Regional Groundwater Model Research Articles

Advances in conceptualizing transport in chalk aquifers

Abstract The conceptualizations of matrix, fracture and fissure porosity are important for understanding relative controls on storage and flow of groundwater, and the transport of solutes (and non-aqueous phase liquids) within chalk aquifers. However, these different types of porosity, rather than being entirely distinct, represent elements in a continuum of void sizes contributing to the total porosity of the aquifer. Here we define such a continuum and critically examine the selection of appropriate values of effective porosity, a widely used parameter for mass transport modelling in aquifers. Effective porosity is a transient phenomenon, related to the porosity continuum by the timescales under which mass transport occurs. An analysis of 55 tracer tests and 20 well inflow tests in English Chalk aquifers identifies spatial scaling in groundwater velocity and groundwater flow respectively, which are interpreted within the context of the wider literature on carbonate aquifers globally. We advance transport modelling in the Chalk by developing a fissure aperture velocity mapping method using transmissivity data from existing regional groundwater models, together with the identified transient and spatial scaling phenomena. The results show that chalk aquifers exhibit widespread rapid groundwater flow which may transport contaminants rapidly in almost any setting.

Modeling Shallow Urban Groundwater at Regional and Local Scales: A Case Study in Detroit, MI

Groundwater plays a significant role in the vitality of the Great Lakes Basin, supplying water for various sectors. Due to the interconnection of groundwater and surface water features in this region, the groundwater quality can be affected, leading to potential economic, political, health, and social issues for the region. Groundwater resources have received less emphasis, perhaps due to an “out of sight, out of mind” mentality. The incomplete characterization of groundwater, especially shallow, near-surface waters in urban centers, is an added source of environmental vulnerability for the Great Lakes Basin. This paper provides an improved understanding of urban groundwater to reduce this vulnerability. Towards that end, two approaches for improved characterization of groundwater in southeast Michigan are employed in this project. In the first approach, we construct a regional groundwater model that encompasses four major watersheds to define the large-scale groundwater features. In the second approach, we adopt a local scale and develop a local urban water budget with subsequent groundwater simulation. The results show the groundwater movement in the two different scales, implying the effect of urban settings on the subsurface resources. Both the regional and local scale models can be used to evaluate and mitigate environmental risks in urban centers.

Impact of model parameterization on predictive uncertainty of regional groundwater models in the context of environmental impact assessment

Parameterization strategy impacts models' outputs and the associated uncertainty. This is particularly true for transient regional groundwater models where parameters can only be weakly constrained by insufficient observations. However, this is rarely investigated under any particular model structure. This study bridges this gap using a regional groundwater model developed to understand the impact of coal seam gas extraction on groundwater systems in a probabilistic framework. Two different parameterization schemes were implemented for hydraulic conductivity and specific storage. The first method solely relies on the relationship between hydraulic properties and burial depths. The second more complex strategy allows more spatial variations of hydraulic parameters using pilot points. The study provides new insights and practical guidance on the application of groundwater modelling for environmental impact assessment. The results suggest that the choice of model parameterization has a significant influence on predictive uncertainty. The model using the simple parameterization provides predictions with a much wider range than the model with a more sophisticated parameterization. This is because that the lowly parameterized model tends to generate more extreme effective hydraulic parameter fields unless the parameterization simplification converts the inverse problem to a (close to) well-posed problem that rarely exists for applied regional groundwater modelling. The potential impact of model parameterization should be discussed explicitly in groundwater modelling applications to support decision making to avoid misinterpretation of the modelling results.

