scholarly journals Groundwater Parameter Inversion Using Topographic Constraints and a Zonal Adaptive Multiscale Procedure: A Case Study of an Alluvial Aquifer

Water ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1899 ◽  
Author(s):  
Dimitri Rambourg ◽  
Philippe Ackerer ◽  
Olivier Bildstein
Keyword(s):  
Parameter Estimation ◽  
Groundwater Flow ◽  
Unconfined Aquifer ◽  
Water Levels ◽  
Specific Yield ◽  
Local Minima ◽  
Diffusion Type ◽  
Aquifer Parameters ◽  
Water Head ◽  
Verification Period

The identification of aquifer parameters (i.e., specific yield and hydraulic conductivity) and forcing terms (recharge) is crucial for the process of modeling groundwater flow and contamination. Inversion techniques allow the unravelling of complex systems’ heterogeneity with more ease than manual calibration by computing parameter fields through an automated minimization between simulated and measured data (i.e., water head or measured aquifer parameters). It also allows the iterative search of multiple, equally plausible solutions, depending on system complexity (e.g., aquifer heterogeneity and variability of the forcing terms such as recharge). A Zoned Adaptive Multiscale Triangulation (ZAMT) is used for parameter estimation. ZAMT is the extension of an adaptive multiscale parameter estimation procedure already applied on different field cases. This extension consists of adding constraints varying over the domain. The ZAMT dissociates the parameter grid from the calculation mesh and allows local parameter grid refinement depending on local criteria, addressing the ill-posedness of inversion problems, decreasing computation time by reducing the amount of possible solutions and local minima, and ensuring flexibility in the parameter’s distribution. Each parameter is defined per vertex of the parameter grid; it can be set with a different range of values in order to integrate more pedo-geological information and help the optimization process by reducing the number of local minima. For the same purpose, a plausibility term based on topological characteristics of the aquifer or minimal and maximal water levels is added to the objective function. Groundwater flow is described by a classical nonlinear diffusion-type equation (unconfined aquifer), which is discretized with a two-dimensional nonconforming finite element method because water head data is unsuitable to invert three-dimensional parameter fields. Therefore, flow is considered mainly horizontal, and the parameters are obtained as average values on the saturated thickness. The study area is an alluvial (unconfined) aquifer of 6.64 km², situated in the southern, Mediterranean part of France. The simulation runs with a chronicle of 191 piezometers over 7 years (2012–2019), using a calibration period of 5 years (2012–2016). The optimization threshold is set to ensure a mean absolute error below 40 cm. The ZAMT and the additional plausibility criterion were found to produce an ensemble of realistic parameter sets with low parameter standard deviation. The model is considered robust as the water head error remains at the same level during the verification period, which includes an exceptionally dry year (2017). Overall, the calibration is best near the rivers (Dirichlet boundaries), while the terraced portion of the site challenges the limits of the 2D approach and the inversion procedure.

Using groundwater levels and Specific Yield to Estimate the Recharge, South of Erbil, Kurdistan Region, Iraq

2018 ◽  
Vol 7 (4) ◽  
pp. 191
Author(s):  
Sherwan Sh. Qurtas
Keyword(s):  
Unconfined Aquifer ◽  
Middle Part ◽  
Water Levels ◽  
Specific Yield ◽  
Aquifer System ◽  
Groundwater Levels ◽  
Monitoring Wells ◽  
Water Table Fluctuation Method ◽  
Recharge Estimation ◽  
Fluctuation Method

Recharge estimation accurately is crucial to proper groundwater resource management, for the groundwater is dynamic and replenished natural resource. Usually recharge estimation depends on the; the water balance, water levels, and precipitation. This paper is studying the south-middle part of Erbil basin, with the majority of Quaternary sediments, the unconfined aquifer system is dominant, and the unsaturated zone is ranging from 15 to 50 meters, which groundwater levels response is moderate. The purpose of this study is quantification the natural recharge from precipitation. The water table fluctuation method is applied; using groundwater levels data of selected monitoring wells, neighboring meteorological station of the wells, and the specific yield of the aquifers. This method is widely used for its simplicity, scientific, realistic, and direct measurement. The accuracy depends on the how much the determination of specific yield is accurate, accuracy of the data, and the extrapolations of recession of groundwater levels curves of no rain periods. The normal annual precipitation there is 420 mm, the average recharge is 89 mm, and the average specific yield is around 0.03. The data of one water year of 2009 and 2010 has taken for some technical and accuracy reasons.

