ANALYSIS OF SEMANTOK RESERVOIR OPERATION PATTERNS IN NGANJUK REGENCY AFTER THE ENLARGEMENT OF THE NORTH WIDAS IRRIGATION SUPPLEMENT CHANNEL

Semantok Dam is located in Sambikerep Village, Rejoso District, Nganjuk Regency, East Java Province where the upstream of Semantok Dam is in the Tritik Irrigation Area and Ngomben Irrigation Area. Semantok Dam has 2 Intakes namely the Main Intake and Ngomben Intake. Due to the limitations of the irrigation supplementary channel that flows from the Ngomben Intake, namely in the North Widas irrigation, it is planned to enlarge the irrigation supplementary channel so that it can flow water to rice fields with a wider coverage than the water flow it passes through.
From the analysis results that have been carried out, several conclusions were obtained, namely the total existing service of 1900 ha and the results of the simulation of water availability in the reservoir, namely the highest average inflow discharge of 11,815 m3/s and the lowest of 0.560 m3/s while the highest outflow discharge of 2,580 m3/s and the lowest of 0.312 m3/s. With the enlargement of irrigation supplementation in North Widas, the results of the simulation of water availability in the reservoir that are most optimal are irrigation services in the Main Intake of 1517.4 ha and irrigation services in the Ngomben Intake of 980.5 ha so that the total irrigation service is 2497.9 ha. The operation pattern of the reservoir after the enlargement of the North Widas irrigation supplement, where the simulation results of water availability in the reservoir, which originally served 1900 ha with the highest outflow discharge of 2,580 m3/sec and the lowest of 0.312 m3/sec, now has a highest outflow discharge of 3,380 m3/sec and the lowest of 0.312 m3/sec.