River Discharge Analysis of Saba Watershed Using MW-SWAT

Abstract

Saba is one of watershed that located in Buleleng, Bali. Length of Saba river is about 36 km. Saba river flows through Buleleng region which is relatively dried. Saba watershed is one of water supplier for irrigate agriculture land in Buleleng region. The main landuse is paddy field. The objectives of this study were to analyze river discharge of Saba watershed using MW-SWAT, to compare discharge from field measurement with simulation result using MW-SWAT, and to know the impact of landuse management towards river discharge. Research methods consisted of several stages, such as preparation, data collecting, data processing, data analyzing, and presentation. The results showed that Saba area was ±14393.20 ha with an elevation of 1 to 2248 m above mean sea-level. Dominant soil types were latosol, regosol, and andosol. Topography was classified in 6 classes, i.e about 6.33% of delineation watershed area had slope 0-3%, about 11,41% area had slope 3-8%, about 19.04% area had slope 8-15%, about 35.61% area had slope 15-30%, about 17.32% area had slope 30-45%, and about 10.29% area had slope >45%. The result of delineation showed that plantation area was 8256.43 ha (57.36%), paddy field was 1831.22 ha (12.72%), and forest area was 1811.94 ha (12.59%) of total area. After simulation, the daily maximum discharge was 109.8 m3/s and daily minimum discharge was 0 m3/sec, with determination coefficient value (R2) of 0.0218 for relation between simulation discharge and field discharge. After calibration, daily maximum discharge of 13.1 m3/s and daily minimum discharge of 0.0032 m3/s were obtained, with determination coefficient value (R2) of 0.4025. After correction on calibration parameter values, daily maximum discharge of 13.83 m3/s and daily minimum discharge of 0.0034 m3/s were obtained, with determination coefficient value (R2) of 0.4114. From field measurement was obtained daily maximum discharge of 77.74 m3/s and daily minimum discharge of 12.05 m3/s.

Daerah aliran sungai (DAS) Saba merupakan salah satu DAS yang ada di Buleleng, Bali. DAS Saba memiliki panjang sekitar 36 km. Sungai Saba mengalir melalui daerah Buleleng yang relatif kering. DAS Saba merupakan salah satu pemasok air untuk kebutuhan irigasi lahan pertanian yang ada di daerah Buleleng. Salah satu penggunaan lahan DAS Saba adalah untuk sawah sehingga kecukupan akan air yang diperlukan untuk sawah tersebut penting diperhatikan. Sawah merupakan salah satu tanaman yang memerlukan banyak air untuk proses pertumbuhannya. Penelitian ini bertujuan untuk (1) Menganalisis debit aliran sungai di DAS Saba dengan menggunakan aplikasi open source software MW-SWAT. (2) Membandingkan debit aliran sungai hasil simulasi dengan hasil pengukuran di lapangan. (3) Mengetahui dampak pengelolaan lahan terhadap debit aliran yang dihasilkan DAS Saba untuk mengairi lahan pertanian di sekitar DAS. Metode penelitian yang dilakukan meliputi beberapa tahap, seperti tahap persiapan, pengumpulan data, pengolahan data, analisis data, dan penyajian hasil.