Simulated Hydraulic Heads Research Articles

Numerical impact of variable volumes of Monte Carlo simulations of heterogeneous conductivity fields in groundwater flow models

The knowledge of aquifer systems, their geological setting, their structure, and subsequent modeling is highly uncertain and is usually faced through Monte Carlo-based methods in hydrogeology. One of the most important uncertainty sources for groundwater models is represented by input hydraulic conductivities, related to the aquifer’s structure. There are no specific rules when simulating hydraulic conductivity fields within Monte Carlo frameworks to instruct numerical models, and information about employed conductivity fields and their numerical convergence is often not given. This technical work aims to fill this gap by investigating the impact of employing conductivity information upon different volumes of Monte Carlo simulations applied to a real case study. Thus, this work estimates the minimum volumes of Monte Carlo hydraulic conductivity fields to be employed in groundwater flow models for achieving numerically stable (i) boundary conditions, (ii) global model performances, and (iii) local ones such as simulated hydraulic heads. The present results aim to be indicative of similar hydrogeological settings and will serve as a basis for more complex ones and for investigating transport problems.

Numerical modeling of site-scale groundwater flow with stochastic parameterized hydraulic conductivity fields for geological disposal of high-level radioactive waste in China

Deep geological disposal is internationally accepted as a feasible and safe approach for high-level radioactive waste (HLW) disposal. To evaluate hydrogeological conditions in support of safety assessments for HLW disposal at the Xinchang preselected site in China, stochastic inverse models of site-scale groundwater flow were developed in this study to generate highly parameterized hydraulic conductivity fields for the fractured medium by adopting pilot point and null-space Monte Carlo methods. The hydraulic influence zones of the faults were carefully considered to have homogenous parameter values across the zones. A total of 120 multiple random realizations were generated to characterize the 3D spatial variations in hydraulic conductivity by conditioning to 1218 fixed pilot points. The simulated hydraulic heads of the realizations were in good agreement with observational data. The hydraulic conductivity fields close to the boreholes could be characterized in detail and had relatively low uncertainties. Furthermore, the hydraulic conductivity (K) values around underground research laboratory (URL) at the HLW disposal zone depth were less than 10−9 m/s. The K values obtained for most of the influence zones of these faults at this depth were consistent with hydraulic test data and ranged from 10−10 to 10−9 m/s, thereby indicating that the surrounding rock has low permeability and is suitable for HLW disposal. These findings offer new insights into hydrogeological conditions by providing key information on the permeability characteristics that need further focus on HLW disposal.

The Simulation of Seepage Through the Foundations: Hilla Canal Main Regulator as Case Study

This abstract describes a study on the Hilla Canal regulator using the SEEP/W program. The study aims to simulate and validate hydraulic head values obtained from the field. It provides information about the soil properties and mesh sizes used in the simulation and the governing equation used in the SEEP/W program. The simulation results are presented in the form of observed and simulated hydraulic head statistical and computational data, including RMSE, ME, and Maximum Relative Error. The study concludes that the model's performance is good, with an efficiency of 99.999%, and that the comparison of observed and simulated hydraulic head values confirms the model's validity. Overall, the study demonstrates the accuracy and applicability of the SEEP/W program for modeling hydraulic systems.

Inverse Modeling of Seepage Parameters Based on an Improved Gray Wolf Optimizer

The seepage parameters of the dam body and dam foundation are difficult to determine accurately and quickly. Based on the inverse analysis, a Gray Wolf Optimizer (GWO) was introduced into this study to search the target hydraulic conductivity. A novel approach for initialization, a polynomial-based nonlinear convergence factor, and weighting factors based on Euclidean norms and hierarchy were applied to improve GWO. The practicability and effectiveness of Improved Gray Wolf Optimizer (IGWO) were evaluated by numerical experiments. Taking Kakiwa dam located on the Muli River of China as a case, an inversion analysis for seepage parameters was accomplished by adopting the proposed optimization algorithm. The simulated hydraulic heads and seepage volume agree with measurements obtained from piezometers and measuring weir. The steady seepage field of the dam was analyzed. The results indicate the feasibility of IGWO in determining the seepage parameters of Kakiwa dam.