Assessment of Aquifer Storage and Recovery Feasibility Using Numerical Modeling and Geospatial Analysis: Application in Louisiana

AbstractAquifer storage and recovery (ASR) is a solution for regions experiencing groundwater shortages, but is unexplored in wet regions such as Louisiana, which is experiencing aquifer overdrafting at alarming rates. Surface storage reservoirs are infeasible in these low‐gradient environments, so ASR can provide an alternative to alleviate groundwater stress and prevent subsidence and saltwater intrusion. The purpose of this study was to assess the feasibility of ASR in the Chicot Aquifer in Southwest Louisiana. The study is based on a regional groundwater model combined with a geospatial analysis of the quantity and quality of surface water and groundwater resources and land use. A statistical distribution was used to rate each criterion and combine them into a suitability index (SI) that defines each watershed’s feasibility considering combinations of criteria determined by the user’s purpose for ASR and the availability of data. The SI was formulated as a hybrid additive‐multiplicative function to provide flexibility in specifying criteria that are deemed most constraining for ASR feasibility. The analysis identified the east‐central zone of the Chicot Aquifer, which is experiencing substantial groundwater stress from agricultural irrigation, as most suited for ASR operations. Besides the criteria on water availability and aquifer characteristics, the quality of the surface water and land‐use considerations were key factors in constraining the feasible watersheds.

Testifying the Aquifer Response Under the Stress of Different Scenarios of an Expected Shortage of Surface Water: Case Study South Eastern Nile Delta Fringes, Egypt

Groundwater is considered one of the important sources in Egypt. However, it is expected to face many challenges in the next few decades. The Eastern Nile delta fringes region, the current area of interest, is one of the most highly developed areas in Egypt for more than three decades. Special attention will be given to the existing large reclamation lands (surface water/groundwater) in the high desert lands and low ones which are adjacent and surrounding the Ismailia canal. Under the expected stress of extensive shortage in surface water of the Nile water system, as a result of the construction of GERD, the rapid population and urbanization, a direct impact on the groundwater system in terms of groundwater levels and water budget will be expected. The main research question of the present study is: what is the response of the Nile Delta Aquifer in the south Eastern Nile Delta Fringes in the case of crisis for the sustainability of existing large projects? Visual MODFLOW was used to simulate the existing condition of the irrigation canals and the expected changes under different scenarios of water shortage. The model was simulated and calibrated for the initial hydrogeological conditions throughout the period (1992-2015). The model was tested for scenarios based on the final calibration as an initial condition. Four scenarios were proposed and simulated for the calibrated regional groundwater model at the study area to evaluate and predict the response of the quaternary aquifer during the decrease of surface water levels for 20 years. These scenarios are: 1. Decrease of the surface water levels by 10% against drainage surplus this expression represents the net recharge to the aquifer all the year, 2. Decrease of the surface water levels by 10% against seasonal drainage surplus for six months (summer, winter), 3. Decrease of the surface water levels by 20% against drainage surplus all the year and 4. Decrease of the surface water levels by 20% against seasonal drainage surplus for six months (summer, winter). The results of simulated scenarios showed a change and fluctuation in the groundwater levels, while the maximum value of the change in storage was found in scenario 4.in which this value was decreased by 52.9 % between 2017 and 2037. but in all scenarios, the change in storage of the aquifer still stable and continuously increase, by 36.5% under scenario 2 and 29 % under scenario 4. This volume of storage will be available for pumping by extraction wells in case of surface water reduction. Keywords: Groundwater, Surface water, GERD, water budget, change in storage. DOI: 10.7176/CER/13-3-04 Publication date: May 31 st 2021

Comparison of Surface Water‐Groundwater Exchange Fluxes Derived From Hydraulic and Geochemical Methods and a Regional Groundwater Model

