Effect of Antecedent Dry Day, Rainfall and Rainfall Intensity on Runoff from Sandy Uplands in Gangwon-do, Korea

Abstract

Discharge characteristics are very various according to geographical features, hydraulic, and hydrologic features. Thus, it is necessary to perform studies on NPS (Non-Point Source) according to the use of land. This study performed a specific monitoring for some gentle sloped dry fields and steep sloped paddy fields from March to December 2008. Also, this study investigated the antecedent dry day, amount of rainfall, and rainfall intensity that affect the runoff in such dry fields. In addition, the effects of the rainfall intensity were investigated through an indoor artificial rainfall test. The amount of rainfall and its runoff showed a high correlation statistically. However, there is a case where the runoff occurred for the amount of rainfall below 20 mm even though the runoff did not occur for the rainfall more than 30 mm. It was investigated that the runoff can be occurred by even a very small amount of rainfall depended on the scale of increases in the instantaneous rainfall intensity. It means that there are no runoffs and no pollutant loads as the rainfall intensity is small, and the duration of rainfall is long enough even though the amount of accumulated rainfall is large. Whereas, the high rainfall intensity occurs runoffs and pollutant loads even though the amount of accumulated rainfall is small. Therefore, there are certain serious problems as the amount of rainfall is solely considered for the application of the estimation of NPS and the TMDL(Total Maximum Daily Load). Thus, it is necessary to continuously study the factor that affects the continuous collection of data and runoffs. The effects of the rainfall intensity were investigated by applying an indoor artificial rainfall test. It was investigated that the rainfall intensity largely affected the results in the case of the application of BMPs(Best Management Practices). Thus, the NPS can be largely influenced by the rainfall intensity. Therefore, it is necessary to improve the performance of the BMPs and develop the BMPs that is suitable for the regional and climate characteristics. In addition, studies on the analysis of the effects of the BMPs are required.