An update on reservoir operating rules following changes on the effective capacity due to land erosion

Abstract

Reservoirs play a role in decreasing the temporal variability of river flow by regulating the reservoir water release for several downstream water needs. The Keuliling Reservoir was built to meet the needs of irrigation water. However, the dry season in Aceh Besar Regency significantly impacts irrigation areas because water from the Keuliling Reservoir cannot meet the demands. During the dry season, which is also the beginning of the second rice planting season (for gadu rice variety), the water source of the Keuliling Reservoir significantly decreases. The rate of land erosion leads to sedimentation, which may cause a reduction in the effective reservoir capacity. A decline in reservoir function due to sedimentation can affect the reservoir’s performance. The reservoir operating rules need to be adjusted due to a decline in capacity caused by sedimentation. This study aims to develop updated reservoir operating rules that can be used as an operational guideline for the Keuliling Reservoir. The study used a non-linear program to optimize the reservoir operation, which required objective functions and constraints. Optimization will result in reservoir operations that can supply water according to the target rice field area in normal and wet years. The irrigation area is 578 hectares for Group I (Keuliling Upstream Irrigation Area) and 1053 ha for Group I (Keuliling Downstream Irrigation Area). However, in the dry year of Group I (DI Keuliling Hulu), with an irrigation area of 578 hectares, the rice planting pattern (one rice planting season) begins with the planting season in October I. In addition, in Group II (DI Keuliling Hilir), with an irrigation area of 781 ha, the rice planting pattern (one rice planting season) starts the planting season in October II. The reduced inflows during dry years have decreased the target irrigation area by 113 ha. This Keuliling Reservoir operating manual can determine the reservoir water release to balance it with needs and storage targets.