Rainfall Runoff and Dissolved Pollutant Transport Processes Over Idealized Urban Catchments

Abstract

Urban stormwater runoff is often considered as one of the most significant contributors to water pollution. Particulates are commonly regarded as the primary form of pollutant transport in the urban environment, but the contribution from the dissolved pollutants can also be significant. This study aims to investigate the dissolved pollutant transport process over urban catchments, especially the effects of buildings and spatial distribution of pollutants. The concept of "exchange layer" has been adopted and an equation has been proposed to describe the release process of dissolved pollutant from the exchange layer to the runoff water. A horizontal two-dimensional water flow and pollutant transport model has been developed for predicting dissolved pollutant runoff based on the shallow water assumptions and the advection-diffusion equation. A series of laboratory experiments have been conducted to verify the proposed model. It has been demonstrated that both the rainfall runoff and the pollutant runoff can be predicted accurately. Buildings slow down the runoff and pollutant transport processes, especially when buildings are staggered. The non-uniform distribution of pollutants over the catchment greatly influences the pollutant transport process over the catchment. This work provides insight into the effects of buildings and initial pollutant distribution on the dissolved pollutant transport phenomenon, which can help better design the pollution mitigation strategies.

Modelling urban sewer flooding and quantitative microbial risk assessment: A critical review

“…Zhang et al (2020) ran a series of laboratory experiments in a rainfall–simulation hall; they validated a numerical model that simulated overland flow, using shallow water equations and a pollutant transport model using advection–diffusion equations. Two building layouts were investigated.…”

A two‐layer model for studying 2D dissolved pollutant runoff over impermeable surfaces

“…Each runoff sample tells the water runoff rate and pollutant concentration at an instant. The detailed information about rainfall‐simulation system, area treatment, pollutant spreading, runoff collection, data recording and concentration determination can be found in Xiao et al (2017), Zhang et al (2018), and Zhang, Xiao, Liang, Tang, Yuan, et al (2020).…”

“…The finite difference method (FDM) was used to solve the set of equations given above. In particular, the SWEs and advection–diffusion equation were numerically solved using a highly efficient total variation diminishing (TVD) MacCormack scheme, which consists of predictor, corrector, and TVD modification steps, and is of second‐order accuracy in both time and space (Zhang, Xiao, Liang, Tang, Yuan, et al, 2020). The detailed theory and treatment regarding this numerical scheme can be found in Liang et al (2006, 2010); Liang, Lin, and Falconer (2007).…”

“…Similar to previous studies (Deng et al, 2005; Xiao et al, 2017; Zhang, Xiao, Liang, Tang, Xu, et al, 2020; Zhang, Xiao, Liang, Tang, Yuan, et al, 2020), table salt (NaCl) was chosen as the dissolved pollutant tracer. Salt was spread uniformly on the area surfaces, except on top of the buildings.…”

“…This simple exponential model neglects the spatial heterogeneity of areas. Imposing the empirical exponential function in the source term of the advection–diffusion equation, Zhang, Xiao, Liang, Tang, Yuan, et al, (2020) developed a two‐dimensional model and investigated the effects of building layout and non‐uniform pollutant distribution on the dissolved pollutant transport process over impervious surfaces. They reported that buildings slow down the pollutant transport process, especially when buildings are staggered.…”