Modeling Monthly Nitrate Concentration in a Karst Spring with and without Discrete Conduit Flow

Understanding the coupled continuum pipe-flow framework for modeling contaminant transport in karst systems is critical for protecting water resources therein. This study simulated point and non-point source nitrate concentration in a karst spring and investigated the results generated from the flow and transport model with and without discrete conduit flow. CFPv2 and CMT3D models were integrated to address the changes in nitrate concentration at a monthly scale in a karst spring, and the results were compared with that from an equivalent porous media (EPM) model with high-hydraulic conductivity (K) zones set in the main karstified area to represent conduits. The results show that the CFPv2+CMT3D model is able to describe well the recession of nitrate concentration in spring discharge, and the relatively larger deviation (slower nitrate recession) from the observed trend for the EPM model is probably a result of the limitation of utilizing high hydraulic conductivity cells to represent conduit. Moreover, simulated hydraulic heads in poorly karstified areas from the two models both show slight differences from the observations (the head RMSE values of calibration/validation for CFPv2 and MODFLOW models are 0.16 m/0.25 m and 0.26 m/0.17 m, respectively), indicating the inclusion of conduits may not affect the simulation considerably, and the lower the proportion of karstic area, the slight effects brought from the inclusion of conduits in the model. For highly karstified areas, the CFPv2+CMT3D model could provide more accurate results (head RMSE of calibration/validation for CFPv2 and MODFLOW are 0.22 m/0.06 and 0.52 m/0.47 m, respectively), showing the coupled continuum pipe-flow framework may be more appropriate for applying to highly and maturely karstified areas where the variations in the behavior of flow and contaminant transport are more affected by turbulent flow regime.

Groundwater Recharge Assessment Using WetSpass and MODFLOW Coupling: The Case of Hormat-Golina Sub-basin, Northern Ethiopia

Water scarcity in northern Ethiopia, as well as its socio-economic relevance in terms of water demand for agriculture and domestic use, are at the root of the search for new groundwater resources and the development of groundwater models that can be used to control and manage the resource. The groundwater recharge of the Hormat-Golina sub basin was assessed using WetSpass-MODFLOW coupling. The goal of this paper is to assess the groundwater recharge in the Hormat-Golina sub-basin. These findings are then used to simulate the hydraulic head distribution using the MODFLOW groundwater flow simulation model. By comparing measured and simulated hydraulic heads, the steady state groundwater flow calibration was obtained. WetSpass calculated the mean annual evapotranspiration, surface runoff, and groundwater recharge to be 516.6, 204.9, and 35.6 mm, respectively. Groundwater recharge accounted for 4.7% of precipitation, while actual evapotranspiration and surface runoff accounted for 27% and 68% of precipitation, respectively. In such seasonal variations, the groundwater head distribution is 9.37 to 29.86 m in the winter (dry season), 9.53 to 29.89 m in the summer (wet season), and 9.58 to 30.17 m in the annual stress periods (recharges). For all stress periods, the estimated hydraulic heads in steady state fit well with the measured ones, with a correlation coefficient of 0.86 (summer, winter, and annual recharge). To preserve the resource's long-term viability, the balance between groundwater recharge and projected abstraction rates for agriculture and domestic water supply must be considered in future groundwater resource development plans in the valley.

A Method to Represent a Well in a Three-Dimensional Discrete Fracture Network Model.

In discrete fracture network (DFN) modeling, fractures are randomly generated and placed in the model domain. The rock matrix is considered impermeable. Small fractures and isolated fractures are often ignored to reduce computational expense. As a result, the rock matrix between fractures could be large and intersections may not be found between a well introduced in the model and the hydraulically connected fracture networks (fracture backbones). To overcome this issue, this study developed a method to conceptualize a well in a three-dimensional (3D) DFN using two orthogonal rectangular fractures oriented along the well's axis. Six parameters were introduced to parameterize the well screen and skin zone, and to control the connectivity between the well and the fracture backbones. The two orthogonal fractures were discretized using a high-resolution mesh to improve the quality of flow and transport simulations around and along the well. The method was successfully implemented within dfnWorks 2.0 (Hyman et al. 2015) to incorporate a well in a 3D DFN and to track particles leaving an injection well and migrating to a pumping well. Verification of the method against MODFLOW/MODPATH found a perfect match in simulated hydraulic head and particle tracking. Using three examples, the study showed that the method ensured the connectivity between wells and fracture backbones, and honored the physical processes of flow and transport along and around wells in DFNs. Recommendations are given for estimating the values of the six introduced well parameters in a real-world case study.

