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Integrated BEM algorithm for transient 2-D flow in unconfined aquifers
74A
932022 Aquifer analysis and modeling in a fractured, heterogeneous medium Lee, R R; Ketelle, R H; Bownds, J M; Rizk, T A Ground Water V30, N4, July-Aug 1992, P589-597 Groundwater flow and contaminant transport studies for a proposed low-level radioactive waste dump site on the Oak Ridge Reservation are described. Tracer migration data under controlled conditions were used as a benchmark against which to test various computer simulations. Reasonable simulation could only be achieved if the effects of geological heterogeneities of the aquifer were included. These features could be verified with additional data and analysis. Results suggest local geology creates discrete flow paths oriented obliquely to the maximum gradient, which are unresolved if the aquifer is assumed homogeneous and with low anisotropy.
932026 Large-scale natural gradient tracer test in sand and gravel, Cape Cod, Massachusetts. 3. Hydraulic conductivity variability and calculated macrodispersivities Hess, K M; Wolf, S H; Celia, M A Water Resour Res 1/28, N8, Aug 1992, P2011-2027 About 1500 hydraulic conductivity (K) measurements were made for a sand and gravel aquifer using borehole flowmeter tests and permeameter tests on cores. The data were subsequently used in stochastic transport theories to estimate macrodispersivities. Geometric mean and variance of K from the flowmeter tests were significantly larger than those from permeameter tests, possibly because of compaction of the cores. Similar spatial correlation structures between the two data sets were revealed by geostatistical analysis applying negative exponential models. Estimates of longitudinal dispersivity are similar to those from earlier natural tracer gradient tests.
932023 Aquifer test with partially penetrating wells: theory and practice Boonstra, J d Hydrol V137, N1/4, Aug 1992, P165-179
932027 Boundary integral technique for multiple-front simulation of incompressible, immiscible flow in porous media Stothoff, S A; Pinder, G F Water Resour Res V28, N8, Aug 1992, P2067-2076
The well-known Hantush modification of the Theis method and a recent solution are presented for the problem of groundwater flow to a partially penetrating well. The new method uses a matching procedure between drawdowns observed in the field and theoretical drawdowns and requires the specially developed computer code SATEM. Both solutions are applied to a theoretical data set. It is indicated that the Theis-Hantush method may lead to overestimation of aquifer thickness. This sensitivity of estimations of thickness to calculation method is repeated when the methods are applied to field data.
A boundary integral flow model is presented which enables large computation domains to be constructed with little impact on computational effort or accuracy, as the mesh is placed only along contours of phase saturation and the domain boundaries. Time stepping is performed by updating the position of the contours based on phase fluxes. Capillary pressure gradients are treated by interpolating saturation between contours using a separate boundary integral step. Examples of one-dimensional and two-dimensional radial two phase flow are simulated, with excellent agreement between output and analytical solutions. Finite element and boundary element analyses of imbibition of trichloroethylene into a clean aquifer also show good agreement.
932024 Integrated BEM algorithm for transient 2-D flow in unconfined aquifers Rizos, D C; Karabalis, D L Mieroeomput Civ Engng V7, N4, 1992, P333-340 A new algorithm for problems of transient or steady state 2-D groundwater flow is presented. It is based on a time-stepping BEM formulation. It can describe the location of moving boundaries and can include forcing effects such as rainfall and tidal action. Formulation and numerical procedures are illustrated. Two numerical examples of its use are shown, unconfined flow in a bank with vertical sides and a coastal aquifer under tidal fluctuation and rainfall.
932025 Semi-analytical model for borehole catchments and time-oftravel zones which incorporates recharge and aquifer boundaries Lerner, D N Q J Engng Geol V25, N2, 1992, P137-144 To assist protection of major water supply boreholes and vulnerable aquifers from pollution, a new model has been developed to predict catchments and time-of-travel zones to boreholes. It takes into account spatially variable recharge and accommodates strip and rectangular aquifers. The model is based on new analytical solutions for the velocity components due to both pumping and recharge from the boreholes. Results are compared to those of standard models, and effects of including recharge and aquifer boundary variations discussed.
932028 Stochastic analysis of dispersion in unsteady flow in heterogeneous aquifers Rehfeldt, K R; Gelhar, L W Water Resour Res V28, N8, Aug 1992, P2085-2099 Stochastic continuum theory is applied to analysis of the dispersion of a solute plume resulting from unsteady flow in a three dimensional, heterogeneous porous medium. Influence of internal storage due to medium and fluid compressibility is ignored to simplify the calculations. The predictive expression developed for the macrodispersivity tensor is the sum of two components, a spatial variability component (identical to previous steady state theory) and an unsteady component. Two special cases are considered: variability in magnitude only or direction only of the hydraulic gradient. Predicted macrodispersivities are of similar value to those from well documented field-scale tracer experiments.
