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A transformed pressure head-based approach to solve Richard's equation for variably saturated soils
IOA
HYDROGEOLOGY:FLUID PRESSURE
The Umm Er Radhuma (EUR) aquifer in that area is the main source of domestic and landscape irrigation demands. Numerical simulation techniques and hydrogeochvmical investigations were carried out to assess the effects of increasing pumping rates on the piezometric surface in the UER aquifer and to predict the future levels and quality of water under different pumping scenarios. A groundwater flow model was developed and calibrated for the area. The results of simulation investigations indicated that if the present trend of the groundwater withdrawal rate continues, the water level is expected to drop by an additional 2 and by the end of the year 2000, by an additional 6 m by the end of 2010. (from Authors) 961075 A three-dimensional miscible transport model for seawater intrusion in China Yuqun Xue, Chunhong Xie, Jichun Wu, Peimin Liu, Jiangi Wang & Qingbo Jiang, Water Resources Research, 31(4), 1995, pp 903-912. A three-dimensional miscible transport model for seawater intrusion in a phreatic aquifer with a transition zone is presented. This model considers many important factors, such as the effect of variable density on fluid flow, the effect of precipitation infiltration and phreatic surface fluctuation on the process of seawater intrusion, the existence of great discharge pumping wells, etc. The difficulty in solving this problem can be tackled by the presented numerical method and iteration technique. This model is used to describe seawater intrusion in Huangheying, Longkou, China. (from Authors)
Chemical and physical changes 961076 Transport of chromium and sdenium in a pristine sand and gravel aquifer: Role of adsorption processes D. B. Kent, J. A. Davis, L. C. D. Anderson & B. A. Rea, Water Resources Research, 31(4), 1995, pp 1041-1050. Field transport experiments were conducted in an oxic sand and gravel aquifer using Br, Cr, Se, and other tracers. Modeling results suggested that the dominant adsorbents in the aquifer solids have lower affinities for anion adsorption than pure hydrous ferric oxide. The steep rising limbs and extensive tails observed in most of the breakthrough curves are qualitatively consistent with the equilibrium surface complexation model; however, slow rates of adsorption and desorption may have contributed to these features. Variations during transport in the concentrations of Cr, Se, and other anions competing for adsorption sites likely gave rise to variations in the extent of adsorption. (from Authors) 961077 Land subsidence in drained Histosois and highly organic mineral soils of California S. Rojstaczer & S. J. Deverel, Soil Science Society of America Journal, 59(4), 1995, pp 1162-1167. Historical subsidence was determined by measuring soil surface elevation loss near electrical tower foundations and by evaluating survey data between 1922 and 1981. The data indicated that subsidence slowed with time. In the western Delta, average subsidence rates were 2.3 cm yr -1 from 1910 to 1988 and 1.5 cm yr "1 from 1952 to 1988. Spatially variability in subsidence was correlated with organic matter content of the soil (r 2 = 0.62), which in turn was related to the depositional and drainage history of the Delta. Subsidence rates appeared to be independent of crops grown. (from Authors)
Fluid flow, measurement and modelling 961078 Solution of muitispecies transport in the unsaturated zone using a moving point method R. J. Lunn & R. Mackay, Journal of Hydrology, 168(1-4), 1995, pp 29-50. The moving point technique has been applied to contaminant transport in groundwater and shown to provide an accurate solution to the convection/dispersion equation for advectiondominated transport. In this paper, the technique has been adapted for the simulation of transport of multiple species through sorbing, dual porosity, unsaturated media. The moving point method is shown to be considerably more accurate than the finite difference solutions for convectiondominated flow. (from Authors) 961079 A transformed pressure heed-based approach to solve Richards' equation for variably saturated soils L. Pan & P. J. Wierenga, Water Resources Research, 31(4), 1995, pp 925-931. Presents a new approach to solve Richards' equation. A nonlinear transformed pressure, Pt is introduced as the dependent variable with the modified Picard method. The new approach was compared to, and contrasted with, two efficient existing methods: the a-based transformation method, and the h-based modified Picard method. A total of 12 different one-dimensional cases were considered. The results show that the new method offers excellent CPU efficiency and, unlike the h-based method, is numerically robust for all cases of variably saturated, heterogeneous media, and first or second type boundary conditions. (from Authors) 961080 Three-dimensional analytical models of contaminant transport from nonaqueons phase liquid pool dissolution in saturated subsurface formations C. V. Chrysikopoulos, Water Resources Research, 31(4), 1995, pp 1137-1145. Closed form analytical solutions are derived for threedimensional transient contaminant transport resulting from dissolution of single-component nonaqueons phase liquid pools in saturated porous media. The solutions are suitable for homogeneous porous media with unidirectional interstitial velocity. The results of several simulations indicate that for short downstream distances, predictions of contaminant concentrations are sensitive to the source structure and orientation with respect to the direction of interstitial flow. (from Author) 961081 The effect of nonlinear sorption on transformation of contaminants during transport in porous media M. L. Brusseau, Journal of Contaminant Hydrology, 17(4), 1995, pp 277-291. The transport of contaminants through porous media is influenced by several processes, two of the most important being sorption and transformation. Several mathematical models have been developed to investigate the effects of sorption and transformation on contaminant transport. Almost all of these models are based on the assumption of linear sorption. However, it is well known that sorption of reactive contaminants is often nonlinear. A mathematical model that describes the transport of solute undergoing nonlinear, rate-limited sorption and first-order transformation is used to investigate the effect of coupled transformation and non-linear sorption on contaminant transport. Results of the analyses show that a model based on linear sorption cannot provide an accurate simulation of the transformation and transport of nonlinearly sorbing solutes when n is less than ~0.9. In addition, the relative impact of non-linear