AbstractIntercomparison of surface water‐groundwater (SW‐GW) exchange fluxes at the regional scale is rarely undertaken, mainly because estimates are method and scale‐dependent and usually associated with large errors. In the present study, we compare SW‐GW exchange fluxes calculated from a multitracer mass balance in the river, an application of Darcy's law using near‐river piezometers and a surface‐subsurface flow model calibrated at the catchment scale. SW‐GW exchange fluxes are estimated for 7 km long reaches along the 140 km long Campaspe River, a tributary of the Murray River, Australia. Differences are found in the directions and magnitudes of the exchange fluxes estimated by the different methods. The application of Darcy's law in near‐river piezometers seems the most appropriate method to infer SW‐GW flow directions and temporal variability. The tracer mass balance is limited to gaining reaches but gives quantitative estimates of the fluxes. While numerical models should overcome deficiencies associated with some of the intrinsic assumptions of the two field‐methods, the regional‐scale calibration is subject to high uncertainties in the simulated heads near the river, resulting in uncertainty of SW‐GW exchange fluxes. In particular, we show that loosely quantified river abstractions and irrigation patterns directly impact the simulated SW‐GW fluxes. In gaining reaches, additional river chemistry data improved model calibration and SW‐GW flux estimates. While numerical models are crucial for water management, their reliability to estimate SW‐GW fluxes can be limited by their complexity and lacking data availability. Therefore, we recommend comparing numerical model results with easily implemented field‐based methods.

Hindcasting multidecadal predevelopment groundwater levels in the Floridan aquifer.

Establishing predevelopment benchmark groundwater conditions is challenging without long-term records to discern impacts of pumping and climate change on aquifer levels. Understanding periodic natural cycles and trends require 100 years or more data which rarely exist. Using limited records, we develop an approach to hindcast multidecadal levels and examine the temporal evolution of climatic and pumping impacts. The methodology includes a wavelet-aided statistical model, constrained by temporal scales of physical processes responsible for groundwater level variation, including rainfall, evapotranspiration and pumping stresses. The model and hindcasts are tested at three sites in Florida using traditional split calibration-verification methods for the period of record and with the documented historical drought and wet years for the period of no-record. The pumping impact is quantified over time and compared with regional groundwater models, revealing that withdrawals are responsible for 30 to 70% of the declines in levels since 1960s. Hindcasting yielding 110 years of monthly levels is used to assess the effect of climate change and pumping on the frequency of critical low levels. At all three sites, the frequencies of critical low levels increase significantly in the 1960 to 2015 period when compared to the 1904 to 1959 period. For example, at site 1, the return period of the critical low level is shortened by 3.9 years due to climate change and 2.2 years due to pumping.

Comparison of Groundwater Storage Changes From GRACE Satellites With Monitoring and Modeling of Major U.S. Aquifers

AbstractGRACE satellite data are widely used to estimate groundwater storage (GWS) changes in aquifers globally; however, comparisons with GW monitoring and modeling data are limited. Here we compared GWS changes from GRACE over 15 yr (2002–2017) in 14 major U.S. aquifers with groundwater‐level (GWL) monitoring data in ~23,000 wells and with regional and global hydrologic and land surface models. Results show declining GWS trends from GRACE data in the six southwestern and south‐central U.S. aquifers, totaling −90 km3 over 15 yr, related to long‐term (5–15 yr) droughts, and exceeding Lake Mead volume by ~2.5×. GWS trends in most remaining aquifers were stable or slightly rising. GRACE‐derived GWS changes agree with GWL monitoring data in most aquifers (correlation coefficients, R = 0.52–0.95), showing that GRACE satellites capture groundwater (GW) dynamics. Regional GW models (eight models) generally show similar or greater GWS trends than those from GRACE. Large discrepancies in the Mississippi Embayment aquifer, with modeled GWS decline approximately four times that of GRACE, may reflect uncertainties in model storage parameters, stream capture, pumpage, and/or recharge rates. Global hydrologic models (2003–2014), which include GW pumping, generally overestimate GRACE GWS depletion (total: approximately −172 to −186 km3) in heavily exploited aquifers in southwestern and south‐central U.S. by ~2.4× (GRACE: −74 km3), underscoring needed modeling improvements relative to anthropogenic impacts. Global land surface models tend to track GRACE GWS dynamics better than global hydrologic models. Intercomparing remote sensing, monitoring, and modeling data underscores the importance of considering all data sources to constrain GWS uncertainties.

