Simulated Drawdown Research Articles

Neural network predictions of drawdown from groundwater abstraction in the Egebjerg catchment, Denmark

Results from numerical simulations play a vital role in the decision process of everyday groundwater management. However, these simulations can be time-consuming for large-scale investigations, and it can be necessary to apply approximate methods instead. This study investigates the abilities of a neural network to replicate simulated drawdown from groundwater abstraction in a numerical groundwater model of the Egebjerg catchment, Denmark. We follow a generalised methodology that uses the information within the deterministic numerical model to create a training set for the neural network to learn from and extend the method to work in a 3D Danish groundwater model case. We compare the abilities of the trained neural network with the results of conventional computations in terms of speed and accuracy and argue that this approach has the potential to improve decision support for decision-makers within groundwater management.

The importance of transboundary aquifer management between Poland and Ukraine for the protection of common water

Transboundary hydrogeological units between Poland and Ukraine within the Bug and San River basins are identified, based on harmonized geological and hydrogeological data used for development of a numerical simulation of groundwater flows across the state border. This numerical model shows that the cross-border exchange of groundwater in aquifers takes place in a limited area and the flow pattern can be disturbed by the groundwater exploitation. Abstraction at current levels slightly increases the transboundary groundwater flow from Poland to Ukraine and minimally reduces the flow in the opposite direction, though not reversing the direction of water flow at the border. The simulated drawdowns do not have a transboundary range, but negative effects on surface water resources are noticeable. Estimates show that groundwater runoff to rivers decreased and infiltration losses through the riverbed increased. The quantitative status of the transboundary aquifers has not deteriorated significantly under the current exploitation but in the light of ambitious maximum allowable values for water abstraction, and in the absence of joint resource management, this problem will arise in the near future. Joint management should focus on a broader legal consensus, improvement of institutional relations, and integration of monitoring and groundwater status assessment systems.

Understanding the Past-Present-Future Hydrogeologic System Through Numerical Groundwater Modeling of South Bengal Basin, India

The quaternary hydrogeologic system of the South Bengal Basin in India with low natural topographic gradients, such as deltas and floodplains, is complex. This research elaborates the hydrogeologic system in and around the twin megacities of Kolkata and Howrah located on this complex delta of the South Bengal Basin and the rapid urbanization pattern during the past 30 years to understand the past, present (2016), and future (2030) behavior of the aquifer system and the advective flow paths of contaminants (wastewater, arsenic, and heavy metals) through hydrogeological simulations and field data. The groundwater model has been calibrated and validated by using the observed and simulated head. The root mean square error of the model is 1.07 m. The built-up area has increased from 142 to 243 km2 between 1985 and 2016, resulting in over-pumping of groundwater. About 93% of the available groundwater is abstracted, and as a result, the piezometric surface is declining at a rate of 13–37 cm/year and the groundwater trough in Kolkata is expanding at the rate of 8.60 km2/year. At places, the confined aquifer is behaving as an unconfined one, increasing the threat of land subsidence. The water quality is deteriorating in parts of Kolkata city where the groundwater is contaminated with wastewater, arsenic, and heavy metals, particularly in boroughs VIII and X. Contaminants from industrial sites may reach the strainer depth (100–120 m bgl) of pumping wells within a period of 20–25 years. The maximum simulated drawdown with respect to the predevelopment head is 22 m. If over-pumping continues, then simulation indicates that the head may drop by another 1.94–2.20 m by 2030. All this may endanger the health and well-being of millions of people living in the area in the near future.

An alternative approach to designing hydrogeological conceptual models in cases of scarce field data

The sensitivity of the derivative analysis to the variation of flow rates allows it to solve ambiguities, provide diagnostics of the flow dimension, and identify the boundary conditions of the tested aquifer. Based on the results of a derivative analysis, it was hypothesized that the set of assumptions for the fitted solution to the drawdown curve are valid for the tested aquifer. Thus, combining the derivative analysis results and the detailed geological characterization, a new approach was developed to build preliminary conceptual hydrogeological models in cases where field data are scarce. Applying this approach, it was concluded that basaltic aquifers in the Serra Geral Aquifer System (SGAS) are comprised of leaky confined aquifers, which the alternation of basalt floods that have permeable horizons at the top and with low permeability of interior flow. The simulated drawdown curve in a transient flow model perfectly matched with the drawdown curve recorded in the field, thus supporting the suitability of the built conceptual model. This statement challenges the prevailing theory that conceptualizes SGAS as a fractured aquifer. Conclusively, the current approach is capable of producing suitable conceptual models in cases of field data scarcity. Future investigations in other complex geological contexts may validate the present approach.

