Effect of spatial variability of land use and rainfall on runoff response in an ungauged watershed

Abstract

Runoff response to a watershed varies according to geological characteristics of the watershed and spatial variation of rainfall. There are many research issues on the runoff response from dividing watershed to transforming geological characteristics to numerical values. In this study, we focus on evaluating effects of spatial variability of land use and rainfall on runoff response in an ungauged watershed. We employ land use data offered by the Ministry of Environment and soil geographic data provided by the National Academy of Agricultural Science in Korea. We need components to calculate the effective rainfall through the NRCS method, and estimate other versatile parameters to calculate runoff derived from Geographic Information System (GIS). First of all, in order to calculate the curve number (CN), we have to classify the hydrologic soil type from the soil geographic data according to the soil survey manual of USDA. And then, land use data are classified into seven groups according to the surface use. Finally, intersecting two classified data set, we can achieve the CN value. The CN value is an index of infiltration, thus the CN value is an important component which is associated in runoff response. The grid of land use data is not sufficiently detailed. Hence, we try a sophisticated access to estimate precise runoff and confirm the difference in the change of CN which is originated by changing the components of land data, closely related with the portion of impervious area. The other aspect we consider in this study is spatial variability of rainfall. Conducting survey of the rainfall gauge stations, we employ the rainfall gauge stations which are in the basin and which are not, and compare the runoff which is calculated by using one rainfall gauge in the basin with that which is calculated by using both rainfall gauges in and out of the basin. Finally, this study compares the runoff response to the change of land use and rainfall spatial variability. We execute the sensitivity analysis among the results.