Curve Number Method to Determine the Runoff Height in the Upper Cimanuk Watershed

Abstract

Run off is one of the most important hydrological variables in supporting water resources development planning and activities. To predict the amount of runoff can be done in various ways one of them with the SCS-CN method. The SCS method was developed from years of rainfall observation and involved many agricultural areas in the United States. This method seeks to link watershed characteristics such as soil, vegetation, and land use with a runoff curve number which indicates the potential runoff water for a particular rainfall. The location of this research is Garut Regency, upstream of the Cimanuk river, which often floods every year due to overflowing of the Cimanuk River. Data used to determine CN values and runoff height are Digital Elevation Model (DEM), land use, soil, and rainfall data for the last 10 years, from 2009 to 2018, then the maps are processed using the Arc-Map program. From the analysis it can be seen that the CN value is 66.54%, and the runoff height is 1.17 cm with a 2 year return period, and 2.84 cm at 25 return period. Based on the CN value, it is known that the type of soil in the upstream Cimanuk watershed has a small infiltration rate and has bad properties in infiltrating water, so that it can cause run off for a long time, because the smaller CN value on a land use, so soil’s retention ability is greater and the less chance of runoff. The results of this study can be used for planning flood control buildings in the upper Cimanuk watershed.