Unlined trench as a falling head permeameter: Analytic and HYDRUS2D modeling versus sandbox experiment

An isosceles triangle in a vertical cross-section of a trench is considered as a boundary from which free water in the trench seeps into a porous bed. A finite, initially impounded water volume vanishes from the channel and soil moisture moves in conjugation with surface water in a transient 2-D saturated-unsaturated regime. If capillarity is ignored and the subjacent soil is assumed to be dry before filling the channel, then a wetting front propagates as a sharp interface mated with drawdown of the channel free water. A Lembke method of consecutive steady states is used to model the interface as a rotating straight-line. A zone of Darcian seepage is a triangle, three sides of which (at each time instance) are a streamline, a constant piezometric head line and isobar. The instantaneous hinge point of the interface demarcates a zone of imbibition from a zone of drainage of this saturated triangle. Mathematically, a Green-Ampt type nonlinear first order ODE is obtained and explicitly integrated by separation of variables and the drawdown time t is explicitly expressed through the water depth H in the trench. In a sandbox with a dune sand, an experimental H(t) is measured in a trench having mild and steep bank slopes. When H(t) > 0 the drawdown rate increases that is attributed to an increase of the effect of capillarity. For this stage, Riesenkampf’s analytical solution for steady 2D tension-saturated flow with a capillary fringe is used. The analytical and experimental results are compared with those obtained by HYDRUS-2D (numerical modeling), involving a reservoir boundary condition introduced for furrow irrigation applications. Model performance parameters including the root mean squared error (RMSE), mean absolute error (MAE), coefficient of determination (r2) and Nash-Sutcliffe efficiency (E) showed a good agreement between the measured and simulated values of drawdown time. Results of the t-test between the measured and simulated drawdown time showed insignificant differences at a 5% confidence interval for all the trenches (p > 0.05). HYDRUS simulations quantified the dynamics of a “sinking” saturated “bubble” under the trench: isobars, isotachs, streamlines and loci of the stagnation points are plotted. We illustrate how to use a drawdown curve H(t) for determination of saturated hydraulic conductivity and air-entrance pressure in the Vedernikov-Bouwer model.

Forensic Hydrology Reveals Why Groundwater Tables in The Province of Noord Brabant (The Netherlands) Dropped More Than Expected

Since the nineteen fifties, groundwater levels in the Netherlands dropped more than as simulated by hydrological models. In the rural sandy part of the Netherlands, the difference amounts to approximately 0.3 m on average. The answer to the question of what or who caused this ‘background decline’ of groundwater tables may have juridical and financial consequences, especially since Dutch farmers are entitled to financial compensation for crop damage caused by groundwater abstractions. In our forensic study, we investigated how anthropogenic changes in groundwater recharge from 1950 to 2010 affected groundwater levels. In this period, crop yields in agriculture have risen sharply, and, because crop water use is proportionate to crop production, this led to more crop evapotranspiration and subsequently less groundwater recharge. Urban expansion and forestation has also led to a decrease in groundwater recharge. We showed that these changes in recharge may have caused a decline of groundwater of 0.2–0.3 m over 60 years (1950–2010). The simulated drawdown caused by groundwater abstractions appeared to depend on the amount of groundwater recharge related to land use and crop yield. This means that to properly evaluate the effects of a particular groundwater abstraction, one should account for the hydrological history of the landscape since the start of that abstraction.

