The continuous city-concentration phenomenon has resulted in a drastic increase in the concrete- and asphalt-covered space and a proportionally drastic decrease in natural green space, weakening the ability of land surface to conserve and retain water. The NRCS (Natural Resources Conservation Service) method is a way of estimating direct runoff, factoring in the pavement conditions of the area. The NRCS method uses soil maps and land use maps to measure physical permeation of water in the area and is most widely used and its reliability is recognized in workplaces.
This study re-categorized the land use maps and detailed soil maps of the Nabulcheon river area for the 1975-2000 period, using the GIS method, and estimated the CN (Curve number value) depending on the years of land use. In addition, the Nabulcheon watershed was divided into 6 small watershed and runoff analysis was conducted for changes of land use years in order to analyze the effect of land pavement factors on the runoff.
The result of the CN-value estimation on the Nabulcheon watershed by land use years showed the CN value tended to increase as the land use years increased, and in the case of Nabulcheon-3 watershed where the increase in pavement ratio recorded 14.76%―the highest among others―the increase of runoff by land use years occupied 45%∼71% of the runoff increase of the entire area. This shows that the increase in CN value as a result of city concentration significantly affects the increase in flooding.