Numerical method approach to determine flood discharge of Moyan weir in Musi Rawas Regency, South Sumatra, Indonesia

This research was conducted to obtain the right discharge plan in the irrigation area with a study of the amount of discharge that can be used upstream of the weir so that the water supply at the intake does not lack water. The Deras II Irrigation Area covering 928 hectares, has two weirs as a source of irrigation water, namely the Moyan weir and Aur Weir. The upstream part of the Moyan weir is a sleeping area in the form of a swamp used by farmers to become a paddy field whose water source comes from the swift river (upstream of Moyan weir). With this water uptake, the impact on the flow of water entering the Moyan intake will be reduced, so it needs to be done with the numerical method approach of the HEC-RAS program. Based on results, graphically depicted at each review station in the channel and the existing discharge obtained from the measurement of the speed with the current meter and water level from each cross-section along the irrigation channel. The simulation results are obtained with the condition of the river crossing, which is not filled, and the discharge is 0.024 m3/sec. The water level at the downstream cross-section is filled as high as 0.75 m with a flow velocity of 0.783 m/sec, and the water level downstream of the irrigation channel is as high as 0.40 m.