Estimation of Flash Flood Guidance Considering Uncertainties of Rainfall-Runoff Models

摘要

Nowdays, the flash flood is characterized as flood leading to damagecaused by heavy rainfall for short duration, steep slope and impervious layer.Furthermore, in Korea, the flood damage risk by flash flood is increasing due toclimate change. So, we could use the Flash Flood Guidance(FFG) which means theamount of effective rainfall needed for flash flood occurrenceThe FFG is calculated from rainfall-runoff relationship curve that is derived fromrainfall-runoff model and threshold runoff. Therefore, the FFG can be changedlargely by the rainfall-runoff models and their parameters. Here we used fourdifferent rainfall-runoff models. Also, the FFG can show different value byThreshold Source Area / Minimum Source Channel Length for calculatingparameters of GcIUH, and by section of stream for calculating bank-full discharge.In this study, we analyzed the uncertainties on rainfall-runoff relationship derivedfrom rainfall-runoff models and their parameters, threshold runoff, and existenceand nonexistence of stream section.As a result, the derived confidence intervals for rainfall-runoff relationship curvesshow different shape and extent of interval. We performed the rainfall analysis asfollows: First, we distributed probabilistic rainfall by 1hr, 3hr and 6hr using Huffmethod. But we can not draw rainfall-runoff relationship curve through oneprobabilistic rainfall. Therefore, we divided that into ten and derived rainfall-runoffrelationship using each distributed probabilistic rainfall by rainfall duration. Then,we suggested the confidence interval on average of sampled rainfall through MonteCarlo simulation for uncertainty analysis of rainfall-runoff relationship curve. Next,we gave weighting factor to each four model and combined one. So, we can suggestone rainfall-runoff relationship curve from four rainfall-runoff models. And wecompared FFG by change for value of CSA(Critical Source Area)/MSCL(Minimum