Analisis Perubahan Koefisien Aliran Permukaan di Sub DAS Gajah Wong

Abstract

Land use changes in the Urban Area of Yogyakarta (KPY), the scope of Gajah Wong subwatershed has affected the regional hydrological cycle. The objectives of study are to analyze the land use changes and calculate the runoff coefficient (c) changes in Gajah Wong subwatershed. The study area is located in 3 cities (Sleman, Yogyakarta and Bantul) consisting of 5 districts and 14 villages with total area about 9.566 km2. Analysis of data using IKONOS imagery on 2008 and 2016 by supervised image classification (SIC) method through Quantum Geographic System (QGIS). Classification of land use divided into seven classes ; water bodies, buildings, roadways, bare soil, settlements, rice fields and vegetation. To calculate the runoff coefficient, used two main variables that cland use and cslope.The results showed the bare soil decrease about 7.12%, 0.89% on rice fields, and 0.47% on vegetation. An increase in the percentage of land use of settlements about 2.96%, 4.76% buildings, and water bodies 0.76%. While the land use in roadways class has no change with overall accuracy about 68,625%. The analysis of topography, Gajah Wong subwatershed is located on the flat area with the average of slope about 1.9%. The land use changes caused increasing surface runoff coefficient, from 0.606 on 2008 to 0.648 on 2016 and as percentage increase about 7.02%.