Regional Groundwater Modeling of the Guarani Aquifer System

The Guarani Aquifer System (GAS) is a strategic transboundary aquifer system shared by Brazil, Argentina, Paraguay and Uruguay. This article presents a groundwater flow model to assess the GAS system in terms of regional flow patterns, water balance and overall recharge. Despite the continental dimension of GAS, groundwater recharge is restricted to narrow outcrop zones. An important part is discharged into local watersheds, whereas a minor amount reaches the confined part. A three-dimensional finite element groundwater-flow model of the entire GAS system was constructed to obtain a better understanding of the prevailing flow dynamics and more reliable estimates of groundwater recharge. Our results show that recharge rates effectively contributing to the regional GAS water balance are only approximately 0.6 km3/year (about 4.9 mm/year). These rates are much smaller than previous estimates, including of deep recharge approximations commonly used for water resources management. Higher recharge rates were also not compatible with known 81Kr groundwater age estimates, as well as with calculated residence times using a particle tracking algorithm.

An integrated modelling approach for assessing the effect of multiscale complexity on groundwater source yields

A new multi-scale groundwater modelling methodology is presented to simulate pumped water levels in abstraction boreholes within regional groundwater models, providing a robust tool for assessing the sustainable yield of supply boreholes and improving our understanding of groundwater availability during drought. A 3D borehole-scale model, which solves the Darcy-Forchheimer equation in cylindrical co-ordinates to simulate both linear and non-linear radial flow to a borehole in a heterogeneous aquifer, is embedded within a Cartesian grid, using a hybrid radial-Cartesian finite difference method. The local-scale model is coupled to a regional groundwater model, ZOOMQ3D, using the OpenMI model linkage software, providing a flexible and efficient tool for assessing the behaviour of a groundwater source within its regional hydrogeological context during historic droughts and under climate change. The advantages of the new method are demonstrated through application to a Chalk supply borehole in the UK.

Relationships between riparian evapotranspiration and groundwater depth along a semiarid irrigated river valley

AbstractEvapotranspiration (ET) from riparian vegetation can be difficult to estimate due to relatively abundant water supply, spatial vegetation heterogeneity, and interactions with anthropogenic influences such as shallower groundwater tables, increased salinity, and nonpoint source pollution induced by irrigation. In semiarid south‐eastern Colorado, reliable ET estimates are scarce for the riparian corridor that borders the Arkansas River. This work investigates relationships between the riparian ecosystem along the Arkansas River and an underlying alluvial aquifer using ET estimates from remotely sensed data and modelled water table depths. Results from a calibrated, finite‐difference groundwater model are used to estimate weekly water table fluctuations in the riparian ecosystem from 1999 to 2009, and estimates of ET are calculated using the Operational Simplified Surface Energy Balance (SSEBop) model with over 200 Landsat scenes covering over 30 km2 of riparian ecosystem along a 70‐km stretch of the river. Comparison of calculated monthly SSEBop ET to estimated alfalfa reference ET from local micrometeorological station data indicated statistically significant high linear correspondence (R2 = .87). Daily calculated SSEBop ET showed statistically significant moderate linear correspondence with data from a local weighing lysimeter (R2 = .59). Simulated monthly SSEBop ET values were larger in drier years compared with wetter years, and ET variability was also larger in drier years. Peak ET most commonly occurred during the month of June for all 11 years of analysis. Relationships between ET and water table depth showed that peak monthly ET was highest when groundwater depths were less than about 3 m, and ET values were significantly lower for groundwater depths greater than 3 m. Negative sample Spearman correlation highlighted riparian corridor locations where ET increased as a result of decreased groundwater depths across years with different hydroclimatic conditions. This study shows how a combination of remotely sensed riparian ET estimates and a regional groundwater model can improve our understanding of linkages between riparian consumptive use and near‐river groundwater conditions influenced by irrigation return flow and different climatic drivers.

