Suplai air dari Jaringan Irigasi Interkoneksi Lombok Selatan belum mampu memenuhi kebutuhan air sebagian daerah irigasi di Lombok Selatan secara optimal, termasuk Daerah Irigasi (DI) Pandanduri dan Swangi. Untuk mengatasi masalah ini pemerintah merencanakan pembangunan Waduk Pandanduri, yang disiapkan menjadi regulator pengelolaan sumberdaya air di daerah Pandanduri dan sekitarnya. Rencana pemanfaatan waduk untuk daerah layanan yang lebih luas membutuhkan informasi tentang kemampuan suplai Waduk Pandanduri yang sesungguhnya. Untuk itu perlu dilakukan studi untuk mengetahui kemampuan optimum Waduk Pandanduri dalam pemanfaatan air. Penelitian ini bertujuan melakukan kajian optimasi pemanfaatan air Waduk Pandanduri untuk keperluan suplesi air irigasi pada Sistem Jaringan Irigasi Pandanduri Swangi. Kemampuan optimum Waduk Pandanduri dalam pemanfaatan air dilihat dengan melakukan analisis optimasi pemanfaatan air menggunakan metode Program Linier, yang dikombinasikan dengan teknik simulasi operasi pengaturan pelepasan air (release) waduk. Kemampuan optimum pemanfaatan air diukur dari pencapaian intensitas tanam per tahun dengan mempertimbangkan nilai rasio antara release nyata dan target release berdasarkan kebutuhan air (faktor k) dan reliabilitas operasi waduk. Simulasi operasi pengaturan release waduk dilakukan untuk tahun 1999 - 2008. Inflow waduk dalam perhitungan menggunakan debit rerata tengah bulanan yang tercatat pada AWLR Suradadi. Besarnya outflow diperhitungkan sebagai target release yang terdiri dari kebutuhan air untuk penggelontoran dan kebutuhan air irigasi dengan beberapa alternatif pola tata tanam dan awal periode tanam. Nilai kebutuhan air irigasi total memperhitungkan nilai return flow dari DI Pandanduri. Analisis neraca air pada kondisi eksisting memperlihatkan rasio potensi annual inflow terhadap annual demand adalah 0,98. Penelitian menunjukkan bahwa air yang tersedia pada Waduk Pandanduri hanya mampu memenuhi kebutuhan air irigasi dengan intensitas tanam maksimum 258,4% untuk areal tanam baku 4.477 ha. Kapasitas suplai berdasarkan nilai rerata faktor k adalah 0.854 dan reliabilitas operasi sebesar 82,40%. Kondisi diatas diperoleh pada penanaman tanpa golongan, periode tanam awal September dan pola tanam padipalawija- palawija. Hasil penelitian menunjukkan bahwa diperlukan upaya lain agar kebutuhan air irigasi untuk seluruh DI Pandanduri dan Swangi dapat terpenuhi.

Water supply from South Lombok Interconnection Irrigation Network has not able to meet water demand of irrigation areas in South Lombok optimally, including Pandanduri and Swangi irrigation areas. To overcome this problem the government has been planned a construction of Pandanduri reservoir, as the regulator of water resource management in Pandanduri and surrounding areas. The plan to expand coverage of Pandanduri reservoir’s service area needs information about actual capacity of reservoir in supplying irrigation water. Therefore, it needs a study to determine the optimum capacity of Pandanduri reservoir in exertion water by considering some proper performance indicators. In order to obtain the optimum water resources development of Pandanduri reservoir, an optimization model based on Linear Programming method was formulated and then a water balance of Standard Operating Rule reservoir simulation model was applied in coupled with the optimization model. Optimum water use was measured by the achievement of annual cropping intensity and ratio between actual release and water demand (k factor) with a minimum reliability level of reservoir operation as one of the defined constraints. Operating simulation of reservoir release has done for the year 1999-2008. The recorded half monthly discharge on AWLR of Suradadi gauge station was used as reservoir inflow for the corresponding simulation time period. The amount of outflow was calculated as target release that consists of river maintenance water and irrigation water requirements with some alternative cropping patterns and beginning of planting periods. Return flow from drainage water of Pandanduri irrigation area to the river was taken into account for calculating net irrigation water demand of the Swangi irrigation area. Analysis of water balance for the existing cropping pattern and cropping schedule shows the ratio of mean annual inflow to the annual demand is 0,98. The research shows that the available water in Pandanduri reservoir is able to meet the irrigation water demand with maximum annual cropping intensity 258,4% for 4.477 ha of command area. The optimum condition would be obtained by planting without rotation water supply and cropping pattern paddy-palawija-palawija that the cultivation is begin in early September. The output of simulation model concludes that supply capacity based on average k factor is 0,854 and the operating reliability is 82,40%. These results indicate that additional effort to serve irrigation water demand in the whole command area is necessary.

Kata Kunci : Pemanfaatan air,Optimasi linier,Simulasi operasi pengaturan release waduk, water use, Linear Programming, Standard Operating Rule