A direct two-way coupling of the hydrologic and 1D-2D hydrodynamic models for watershed flood simulation

Abstract

A direct two-way coupling of hydrologic and 1D-2D hydrodynamic models (DCM2D) for watershed flood simulation was proposed. This coupling included three models (i.e., fully distributed hydrologic, 1D hydrodynamic, and 2D hydrodynamic models) and three coupling strategies: the bidirectionally coupled hydrologic-2D hydrodynamic module, two-way coupled hydrologic-1D hydrodynamic module (HH1D), and two-way coupled 1D-2D hydrodynamic module (HH2D). The refined river links (RLs) were used to couple the hydrologic and 1D hydrodynamic models, and the exchange discharge between these models was determined using either the weir flow equations or hydrologic model, depending on the flow transitions. Four cases were used to evaluate the proposed DCM2D. The results indicated that the discharge obtained from the proposed HH1D exhibited a high level of consistency with analytical solutions, with NSE of 0.986. This finding supported the validity of the proposed coupling schemes for hydrologic and 1D hydrodynamic models, particularly in scenarios where there were no distinct flow transitions. The DCM2D accurately represented the physical flood process by allowing rainfall runoff discharge into both 2D low-lying inundation regions and 1D rivers. This contrasted with the indirect coupling models (ICM2D), which required runoff to enter the 1D rivers before flowing into the 2D inundation regions. It exhibited reasonable flow directions and achieved satisfactory simulation accuracy, with higher NSE compared to the ICM2D. The proposed DCM2D model can effectively adapt to the real-life flood evolution process and offer practical and reliable solutions for simulating floods in watersheds.