Determination of groundwater sustainable yield using a numerical modelling approach for the Table Mountain Group sandstone aquifer, Rawsonville, South Africa

Sustainable yield is defined as the amount of groundwater abstraction that can be maintained for an indefinite time without causing unacceptable environmental, economic and social consequences. It is usually determined by monitoring the water-table depth, without the need for costly pumping exercises and subsequent deterioration of the groundwater and ecological environment. Groundwater numerical modelling provides an effective way to determine the yield by analysing the responding water levels to various pumping scenarios. In this study, the natural flow system and flow with pumping scenarios were simulated using FEFLOW for the fractured-rock aquifer in Table Mountain Group, South Africa. Results for different pumping rates show the distinct impact of groundwater abstraction on hydraulic head, which indicates that long-term abstraction slowly increases the well drawdown, but it would stabilize at a level that is dependent on pumping rate and induced recharge. To estimate the aquifer sustainable yield, a relationship between simulated drawdown and pumping rate was established, namely an exponential function with parameters that may change value between sites. This empirical relation, derived from this site-specific study, provides an option for informed decision-making. The issue of how to sustainably abstract groundwater might rely on a compromise between the groundwater user and the governmental authority.

On the interpretation of multi-well aquifer-pumping tests in confined porous aquifers using the Cooper and Jacob (1946) method

The Cooper and Jacob (Trans Am Geophys Union 27:526–534. https://doi.org/10.1029/TR027i004p00526 ; Cooper, Jacob, Trans Am Geophys Union 27:526534, 1946) method is widely used to interpret data from both single- and multi-well aquifer-pumping tests in a porous homogenous and isotropic confined aquifer system. The method can be used to interpret both pumping and observation well drawdown. For observation wells (piezometers), the method said to be valid when u < 0.01 when drawdown observations are made in the near vicinity of the pumping well after a sufficiently long time of pumping. Despite the wide use of the method, the effects of using the Cooper and Jacob method to interpret multi-well aquifer-pumping test data are hardly discussed. The study illustrates and discusses the effect of using the Cooper and Jacob method to interpret multi-well aquifer-pumping tests. This is achieved with the help of simulations in 3 homogeneous one-layered confined and isotropic aquifer models using MODFLOW. Simulated drawdown is interpreted using the Cooper–Jacob method. The study shows that the transmissivity estimated from observation well data exponentially increases with the observation distance irrespective of the value of u. Only interpretation of pumping-well data with the Cooper and Jacob method correctly estimated the prescribed model transmissivity. Storativity estimates from observation data appears to decrease with increase in the observation distance as controlled by the Copper and Jacob equation but remained in the same order of magnitude as the prescribed model storativity. The study contributes towards a better practical understanding of the effects of using of using the Cooper and Jacob method to interpret multi-well aquifer-pumping test data for groundwater practitioners.

Probabilistic assessment of the impact of coal seam gas development on groundwater: Surat Basin, Australia

Modelling cumulative impacts of basin-scale coal seam gas (CSG) extraction is challenging due to the long time frames and spatial extent over which impacts occur combined with the need to consider local-scale processes. The computational burden of such models limits the ability to undertake calibration and sensitivity and uncertainty analyses. A framework is presented that integrates recently developed methods and tools to address the computational burdens of an assessment of drawdown impacts associated with rapid CSG development in the Surat Basin, Australia. The null space Monte Carlo method combined with singular value decomposition (SVD)-assisted regularisation was used to analyse the uncertainty of simulated drawdown impacts. The study also describes how the computational burden of assessing local-scale impacts was mitigated by adopting a novel combination of a nested modelling framework which incorporated a model emulator of drawdown in dual-phase flow conditions, and a methodology for representing local faulting. This combination provides a mechanism to support more reliable estimates of regional CSG-related drawdown predictions. The study indicates that uncertainties associated with boundary conditions are reduced significantly when expressing differences between scenarios. The results are analysed and distilled to enable the easy identification of areas where the simulated maximum drawdown impacts could exceed trigger points associated with legislative ‘make good’ requirements; trigger points require that either an adjustment in the development scheme or other measures are implemented to remediate the impact. This report contributes to the currently small body of work that describes modelling and uncertainty analyses of CSG extraction impacts on groundwater.

