ENHANCED RAINFALL-RUNOFF-FLOOD SIMULATION WITH RRI MODEL INCORPORATING RIVER VEGETATION RESISTANCE BASED ON 2D NUMERICAL CALCULATION RESULTS AND SLOPE DIRECTION SURFACE FLOW FLUX

Abstract

 The one-dimensional (1D) flood flow calculation method coupled with existing runoff models has a limitation in the accuracy of water-level prediction, because of its disability to take the effect of the river vegetation resistance into account. This study proposed a method to improve the accuracy of water-level calculation during floods using the 1D flood flow calculation method in the Rainfall-Runoff-Inundation (RRI) model. We derived the surface flux vector using the two-dimensional (2D) diffusion wave approximation from the shallow water flow equation. From 2D flood-flow analysis results, it is clarified that the roughness coefficient considering vegetation can be expressed as a function of water depth. The modified RRI model is confirmed to reproduce well the water-level hydrograph during a big flood event in the Nuta River basin.