Open questions about the hydrodynamic behaviour of the deep, coastal aquifer of the Salento peninsula (south-eastern Italy): Coupling expert knowledge, data, and numerical modelling for testing hydrogeological conceptual models.

This paper investigates the role of numerical models for testing the suitability of Hydrogeological Conceptual Models (HCMs). This approach has been applied to model the hydrodynamics of the deep, karst aquifer of the Adriatic portion of the Salento peninsula (south-eastern Italy), focusing on a coastal sub-area between Lecce and Otranto. The scope was to test two HCMs for the explanation of anomalous piezometric levels close to the coast (from 4.0m to 4.5m above mean sea level) occurring in this sub-area. Two different hypothesis were tested, assuming that the hydraulic contact between the aquifer and the sea in this sub-area occurs (a) offshore (HCM-A), or (b) at the shoreline (HCM-B). In HCM-B, we assumed a hydraulic connection between the deep aquifer and the Pliocene superficial aquifer. Results show that both HCMs can explain the anomalous piezometric values recorded close to the coast, but HCM-B would not completely clarify such occurrence. Calibration results for HCM-B, indeed, show two points located north of Otranto where the simulated hydraulic head is underestimated by the model and shows a poor sensitivity to any model parameter. As such, this is probably due to local phenomena not considered in the modelling framework and requiring further investigations.

APPLIED FINITE DIFFERENCE METHOD FOR GROUNDWATER FLOW MODELING IN XAYSOMBOUN PROVINCE, LAO PDR

Groundwater modeling has become a popular approach and common of conducting groundwater flow and contaminant transport simulation. Consequently, in order to understand the behavior of groundwater flow, this study has established and developed conceptual model of groundwater at Phukham Copper - Gold operations mining. In addition, this study is applied Groundwater Modeling System (GMS) 6.5 software and using MOFLOW Package which employs advanced mathematics as Finite Difference Method (FDM). Steady Flow model is set up and calibrated within target ± 2 meters; then the model is run in MOFLOW in order to obtain acceptable observed and simulated hydraulic head by adjusting hydraulic conductivities and recharge values. Recharge rate is adjusted between 2% to 12% from annual rainfall 0.00475 m/d and it is found out to be 7.22 % or 0.00034 m/d. Model has come up with reasonable finding. Hence, root mean square error of steady state: layer1, 2, 3 and 4 are 1.840 m, 1.767 m, 1.963 m and 0.574 m, respectively. The coefficient of determination of steady state for layer1, 2, 3 and 4 are 0.965, 0.96, 0.959 and 0.985, respectively.

Spatially distributed sensitivity of simulated global groundwater heads and flows to hydraulic conductivity, groundwater recharge, and surface water body parameterization

Abstract. In global hydrological models, groundwater storages and flows are generally simulated by linear reservoir models. Recently, the first global gradient-based groundwater models were developed in order to improve the representation of groundwater–surface-water interactions, capillary rise, lateral flows, and human water use impacts. However, the reliability of model outputs is limited by a lack of data and by uncertain model assumptions that are necessary due to the coarse spatial resolution. The impact of data quality is presented in this study by showing the sensitivity of a groundwater model to changes in the only available global hydraulic conductivity dataset. To better understand the sensitivity of model output to uncertain spatially distributed parameters, we present the first application of a global sensitivity method for a global-scale groundwater model using nearly 2000 steady-state model runs of the global gradient-based groundwater model G3M. By applying the Morris method in a novel domain decomposition approach that identifies global hydrological response units, spatially distributed parameter sensitivities are determined for a computationally expensive model. Results indicate that globally simulated hydraulic heads are equally sensitive to hydraulic conductivity, groundwater recharge, and surface water body elevation, though parameter sensitivities vary regionally. For large areas of the globe, rivers are simulated to be either losing or gaining, depending on the parameter combination, indicating a high uncertainty in simulating the direction of flow between the two compartments. Mountainous and dry regions show a high variance in simulated head due to numerical instabilities of the model, limiting the reliability of computed sensitivities in these regions. This is likely caused by the uncertainty in surface water body elevation. We conclude that maps of spatially distributed sensitivities can help to understand the complex behavior of models that incorporate data with varying spatial uncertainties. The findings support the selection of possible calibration parameters and help to anticipate challenges for a transient coupling of the model.