The upper pannonian thermal aquifer: Cross border cooperation as an essential step to transboundary groundwater management

Study RegionPannonian Basin, Central and Eastern Europe. Study focusThis study, carried out by the geological surveys of Hungary, Slovenia, Austria and Slovakia, combines a joint characterization of a transboundary thermal groundwater system based on harmonised geological and hydrogeological data, with hydrodynamic modelling, delivering recommendations for authorities and policy makers on how they could improve the long term management of thermal groundwater. A porous, intergranular, multi-layered, Upper Pannonian aquifer system was the focus of this investigation. This deep sedimentary basin, up to 8000 m deep, has favourable conditions for geothermal exploitation, with centuries old thermal water usage and plans for increased utilization in all countries. New hydrological insights for the regionCross border areas with significant transboundary flow rates were identified, which have decreased due to thermal water production, with flow direction reversal across the Hungarian-Slovakian border. Thermal water production causes significant transboundary effects with depression cones that can penetrate several tens of kilometres into the neighbouring countries. Simulated drawdowns at the state borders are in the range of 2–10 m. Thermal water should therefore be exploited using doublets.Nine benchmark indicators (monitoring status, best available technology, thermal efficiency, utilisation efficiency, re-injection rate, quality of discharged thermal water, over-abstraction, status of water balance assessment, public awareness) were defined and tested at different transboundary regions and are demonstrated to be highly effective in groundwater management.

Impact of model complexity and multi-scale data integration on the estimation of hydrogeological parameters in a dual-porosity aquifer

This study investigates the impact of model complexity and multi-scale prior hydrogeological data on the interpretation of pumping test data in a dual-porosity aquifer (the Chalk aquifer in England, UK). In order to characterize the hydrogeological properties, different approaches ranging from a traditional analytical solution (Theis approach) to more sophisticated numerical models with automatically calibrated input parameters are applied. Comparisons of results from the different approaches show that neither traditional analytical solutions nor a numerical model assuming a homogenous and isotropic aquifer can adequately explain the observed drawdowns. A better reproduction of the observed drawdowns in all seven monitoring locations is instead achieved when medium and local-scale prior information about the vertical hydraulic conductivity (K) distribution is used to constrain the model calibration process. In particular, the integration of medium-scale vertical K variations based on flowmeter measurements lead to an improvement in the goodness-of-fit of the simulated drawdowns of about 30%. Further improvements (up to 70%) were observed when a simple upscaling approach was used to integrate small-scale K data to constrain the automatic calibration process of the numerical model. Although the analysis focuses on a specific case study, these results provide insights about the representativeness of the estimates of hydrogeological properties based on different interpretations of pumping test data, and promote the integration of multi-scale data for the characterization of heterogeneous aquifers in complex hydrogeological settings.

Anthropogenic influences on groundwater in the vicinity of a long‐lived radioactive waste repository

AbstractThe groundwater flow system in the Culebra Dolomite Member (Culebra) of the Permian Rustler Formation is a potential radionuclide release pathway from the Waste Isolation Pilot Plant (WIPP), the only deep geological repository for transuranic waste in the United States. In early conceptual models of the Culebra, groundwater levels were not expected to fluctuate markedly, except in response to long‐term climatic changes, with response times on the order of hundreds to thousands of years. Recent groundwater pressures measured in monitoring wells record more than 25 m of drawdown. The fluctuations are attributed to pumping activities at a privately owned well that may be associated with the demand of the Permian Basin hydrocarbon industry for water. The unprecedented magnitude of drawdown provides an opportunity to quantitatively assess the influence of unplanned anthropogenic forcings near the WIPP. Spatially variable realizations of Culebra saturated hydraulic conductivity and specific storage were used to develop groundwater flow models to estimate a pumping rate for the private well and investigate its effect on advective transport. Simulated drawdown shows reasonable agreement with observations (average Model Efficiency coefficient = 0.7). Steepened hydraulic gradients associated with the pumping reduce estimates of conservative particle travel times across the domain by one half and shift the intersection of the average particle track with the compliance boundary by more than 2 km. The value of the transient simulations conducted for this study lies in their ability to (a) improve understanding of the Culebra groundwater flow system and (b) challenge the notion of time‐invariant land use in the vicinity of the WIPP.

