Jung-Sik Lee

A Study on the Critical Duration of Design Rainfall in Midsize Catchment

This study is to propose the temporal pattern of design rainfall which causes maximum peak discharge, and to analyze the relation of catchment characteristics and critical durations for gauged midsize catchment. Hydrologic analysis has done over the 44 midsize catchments with 50-5,000. The type of temporal pattern of design rainfall which causes maximum peak discharge has resulted in Huff`s 4 quartile distribution method for effective rainfall(AMC III) The peak discharges of 24hr rainfall duration are similar to those of critical duration for 50-600, and the peak discharges of 48hr rainfall duration are similar to those of critical duration for 600-5,000. Therefore, if the proper rainfall intensity formula is selected, 24hr or 48hr rainfall duration may be regarded as the critical duration of midsize catchment. A simple regression equation is derived by using a catchment area and critical duration with high correlation for the case of effective rainfall(AMC III). Therefore, it can be used to determine the critical duration of ungauged catchment with 50-5,000. Also, dimensionless regression equation is derived by using characteristic values of unit hydrograph.

Estimation of Rainfall Quantile using the Probability Distribution Parameter Map in Ungauged Site

The objective of this study is to produce a probability distribution parameter map for evaluation of probable rainfall quantile in ungauged site. The rainfall data used in this study are annual maximum rainfalls at 58 stations during the period of more than 30 years for 12 durations. The 16 probability distributions which have been widely used in hydrologic frequency analysis are applied to the basic data and to determine the representative appropriate distribution. The location, scale, and shape parameters of the representative appropriate distribution for each station and each duration are calculated using L-moments method. These parameters are contoured using spatial interpolation, based on the geostatistical method of Kriging to produce parameter maps that depict the spatial variation and magnitude of each parameter. The results of this study are as followings; (1) The GEV distribution is determined as the representative probability distribution in Korea. (2) The parameters for any location in Korea can be estimated using the parameter maps and the rainfall quantile is obtained from GEV distribution equation using parameter about the selected rainfall duration. (3) Comparative analysis of the results shows that the probable rainfall quantiles by the parameter maps are little different from those existing researches. (4) In the result by probability distribution parameter map, rainfall quantile is better easy to evaluate in ungaged site without restriction of return period.