Groundwater resource management based on three-dimensional flow modeling of Wadi Baysh aquifer system: southwestern Saudi Arabia

Regional groundwater modeling is a valuable tool for ensuring the sustainable development and management of groundwater resources as it allows the assessment of the aquifer behavior under different types of hydrological stresses. The objective of this study was to use 3D flow modeling to assess the best options for managing groundwater in the Wadi Baysh basin in Saudi Arabia. The model for the Wadi Baysh aquifer system was based on groundwater monitoring data for 10-year period from 2007 to 2016. The model was tested with different hydrological stresses until the year 2050. The model behavior shows that groundwater levels in Wadi Baysh aquifer show no signs of depletion at the current pumping rates. The impact of the water stored in the dam reservoir is clearly seen and the zone of influence is very well demarcated. At this stage, groundwater use in the Wadi Baysh aquifer system is sustainable and no decline in groundwater levels is observed.

Assessment of Groundwater Recharge, Evaporation, and Runoff in the Drava Basin in Hungary with the WetSpass Model

The assessment of spatial and temporal distribution of groundwater recharge is required as an input to develop the regional groundwater model in the Drava flood plain for more accurate simulations of different management scenarios. WetSpass-M, a GIS-based spatially-distributed water balance model, was implemented to assess monthly, seasonal, and the annual averages of groundwater recharge, surface runoff and actual evapotranspiration in the Drava basin, Hungary for the period between 2000–2018. The basic relevant input-data for the Wetspass-M model is prepared in grid-maps using the tool ARCGIS tool. It comprises monthly climatological recordings (e.g., rainfall, temperature, wind speed), distributed land cover, soil map, groundwater depth, topography, and slope. The long-term temporal and spatial average monthly precipitation (58 mm) is distributed as 29% (17 mm) surface runoff, 27% (16 mm) actual evapotranspiration, and 44% (25 mm) groundwater recharge. The mean annual groundwater recharge, actual evapotranspiration, and surface runoff were 307, 190, and 199 mm, respectively. The findings of the WetSpass-M model are intended to support integrated groundwater modeling. The analysis of simulation results shows that WetSpass-M model works properly to simulate hydrological water budget components in the Drava basin. Moreover, a better understanding of the simulated long-term average spatial distribution about water balance components is useful for managing and planning the available water resources in the Drava basin.

Regional-Scale Analysis of the Effect of Managed Aquifer Recharge on Saltwater Intrusion in Irrigated Coastal Aquifers: Long-Term Groundwater Observations and Model Simulations in NE Tunisia

Bachtouli, S. and Comte, J.-C., 2019. Regional-scale analysis of the effect of managed aquifer recharge on saltwater intrusion in irrigated coastal aquifers: Long-term groundwater observations and model simulations in NE Tunisia. Journal of Coastal Research, 35(1), 91–109. Coconut Creek (Florida), ISSN 0749-0208.In overexploited coastal aquifers threatened or affected by saline intrusion, managed aquifer recharge (MAR) is increasingly applied in the aim of maintaining or recovering freshwater quantity and quality. The long-term regionalscale effectiveness of MAR, however, lacks field examples. The Korba coastal aquifer (Tunisia) has been increasingly overexploited since the 1960s and intensively studied over the last few decades. Groundwater abstraction has resulted in a decline of groundwater levels and a dramatic increase in salinity through both lateral seawater intrusion and shallow salinization from irrigation. MAR strategies, including freshwater injection wells and sewage-water infiltration basins, have been progressively implemented since 1990. Using 50 years of groundwater head and salinity records, a regional three-dimensional numerical groundwater model is calibrated to study the spatiotemporal dynamics of groundwater salinization including the past and future impact of the MAR operations. Results suggest that lateral seawater intrusion from the coast and shallow infiltration of evapoconcentrated saline irrigation water are the two interlinked dominant regional processes of groundwater salinization, equivalent in magnitude. In accordance with the groundwater observations, simulated historical MAR operations are shown to have contributed to slowdown and stabilized the regional salinization, which contrasts with the steady rise that is obtained in the hypothetical absence of MAR. The future MAR simulation scenarios suggest that spatial management of irrigation supplies and injection points from dam freshwater has a potential for further reducing the salinization of shallow groundwater and potentially reversing the inland progression of the seawater front. Further works should look at reconciling modelling recommendations with management practice options.