Predicting Open Pit Mine Inflow and Recovery Depth in the Durvuljin soum, Zavkhan Province, Mongolia

Increasingly, mine issues and water resources are being managed on a watershed basis, while addressing problems at the local mine scale. A good example of this developed when empirical and analytical modelling of the potential inflow to an open pit mine in the Durvuljin soum, a region in northwest Mongolia, indicated that inflow would be on the order of 0.3 to 10.5 L/s. In this study, the radius of influence due to open pit mining was estimated to be between 0.6 and 3 km. Based on simulated drawdown contours and transient pit inflow figures that captured the impact of mining and groundwater inflow rate variations over a period of time, it appeared that advanced dewatering will not be required at this mine, unless currently unknown major fractured structures are intercepted. In-pit basal sumps and pumps should be sufficient to remove water from the mine floor. However, an assessment of the final pit level is also crucial to planning the post-mining surface and groundwater quality/eco-system and mitigation requirements during recovery. Our post-mining water table recovery estimate indicated that inflow will exceed evaporation and that a shallow lake will likely form. While such solutions, which do not rely on complex numerical models nor excessive input data, are not appropriate for all hydrogeologic situations, they are relevant to the conditions encountered at most mine sites.

Using Particle Swarm Optimization (PSO) Algorithm in Nonlinear Regression Well Test Analysis and Its Comparison with Levenberg-Marquardt Algorithm

Since two of the most important disadvantages of the classical nonlinear regression methods, such as Levenberg-Marquardt (LM), are to calculate error derivative function and use an initial point to get the results, PSO algorithm, which lies in the category of population based meta-heuristic algorithms, is used in this study to implement nonlinear regression in well test analysis. Root Mean Square Error (RMSE) over pressure and pressure derivative data are used in the cost function formulation and the multi-objective problem is reduced to single objective one by including the weight for each of the cost functions related to pressure and pressured derivative data. The superiority of the procedure developed in this study is verified through a simulated drawdown test and one field case. Error comparison over estimated reservoir parameters and analysis of 95% confidence interval reveal that implemented PSO algorithm can be used accurately to estimate reservoir properties.

Simulated drawdown and rewetting of littoral sediments: implications for Lobelia lake management

This study aims to answer the question if temporary drawdowns could be a beneficial restoration measure for endangered Lobelia lakes. Intact littoral sediment cores with and without plants were used to simulate a drawdown over an almost 5 months period and a subsequent rewetting. During drawdown, the initial low saturation of sorption sites for phosphorus (P) increased due to increased contents of mobile P forms in the surface layers. Contents of P binding iron forms remained constant. The increase of mobile P forms was mostly derived from decayed plant material since the experimental set up caused dying of plants. Upon rewetting effluxes of total dissolved phosphorus and dissolved organic carbon were observed which are most likely attributable to the degraded plant material. A phosphorus uptake experiment with dried and rewetted sediment cores without plants showed that the initial high P binding capacity had been retained during drying and rewetting. These findings were confirmed by a small scale long-term drying (348 days) and rewetting (228 days) experiment which overall did not show a significant reduction in P adsorption capacity. Therefore, drawdowns can be an appropriate restoration measure for endangered Lobelia lakes given that the isoetid plants spread during the drying period.

Mitigation of groundwater level deterioration of the Nubian Sandstone aquifer in Farafra Oasis, Western Desert, Egypt

