强降雨条件下非均匀介质污染物运移数值模拟

Numerical Simulation of Contaminant Transport in Heterogeneous Aquifer under Heavy Rainfall

为研究强降雨条件下污染物在非均匀介质中的运移特征及对地下水环境的影响,基于随机理论,利用MATLAB工具,考虑不同降雨强度下降雨入渗速率、表现含水层非均质介质特性的渗透系数及纵向弥散度3个主要因素对溶质运移的影响,调用MODFLOW和MT3DMS程序求解和分析地下水流和溶质运移问题。结果表明强降雨通过影响地下水流动场的相关参数,增强了污染物迁移的速度及污染程度:饱和渗透系数变异系数一定时(CoV=100%),360 mm/d、280 mm/d及240 mm/d雨强条件下污染物运移至3#观测点需要大约60 d、72 d和84 d,且运移时间120 d时浓度分别达到0.488 mg/L、0.187 mg/L及0.088 mg/L;雨强一定时(P=360 mm/d),运移初期KS变异系数越大,污染程度越大,而随着时间的延长至108 d,CoV=50%条件下浓度值超越变异系数为100%、150%、200%时的浓度,120 d超越250%;最后,相对低雨强条件下,观测点污染浓度与K_S变异系数成正比,随着雨强的增大则成反比。以上研究结果可为强降雨条件下大尺度地下水环境污染预报、评估与治理提供理论依据。

This paper is devoted to the research on the migration characteristics of contaminant in heterogeneous aquifer and the influence ongroundwater environment under heavy rainfall. On the basis of stochastic theory, considering the effects of three main factors, such as rainfall infiltration rate, permeability coefficient and longitudinal dispersion, on solute transport un-der different rainfall intensities by using MATLAB tools, then the MODFLOW and MT3DMS program,the groundwater flow and solute transport problems were solved and analyzed. Results of the research suggested that heavy rainfall enhanced the velocity and degree of contaminant migration by affecting the parameters of groundwater flow field, i.e. when thevariation co-efficient of KSis constant（CoV=100%）, under the condition of rainfall intensities of 360 mm/d, 280 mm/d and 240 mm/d, the migration time of contaminants to the 3# observation well were ca. 60 d, 72 d and 84 d, respectively; and the concentrations of the contaminant respectively reached 0.488 mg/L, 0.187 mg/L and 0.088 mg/L after 120 d migration; when rainfall intensi-ty remained constant（P=360 mm/d）, the larger, the greater degree of pollution of rainfall infiltration; finally, under the condi-tion of relatively low rainfall intensity, the concentration of observation wells is directly proportional to the variation coeffi-cient KS, which is inversely proportional as rainfall progresses. In conclusion, the research provided reference and basis for the prediction, evaluation and management of large scale groundwater environmental pollution under heavy rainfall.