Quasi-2D Approach in Modeling the Transport of Contaminated Sediments in Floodplains during River Flooding—Model Coupling and Uncertainty Analysis

Abstract

In flood modeling, many one-dimensional (1D) hydrodynamic and water-quality models are too restricted in capturing the spatial differentiation of processes within the floodplain and two-dimensional (2D) models are too demanding in data requirements and computational resources. The latter is an important consideration when uncertainty analyses using the Monte Carlo techniques are to complement the modeling exercises. This paper describes the development of a quasi-2D modeling approach that still calculates the dynamic wave in 1D but the discretization of the computational units is in 2D, allowing a better spatial representation of the flow and substance transport processes in the floodplain without a large additional expenditure on data preprocessing and simulation processing. The DYNHYD (1D hydrodynamics) and TOXI (sediment and micropollutant transport) models from the WASP5 modeling package were used as a basis for the simulations. The models were extended to incorporate the quasi-2D approach and a Monte Carlo analysis was used to investigate the contribution of uncertainty from parameters and boundary conditions to the resulting substance concentrations. A flood event on the Saale River, Germany, was simulated as a test case. The results show a plausible differentiation of suspended sediment and zinc concentrations between the floodplain and the main channel. Based on the results it appears that for flood simulations, uncertainties in boundary conditions are higher and need to be given more attention that uncertainties in model parameters.