern part. In contrast, the Barind Tract (i.e. the southwestern and the southcentral parts) area shows 'very low' groundwater prospect. Such fused interpretations are expected to contribute to the planning of integrated management of water resources.

Groundwater age of spring discharges under changing permafrost conditions: the Khangai Mountains in central Mongolia

Obtaining a better understanding of groundwater dynamics in permafrost zones is a critical issue in permafrost hydrology. This includes assessing the impacts of climate change on permafrost thaw and ground ice-melt. Both permafrost thaw and ground ice-melt can be related to groundwater discharges (i.e. spring discharges), and spring water is an important local water resource; accordingly, changes in these processes can have large impacts on local people and their subsistence activities. To detect permafrost thaw and ground ice-melt in the permafrost zone of Mongolia, groundwater ages of several spring discharges were determined using two transient tracers: tritium (3H) and chlorofluorocarbons (CFCs). Spring water samples were collected seasonally from 2015 to 2019 at seven spring sites around the Khangai Mountains in central Mongolia. The sites included two thermokarst landscapes on the northern and southern sides of the mountains. The 3H and CFC concentrations in the spring water in the thermokarst landscapes were very low, especially on the southern side of the mountains, and the estimated mean groundwater age for these sites was older than that for the other sampled springs. Consequently, the young water ratios of the thermokarst sites were lower than those for the other springs. This ratio, however, showed a gradual increase with time, which indicates that recently recharged rainwater began to contribute to the spring discharge at the thermokarst sites. An atmospheric water budget analysis indicated that net recharge from modern and recent precipitation to shallow groundwater in the summer season was almost zero on the southern side of the mountains. Thus, we inferred that the spring water at the thermokarst sites on the southern side of the mountains contained large amounts of ground ice-melt water.

Groundwater Vulnerability Assessment of Pingtan Island in Fuzhou City, China, Based on DRASLI-QUE

AbstractBased on the DRASTIC model [A model for groundwater vulnerability assessment including seven indexes: depth to groundwater (D), net recharge (R), aquifer medium (A), soil type (S), topograp...

Anthropogenic influence on monthly groundwater utilization in an irrigation dominated Ganga river Sub-Basin

In the last three decades, the low-income and highly-populated Kosi River's alluvial plain have improved its agricultural production by adapting a million groundwater pumping systems. As the farmers have less land holding for agriculture activities, site-specific water, and nutrient management are adopted for agriculture production. The study represents the impact of intensified agricultural activities aided by additional groundwater pumping system over the groundwater recharge/pumping rate. We analysed groundwater utilization variation due to farmers' empowerment through the green revolution and adaption of a million-groundwater pumping system via satellite-based Actual Evapotranspiration (AET). Throughout the year, groundwater accessibility has reduced the study area's agricultural dependency on monsoonal rainfall and allowed agricultural activities all season. In this study, hydrological modelling with spatial input data from different sources estimated monthly groundwater recharge/pumping and its variation during wet/dry years. The observed groundwater recharge/ extraction was compared with the corresponding rainfall patterns and validated using measured seasonal groundwater depths. We present the relative change in groundwater recharge or extraction statistics using a set of standardized seasonal indices. Improved socio-economic condition and the risk of recurring floods/ droughts has increased the dependency on groundwater aided irrigation in the region. Since the farmers have to pay for pumping fuel, they opt for more efficient groundwater-aided agricultural activities, especially in dry years. This additional dependency on groundwater has significantly increased the annual groundwater extraction rate and reduced the area's net recharge.

Potential and net recharge assessment in paddy dominated Hirakud irrigation command of eastern India using water balance and geospatial approaches

Spatially distributed potential and net recharge rates were assessed in the paddy dominated Hirakud command area (Eastern India) at 100 m grid resolution using surface water balance and Water Table Fluctuation (WTF) methods, respectively, for the period 2001–05. Net recharge estimated using the WTF method corresponding to observation well locations was further interpolated using kriging technique available in the ArcGIS software. Net recharge to potential recharge ratios (%) were also assessed spatially. Water balance components (i) runoff was estimated using the Natural Resources Conservation Service-Curve Number (NRCS-CN) method (ii) reference evapotranspiration by (Hargreaves and Samani, Applied Engineering Agriculture ASABE 1:96–99, 1985)), crop evapotranspiration by (Allen et al., Crop evapotranspiration: Guidelines for computing crop water requirements, FAO Irrigation and Drainage, Food and Agriculture Organization, Rome, Italy, 1998) and evaporation from uncultivated lands by Ritchie (1972) approaches, and (iii) canal seepage using simple canal flow model. Annual groundwater draft during Kharif and Rabi was found to be 144.41 and 112.49 ha-m, respectively. Nearly, 90% of the study area contributed runoff in the range of 200–400 mm during the years 2002–03, 2003–04, and 2004–05. The estimated seepage losses vary between 5 and 15% of irrigation depth for all distributaries. Potential groundwater recharge during wet, normal, and dry years ranges between 650 and 1033 mm, and equivalent to 67%, 78%, and 60% of annual rainfall, respectively. Net recharge ranges between 8 and 11% of the annual rainfall. Mean ratio between net recharge to potential recharge is nearly 30%, indicating that nearly 70% of potential recharge is accounted as outflow from the study area. Parmanpur distributary canal located at the centre of the study area that exhibited higher potential recharge can be scheduled at the end to avoid water logging problem. Further, extraction of groundwater during non-monsoon period for irrigation purpose not only helps in controlling waterlogging but also helps in maintaining stable groundwater level. Overall, spatio-temporal distribution of recharge in the command area indicated that the irrigation demands during non-monsoon season can be met through sustainable management of underexploited groundwater resources. Such an integrated management of surface and groundwater can help in improving water use efficiencies as well as agricultural productivity.