El Farafra Oasis is included in the New Valley Project which started in the 1960s. This project is based exclusively on groundwater of the well-known Nubian Sandstone aquifer (NSA). The hydraulic head drawdown problem in Farafra Oasis constitutes a big problem because it threatens the availability of the only water source in the Oasis. Hydrogeologically, Farafra Oasis belongs to the huge, artesian, unrenewable fossil water Nubian from sandstone aquifer. The problem began to appear at the end of the 1990s instantaneously with increased drilling of deep water wells. Huge quantities of water (267 million m3) are derived from the aquifer every year. Hydraulic head depression cones are formed around the main reclamation areas where the groundwater surface lowered by 35 m below the ground surface. Numerical modeling was used to investigate the hydrodynamic impacts of the present and planned groundwater extraction on the groundwater levels besides the possible means of mitigating the continuous decrease of the groundwater levels. The aquifer simulation indicated that there is a significant head decline of the groundwater, particularly in the first productive zone. Four scenarios were applied to signify the present and future development plans for the next 20 years, i.e., year 2033. Applying the present conditions reveal that heads are more declined than now. Another 30 and 17.8 m in the first and second productive zones, respectively, are expected to be added to the present groundwater drawdowns. Groundwater is expected to decline significantly if the pumping rates are to be increased by 50 % in response to natural development of the agricultural society and continuous need to more cultivation lands. Groundwater heads are expected to be lower by about 40 m in the first productive zone and 24 m in the second productive zone. The third plan examines the impact of reducing the pumping rate by about 25 % on groundwater levels by applying recent irrigation techniques as drop and sprinkler irrigation methods instead of the presently used flood irrigation. In this case, simulated drawdowns are expected to decline, and the maximum drawdowns recorded are 19 and 10 m through the next 20 years in the first and second productive zones, respectively. To mitigate the groundwater level deterioration, the study suggests the reduction of pumping rates by about 20 % by applying the recent irrigation techniques besides reclamation of about 11,000 feddan (4620 hectare) to accommodate the increasing population and need of cultivation lands in the Oasis in the next 20 years. According to plan, the simulated groundwater levels are expected to decrease by about 20.3 and 12 m at the end of the simulation period (year 2033). This means that the rate of head decline is lowered to about 1 m/year for the first productive zone and 0.6 m/year for the second productive zone with the increase in the cultivation area by about 16 %. Therefore, the study recommends the fourth plan to manage the groundwater resource in Farafra Oasis.

Simulation of fully coupled finite element analysis of nonlinear hydraulic properties in land subsidence due to groundwater pumping

A fully coupled mathematical model of land subsidence caused by groundwater pumping was established based on the mechanics of porous seepage and the theory of fluid–solid interaction. The mathematical model employing the Galerkin finite element method was proposed to simulate the deformation dependencies of hydraulic properties due to the water pressure decrease in aquifers. This model has been verified by comparing with the known analytical solutions in the confined aquifer. Results show that the simulated drawdown and displacements match well with those of analytical solutions. To evaluate the nonlinear effects of hydraulic properties in the seepage and consolidation coupling phenomena, the numerical model is applied to an ideal three layers numerical experiment. The results show that the subsidence rate is faster than conventional groundwater theory when the nonlinear hydraulic properties (NHP) are considered in the coupled model. The reason is that the water level decline due to groundwater withdrawal induces the soil compression and the porosity and permeability decrease. Decrease of permeability in regions adjacent to the pumping well produces hydraulic gradient and seepage forces that may result in accelerated subsidence. Therefore, the effect of the NHP is an interaction process of pore water pressure and soil consolidation deformation and should not be ignored. Further studies of various hydrogeology problems are recommended to consider the heterogeneity concerning different stratigraphic condition in the field.

