<![CDATA[ABSTRAK: Potensi sumberdaya air yang semakin menurun dan eksplorasi sumberdaya air yang sangat tinggi seiring berkembangnya kebutuhan masyarakat sehingga perlunya dilakukan Analisa Neraca Air di Daerah Aliran Sungai Gandong, Kabupaten Magetan, Provinsi Jawa Timur. Hasil analisa didapatkan total ketersediaan air permukaan Q93,75% sebesar 35,144 m3/detik, Q75,3% sebesar 48,050 m3/detik, Q50,7% sebesar 59,833 m3/detik, Q26,0% sebesar 78,163 m3/detik dan total ketersediaan air bawah permukaan sebesar 163,650 m3/detik. Kebutuhan air permukaan sebesar 183,58 m3/detik dengan luas Daerah Irigasi (D.I) sebesar 7.945 ha, kebutuhan air bawah permukaan sebesar 118,990 m3/detik. Neraca air permukaan dengan Microsoft excel menunjukkan D.I Jejeruk dengan kondisi defisit tertinggi sebesar 13,68 m3/det atau hanya 1,23% kebutuhan yang mampu terpenuhi, neraca air permukaan dengan paket program Water Evaluation and Planning (WEAP) menunjukkan D.I Gemblung dengan besar surplus air tertinggi sebesar 0,43 m3/detik atau 100% kebutuhan mampu terpenuhi, neraca air bawah permukaan menunjukkan bahwa surplus air untuk bulan januari hingga desember, neraca air lahan metode Thornthwaite Mather sebagian besar wilayah DAS Gandong masih defisit lengas tanah terutama pada bulan mei sampai desember.Kata Kunci: Neraca air, irigasi, thornthwaite matter, water evaluation and planning. ABSTRACT: The Potential water resources are declining and the exploration of water resources is very high as the needs of the citizens so that the need for an analysis of Water Balance in the Gandong Watershed, Magetan Regency, East Java Province. The results of this analysis obtained the availability of surface water that comes from discharges, springs, and the wells bore of 35,144 m3/s in dry season, 48,050 m3/s in the low season, 59,833 m3/s in normal season, and 78,163 m3/s in enough season. The availability of subsurface water was 163,650 m3/s. The surface water requirement of Gadong Watershed was 183,580 m3/s with 55 irigation areas and the subsurface water requirement was 118,990 m3/s. The highest water surface deficit in Irrigation Area of Jejeruk was 13,680 m3/s or only 1,23% of the needs were met in December of the dry season and the highest surplus in Irrigation Area of Gemblung was 10,430 m3/s or 100% of the need fulfilled in February in enough season. Water balance with Water Evaluation and Planning Software (WEAP) only Irrigation Area of Becokan, Dung biru, Kresekan, Maden, Menco, Mendi, Modang, Mojosemi, Ngadiloyo, dan Ngunut have 100% coverage demand. Subsurface water balance under surplus condition in January to December. Land water balance under deficit condition in May to December.Keywords: Water balance, irrigation, thornthwaite matter, water evaluation and planning.]]>
