Optimasi Pemanfaatan Air Di Daerah Irigasi Siman, Kabupaten Jombang (Studi Kasus Pada Wilayah Di Siman Mojoagung)

The Siman Mojoagung Irrigation Area in Jombang Regency serves 1,031 ha. This study compared the existing cropping-pattern water requirement in the Global Cropping Plan with available discharge, developed alternative patterns, estimated irrigation requirements using a climatological method, and selected the best alternative through a water-balance analysis. Rainfall, climatological, intake-discharge, cultivated-area, and cropping-plan data were analyzed for ten-day periods. The existing-plan Water Balance showed deficits in 35 of 39 periods, with a maximum deficit of 2,380.88 L/s. Eight alternative cropping patterns were evaluated. Their maximum requirements during critical periods ranged from 793.26 to 1,383.03 L/s. Alternative VII—rice–maize–maize with year-round sugarcane—required a maximum of 970.62 L/s. The seasons begin in the first ten-day periods of January, May, and September, covering 901 ha, 700 ha, and 60 ha, respectively, with 130 ha of sugarcane. Its Water Balance produced five deficit periods, a maximum deficit of 323.03 L/s, and an annual deficit volume of 928,213.89 m³. Alternative VII required 15 pumps and generated the highest agricultural revenue after pumping costs, amounting to IDR 81,694,553,679.26 per year; therefore, it was selected as the best cropping pattern.