WATER BALANCE ANALYSIS IN PIJENAN BANTUL IRRIGATION AREA

Untuk melihat ketersediaan air irigasi di suatu daerah digunakan analisa neraca air. Neraca air adalah gambaran potensi penyediaan air dan potensi kebutuhan air. Tujuan dari penelitian ini adalah menghitung debit masukan dan keluaran dari air irigasi Pijenan Bantul yang akan disesuaikan dengan pola tata tanam di daerah tersebut. Metodologi dalam penelitian ini adalah eksperimental dengan pengambilan data di daerah irigasi Pijenan Bantul. Alat dan bahan yang digunakan adalah current meter, pita ukur, blangko kebutuhan air irigasi. Hasil penelitian menunjukkan debit selama 10 tahun (2003-2013) sebesar 683,730 hingga 10.237,338 l/dt dan debit kebutuhan rata-rata 1823 l/dt. Hubungan antara debit ketersediaan dan debit kebutuhan di pintu tersier dapat ditunjukkan dari analisis neraca air dimana pada daerah hulu kebutuhan irigasi selalu lebih kecil dari debit yang tersedia, di daerah tengah debit kebutuhan seimbang dengan debit ketersediaan, sedangkan di daerah hilir debit kebutuhan lebih besar daripada debit ketersediaan. Hasil perhitungan faktor K didapatkan lebih kecil dari 0,7 yang artinya terjadi defisit air sehingga perlu system irigasi giliran.To see the availability of irrigation water in an area water balance analysisis used. Water balance is a description of potential water supply and potential water requirement. The purpose of this research was to calculate the input and output irrigation waterdischarge from PijenanBantul that will be adjusted with the pattern of planting system in the area.The methodology in this research was experimental with data retrieval in PijenanBantul irrigation area. Tools and materials used were current meters, measuring tape, form of irrigationwater requirement. The results showed that thedischarge for 10 years (2003-2013) was 683.730 to 10,237.338 l/dt and the average requirement was 1823 l/dt. The relationship between the availability and the requireddischarge of the tertiary gate could be shown from the water balance analysis where upstream irrigation water requirements were always smaller than the available discharge; in the middle area the required discharge was equal with the available discharge; whereas in the downstream area, the requireddischarge was greater than the available discharge. The calculation result of K factor was smaller than 0,7 which means water deficit was existed, therefore the rotation irrigation system was necessary.