수막재배지역에서 일최저기온과 지하수 이용량의 상관관계를 이용한 지하수위 변화 분석

대규모 수막재배 시설은 동절기 수막재배 기간 동안 군집 취수정의 영향으로 지하수위가 하강하고 이로 인해 지하수 취수량 확보에 어려움을 겪고 있다. 본 연구에서는 동절기 수막재배지역에서의 집중취수에 따른 정밀한 지하수위 변화 분석을 수행하고자 한다. 대상지역인 청원군의 수막재배지역을 포함한 소유역의 지하수 유동을 모의하기 위해 3차원 유한차분모형인 MODFLOW를 구축하였으며, 중요한 입력자료인 지하수 함양량 시계열 자료는 유역수문모형 SWAT모형을 이용하여 구하였다. 여기에 수막재배지의 일최저기온과 취수가동시간과의 관계를 통해 지하수 이용량을 추정한 선행 연구(Moon et al., 2012)를 참고하여 취수계획을 수립, 지하수 모델링에 반영하였다. 부정류 모델링의 적합도를 평가하기 위해 동절기의 모의된 지하수위 강하 패턴을 관측지하수위 자료와 비교하였다. 모델링 기간은 수막재배가 본격적으로 이루어지는 2012년 11월부터 2013년 3월까지의 107일간으로 정하였다. 모의결과 동절기 지하수위 관측값과 비교적 유사한 지하수 하강을 재현할 수 있었고, 일최저기온을 이용한 취수계획방식이 다른 수막재배지역의 지하수 유동해석에도 적용가능할 것으로 판단되었다. Water curtain cultivation (WCC) systems in Korea have depleted water resources in shallow aquifers through massive pumping of groundwater. The goal of this study is to simulate the groundwater variations observed from massive groundwater pumping at a site in Cheongweon. MODFLOW was used to simulate three-dimensional regional groundwater flow, and the SWAT (Soil and Water Assessment Tool) watershed hydrologic model was employed to introduce temporal changes in groundwater recharge into the MODFLOW model input. Additionally, the estimation method for groundwater discharge in WCC areas (Moon et al., 2012) was incorporated into a groundwater pumping schedule as a MODFLOW input. We compared simulated data and field measurements to determine the degree to which winter season groundwater drawdown is effectively modeled. A simulation time of 107 days was selected to match the observed groundwater drawdown from November, 2012 to March, 2013. We obtained good agreement between the simulated drawdown and observed groundwater levels. Thus, the estimation method using daily minimum temperatures, may be applicable to other cultivation areas and can serve as a guideline in simulating the regional flow of riverside groundwater aquifers.

Evaluation of Pumping Induced Flow in Observation Wells During Aquifer Testing

The vertical variation of drawdown around pumping wells generates an induced flow in the observation wells. A set of governing equations is presented to couple the drawdown variation and the vertical flux distribution in observation wells. A numerical example is performed to justify the governing equations and to verify the solution methods used by the simulation software WT. The example analyzes the effect of skin loss, wellbore storage, and vertical segmentation on the drawdown and induced flow in observation well during pumping. The evaluation of the Fairborn pumping test involves a vertically homogeneous and anisotropic water table aquifer, uniform well-face drawdown conditions in the pumping well and simulation of the drawdown evolution in the observation well with and without the effect of induced flow. The computer calibrations resulted in small differences between the measured and simulated drawdown curves.

Simulating the effect of groundwater withdrawals on intermittent‐pond vegetation communities

ABSTRACTGroundwater withdrawals in a shallow unconfined aquifer can reduce water levels in connected wetlands and lead to changes in vegetation. I simulated the effect of withdrawals on the vegetation of intermittent ponds in the New Jersey Pinelands by first characterising the vegetation communities and associated hydrologic regimes of 15 ponds. A model, which was based on these results, was used in conjunction with simulated water‐level drawdowns to predict changes in plant communities. Five dominant vegetation communities found at the study ponds included Carex striata, Chamaedaphne calyculata, and Vaccinium corymbosum patch types and aquatic‐herbaceous and wetland‐herbaceous types, which represent combinations of other vegetation types. A vegetation‐hydrology model related mean vegetation cover for the five patch types to water level in 5‐cm classes. Groundwater withdrawals were simulated by reducing pond‐water depth by 5‐cm intervals, and the resulting changes in modelled vegetation were assessed. Aquatic‐herbaceous and wetland‐herbaceous patch types displayed reductions in area beginning at the smallest simulated drawdowns evaluated. C. striata patch area changed only slightly for drawdowns ≤10 cm, but decreased steadily in response to greater drawdowns. C. calyculata and V. corymbosum patch areas increased for water‐level reductions ≤15 cm and then decreased at drawdowns ≥20 cm. The area of combined pond‐vegetation types, which represents the entire pond as a single vegetation community, consistently decreased at reductions of ≥10 cm. These simulations suggest that groundwater withdrawals favour the expansion of woody species into intermittent ponds, with eventual replacement of pond vegetation by adjacent forest vegetation if extreme hydrologic modifications occur. Copyright © 2011 John Wiley &amp; Sons, Ltd.