Addressing sedimentation issues: Modelling the rating curve and river sediment transport using HEC-RAS 6.1 application

Fluvial sedimentation refers to the deposition of materials transported by water along the river, which can reduce the river’s holding capacity. Over time, the process has become a serious global issue, significantly contributing to recurrent flooding. This study aims to develop a sediment rating curve and transport model to address the high sedimentation in the Krueng Langsa River, an issue requiring urgent action. The data set includes bedload measurements using a grab sampler, suspended load collected using a 1-dm3 scale plastic bottle, hydrometric measurements using a currentmeter, as well as planned flood discharge, river geometry, and roughness. Sediment transport was modelled using the HEC-RAS 6.1 application. The results indicated sediment transport and movement (τ0 > τc). Based on the sediment rating curve, the regression equations were: Qs = 0.0707Qw2 + 109.72Qw (upstream), Qs = 0.0075Qw2 + 122.25Qw (midstream), and Qs = 0.0043Qw2 + 103.97Qw (downstream), where Qs is the sediment discharge and Qw is the water discharge. The coefficient of determination (R2) values were 0.9761 (upstream), 0.9782 (midstream), and 0.9796 (downstream), indicating an excellent correlation close to 1. The sediment transport model revealed changes in the riverbed due to sediment movement, with degradation of 0.365 m at the upstream review point (RS 346), aggradation of 1.655 m at the midstream point (RS 270), and aggradation of 0.218 m at the downstream point (RS 209). Extreme aggradation occurred at RS 364 (2.08 m), while extreme degradation occurred at RS 271 (0.482 m). The sediment rating curve and transport model provide valuable river improvement and management insights, offering a potential solution for mitigating recurrent flooding.