| Summary: | 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.
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