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91.
使用基于棚格的地理信息系统,采用径流曲线方法和污染物流失方程.计算环罗源湾陆域氮磷污染物人海通量及其空问分布.站果表明,起步溪流域是罗源湾海域最主要的陆域污染来源.水土流失和生活污染对海域的污染输入显著. 相似文献
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94.
David Ching‐Fang Shih 《水文研究》2007,21(16):2135-2143
A semi‐analytical solution of the one‐dimensional transport for considering a three‐member decay chain in a single fracture with pulse and Heaviside input sources has been studied using the Laplace transform and its numerical inversion. The results reveal that breakthrough curves of dimensionless concentration for the decay chain of Np‐237, U‐233, and Th‐229 in the fracture can be well demonstrated in the temporal and spatial domains. The conditions with and without retardation effects are also compared. During the preliminary screening phase the solutions are suitable for performance assessment on radioactive waste disposal sites under a one‐dimensional single fracture condition. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
95.
A three‐dimensional finite‐element model of contaminant migration in fissured clays or contaminated sand which includes multiple sources of non‐equilibrium processes is proposed. The conceptual framework can accommodate a regular network of fissures in 1D, 2D or 3D and immobile solutions in the macro‐pores of aggregated topsoils, as well as non‐equilibrium sorption. A Galerkin weighted‐residual statement for the three‐dimensional form of the equations in the Laplace domain is formulated. Equations are discretized using linear and quadratic prism elements. The system of algebraic equations is solved in the Laplace domain and solution is inverted to the time domain numerically. The model is validated and its scope is illustrated through the analysis of three problems: a waste repository deeply buried in fissured clay, a storage tank leaking into sand and a sanitary landfill leaching into fissured clay over a sand aquifer. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
96.
Modelling of contaminant transport through landfill liners and natural soil deposits is an important area of research activity in geoenvironmental engineering. Conventional mesh‐based numerical methods depend on mesh/grid size and element connectivity and possess some difficulties when dealing with advection‐dominant transport problems. In the present investigation, an attempt has been made to provide a simple but sufficiently accurate methodology for numerical simulation of the two‐dimensional contaminant transport through the saturated homogeneous porous media and landfill liners using element‐free Galerkin method (EFGM). In the EFGM, an approximate solution is constructed entirely in terms of a set of nodes and no characterization of the interrelationship of the nodes is needed. The EFGM employs moving least‐square approximants to approximate the function and uses the Lagrange multiplier method for imposing essential boundary conditions. The results of the EFGM are validated using experimental results. Analytical and finite element solutions are also used to compare the results of the EFGM. In order to test the practical applicability and performance of the EFGM, three case studies of contaminant transport through the landfill liners are presented. A good agreement is obtained between the results of the EFGM and the field investigation data. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
97.
Scott C. James Tanya K. Bilezikjian Constantinos V. Chrysikopoulos 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(4):266-279
A quasi-three-dimensional particle tracking model is developed to characterize the spatial and temporal effects of advection, molecular diffusion, Taylor dispersion, fracture wall deposition, matrix diffusion, and co-transport processes on two discrete plumes (suspended monodisperse or polydisperse colloids and dissolved contaminants) flowing through a variable aperture fracture situated in a porous medium. Contaminants travel by advection and diffusion and may sorb onto fracture walls and colloid particles, as well as diffuse into and sorb onto the surrounding porous rock matrix. A kinetic isotherm describes contaminant sorption onto colloids and sorbed contaminants assume the unique transport properties of colloids. Sorption of the contaminants that have diffused into the matrix is governed by a first-order kinetic reaction. Colloids travel by advection and diffusion and may attach onto fracture walls; however, they do not penetrate the rock matrix. A probabilistic form of the Boltzmann law describes filtration of both colloids and contaminants on fracture walls. Ensemble-averaged breakthrough curves of many fracture realizations are used to compare arrival times of colloid and contaminant plumes at the fracture outlet. Results show that the presence of colloids enhances contaminant transport (decreased residence times) while matrix diffusion and sorption onto fracture walls retard the transport of contaminants. Model simulations with the polydisperse colloids show increased effects of co-transport processes. 相似文献
98.
A theoretical technique for conditioning simulations in frequency domain is developed and then applied to a hydraulic-head data set from Pittman, Nevada. Frequency-domain simulation rapidly generates simulations while requiring minimal computer memory. This makes it possible by using a personal computer to create large numbers of simulations of a physical parameter field for use in studying stochastic processes. In our application, groundwater flowlines are constructed from the simulations of the hydraulic head field. Then, the crossings of the flowlines at a transect down-stream from a contaminant point source generate histograms for predicting the probability of plume interception by groundwater monitoring wells. The simulation process is discussed in detail for the Pittman study site. 相似文献
99.
Many problems in hydraulics and hydrology are described by linear, time dependent partial differential equations, linearity being, of course, an assumption based on necessity.Solutions to such equations have been obtained in the past based purely on deterministic consideration. The derivation of such a solution requires that the initial conditions, the boundary conditions, and the parameters contained within the equations be stipulated in exact terms. It is obvious that the solution so derived is a function of these specified, values.There are at least four ways in which randomness enters the problem. i) the random initial value problem; ii) the random boundary value problem; iii) the random forcing problem when the non-homogeneous part becomes random and iv) the random parameter problem.Such randomness is inherent in the environment surrounding the system, the environment being endowed with a large number of degrees of freedom.This paper considers the problem of groundwater flow in a phreatic aquifer fed by rainfall. The goveming equations are linear second order partial differential equations. Explicit form solutions to this randomly forced equation have been derived in well defined regular boundaries. The paper also provides a derivation of low order moment equations. It contains a discussion on the parameter estimation problem for stochastic partial differential equations. 相似文献
100.
硼及其同位素对水体污染物的示踪研究 总被引:2,自引:0,他引:2
硼的易溶性和硼化合物的广泛使用 ,以及污水处理过程中除硼的困难 ,最终导致地表地下水体富集硼及有关污染物。海滨地下水受到海水入侵 ,硼含量及 ρ(B) / ρ(Cl)比值发生明显变化。混合、吸附、水岩等作用使得硼同位素发生分馏 ,显著区别于区域背景值。因此 ,结合其它同位素、水化学等信息 ,硼及其同位素作为良好示踪剂为研究水圈中物质的地球化学循环过程提供了新的手段。文中总结了部分天然水体的硼含量和硼同位素组成特征 ,综述了近年来用硼同位素示踪水体的污染物来源、程度和范围等方面新的研究成果。 相似文献