Application of DRASTIC model for assessing groundwater vulnerability: a study on Birbhum district, West Bengal, India

Groundwater is one of the important necessary renewable resources of the world. Without water, no life can be possible on this earth. It is not only sustaining all biotic elements of the earth but also it helps to fulfill the requirement of various sectors like agriculture, industries, and other domestic purposes. Not all types of water but the mineral added purified water is safe for the human being. Unfortunately, in this age of development, it's very difficult to get naturally purified water because of the application of chemical fertilizer to get more production from agriculture, extensive industrialization pollutes groundwater resources badly. So, it’s high time to think about this most valuable resource. In this context, current research aims to identify the most polluted or vulnerable zones of groundwater in the Birbhum district. From several studies, it has been found that Birbhum district is one of the fluoride contaminated districts. Except, fluoride, another chemical component i.e. iron is also another harmful component in this district. Therefore, to assess the most vulnerable groundwater zones DRASTIC model has been applied here. DRASTIC is a widely used model for this purpose. This study deals with how the application of the DRASTIC model can help to extract the vulnerable zones of groundwater. To run the DRASTIC model various parameters viz. Depth to water level, Net recharge, Aquifer media, Soil media, Topography, Impact of the vadose zone, and Hydraulic conductivity have been used here. The final vulnerable map shows that the western part is more vulnerable than the eastern part because the western part consists of the plateau fringe area with basalt and granite and more weathering prone that’s why contamination of harmful minerals dissolve with groundwater most quickly. Moreover, the groundwater level is near to surface in the western part due to the presence of hard rocks near the surface than the eastern part. The applied DRASTIC model has been validated using the receiver operating characteristic curve (ROC) and this curve has been prepared based on some random points composed of various harmful chemical components. The result of the receiver operating characteristic curve depicts that this model is 73% valid in this concerned region.

Drastic model application to groundwater vulnerability elucidation for decision making: the case of south western coastal basin, Ghana

The health of the population is intertwined with the availability and supply of potable water. With many people around the world resorting to groundwater resources as a source potable water supply, it becomes imperative that the state of groundwater susceptibility to contamination is known. The DRASTIC model has been applied to determine the state of aquifer vulnerability to contaminants. The seven hydrogeological parameters were considered in the standard model and the resulting vulnerability, DI were classified into three vulnerability zones; low, moderate and high. The model was then modified to include land use/land cover (LU) and lineament density (LIN) parameters and net recharge (rm). The modified vulnerability indices were designated as DI-LU, DI-LIN, DIrm and MDI (combined modification). The results revealed the land area under high vulnerability under DI, DI-LU, DI-LIN, DIrm and MDI were 32.2, 26.2, 33.7, 26.2 and 40.4% respectively. There were no significant difference between the standard moderate vulnerability class and the modified derivatives (DI + LU, DI + Lin). The combined modification (MDI) however led to 17% decrease in this class of vulnerability. The model was validated using a nitrate concentration of 36 samples collected for the purpose. The validation assessment revealed that the performance of the model was improved with modification.

DRASTIC framework improvement using Stepwise Weight Assessment Ratio Analysis (SWARA) and combination of Genetic Algorithm and Entropy.