932029 Behaviour of dense aqueous phase leachate plumes in homogeneous porous media Oostrom, M; Hayworth, J S; Dane, J H; Guven, O Water Resour Res V28, N8, Aug 1992, P2123-2134 The behaviour of surface contaminant plumes of different densities was examined in model tests using homogeneous porous media (glass beads and a medium sand) to represent an unconfined aquifer. A horizontal groundwater stream was established in the container and contaminant plumes containing dye tracers introduced from a line source. Dense plumes were
© 1993 Pergamon Press Ltd. Reproduction not permitted
932022 Aquifer analysis and modeling in a fractured, heterogeneous medium Lee, R R; Ketelle, R H; Bownds, J M; Rizk, T A Ground Water V30, N4, July-Aug 1992, P589-597 Groundwater flow and contaminant transport studies for a proposed low-level radioactive waste dump site on the Oak Ridge Reservation are described. Tracer migration data under controlled conditions were used as a benchmark against which to test various computer simulations. Reasonable simulation could only be achieved if the effects of geological heterogeneities of the aquifer were included. These features could be verified with additional data and analysis. Results suggest local geology creates discrete flow paths oriented obliquely to the maximum gradient, which are unresolved if the aquifer is assumed homogeneous and with low anisotropy.
932026 Large-scale natural gradient tracer test in sand and gravel, Cape Cod, Massachusetts. 3. Hydraulic conductivity variability and calculated macrodispersivities Hess, K M; Wolf, S H; Celia, M A Water Resour Res 1/28, N8, Aug 1992, P2011-2027 About 1500 hydraulic conductivity (K) measurements were made for a sand and gravel aquifer using borehole flowmeter tests and permeameter tests on cores. The data were subsequently used in stochastic transport theories to estimate macrodispersivities. Geometric mean and variance of K from the flowmeter tests were significantly larger than those from permeameter tests, possibly because of compaction of the cores. Similar spatial correlation structures between the two data sets were revealed by geostatistical analysis applying negative exponential models. Estimates of longitudinal dispersivity are similar to those from earlier natural tracer gradient tests.
932023 Aquifer test with partially penetrating wells: theory and practice Boonstra, J d Hydrol V137, N1/4, Aug 1992, P165-179
932027 Boundary integral technique for multiple-front simulation of incompressible, immiscible flow in porous media Stothoff, S A; Pinder, G F Water Resour Res V28, N8, Aug 1992, P2067-2076
The well-known Hantush modification of the Theis method and a recent solution are presented for the problem of groundwater flow to a partially penetrating well. The new method uses a matching procedure between drawdowns observed in the field and theoretical drawdowns and requires the specially developed computer code SATEM. Both solutions are applied to a theoretical data set. It is indicated that the Theis-Hantush method may lead to overestimation of aquifer thickness. This sensitivity of estimations of thickness to calculation method is repeated when the methods are applied to field data.
A boundary integral flow model is presented which enables large computation domains to be constructed with little impact on computational effort or accuracy, as the mesh is placed only along contours of phase saturation and the domain boundaries. Time stepping is performed by updating the position of the contours based on phase fluxes. Capillary pressure gradients are treated by interpolating saturation between contours using a separate boundary integral step. Examples of one-dimensional and two-dimensional radial two phase flow are simulated, with excellent agreement between output and analytical solutions. Finite element and boundary element analyses of imbibition of trichloroethylene into a clean aquifer also show good agreement.
932024 Integrated BEM algorithm for transient 2-D flow in unconfined aquifers Rizos, D C; Karabalis, D L Mieroeomput Civ Engng V7, N4, 1992, P333-340 A new algorithm for problems of transient or steady state 2-D groundwater flow is presented. It is based on a time-stepping BEM formulation. It can describe the location of moving boundaries and can include forcing effects such as rainfall and tidal action. Formulation and numerical procedures are illustrated. Two numerical examples of its use are shown, unconfined flow in a bank with vertical sides and a coastal aquifer under tidal fluctuation and rainfall.
932025 Semi-analytical model for borehole catchments and time-oftravel zones which incorporates recharge and aquifer boundaries Lerner, D N Q J Engng Geol V25, N2, 1992, P137-144 To assist protection of major water supply boreholes and vulnerable aquifers from pollution, a new model has been developed to predict catchments and time-of-travel zones to boreholes. It takes into account spatially variable recharge and accommodates strip and rectangular aquifers. The model is based on new analytical solutions for the velocity components due to both pumping and recharge from the boreholes. Results are compared to those of standard models, and effects of including recharge and aquifer boundary variations discussed.
932028 Stochastic analysis of dispersion in unsteady flow in heterogeneous aquifers Rehfeldt, K R; Gelhar, L W Water Resour Res V28, N8, Aug 1992, P2085-2099 Stochastic continuum theory is applied to analysis of the dispersion of a solute plume resulting from unsteady flow in a three dimensional, heterogeneous porous medium. Influence of internal storage due to medium and fluid compressibility is ignored to simplify the calculations. The predictive expression developed for the macrodispersivity tensor is the sum of two components, a spatial variability component (identical to previous steady state theory) and an unsteady component. Two special cases are considered: variability in magnitude only or direction only of the hydraulic gradient. Predicted macrodispersivities are of similar value to those from well documented field-scale tracer experiments.
932029 Behaviour of dense aqueous phase leachate plumes in homogeneous porous media Oostrom, M; Hayworth, J S; Dane, J H; Guven, O Water Resour Res V28, N8, Aug 1992, P2123-2134 The behaviour of surface contaminant plumes of different densities was examined in model tests using homogeneous porous media (glass beads and a medium sand) to represent an unconfined aquifer. A horizontal groundwater stream was established in the container and contaminant plumes containing dye tracers introduced from a line source. Dense plumes were
© 1993 Pergamon Press Ltd. Reproduction not permitted