HydroPol2D -- Distributed Hydrodynamic and Water Quality Model: Challenges and Opportunities in Poorly-Gauged Catchments

Floods are one of the deadliest natural hazards and are fueled by excessive urbanization. Urban development decreases infiltration by reducing pervious areas and increases the accumulation of pollutants during dry weather. During wet weather events, there is an increase in the levels of pollution concentrations and stormwater runoff that eventually reach creeks and rivers. Polluted stormwater runoff may be sources of water supply. Modeling the quantity and quality dynamics of stormwater runoff requires a coupled hydrodynamic module capable of estimating the transport and fate of pollutants. In this paper, we evaluate the applicability of a distributed hydrodynamic model coupled with a water quality model (HydroPol2D). First, the model is compared to GSSHA and WCA2D in the V-Tilted catchment, and the limitation of the critical velocity of WCA2D is investigated. We also applied the model in a laboratory wooden board catchment, focusing on the validation of the numerical approach to simulate water quality dynamics. Then, we apply HydroPol2D in the Tijuco Preto catchment, in Sao Carlos - Brazil, and compare the modeling results with the full momentum solver of the Hydrologic Engineering Center - River System Analysis (HEC-RAS). The model implementation, the governing equations, and the estimation of input data are discussed, indicating the challenges and opportunities of the application of distributed models in poorly-gauged catchments. For a 1-yr return period of rainfall and antecedent dry days and assuming an uncertainty of $40\%$ in the water quality parameters, the results indicate that the maximum concentration of total suspended solids (TSS), the maximum load and the mass of the pollutant washed in $30\%$ of the volume are, $456~\pm~260~\mathrm{mg.L^{-1}.km^{-2}}$, $\mathrm{2.56 \pm 0.4~kg.s^{-1}.km^{-2}}$, and $\mathrm{89\%~\pm~10\%}$, respectively.