scholarly journals Approximate analysis of three-dimensional groundwater flow toward a radial collector well in a finite-extent unconfined aquifer

2016 ◽  
Vol 20 (1) ◽  
pp. 55-71 ◽  
Author(s):  
C.-S. Huang ◽  
J.-J. Chen ◽  
H.-D. Yeh
Keyword(s):  
Groundwater Flow ◽  
Integral Transform ◽  
Three Dimensional ◽  
Vertical Component ◽  
Hydraulic Head ◽  
Unconfined Aquifer ◽  
Specific Yield ◽  
Specific Storage ◽  
Sink Term ◽  
Radial Collector Well

Abstract. This study develops a three-dimensional (3-D) mathematical model for describing transient hydraulic head distributions due to pumping at a radial collector well (RCW) in a rectangular confined or unconfined aquifer bounded by two parallel streams and no-flow boundaries. The streams with low-permeability streambeds fully penetrate the aquifer. The governing equation with a point-sink term is employed. A first-order free surface equation delineating the water table decline induced by the well is considered. Robin boundary conditions are adopted to describe fluxes across the streambeds. The head solution for the point sink is derived by applying the methods of finite integral transform and Laplace transform. The head solution for a RCW is obtained by integrating the point-sink solution along the laterals of the RCW and then dividing the integration result by the sum of lateral lengths. On the basis of Darcy's law and head distributions along the streams, the solution for the stream depletion rate (SDR) can also be developed. With the aid of the head and SDR solutions, the sensitivity analysis can then be performed to explore the response of the hydraulic head to the change in a specific parameter such as the horizontal and vertical hydraulic conductivities, streambed permeability, specific storage, specific yield, lateral length, and well depth. Spatial head distributions subject to the anisotropy of aquifer hydraulic conductivities are analyzed. A quantitative criterion is provided to identify whether groundwater flow at a specific region is 3-D or 2-D without the vertical component. In addition, another criterion is also given to allow for the neglect of vertical flow effect on SDR. Conventional 2-D flow models can be used to provide accurate head and SDR predictions if satisfying these two criteria.

scholarly journals Analysis of three-dimensional groundwater flow toward a radial collector well in a finite-extent unconfined aquifer

2015 ◽  
Vol 12 (8) ◽  
pp. 7503-7540 ◽  
Author(s):  
C.-S. Huang ◽  
J.-J. Chen ◽  
H.-D. Yeh
Keyword(s):  
Groundwater Flow ◽  
Integral Transform ◽  
Three Dimensional ◽  
Vertical Component ◽  
Hydraulic Head ◽  
Unconfined Aquifer ◽  
Specific Yield ◽  
Specific Storage ◽  
Sink Term ◽  
Radial Collector Well

Abstract. This study develops a three-dimensional mathematical model for describing transient hydraulic head distributions due to pumping at a radial collector well (RCW) in a rectangular confined or unconfined aquifer bounded by two parallel streams and no-flow boundaries. The governing equation with a point-sink term is employed. A first-order free surface equation delineating the water table decline induced by the well is considered. The head solution for the point sink is derived by applying the methods of double-integral transform and Laplace transform. The head solution for a RCW is obtained by integrating the point-sink solution along the laterals of the RCW and then dividing the integration result by the sum of lateral lengths. On the basis of Darcy's law and head distributions along the streams, the solution for the stream depletion rate (SDR) can also be developed. With the aid of the head and SDR solutions, the sensitivity analysis can then be performed to explore the response of the hydraulic head to the change in a specific parameter such as the horizontal and vertical hydraulic conductivities, streambed permeability, specific storage, specific yield, lateral length and well depth. Spatial head distributions subject to the anisotropy of aquifer hydraulic conductivities are analyzed. A quantitative criterion is provided to identify whether groundwater flow at a specific region is 3-D or 2-D without the vertical component. In addition, another criterion is also given to allow the neglect of vertical flow effect on SDR. Conventional 2-D flow models can be used to provide accurate head and SDR predictions if satisfying these two criteria.

