An embedded VPMM-AD model for riverine transient flow and non-reactive contaminant transports

Although umpteen studies are available in the hydrologic literature for modeling the contaminant transports under steady flow conditions, similar trend is not seen while modeling this process under unsteady flow conditions and, thereby, limiting their field application for pollution monitoring in semi-gauged rivers. In this study, three simple model variants, namely, VPMM-AD(ΨDc), VPMM-AD(ΦDf) and VPMM-AD(Dc) were developed for unsteady state contaminant routing by tight-coupling the physically-based Variable Parameter McCarthy- Muskingum (VPMM) flow-transport sub-model with the Advection-Dispersion (AD) contaminant-transport sub-model. These model variants were extensively tested under unsteady and steady flow conditions using the numerical experiments, and USGS laboratory and real-world river application datasets considering the popular MIKE11-AD model as the benchmark. The study results revealed the consistent superior performance of the VPMM-AD(ψDc) and VPMM-AD(ΦDf) model variants over the benchmark model. The developed approach is a novel one as it is fully physically-based, free from numerical stability problem as the governing equations are solved iteratively, can work at meso-scale with the same computational space and time-steps in the flow and solute routings compatible with the spatiotemporal scales of observation, very simple to use, and do not compromise with the routing accuracy as encountered in the benchmark hydrodynamic model even with a fully implicit finite difference scheme.