Case study: Modeling tidal transport of urban runoff in channels using thefinite-volume method

A coupled flow and pollutant transport model based on the finite-volume met hod is developed and applied to predict the tidal transport of urban runoff in a southern California network of flood control channels that drain to n ear-shore bathing waters. Urban runoff in southern California contains elev ated levels of indicator bacteria that signal the presence of fecal polluti on and pose a risk to human health, and model predictions are used to under stand the transport of these pollutants toward the coastline. The model is based on 1D conservation equations for fluid mass, momentum, and pollutant mass that are solved in integral form along channel reaches. A 2D formulati on is solved at channel junctions. The model incorporates the monotone upwi nd scheme for conservation laws approach to give a high-resolution, nonosci llatory prediction of water level, velocity, and pollutant concentration, M odel predictions and field measurements of water level, velocity, and a con servative urban runoff tracer are presented and compare favorably. This cas e study demonstrates that this finite-volume method-based scheme results in an accurate, stable, nonoscillatory and computationally manageable model. The nonoscillatory behavior is particularly beneficial in this study, since runoff enters the channels in pulses that create large gradients in pollut ant concentration.