scholarly journals A high-resolution global-scale groundwater model

2015 ◽  
Vol 19 (2) ◽  
pp. 823-837 ◽  
Author(s):  
I. E. M. de Graaf ◽  
E. H. Sutanudjaja ◽  
L. P. H. van Beek ◽  
M. F. P. Bierkens
Keyword(s):  
Groundwater Flow ◽  
Land Surface ◽  
Regional Scale ◽  
Unconfined Aquifer ◽  
Global Scale ◽  
Water Levels ◽  
Natural State ◽  
Groundwater Model ◽  
Groundwater Levels ◽  
Aquifer Systems

Abstract. Groundwater is the world's largest accessible source of fresh water. It plays a vital role in satisfying basic needs for drinking water, agriculture and industrial activities. During times of drought groundwater sustains baseflow to rivers and wetlands, thereby supporting ecosystems. Most global-scale hydrological models (GHMs) do not include a groundwater flow component, mainly due to lack of geohydrological data at the global scale. For the simulation of lateral flow and groundwater head dynamics, a realistic physical representation of the groundwater system is needed, especially for GHMs that run at finer resolutions. In this study we present a global-scale groundwater model (run at 6' resolution) using MODFLOW to construct an equilibrium water table at its natural state as the result of long-term climatic forcing. The used aquifer schematization and properties are based on available global data sets of lithology and transmissivities combined with the estimated thickness of an upper, unconfined aquifer. This model is forced with outputs from the land-surface PCRaster Global Water Balance (PCR-GLOBWB) model, specifically net recharge and surface water levels. A sensitivity analysis, in which the model was run with various parameter settings, showed that variation in saturated conductivity has the largest impact on the groundwater levels simulated. Validation with observed groundwater heads showed that groundwater heads are reasonably well simulated for many regions of the world, especially for sediment basins (R2 = 0.95). The simulated regional-scale groundwater patterns and flow paths demonstrate the relevance of lateral groundwater flow in GHMs. Inter-basin groundwater flows can be a significant part of a basin's water budget and help to sustain river baseflows, especially during droughts. Also, water availability of larger aquifer systems can be positively affected by additional recharge from inter-basin groundwater flows.

scholarly journals Groundwater flow to a horizontal or slanted well in an unconfined aquifer

2002 ◽  
Vol 38 (7) ◽  
pp. 13-1-13-11 ◽  
Author(s):  
Hongbin Zhan ◽  
Vitaly A. Zlotnik
Keyword(s):  
Groundwater Flow ◽  
Unconfined Aquifer

Flow pattern and residence time of conduit flow and diffuse flow in calcareous sandstones (Bohemian Cretaceous Basin, Czech Republic)

2021 ◽  
Author(s):  
Iva Kůrková ◽  
Jiří Bruthans
Keyword(s):  
Czech Republic ◽  
Groundwater Flow ◽  
Residence Time ◽  
Dispersion Model ◽  
Tracer Tests ◽  
Water Levels ◽  
Northwestern Part ◽  
Residence Times ◽  
Karst Springs ◽  
Bohemian Cretaceous Basin

