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  • 1
    In: Water Resources Research, July 2015, Vol.51(7), pp.5855-5868
    Description: This work reports numerical stability conditions in two‐dimensional solute transport simulations including discrete fractures surrounded by an impermeable rock matrix. We use an advective‐dispersive problem described in Tang et al. (1981) and examine the stability of the Crank‐Nicolson Galerkin finite... The von Neumann number ≥ 0.373 is required to avoid undershooting in the matrix The Courant number has a lower bound in the fracture for low dispersivity...
    Keywords: Discrete Fracture ; Solute Transport ; Numerical Stability
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 2
    Language: English
    In: Hydrological Processes, June 30, 2017, Vol.31(13), p.2395(17)
    Description: Byline: Agnes Sachse, Christian Fischer, Jonathan B. Laronne, Hanna Hennig, Amer Marei, Olaf Kolditz,Tino Rodiger Keywords: data scarcity; Dead Sea; hydrological model; J2000g; water balance Abstract Water budget analyses are important for the evaluation of the water resources in semiarid and arid regions. The lack of observed data is the major obstacle for hydrological modelling in arid regions. The aim of this study is the analysis and calculation of the natural water resources of the Western Dead Sea subsurface catchment, one which is highly sensitive to rainfall resulting in highly variable temporal and spatial groundwater recharge. We focus on the subsurface catchment and subsequently apply the findings to a large-scale groundwater flow model to estimate the groundwater discharge to the Dead Sea. We apply a semidistributed hydrological model (J2000g), originally developed for the Mediterranean, to the hyperarid region of the Western Dead Sea catchment, where runoff data and meteorological records are sparsely available. The challenge is to simulate the water budget, where the localized nature of extreme rainstorms together with sparse runoff data results in few observed runoff and recharge events. To overcome the scarcity of climate input data, we enhance the database with mean monthly rainfall data. The rainfall data of 2 satellites are shown to be unsuitable to fill the missing rainfall data due to underrepresentation of the steep hydrological gradient and temporal resolution. Hydrological models need to be calibrated against measured values; hence, the absence of adequate data can be problematic. Therefore, our calibration approach is based on a nested strategy of diverse observations. We calculate a direct surface runoff of the Western Dead Sea surface area (1,801 km.sub.2) of 3.4 mm/a and an average recharge (36.7 mm/a) for the 3,816 km.sub.2 subsurface drainage basin of the Cretaceous aquifer system.
    Keywords: Aquifers – Analysis ; Groundwater Flow – Analysis ; Groundwater – Analysis ; Water Balance (Hydrology) – Analysis ; Water Resources – Analysis ; Runoff – Analysis ; Arid Regions – Analysis
    ISSN: 0885-6087
    E-ISSN: 10991085
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  • 3
    In: Ground Water, September 2006, Vol.44(5), pp.687-696
    Description: We present a sequence of purely advective transport models that demonstrate the influence of small‐scale geometric inhomogeneities on contaminant transport in fractured crystalline rock. Special weight is placed on the role of statistically generated variable fracture apertures. The fracture network geometry and the aperture distribution are based on information from an in situ radionuclide retardation experiment performed at Grimsel test site (Swiss Alps). The obtained breakthrough curves are fitted with the advection dispersion equation and continuous‐time random walks (CTRW). CTRW is found to provide superior fits to the late‐arrival tailing and is also found to show a good correlation with the velocity distributions obtained from the hydraulic models. The impact of small‐scale heterogeneities, both in fracture geometry and aperture, on transport is shown to be considerable.
    Keywords: Scientific Research ; General;
    ISSN: 0017-467X
    E-ISSN: 1745-6584
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  • 4
    Language: English
    In: International Journal for Numerical Methods in Engineering, 01 January 2007, Vol.69(1), pp.162-201
    Description: The design, implementation and application of a concept for object‐oriented in finite element analysis of multi‐field problems is presented in this paper. The basic idea of this concept is that the underlying governing equations of porous media mechanics can be classified into different types of partial differential equations (PDEs). In principle, similar types of PDEs for diverse physical problems differ only in material coefficients. Local element matrices and vectors arising from the finite element discretization of the PDEs are categorized into several types, regardless of which physical problem they belong to (i.e. fluid flow, mass and heat transport or deformation processes). Element (ELE) objects are introduced to carry out the local assembly of the algebraic equations. The object‐orientation includes a strict encapsulation of geometrical (GEO), topological (MSH), process‐related (FEM) data and methods of element objects. Geometric entities of an element such as nodes, edges, faces and neighbours are abstracted into corresponding geometric element objects (ELE–GEO). The relationships among these geometric entities form the topology of element meshes (ELE–MSH). Finite element objects (ELE–FEM) are presented for the local element calculations, in which each classification type of the matrices and vectors is computed by a unique function. These element functions are able to deal with different element types (lines, triangles, quadrilaterals, tetrahedra, prisms, hexahedra) by automatically choosing the related element interpolation functions. For each process of a multi‐field problem, only a single instance of the finite element object is required. The element objects provide a flexible coding environment for multi‐field problems with different element types. Here, the C++ implementations of the objects are given and described in detail. The efficiency of the new element objects is demonstrated by several test cases dealing with thermo‐hydro‐mechanical (THM) coupled problems for geotechnical applications. Copyright © 2006 John Wiley & Sons, Ltd.
