Optimization of Irrigation Water Allocation at The Meninting Dam to Substitute The Water Discharge to The Jangkok - Babak HLD

Abstract

Water resources are vital components for sustaining life and supporting economic development; therefore, their management must be carried out in an integrated and sustainable manner. The Lombok River Basin (WS Lombok), as one of Indonesia’s National Strategic River Basins, comprises 197 watersheds (DAS), 52 of which have been utilized for water supply. The imbalance of water distribution between the western region (which tends to have a surplus) and the southern region (which faces a deficit) necessitates an efficient and equitable water management system. One of the key solutions developed to address this issue is the construction of the Meninting Dam, designed to balance water availability through the High-Level Diversion (HLD) Jangkok–Babak Channel. This study aims to simulate and optimize water allocation from the Meninting Dam to several major irrigation areas, namely D.I. Sesaot, D.I. Jurang Sate Hulu, D.I. Jurang Sate Hilir, and D.I. Jurang Batu. The methodology includes hydrological simulation and water allocation optimization using a trial-and-error approach to achieve flow balance between the supplying rivers (Meninting, Jangkok, and Sesaot) and the HLD as the receiving system. The results indicate that water availability in each irrigation area reaches 2,480 L/s for D.I. Sesaot, 10,049 L/s for D.I. Jurang Sate Hulu, 8,596 L/s for D.I. Jurang Sate Hilir, and 4,536 L/s for D.I. Jurang Batu, with a total inflow to the HLD system of 13,970 L/s. Following the operation of the Meninting Dam, irrigation efficiency (K Factor) increased from 85.6% to 98.3% in D.I. Sesaot, and from 86.3% to 87.7% in the Jurang Sate–Jurang Batu system. Water distribution also shifted, with 61.4% of the flow directed to the HLD system and 38.6% to D.I. Sesaot, as the dam fully meets the irrigation demand in D.I. Sesaot. These findings demonstrate that integrated inter-watershed water management through the operation of the Meninting Dam and the HLD system significantly improves water distribution efficiency and supports the enhancement of cropping intensity in southern Lombok.