Impacts of groundwater depth on regional scale soil gleyization under changing climate in the Poyang Lake Basin, China

Various natural and anthropogenic factors affect the formation of gleyed soil. It is a major challenge to identify the key hazard factors and evaluate the dynamic evolutionary process of soil gleyization at a regional scale under future climate change. This study addressed this complex challenge based on regional groundwater modelling for a typical agriculture region located in the Ganjiang River Delta (GRD) of Poyang Lake Basin, China. We first implemented in-situ soil sampling analysis and column experiments under different water depths to examine the statistical relationship between groundwater depth (GD) and gleyization indexes including active reducing substance, ferrous iron content, and redox potential. Subsequently, a three-dimensional groundwater flow numerical model for the GRD was established to evaluate the impacts of the historical average level and future climate change on vadose saturation and soil gleyization (averaged over 2016–2050) in the irrigated farmland. Three climate change scenarios associated with carbon dioxide emission (A1B, A2, and B1) were predicted by the ECHAM5 global circulation model published in IPCC Assessment Report (2007). The ECHAM5 outputs were applied to quantify the variation of groundwater level and to identify the potential maximum gleyed zones affected by the changes of meteorological and hydrological conditions. The results of this study indicate that GD is an indirect indicator for predicting the gradation of soil gleyization at the regional scale, and that the GRD will suffer considerable soil gleyization by 2050 due to fluctuations of the water table induced by future climate changes. Compared with the annually average condition, the climate scenario B1 will probably exacerbate soil gleyization with an 8.8% increase in total gleyed area in GRD. On average, the highly gleyed areas will increase in area by 29.7 km2, mainly on the riverside area, and the medium-slightly gleyed area will increase by 19.2 km2 in the middle region.

A Regional Scale Hydrostratigraphy Generated from Geophysical Data of Varying Age, Type, and Quality

In the present study, we show how persistent management and collection of hydrological and geophysical data at a national scale can be combined with innovative analysis methods to generate decision support tools for groundwater and surface water managers. This is exemplified by setting up a regional scale groundwater model in an area with geophysical data of varying age, type, and quality. The structure for the regional model is derived from a newly developed resistivity clay-fraction cluster analysis. This modelling strategy can be used in combination with local detailed geological modelling thus utilizing the detailed expertise locally, while securing a cost-effective (price vs. performance) solution to the numerical simulations of the regional scale water balance. In this way we avoid unwanted boundary effects on the local model simulations due to the presence of artificial numerical boundaries located proximate to the areas of interest. In this application, it is particularly important that boundary conditions are remote, due to the presence of a dense network of buried valley structures. Simulated impacts of groundwater abstraction from two existing well-fields spread through the valley system far beyond the local focus areas of the study.

Hydrogeology of an arid endorheic basin (Tsagaan Els, Dornogobi, Mongolia): field data and conceptualization, three-dimensional groundwater modeling, and water budget

The Tsagaan Els basin is a ~16,300 km2 endorheic basin located in the Gobi Desert in Mongolia. This Cretaceous sedimentary basin is crossed by the North Zuunbayan fault, which determines two partially connected hydrogeological sub-basins: Zuunbayan and Unegt. Two roll-front uranium ore deposits have been discovered in these sub-basins by Orano Mining and its subsidiary COGEGOBI LLC, and the regional aquifers have been surveyed for several years. Based on that knowledge, this study presents the regional hydrogeological functioning of this multi-layered aquifer system supported by a regional groundwater model. The latter was implemented with MODFLOW and calibrated through PEST using piezometric levels. Recharge rates were adjusted to between 0.6 and 3.1 mm/year. The resulting water budget indicates an important transfer of water from Unegt sub-basin toward Zuunbayan sub-basin, occurring at a few main springs located along the North Zuunbayan fault. Evaporation loss is potentially high during these transfers but the remaining water seeps through and later evaporates in the depression located at the center of Zuunbayan sub-basin, which is the terminal discharge playa of the entire basin. These results can be helpful for future water management plans.