HYDROGEOLOGY:FLUID PRESSURE
The Umm Er Radhuma (EUR) aquifer in that area is the main source of domestic and landscape irrigation demands. Numerical simulation techniques and hydrogeochvmical investigations were carried out to assess the effects of increasing pumping rates on the piezometric surface in the UER aquifer and to predict the future levels and quality of water under different pumping scenarios. A groundwater flow model was developed and calibrated for the area. The results of simulation investigations indicated that if the present trend of the groundwater withdrawal rate continues, the water level is expected to drop by an additional 2 and by the end of the year 2000, by an additional 6 m by the end of 2010. (from Authors) 961075 A three-dimensional miscible transport model for seawater intrusion in China Yuqun Xue, Chunhong Xie, Jichun Wu, Peimin Liu, Jiangi Wang & Qingbo Jiang, Water Resources Research, 31(4), 1995, pp 903-912. A three-dimensional miscible transport model for seawater intrusion in a phreatic aquifer with a transition zone is presented. This model considers many important factors, such as the effect of variable density on fluid flow, the effect of precipitation infiltration and phreatic surface fluctuation on the process of seawater intrusion, the existence of great discharge pumping wells, etc. The difficulty in solving this problem can be tackled by the presented numerical method and iteration technique. This model is used to describe seawater intrusion in Huangheying, Longkou, China. (from Authors)
Chemical and physical changes 961076 Transport of chromium and sdenium in a pristine sand and gravel aquifer: Role of adsorption processes D. B. Kent, J. A. Davis, L. C. D. Anderson & B. A. Rea, Water Resources Research, 31(4), 1995, pp 1041-1050. Field transport experiments were conducted in an oxic sand and gravel aquifer using Br, Cr, Se, and other tracers. Modeling results suggested that the dominant adsorbents in the aquifer solids have lower affinities for anion adsorption than pure hydrous ferric oxide. The steep rising limbs and extensive tails observed in most of the breakthrough curves are qualitatively consistent with the equilibrium surface complexation model; however, slow rates of adsorption and desorption may have contributed to these features. Variations during transport in the concentrations of Cr, Se, and other anions competing for adsorption sites likely gave rise to variations in the extent of adsorption. (from Authors) 961077 Land subsidence in drained Histosois and highly organic mineral soils of California S. Rojstaczer & S. J. Deverel, Soil Science Society of America Journal, 59(4), 1995, pp 1162-1167. Historical subsidence was determined by measuring soil surface elevation loss near electrical tower foundations and by evaluating survey data between 1922 and 1981. The data indicated that subsidence slowed with time. In the western Delta, average subsidence rates were 2.3 cm yr -1 from 1910 to 1988 and 1.5 cm yr "1 from 1952 to 1988. Spatially variability in subsidence was correlated with organic matter content of the soil (r 2 = 0.62), which in turn was related to the depositional and drainage history of the Delta. Subsidence rates appeared to be independent of crops grown. (from Authors)
Fluid flow, measurement and modelling 961078 Solution of muitispecies transport in the unsaturated zone using a moving point method R. J. Lunn & R. Mackay, Journal of Hydrology, 168(1-4), 1995, pp 29-50. The moving point technique has been applied to contaminant transport in groundwater and shown to provide an accurate solution to the convection/dispersion equation for advectiondominated transport. In this paper, the technique has been adapted for the simulation of transport of multiple species through sorbing, dual porosity, unsaturated media. The moving point method is shown to be considerably more accurate than the finite difference solutions for convectiondominated flow. (from Authors) 961079 A transformed pressure heed-based approach to solve Richards' equation for variably saturated soils L. Pan & P. J. Wierenga, Water Resources Research, 31(4), 1995, pp 925-931. Presents a new approach to solve Richards' equation. A nonlinear transformed pressure, Pt is introduced as the dependent variable with the modified Picard method. The new approach was compared to, and contrasted with, two efficient existing methods: the a-based transformation method, and the h-based modified Picard method. A total of 12 different one-dimensional cases were considered. The results show that the new method offers excellent CPU efficiency and, unlike the h-based method, is numerically robust for all cases of variably saturated, heterogeneous media, and first or second type boundary conditions. (from Authors) 961080 Three-dimensional analytical models of contaminant transport from nonaqueons phase liquid pool dissolution in saturated subsurface formations C. V. Chrysikopoulos, Water Resources Research, 31(4), 1995, pp 1137-1145. Closed form analytical solutions are derived for threedimensional transient contaminant transport resulting from dissolution of single-component nonaqueons phase liquid pools in saturated porous media. The solutions are suitable for homogeneous porous media with unidirectional interstitial velocity. The results of several simulations indicate that for short downstream distances, predictions of contaminant concentrations are sensitive to the source structure and orientation with respect to the direction of interstitial flow. (from Author) 961081 The effect of nonlinear sorption on transformation of contaminants during transport in porous media M. L. Brusseau, Journal of Contaminant Hydrology, 17(4), 1995, pp 277-291. The transport of contaminants through porous media is influenced by several processes, two of the most important being sorption and transformation. Several mathematical models have been developed to investigate the effects of sorption and transformation on contaminant transport. Almost all of these models are based on the assumption of linear sorption. However, it is well known that sorption of reactive contaminants is often nonlinear. A mathematical model that describes the transport of solute undergoing nonlinear, rate-limited sorption and first-order transformation is used to investigate the effect of coupled transformation and non-linear sorption on contaminant transport. Results of the analyses show that a model based on linear sorption cannot provide an accurate simulation of the transformation and transport of nonlinearly sorbing solutes when n is less than ~0.9. In addition, the relative impact of non-linear