Author(s): I. Gede Tunas; Sukandi Samatan

Linked Author(s):

Keywords: Water depth; Velocity distribution; Flood; HEC - RAS Mapper

Abstract: River channel management related to flood control is highly dependent on flow characteristics. These parameters are influenced by the geometry of the river cross-section and the intensity of rainfall as a source of flow that is transformed through the watershed system, especially extreme rainfall. This paper aims to model the flow in one of the river sections in Palu, Indonesia (Poboya River) where this segment is the gold mining exploitation area of PT. Citra Palu Minerals which must be protected from flooding and riverbank erosion. The protection strategy and method are based on information on flow characteristics in the reviewed river segment. This modeling is performed using HEC-RAS 2D with three variations of discharge: average discharge of dry season, average discharge of rainy season and discharge caused by extreme rainfall. Discharge data are obtained from rainfall-runoff transformation using HEC – HMS Model with input data: rainfall intensity (3 scenarios representing average rainfall of dry season: 5.5 mm, average rainfall of rainy season: 80.8 mm and extreme rainfall: 155.20 mm), land use and land cover (LULC), soil type and other supporting data. Calibration is applied to the models both HEC – HMS Model by optimizing the sub model parameters (loss, transformation, and base flow) and HEC -RAS 2D Model by setting the Manning roughness parameters. The goodness of calibration was evaluated by the root mean square error (RMSE) between simulated discharge and observed discharge (HEC – HMS) and the RMSE of observed flow depth and simulated flow depth (HEC – RAS), which were 0.15 and 0.05, respectively. The modeling results showed that flow depth and flow velocity increased drastically due to extreme rainfall of 2.3 meters passing through the right overbank of the river and 4.5 m/sec on the outside of the river bend. The water surface area also increased to cause inundation on the right side of the river. The results of the study showed that extreme rainfall caused a major influence on the flow characteristics in the river.

DOI: https://doi.org/10.64697/978-90-835589-7-4_41WC-P1799-cd

Year: 2025