Challenges in developing a global gradient-based groundwater model (G<sup>3</sup>M v1.0) for the integration into a global hydrological model

Abstract. In global hydrological models, groundwater (GW) is typically represented by a bucket-like linear groundwater reservoir. Reservoir models, however, (1) can only simulate GW discharge to surface water (SW) bodies but not recharge from SW to GW, (2) provide no information on the location of the GW table, and (3) assume that there is no GW flow among grid cells. This may lead, for example, to an underestimation of groundwater resources in semiarid areas where GW is often replenished by SW or to an underestimation of evapotranspiration where the GW table is close to the land surface. To overcome these limitations, it is necessary to replace the reservoir model in global hydrological models with a hydraulic head gradient-based GW flow model. We present G3M, a new global gradient-based GW model with a spatial resolution of 5′ (arcminutes), which is to be integrated into the 0.5∘ WaterGAP Global Hydrology Model (WGHM). The newly developed model framework enables in-memory coupling to WGHM while keeping overall runtime relatively low, which allows sensitivity analyses, calibration, and data assimilation. This paper presents the G3M concept and model design decisions that are specific to the large grid size required for a global-scale model. Model results under steady-state naturalized conditions, i.e., neglecting GW abstractions, are shown. Simulated hydraulic heads show better agreement to observations around the world compared to the model output of de Graaf et al. (2015). Locations of simulated SW recharge to GW are found, as is expected, in dry and mountainous regions but areal extent of SW recharge may be underestimated. Globally, GW discharge to rivers is by far the dominant flow component such that lateral GW flows only become a large fraction of total diffuse and focused recharge in the case of losing rivers, some mountainous areas, and some areas with very low GW recharge. A strong sensitivity of simulated hydraulic heads to the spatial resolution of the model and the related choice of the water table elevation of surface water bodies was found. We suggest to investigate how global-scale groundwater modeling at 5′ spatial resolution can benefit from more highly resolved land surface elevation data.

Numerical prediction of the long-term evolution of acid mine drainage at a waste rock pile site remediated with an HDPE-lined cover system

Remediation at former mining sites containing waste rock piles (WRPs) commonly involves the installation of a cover system over the waste rock to limit water and oxygen ingress and attenuate the impacts of acid mine drainage (AMD) to the environment. Cover systems containing high-density polyethylene (HDPE) liners have the attributes to be highly effective; however, their performance over the long-term is unknown. The objective of this study was to assess the long-term effectiveness of an ‘in-service’ HDPE-lined cover system for reducing AMD contamination at WRP sites. A numerical investigation of a former mining site containing a large WRP reclaimed with an HDPE cover is presented. A 3-D groundwater flow and contaminant transport model of the site was developed in FEFLOW to predict the spatial and temporal evolution of AMD over 100 years. Field parameters observed at 46 monitoring wells over a 5-year monitoring period (including hydraulic head, recharge, hydraulic conductivity and water quality) were used as key input and calibration parameters. The HDPE cover significantly reduced both water recharge to the waste rock (i.e., 512 to 50 mm/year) and AMD seepage to groundwater. Both the groundwater flow and contaminant transport (sulfate was used as an AMD tracer) components of the model were calibrated and verified to the observed field data, with strong correlations evident between observed and simulated hydraulic heads and sulfate concentrations, respectively. Long-term model predictions of AMD evolution indicated significant and continual reductions in sulfate concentrations over time at all well locations. Background concentration levels (25 mg/L) are expected to be reached within 40 years. This study has demonstrated that HDPE-lined cover systems can be highly effective in reducing AMD loading from WRPs and its impacts on the receiving environment.

