Sediment Flushing Simulation and Sediment Distribution in Wlingi Reservoir

Wlingi Dam is one of the dams in Indonesia which is part of the Brantas River Basin, that has an area of 2,890 km2 of catchment area and serves as a collection point and water provider for irrigation in Lodoyo and Tulungagung Timur areas by irrigating 15,132 Ha rice fields. One of the problems in the Wlingi Dam is sedimentation in its reservoir. Data shows that from the Wlingi Dam was built in 1977 the total volume of storage capacity declined from 24.00 million m3 in 1977 to 2.20 million m3 in 2015. This is the basis of this research this is done to find out alternative solutions that can be done to restore the total volume of the reservoir by using the efficiency of flushing sediment in the reservoir. This research was carried out by using 2 flushing scenarios, namely scenario A by using an inflow discharge for 49 hours and scenario B using an inflow discharge for 56 hours with each scenario having 7 alternative scenarios by increasing and reducing the inflow discharge based on the percentage of 10% to 30%. The results obtained in the simulation using HEC-RAS are the highest efficiency of sediment flushing obtained by increasing the inflow discharge to 110%. So in this study it was concluded that by reducing the inflow discharge in percentages for flushing the sediment it is not always directly proportional to the volume value of the sediment being flushed or to the efficiency of the sediment flushing value. The results of the sediment distribution that occurred after sediment flushing simulations on Brantas River from cross section CRB 19 to CRB 140 were the largest river scouring occurred on CRB 117 up to CRB 130 or around 700 to 1,300 m from Wlingi Dam.