PEMODELAN SEDIMENTASI SUNGA SURUMANA MENGGUNAKAN HEC-RAS TERHADAP PERUBAHAN ELEVASI DASAR SUNGAI

The Surumana River, located in South Banawa Subdistrict, Donggala Regency, Central Sulawesi,
is one of the rivers experiencing sedimentation problems, as evidenced by a series of recurring
floods. This sedimentation process can cause changes in the riverbed elevation, which may
potentially affect the river’s flow capacity. This study aims to analyze changes in the Surumana
River’s riverbed elevation due to sedimentation based on HEC-RAS modeling results, as well as to
evaluate its response to variations in design flood discharge at each cross-section. Modeling was
performed using a one-dimensional (1D) hydraulic and sediment transport approach with HECRAS 6.6 software, on a river section approximately 2 km long (CR 106–CR 73) consisting of 34
cross-sections, using the Meyer-Peter Müller sediment transport function and an upstream
equilibrium load boundary condition. Simulations were performed for three design flood discharge
scenarios, namely 2-, 10-, and 50-year return periods (Q2, Q10, and Q50). The results of the study
show that changes in riverbed elevation occurred at 33 of the 34 cross-sections, consisting of 16
cross-sections that experienced aggradation and 17 that experienced degradation, while one crosssection (RS 106) remained relatively unchanged. Elevation changes in the meandering river
segments (RS 73–RS 89) were consistently greater than those in the straight segments (RS 90–RS
106), with a range of ?0.193 m to +0.183 m under Q2 conditions. These elevation changes tend to
increase as the design flood discharge rises, with the overall range reaching ?0.279 m to +0.241 m
under Q50 conditions, although this increase is not uniform across all cross-sections. The most
significant elevation changes—which consistently increase with rising discharge—occur at the
cross-sections around RS 74 through RS 77.
Keywords: Surumana River, HEC-RAS, sedimentation, riverbed elevation, sediment transport.