Simulation of Groundwater Flow and Migration of the Radioactive Cobalt-60 from LAMA Nuclear Facility-Iraq

This study provides a simulation of groundwater flow and advective-dispersive migration of radioactive Co-60 through an aquifer with three layers, which release or leak to groundwater from the Active Metallurgy Testing Laboratory (LAMA) Nuclear Facility-Iraq due to the nuclear accident scenario. Processing Modflow for windows (PMWIN) and Modular Three-Dimensional Multispecies Transport (MT3DMS) Models were used for this purpose. The study area and the contaminated area were 12.7 km2 and 0.005625 km2, respectively. Water levels of the groundwater have been measured in six monitoring wells. The simulation time was assumed to have started in 2016. The PMWIN model simulated the flow for two scenarios of water level in Tigris River (average and minimum water levels). The MT3DMS model simulated 10 years of plume travel, beginning in 2016. The simulated Co-60 concentrations after five years of travel were 32.34 and 34.44 μg/m3 for the two scenarios. The maximum predicted Co-60 concentrations at the end of Year 10 were 34.86 and 37.31 μg/m3, respectively. The sensitivity analysis showed that the simulated hydraulic heads in the observation wells and the simulated plume of Co-60 were highly sensitive to changes in the effective porosity but less sensitive to changes in other parameters of the dispersion and chemical reaction processes. The time necessary to reach steady state condition was predicted to be approximately 16 years. The contaminated area was isolated by using remedial process which is represented by three fully penetrating pumping wells with a suitable flow rate (0.045 m3/s) for controlling the movement of Co-60 pollutant.

Coupling WetSpass and MODFLOW for groundwater recharge assessment: case study of the Takelsa multilayer aquifer, northeastern Tunisia

The water scarcity and its socio-economic significance with respect to water demand for agriculture, industry and tourism, in the northeastern Tunisia (Cap-Bon), are at the origin for prospecting new groundwater resources and for developing groundwater models that can be used to their control and management. The Takelsa multilayer aquifer is one of the important aquifers of the northeast in Tunisia. It is among the aquifers which are still slightly known in spite of its exploitation since the 80s. This paper is aimed to quantify the groundwater recharge of the Takelsa multilayer aquifer. The groundwater recharge is assessed using WetSpass which is a physically based model integrated in GIS ArcView as a raster model. The simulated results are given seasonally and yearly at the grid level. These results are subsequently incorporated in the groundwater flow simulation model MODFLOW in order to simulate the hydraulic head distribution. The steady state groundwater flow calibration was obtained by comparing the observed and the simulated hydraulic heads. The mean annual evapotranspiration, surface runoff and groundwater recharge simulated by WetSpass, are 461, 92 and 22 mm, respectively. The groundwater recharge represented 4.3% of the precipitation while 17.8% and 89% are respectively lost by surface runoff and evapotranspiration.

Hydraulic head and groundwater <sup>111</sup>Cd content interpolations using empirical Bayesian kriging (EBK) and geo-adaptive neuro-fuzzy inference system (geo-ANFIS)

In this study, hydraulic head and 111 Cd interpolations based on the geo-adaptive neuro-fuzzy inference system (Geo-ANFIS) and empirical Bayesian kriging (EBK) were performed for the alluvium unit of Karabaglar Polje in Mugla, Turkey. Hydraulic head measurements and 111 Cd analyses were done for 42 water wells during a snapshot campaign in April 2013. The main objective of this study was to compare Geo-ANFIS and EBK to interpolate hydraulic head and 111 Cd content of groundwater. Both models were applied on the same case study: alluvium of Karabaglar Polje, which covers an area of 25 km 2 in Mugla basin, in the southwest of Turkey. The ANFIS method (called ANFIS XY ) uses two reduced centred pre-processed inputs, which are cartesian coordinates (XY). Geo-ANFIS is tested on a 100-random-data subset of 8 data among 42, with the remaining data used to train and validate the models. ANFISXY and EBK were then used to interpolate hydraulic head and heavy metal distribution, on a 50 m 2 grid covering the study area for ANFIS XY , while a 100 m 2 grid was used for EBK. Both EBK- and ANFIS XY -simulated hydraulic head and 111 Cd distributions exhibit realistic patterns, with RMSE < 9 m and RMSE < 8 μg/L, respectively. In conclusion, EBK can be considered as a better interpolation method than ANFIS XY for both parameters. Keywords: ANFIS, EBK, interpolation, hydraulic head, metal, 111 Cd, alluvium, Mugla

Groundwater Resources Assessment and Impact Analysis Using a Conceptual Water Balance Model and Time Series Data Analysis: Case of Decision Making Tool

