DAMPAK PERUBAHAN PENGGUNAAN LAHAN TERHADAP PERUBAHAN RUNOFF DI DAERAH ALIRAN SUNGAI (DAS) BEDOG YOGYAKARTA

Bedog watershed is one of the watersheds in the area of Yogyakarta through the process of urban development. The process of urban development in the Bedog watershed this happened in the past 10 years. The parameters of the process of urban development in the Bedog watershed is the increase in land use "settlement" from 15,29% (2004) to 16,94% (2008) and 17,72% in 2010 or an increase of 0.4% per year. The main objective of this research is is to analyze the impact of land use change on runoff and formulate of the simulation / scenarios of land use in reducing runoff in the Bedog watershed using the Curve number -USSCS (CN-USSCS). Based on the calculation of CN-USSCS in 2004, 2008 and 2010, due to the impact of changes in land use resulted runoff of 1353.0 mm (66% of the amount of rain / year), 1277.2 mm (55.5% of the amount of rain / year), and 1536, 4 mm (57.6% of the amount of rain / year). Settlement and Bareland contributed to the greatest increase in runoff in the Bedog watershed, due to having a high value of CN and has a large area. Validation of the methods of CN-USSCS using statistical test, T-test produced values of 0.00 and 0.092 below the T-table values of 1.67 and 1.71, and the coefficient of determination above 0.5, which means CN-USSCS method can be applied in the Bedog watershed to predict the runoff. The results of the formulation of land use change scenarios in Bedog watershed that the change in land use for the next 6 years ( 2016) to change the runoff by 4% from the 2010 (scenario 1). Decrease runoff in the Bedog watershed to do with the increase in forest area in the form of mixed garden and herba plants (shrubs) in Bantul for >50% of the total Bedog watershed (scenario 4)