Reliability of Runoff Hydrograph Model for Extreme Rainfall Events using HEC-RAS 2D Flow Hydrodynamics Rain-On-Grid

Abstract

Hydrological modeling is a valuable tool for analyzing water resources and predicting the impacts of extreme rainfall events, particularly for flood risk mitigation. Accurate results from hydrological models rely heavily on detailed input of watershed characteristics, including morphometric factors, land cover, and slope. In the face of the increasing frequency and severity of floods due to climate change, hydrological modeling has become an essential tool for disaster risk mitigation and management. HEC-RAS is a widely used software for river flow modeling and floodplain analysis. HEC-RAS 2D with the rain-on-grid meteorological model is a powerful tool for simulating flood events in complex river systems. The rain-on-grid method enables the simulation of spatially distributed rainfall events and their impact on runoff, which is crucial for modeling extreme runoff hydrographs. Previous studies have demonstrated the accuracy and effectiveness of HEC-RAS 2D with rain-on-grid in modeling extreme runoff hydrographs. This study aims to validate the reliability of HEC-RAS 2D hydrodynamics in simulating unsteady flow with meteorological data will be examined within a laboratory-scale physical model of the watershed. Additionally, the performance of HEC-RAS 2D will be evaluated in a observed watershed, specifically the Bangga watershed in Central Sulawesi to assess the performance of the HEC-RAS 2D Hydrodynamics model. The runoff hydrograph reliability model using HEC-RAS 2D rain-on-grid yielded close results when compared to a laboratory-scale physical model with a rainfall simulator and HEC-RAS 2D simulation using meteorological input data. The error in Time of Peak (Tp) and Peak Discharge (Qp) between the physical and numerical models was 7% and 3.5%, respectively. Additionally, in the HEC-RAS 2D simulation, a Manning roughness coefficient value of 0.04 closely matched the results of the physical model, while there was some variability when comparing HEC-RAS 2D results with measured data in Bangga watershed of Central Sulawesi. However, the numerical model exhibited relatively approaching result with the HEC-HMS SCS hydrograph model.