The allocation of groundwater resources has been a challenge for many years due to its unforeseen side effect and lag time issues, which are often overlooked. The full impact of groundwater utilization/abstraction takes time to realize its effect at its full. In this paper, long-term effects and groundwater dynamics were assessed using a water balance model and a time series analysis, respectively. Undeveloped groundwater systems are commonly found in a state of equilibrium, where, on average, equal amounts of water are recharged and discharged. A water budget is a static accounting of the state of the system at a given time, often before the system is developed. Water balance analysis was carried out together with the groundwater through flow, hydrograph, and surface-groundwater interaction analysis (base flow index) to develop a conceptual water balance model, which is a very basic representation of a complex natural aquifer system and is instrumental to constrain and build a robust numerical model that can be readily justified and updated. A noble approach was employed to assess and constrain the discharge coming out of the model area to sustain the lake level, located to the north of the study area, using the whole lake catchment and lake water balance analysis. Based on the lake water balance, there is a deficit between input and output computation, and hence there should be a groundwater input to sustain the historical lake area. The analysis showed that the model area contributes 40% of the lake catchment, and hence the portion of the groundwater inflow feeding the lake was computed. This is one of the means to constrain the discharge, which adds more confidence to the recharge estimation. This is very important because the size of a sustainable groundwater development usually depends on how much of the discharge from the system can be captured by the development. Capture is independent of the recharge. Instead, it depends on the dynamic response of the aquifer system to the development. The idea that knowing the recharge is important in determining the size of a sustainable groundwater development is a myth and has no basis. The important entity in determining how a groundwater system reaches a new equilibrium is capture. How capture occurs in an aquifer system is a dynamic process. Following this study, lake water balance assessment was indirectly considered as prior information for the numerical model calibration of the discharge from the model area using a conductance parameter. Conductance is a key parameter to estimate the discharge volume together with the change in the simulated hydraulic head between time steps. The water balance error highlights which one is more sensitive, and this could help to assist in planning for future data collection/field work and where to invest the money. The water balance computation helps to figure out the degree of surface-groundwater interaction, uncertainty, sensitive parameter, helps in the decision to invest time and money, and operates as a cross check with other analytical or numerical modelling.

Comparison of a black-box model to a traditional numerical model for Hydraulic Head Prediction

&lt;p&gt;Two different methodologies for hydraulic head simulation were compared in this study. The first methodology is a classic numerical groundwater flow simulation model, Princeton Transport Code (PTC), while the second one is a black-box approach that uses Artificial Neural Networks (ANNs). Both methodologies were implemented in the Bavaria region in Germany at thirty observation wells. When using PTC, meteorological and geological data are used in order to compute the simulated hydraulic head following the calibration of the appropriate model parameters. The ANNs use meteorological and hydrological data as input parameters. Different input parameters and ANN architectures were tested and the ANN with the best performance was compared with the PTC model simulation results. One ANN was trained for every observation well and the hydraulic head change was simulated on a daily time step. The performance of the two models was then compared based on the real field data from the study area. The cases in which one model outperforms the other were summarized, while the use of one instead of the other depends on the application and further use of the model.&amp;nbsp;&lt;/p&gt;

Fluctuations of fresh-saline water interface and of water table induced by sea tides in unconfined aquifers

This study examines effects of tides on fluctuations of the fresh-saline water interface and the groundwater level in unconfined coastal aquifers using a two-dimensional numerical model. The time-lags of the simulated hydraulic heads and salinities fluctuations compared to sea level fluctuations are analyzed using cross-correlation analysis. The results show that both the fresh-saline water interface and the groundwater level are affected harmonically by sea tide fluctuations. However, significantly different time-lags are obtained between the hydraulic head in the deeper and upper parts of the aquifer, and between head and salinity in the fresh-saline water interface. The hydraulic head in the deeper part of the aquifer responses much faster to sea level fluctuations than in the upper part. Surprisingly, a similar difference is detected between the time-lag of the hydraulic head in the fresh-saline water interface and the time-lag of the salinity at the same location. Furthermore, the time-lag of the salinity in the fresh-saline water interface is similar to the time-lag of the water table. We suggest a comprehensive mechanism for tidal influence on the coastal groundwater system, in which two main processes act simultaneously. First, sea tide causes a pressure head wave which propagates into the saturated zone of the aquifer, governed by the diffusivity of the aquifer (Ks/Ss). Second, this pressure head wave is attenuated at the water table due to the unsaturated flow within the capillary fringe which occurs during groundwater level oscillations. Because the tidal forcing acts on the sea-floor boundary and the attenuation of the groundwater level due to capillary effect acts on the groundwater table, two dimensional distributions of time-lag and hydraulic head amplitude are created. The capillary effect in the unsaturated zone plays a key role not only in the water table fluctuations as shown previously, but also on the salinity fluctuations in the fresh-saline water interface. Unsaturated flow dynamics controls the actual movement of the entire fresh water body, which results in simultaneous fluctuations of the groundwater level and the fresh-saline water interface.