A novel framework for filling data gaps in groundwater level observations

Abstract Groundwater level knowledge is one of the crucial information for sustainable use of groundwater resources and efficient and effective conjunctive management of surface and groundwater resources. Despite the fact that there is an increase of water related datasets collected, still groundwater information remains one of the Achilles heel in terms of analysis and modeling. The present paper is introducing a novel framework for filling data gaps in groundwater time series in an efficient scheme with low computational cost. It utilizes direct (known measurements) and auxiliary (regional groundwater model) available information. The framework employs an exogenous seasonal autoregressive integrated moving average (SARIMAX) stochastic model to describe the simulated groundwater level fluctuation process of a regional physical groundwater model and the Ensemble Smoother (ES) for predicting the water table level. The framework was evaluated by conducting three numerical experiments for five groundwater wells in the South Platte alluvial aquifer. The results indicate that this framework could serve as a valuable tool for the enhancement of groundwater time series, for both intermittent missing data and of continuous gaps with short span, which could then lift hindrances in their analysis and use in groundwater models, and thus aid water management decisions.

Regional groundwater flow model for Abu Dhabi Emirate: scenario-based investigation

Despite the continuous increase in water supply from desalination plants in the Emirate of Abu Dhabi, groundwater remains the major source of fresh water satisfying domestic and agricultural demands. Groundwater has always been considered as a strategic water source towards groundwater security in the Emirate. Understanding the groundwater flow system, including identification of recharge and discharge areas, is a crucial step towards proper management of this precious source. One main tool to achieve such goal is a groundwater model development. As such, the main aim of this paper is to develop a regional groundwater flow model for the surficial aquifer in Abu Dhabi Emirate using MODFLOW. Up to our knowledge, this is the first regional numerical groundwater flow model for Abu Dhabi Emirate. After steady state and transient model calibration, several future scenarios of recharge and pumping are simulated. Results indicate that groundwater pumping remains several times higher than aquifer recharge from rainfall, which provides between 2 and 5% of total aquifer recharge. The largest contribution of recharge is due to subsurface inflow from the eastern Oman Mountains. While rainfall induced groundwater level fluctuation is absent in the western coastal region, it reaches a maximum of 0.5 m in the eastern part of the Emirate. In contrast, over the past decades, groundwater levels have declined annually by 0.5 m on average with local extremes spanning from 93 m of decline to 60 m of increase. Results also indicate that a further decrease in groundwater levels is expected in most of Emirate. At other few locations, upwelling of groundwater is expected due to a combination of reduced pumping and increased infiltration of water from nonconventional sources. Beyond results presented here, this regional groundwater model is expected to provide an effective tool to water resources managers in Abu Dhabi. It will help to accurately estimate sustainable extraction rates, assess groundwater availability, and identify pathways and velocity of groundwater flow as crucial information for identifying the best locations for artificial recharge.

Improving the Reliability of Numerical Groundwater Modeling in a Data-Sparse Region

In data-sparse areas, due to the lack of hydrogeological data, numerical groundwater models have some uncertainties. In this paper, a nested model and a multi-index calibration method are used to improve the reliability of a numerical groundwater model in a data-sparse region, the Nalinggele River catchment in the Qaidam Basin. Referencing this key study area, a regional three-dimensional groundwater flow model is developed in a relatively complete hydrogeological unit. A complex set of calibration indices, including groundwater fitting errors, dynamic groundwater trends, spring discharges, overflow zone location, and groundwater budget status, are proposed to calibrate the regional numerical groundwater model in the Nalinggele alluvial–proluvial fan. Constrained by regional groundwater modeling results, a local-scale groundwater model is developed, and the hydrogeological parameters are investigated to improve modeling accuracy and reliability in this data-sparse region.