THE INFLUENCE OF SEMBAYAT WEIR ON SEDIMENT TRANSPORT RATE IN THE ESTUARY OF BENGAWAN SOLO RIVER, INDONESIA
Keywords:Bengawan Solo River, Sediment Transport Rate,Seasonal Changing, HEC-RAS, Field Investigation
This research is aimed to assess the sediment transport rate under different conditions of estuary geometry by comparing the situations before and after the construction of Sembayat Weir. Sediment concentration, flow velocity, and temperature were obtained via field investigation from October 2016 to September 2017. River discharge and tidal discharge phenomenon are analyzed in the estuary, which affect hydraulic head changes. The HEC-RAS model was used for numerical modelling simulation of the hydrodynamics. The results revealed that the sediment transport rate increased under the influence of erosion in the river branches. BH2 and BH3 were the observation sites located before and after the tributary junction. Those location present the sediment transport rates decreased by 30% and 26%, respectively, in the rainy season because after weir construction. The results agree with previous research results in that sediments were deposited around the estuary weir. Meanwhile, in the river branches, a higher sediment transport rate was observed because of the tidal current that provided sediment transport over a longer term in the dry season. The findings extend the knowledge on the influence of Sembayat Weir on sediment transport rate characteristics with respect to seasonal changes.