PEMODELAN HIDROLOGI UNTUK PENENTUAN TINGKAT PRIORITAS SUB SUB DAS DALAM PENGENDALIAN BANJIR MENGGUNAKAN CITRA PENGINDERAAN JAUH DAN SISTEM INFORMASI GEOGRAFIS (STUDI KASUS: SUB DAS KARANG MUMUS, KALIMANTAN TIMUR

Aim of this research was to determine sub-sub-watershed priority level in the Karang Mumus Sub Watershed in flood control of Samarinda City based on information of runoff flow accumulation that was chance to be runoff floodwaters. Surface runoff was modeled from analysis of watershed physical characteristics (slope, soil infiltration, vegetation cover, and drainaege density) using Cook Method modified by SCDT (2011). Slope was derived from DEM extracted from SRTM and ASTER GDEM images. Soil infiltration was acquired from land units approach using land cover map of Landsat 7 ETM+ interpretation and field measurement. Vegetation cover was assessed from NDVI vegetation index from Landsat 7 ETM+ image and measurement of vegetation cover using GeoEye image. Drainage density was examined from data of watershed topography. Surface runoff was modeled with design rainfall using Rational Method. Design rainfall used was extreme rainfall in some periods of short term to long term. Acquisition of surface runoff flow accumulation was carried by GIS Surface Hydrology using DEM. For comparison, maximum capacity of river on each sub-sub-watershed was calculated by field measurement using Manning Method. The results showed remote sensing image quite accurate to land variable information extraction (86.3% for DEM data, 85.8% for slope, and 84.6% for land cover). Effect of slope on surface runoff with a contribution of 47.97%, while land cover as the basis of soil infiltration and vegetation cover affected surface runoff also with a contribution of 32.79%. Priority of sub-sub-watersheds had dominance characteristics of high slope and land cover as built land and bare land that increasing surface runoff. The surface runoff flow accumulation model to the maximum capacity of the river at the potential flood area showed that the Karang Mumus Hulu sub-sub-watershed was a high priority of flood control. It can be seen that the outlet of upstream sub-sub-watershed group to the outlet of center sub-subwatershed group, the excess surface runoff flow discharge that cannot be accommodated at the Karang Mumus River reached 245.09 to 559.10m3/s in period of 5 years and increased to 848.91 to 1617.01m3/s in period of 100 years