Ground water flow modeling for calibrating steady state using MODFLOW software: a case study of Mahesh River basin, India

MODFLOW is a groundwater modelling program. It can be compiled and remedied according to the practical applications. Because structure and fixed data format, MODFLOW can be integrated with geographic information system (GIS) for ground water resource management. Groundwater is a distinguished component of the hydrologic cycle. Groundwater is the water which occupies the voids in the saturated zone of earth’s crust (rocks). It moves and stores in pore space (voids) of sedimentary rocks or in the fractures and joints of hard rocks. The uncertainty about the occurrence, distribution and quality aspect of groundwater and the energy requirement for its withdrawal impose restriction on exploitation of groundwater. In spite of its uncertainty, groundwater is much protected from pollution; it requires little treatment before it use; it is available almost everywhere; it can be developed with little gestation period and can be supplied at a fairly steady rate. A groundwater model is thus a simplified version of the real system that approximately simulates the input–output stresses and response relations of the system. One has to understand here that normally the real system is simplified to model the system as such there is no unique model for a given groundwater system. Groundwater flow models are used to calculate the rate and direction of movement of groundwater through aquifers. The outputs from model simulation are the hydraulic heads and groundwater flow rates which are in equilibrium with the specified hydrogeological conditions (i.e. hydrogeological framework, hydrologic boundaries, initial and transient conditions, hydraulic properties and sources) defined for the modelled area. Groundwater models play an important role in the development and management of groundwater resources, and in predicting effects of management measures. With rapid increases in computation power and the wide availability of computers and model software, groundwater modelling has become a standard tool for professional hydrogeologists to effectively perform most tasks. Then, boundary conditions are adjusted with the aid of a scattergram to reduce bias of the simulated hydraulic head distribution of the equivalent homogeneous aquifer. The differences between the simulated mean hydraulic head and the observed hydraulic head, resulting from small-scale heterogeneities are then reduced by adjustment of local transmissivity values based on the hydrological and geological information. The results of this case study, which produced a number of reasonable as well as some unsatisfying simulations, demonstrate the potential of coupling a surface water model and a groundwater model to obtain more complex and accurate analyses and simulations of hydrologic systems. This paper presents the results of a mathematical groundwater model developed for the Mahesh River basin in the Akola and Buldhana districts, employing conceptual groundwater modelling approach. For this purpose, groundwater modelling software (GMS) was used which supports the Visual Modular three Dimensional Flow-20011 code. For the purpose of modelling the source/sink coverage, recharge coverage, extraction coverage, return flow coverage and soil coverage were considered. The model was calibrated against the historical and observed water level data for the period of 2013 and 2014.

Quantifying the Response Time of a Lake–Groundwater Interacting System to Climatic Perturbation

Response time, describing how quickly a disturbed system would reach a new equilibrium, has been helpful to hydrogeologists in characterizing and understanding the hydrogeological systems. This study examined the complex response times associated with lake–groundwater perturbed by climate. Simulated hydraulic heads and lake stage values derived from a 3-D, MODFLOW-based model were used to calculate the response times for a closed, groundwater-fed lake system. Although obviously coupled, the response times of the lake and groundwater systems were different from one another. Typically, the adjustments in hydraulic heads occurred more rapidly than lake stage. Response times for groundwaters close to the lake were controlled by the lake because of the slow transient response in stage. However, the influence of the lake declined toward the basin boundaries. This behavior occurred because critical parameters controlling the response-time behavior of the groundwater system (e.g., recharge rate) differed from those controlling the response-time behavior of the lake (e.g., bed leakance). An improved understanding of lake–groundwater behaviors have the potential to evaluate how lakes function as systems for recording paleoclimates.