We use the hydrologic data such as rainfall and runoff for the construction of hydraulic structures and levees in the arable land according to water resources plan and irrigation improvement plan. However, mostly we do not have enough hourly rainfall and runoff data required in the rainfall-runoff analysis in the study watershed. Therefore we have used CN(runoff Curve Number) Method which was developed in NRCS(Natural Resources Conservation Service) of USA for the rainfall-runoff analysis in the ungaged watershed but we did not have the evaluation of the applicability of CN in Korea.
In this study, Gwang ju Dam is selected as a model to be applied and we considered the characteristics of capacity in rainfall, the quantity of storage, irrigation, and outflow of duty at watercourse(the quantity for maintaining watercourse) using the period of data from 1982 to 2001 during the past 20 years with the results of dam operation in those periods, and presumed the quantity of inflow with analysis of storage of water from the data of daily Dam operation, computed the modulus of outflow within basin and SCS exponent of outflow curve, and also calculated SCS exponent of outflow curve for comparison-analysis using ArcGIS, the program of basin characteristic analysis.
The outflow indexes we obtained from the water balance analysis are followed : CNII is 92.67, and CNIII is 98.37. And the value calculated from using analysis program ArcGIS is followed : CNII is 83.5, and CNIII is 92.0 on the other hand.
The results from the whole basin of Gwang ju Dam investigated in former times are followed : CNII is 77.96, and CNIII is 89.06. Those results are smaller than CN which is computed with analysis program ArcGIS. So it needs to be considered reflecting these results to the management of dam and water resources use as the outflow potential capability of basin is larger than previous one.
The results of this study show that it's possible not being same as analysis methods even though the object which is choosen has same condition of hydrologic characteristics.
Above research results are carried out locally nearby Gwang ju Dam. So it has to be considered to research continuously to evaluate amount of outflow aimed at dams for agriculture which has insufficient hydrologic and runoff specified material.