Wilayah DAS Serayu Hulu merupakan DAS prioritas yang memerlukan langkah pengelolaan yang komprehensif. Aplikasi model Soil and Water Assessment Tool (SWAT) dapat digunakan sebagai media untuk perencanaan konservasi ataupun evaluasi respon DAS (debit aliran permukaan, sedimen dan pencemaran sungai). Tujuan utama dari penelitian ini adalah menjalankan model SWAT di DAS Serayu Hulu untuk mengetahui laju sedimen di wilayah ini. Pemodelan SWAT membutuhkan sejumlah input parameter berupa relief, tanah, tutupan lahan dan pengelolaan lahan. Pedogeomorfologi digunakan sebagai batas satuan tanah karena tidak tersedianya peta tanah di wilayah penelitian. Hasil Penerapan model SWAT di DAS Serayu Hulu menghasilkan nilai yang cukup memuaskan, hal ini ditunjukkan nilai R2 mencapai 0,94. Hasil pemodelan SWAT dengan menggunakan data selama 10 tahun (2004-2013) menunjukkan bahwa DAS Serayu Hulu memiliki rerata hasil sedimen sebesar 1.926.900 ton/tahun. Sub DAS 8,9 11, 17, 18, dan 19 merupakan penghasil sedimen tertinggi di DAS Serayu Hulu dengan hasil sedimen 43.931– 121.434 ton/ha/tahun.
Water, a vital natural resource for a human being, could bring negative effects such as flood and landslides. The best way to show the hydrological process is called “model”. One of them is Modified Rational Method (MRM). There are several types of MRM base on its equation modification. Hydrological mass balance or kinematic wave in order to route the flow. With this model modification, the output of the model is not only peak discharge but also unit hydrograph. Model modification was done in the calculation of peak discharges by assigning the C value (coefficient runoff), A value (area) and land characteristic (soil texture, Manning roughness coefficient, and saturation coefficient in the pixel basis. PCRaster software allows us to perform discharge calculation on each pixel. Flow accumulation by using kinematic wave was done to get the unit hydrograph. Three (3) flood events were used to run the model validation, i.e. January 21, January 22, and February 10, 2016. Each event has different rainfall characteristics. The result of this model was DRO hydrograph. Based on the baseflow separation of the observed hydrograph as well as the hydrograph from the model, we found that the flow through the outlet during discharge recession is the base flow. The accuracy value is quite good, i.e. 10–30 %. The result of the model shows a different response between direct runoff and base flow, while time to peak was faster than the recession time.
Tambakbayan is one of the watersheds in Yogyakarta, Indonesia that is experiencing changes in land use. The research aims to analyze the distribution of intrinsic and specific groundwater vulnerability in the watershed that was influenced by land-use changes from 2006 to 2017. The data used are the RBI maps (containing topographic and land-use information, 2006 and 2017), SRTM imagery, rainfall recorded at the Kambil, Prumpung, Bronggang, Santan, Gemawang, and Karang Ploso stations (2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017), soil map, and aquifer map. Land-use change was analyzed by comparing the RBI maps of 2006 and 2017; while the groundwater vulnerability was assessed with the Susceptibility Index a development of the DRASTIC method. The intrinsic groundwater vulnerability was generated based on physical conditions, including depth to the water table, aquifer media, groundwater recharge, and topography, while the specific groundwater vulnerability was a function of these attributes added with one anthropogenic parameter: land use. Then, all of these parameters were analyzed with a map overlay. The results showed two levels of intrinsic vulnerability: low (2.18% of the watershed area) and medium (97.8%); and three classes of specific vulnerability: low (0.02%), medium (5.06%), and high (94.92%) in 2006. From 2006 through 2017, the areal percentage of the medium vulnerability increased, while that of the high vulnerability decreased due to the conversion of agricultural land to a reservoir in 2009.
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