<p>Localities containing karst features were studied in the northwestern part of Bohemian Cretaceous Basin. Namely Turnov area in facies transition between coarse-delta sandstones and marlstones (Jizera Formation, Turonian) and Miskovice area in limestones and sandy limestones - sandstones (Peruc-Korycany Formation, Cenomanian). Evolution of karst conduits is discussed elsewhere (Kůrková et al. 2019).</p><p>In both localities, disappearing streams, caves and karst springs with maximum discharge up to 100 L/s were documented. Geology and hydrogeology of this area was studied from many points of view to describe formation of karst conduits and characterize groundwater flow. Tracer tests were performed using NaCl and Na-fluoresceine between sinkholes and springs under various flow rates to evaluate residence times of water in conduits and to describe geometry of conduits. Breatkthrough curves of tracer tests were evaluated by means of Qtracer2 program (Field 2002). Groundwater flow velocity in channels starts at 0.6 km/day during low water levels up to 15 km/day during maximum water levels, the velocity increases logarithmically as a function of discharge. Similar karst conduits probably occur in other parts of Bohemian Cretaceous Basin where lot of large springs can be found.</p><p>Mean residence time of difussed flow based on tritium, CFC and SF<sub>6</sub> sampled at karst springs is 20 years for 75% of water and 100 years for remaining 25%, based on binary mixing dispersion model. This shows that most of the water drained by karst conduits is infiltrated through the soil and fractured environment with relatively high residence time. Residence times in different types of wells and springs were also measured in whole north-western part of Bohemian Cretaceous Basin. Results indicate long residence times in semi-stagnant zones represented by monitoring wells and short residence times in preferential zones represented by springs and water-supply wells.</p><p> </p><p>Research was funded by the Czech Science Foundation (GA CR No. 19-14082S), Czech Geological Survey – internal project 310250</p><p> </p><p>Field M. (2002): The QTRACER2 program for Tracer Breakthrough Curve Analysis for Tracer Tests in Karstic Aquifers and Other hydrologic Systems. – U.S. Environmental protection agency hypertext multimedia publication in the Internet at http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=54930.</p><p>Kůrková I., Bruthans J., Balák F., Slavík M., Schweigstillová J., Bruthansová J., Mikuš P., Grundloch J. (2019): Factors controlling evolution of karst conduits in sandy limestone and calcareous sandstone (Turnov area, Czech Republic). Journal of Hydrology: 574: 1062-1073</p>

Quantitative investigations of the hydraulic connection between a large reservoir and a buried valley aquifer in southern Alberta

2005 ◽  
Vol 42 (5) ◽  
pp. 1461-1473 ◽  
Author(s):  
B D Smerdon ◽  
C A Mendoza ◽  
A M McCann
Keyword(s):  
Groundwater Flow ◽  
Flow Model ◽  
Hydraulic Head ◽  
Water Levels ◽  
Groundwater Flow Model ◽  
Reservoir Level ◽  
Hydraulic Connection ◽  
Southern Alberta ◽  
Approximate Location ◽  
Pumping Rates

Quantitative investigations, including two aquifer tests and development of a three-dimensional (3D) groundwater flow model, were required to determine the hydraulic connection between an irrigation reservoir and a buried valley aquifer in southern Alberta. Evidence of seepage was detected in the buried valley aquifer 10 km east of the Pine Coulee reservoir at the onset of filling in 1999, when the reservoir level exceeded an elevation of 1035 m above sea level (a.s.l.). Concern for an increase in the local water table and the creation of artesian conditions in the aquifer prompted this study to determine the approximate location of a seepage window that appeared to be connecting the reservoir and aquifer. Observations of hydraulic head in the aquifer during the pumping tests revealed a barrier boundary when the reservoir level was at an elevation of 1035 m a.s.l. and a recharge boundary condition when the elevation exceeded 1039 m a.s.l. These data were used to calibrate a 3D groundwater flow model, which was needed to determine the hydraulic properties and approximate location of the leakage zone. The quantitative investigation showed that seepage likely occurred through the sideslopes of the flooded coulee, rather than through the low-permeability coulee floor sediments or the embankment dam. Further simulations illustrated the expected seepage rates at various reservoir supply levels and the pumping rates required for relief wells installed in the buried valley aquifer to maintain historic aquifer hydraulic head. A brief postanalysis indicated that the forecasted pumping rates were only 15% lower than have been required to maintain preconstruction water levels in the buried valley aquifer.Key words: dams, seepage analysis, groundwater modelling, buried valley aquifer, pumping test.

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