Hybrid and integrated techniques can be used to investigate intrinsic uncertainties of the overlay and index groundwater vulnerability assessment methods. The development of a robust groundwater vulnerability assessment framework for precise identification of susceptible zones may contribute to more efficient policies and plans for sustainable managements. To achieve an overall view of the groundwater pollution potential, the DRASTIC framework (Depth to the water table, net Recharge, Aquifer media, Soil media, Topography, Impact of the vadose zone, and hydraulic Conductivity) can be used for intrinsic vulnerability assessment. However, the unreliability of this index is because of its inherent drawbacks, including the weight and rating assignment subjectivity. To modify the rating range, this study recommended a new DRASTIC modification using a recently introduced Multi-Criteria Decision-Making (MCDM) method, namely the Stepwise Weight Assessment Ratio Analysis (SWARA); in addition, the Entropy and Genetic Algorithm (GA) methods were employed to alter the relative weights of DRASTIC parameters. To improve the DRASTIC index, nitrate concentration data from 50 observation wells in the study site were used. To assess the models' overall performance, the datasets obtained from new observation wells, receiver operating characteristic (ROC) curve, and area under the ROC curve (AUC) were studied. The experiments were carried out in the aquifer of the Qazvin Plain in Iran. The results indicated the higher performance of the modified DRASTIC framework, manifested as an increase in the AUC value from 0.58 for generic DRASTIC to 0.68 for the SWARA-Ent framework and 0.74 for the SWARA-GA framework. The application of the SWARA technique, as an effective MCDM method, resulted in the DRASTIC rating system enhancement. The generic DRASTIC optimization by integrating SWARA and GA provided an effective framework to assess groundwater vulnerability to nitrate contamination in the Qazvin Plain.

Interplay of changing irrigation technologies and water reuse: example from the upper Snake River basin, Idaho, USA

Abstract. Careful allotment of water resources for irrigation is critical for ensuring the resiliency of agriculture in semiarid regions, and modernizing irrigation technology to minimize inefficient water losses is an important tool for farmers and agricultural economies. While modernizing irrigation technology can achieve reductions in the nonbeneficial use of water, such as bare soil evaporation and nonconsumptive losses, water returned to the landscape is also reduced, often eliminating flow paths that other users rely on. In basins using a combination of surface and groundwater, replenishing aquifer storage by the managed aquifer recharge (MAR) of seasonally available water can mitigate the aquifer drawdown that results from reduced recharge when irrigation efficiency is improved. We examine the effects of MAR on the system-scale efficiency of modernizing irrigation technology and the resulting changes in the reuse of nonconsumptive losses, using a macroscale hydrologic model applied to the semiarid upper Snake River basin (USRB) of western Wyoming and southern Idaho, USA. Irrigation technologies were represented explicitly in the model, and available data informed baseline parameterizations of the irrigation technology. A suite of parameterizations were simulated that updated the existing technologies to be more efficient, both with and without sufficient MAR to cause a stabilization of the aquifer at the present-day head. As expected, simulated changes in irrigation technology resulted in greater downstream export of pristine water and a higher rate of aquifer drawdown when MAR was not simulated. Under current water use and cropping patterns, we were not able to simulate aquifer stabilization and maintain discharge downstream at any level of irrigation efficiency. We found support for the hypothesis that, as efficiency improves, less MAR is required to maintain a stable aquifer than when return flows are reduced due to increased efficiency. To evaluate the hypothesis, we defined the management benefit as a metric that compared the difference between the change in irrigation's net recharge and the change in MAR required as irrigation technology became more efficient. The metric generally indicated that less MAR was needed than net recharge was lost, but only for the most efficient case did the management benefit exceed the MAR needed at the baseline to stabilize the aquifer. Increasing efficiency of irrigation technology reduced the reuse of the gross irrigation derived from prior nonconsumptive losses, but simulating MAR increased reuse for a given parameterization, leading to higher effective irrigation efficiency. We find that local groundwater storage that users depend on is generally more sensitive to management decisions than downstream flows, and the drawdown of the aquifer without MAR always exceeded any decrease in discharge induced by MAR. Improving resource sufficiency in semiarid systems like the USRB will require an array of solutions that will need to balance benefits to local and downstream users.

A Novel Approach to Harmonize Vulnerability Assessment in Carbonate and Detrital Aquifers at Basin Scale

The DRASTIC (D: Depth to water; R: Net recharge; A: Aquifer media; S: Soil media; T: Topography; I: Impact of vadose zone; C: Hydraulic conductivity) index is usually applied to assess intrinsic vulnerability in detrital and carbonate aquifers, although it does not take into account the particularities of karst systems as the COP (C: Concentration of flow; O: Overlying layers above water table; P: precipitation) method does. In this paper we aim to find a reasonable correspondence between the vulnerability maps obtained using these two methods. We adapt the DRASTIC index in order to obtain reliable assessments in carbonate aquifers while maintaining its original conceptual formulation. This approach is analogous to the hypothesis of “equivalent porous medium”, which applies to karstic aquifers the numerical solution developed for detrital aquifers. We applied our novel method to the Upper Guadiana Basin, which contains both carbonate and detrital aquifers. Validation analysis demonstrated a higher confidence in the vulnerability assessment provided by the COP method in the carbonate aquifers. The proposed method solves an optimization problem to minimize the differences between the assessments provided by the modified DRASTIC and COP methods. Decision trees and spatial statistics analyses were combined to identify the ranges and weights of DRASTIC parameters to produce an optimal solution that matches the COP vulnerability classification for carbonate aquifers in 75% of the area, while maintaining a reliable assessment of the detrital aquifers in the Basin.