    Keywords: Object‐Oriented Programming ; Finite Element Method ; Multi‐Field Problems ; Porous Media
    ISSN: 0029-5981
    E-ISSN: 1097-0207
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  • 5
    In: Transactions in GIS, August 2015, Vol.19(4), pp.493-498
    Keywords: Geography;
    ISSN: 1361-1682
    E-ISSN: 1467-9671
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  • 6
    In: Water Resources Research, February 2014, Vol.50(2), pp.1531-1549
    Description: There are a growing number of large‐scale, complex hydrologic models that are capable of simulating integrated surface and subsurface flow. Many are coupled to land‐surface energy balance models, biogeochemical and ecological process models, and atmospheric models. Although they are being increasingly applied for hydrologic prediction and environmental understanding, very little formal verification and/or benchmarking of these models has been performed. Here we present the results of an intercomparison study of seven coupled surface‐subsurface models based on a series of benchmark problems. All the models simultaneously solve adapted forms of the Richards and shallow water equations, based on fully 3‐D or mixed (1‐D vadose zone and 2‐D groundwater) formulations for subsurface flow and 1‐D (rill flow) or 2‐D (sheet flow) conceptualizations for surface routing. A range of approaches is used for the solution of the coupled equations, including global implicit, sequential iterative, and asynchronous linking, and various strategies are used to enforce flux and pressure continuity at the surface‐subsurface interface. The simulation results show good agreement for the simpler test cases, while the more complicated test cases bring out some of the differences in physical process representations and numerical solution approaches between the models. Benchmarks with more traditional runoff generating mechanisms, such as excess infiltration and saturation, demonstrate more agreement between models, while benchmarks with heterogeneity and complex water table dynamics highlight differences in model formulation. In general, all the models demonstrate the same qualitative behavior, thus building confidence in their use for hydrologic applications. Seven hydrologic models were intercompared on standard benchmark problems In general, though there are differences in approach, these models agree Model differences can be attributed to solution technique and coupling strategy
    Keywords: Model Intercomparison
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 7
    In: Ground Water, November 2007, Vol.45(6), pp.774-785
    Description: In this article, different strategies for estimating first‐order degradation rate constants from measured field data are compared by application to multiple, synthetic, contaminant plumes. The plumes were generated by numerical simulation of contaminant transport and degradation in virtual heterogeneous aquifers. These sites were then individually and independently investigated on the computer by installation of extensive networks of observation wells. From the data measured at the wells, that is, contaminant concentrations, hydraulic conductivities, and heads, first‐order degradation rates were estimated by three 1D centerline methods, which use only measurements located on the plume axis, and a two‐dimensional method, which uses all concentration measurements available downgradient from the contaminant source. Results for both strategies show that the true rate constant used for the numerical simulation of the plumes in general tends to be overestimated. Overestimation is stronger for narrow plumes from small source zones, with an average overestimation factor of about 5 and single values ranging from 0.5 to 20, decreasing for wider plumes, with an average overestimation factor of about 2 and similar spread. Reasons for this overestimation are identified in the velocity calculation, the dispersivity parameterization, and off‐centerline measurements. For narrow plumes, the one‐ and the two‐dimensional strategies show approximately the same amount of overestimation. For wider plumes, however, incorporation of all measurements in the two‐dimensional approach reduces the estimation error. No significant relation between the number of observation wells in the monitoring network and the quality of the estimated rate constant is found for the two‐dimensional approach.
    Keywords: Models, Theoretical ; Environmental Monitoring -- Methods ; Water Pollutants, Chemical -- Analysis;
    ISSN: 0017-467X
    E-ISSN: 1745-6584
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  • 8
    In: Sedimentology, February 2012, Vol.59(2), pp.337-355
    Description: The barrier islands of the southern North Sea were formed during the Holocene sea‐level rise. These islands form part of a highly dynamic environment whose evolution continues today. Subjected to sea‐level changes, tides and storm events, the sedimentary record reflects processes occurring under varying energy conditions. This article presents geochemical, mineralogical and diatom investigations carried out in the salt marsh of the East Frisian barrier island of Langeoog, which is re‐exposed to a rising sea‐level due to de‐embankment. The major aim of this study is to improve the knowledge of the sedimentological and geochemical development of these deposits under the influence of sea‐level rise, with a special focus on the geochemistry and distribution of heavy mineral‐associated elements. Correlation diagrams between FeO, TiO and MnO, as well as ternary plots (AlO–SiO–Zr or TiO), clearly indicate the variable appearance of heavy minerals in different lithological facies, comprising marsh soil, mixed and sand flat, and relocated beach sands. A dominating abundance of ilmenite followed by zircon, garnets and some other heavy minerals is evidenced by Scanning Electron Microscope‐Energy Dispersive X‐ray measurements. The data presented here suggests that these geochemical proxies are useful tools for characterizing depositional energy conditions. Increasing depositional energy is evident for the lithological units in the following order: marsh soil, mixed flat, sand flat and relocated beach sand. The energetic conditions during sediment deposition, as well as the sedimentary history, are confirmed by diatom analyses as an additional independent indicator. Depending on source rock composition, the geochemical parameters used in this study may also help to investigate depositional energy regimes of other siliciclastic sedimentary systems.
    Keywords: Depositional Energy ; Diatoms ; Heavy Minerals ; Inorganic Geochemistry ; North Sea ; Salt Marsh ; Tidal Flat
    ISSN: 0037-0746
    E-ISSN: 1365-3091
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