Simulation of contaminant transport due to rain runoffs by a Lagrangian particle method

Abstract

A mesh-free Lagrangian particle method of modelling the overland flow due to rainfalls is applied to track runoff water to examine the transports and the fate of contaminants in flat urban-agriculture mixed land use area. In contrast to most existing methods that are based on two-dimensional fixed Eulerian grids, the Lagrangian particle method naturally tracks the motion of the runoff water and the passive contaminants without additional calculation and is flexible to cope with various terrain conditions including three-dimensional topography, building structures and drainage systems. The proposed method is based on the Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) method developed to simulate rain runoffs by the present authors. The calculation of contaminant diffusion from a line source was found to agree well with the exact analytical solution. The simulation of overland flow on a real terrain of 2.5km x 2.5km with a resolution of 2m indicated tracing of passive contaminants could be examined effectively on the ground with no distinct topographical features.