Abstract:
In this study, a bootstrap method for estimating multiple-storm unit hydrograph and for analysinguncertainty involved was proposed. Five watersheds in Ping and Wang River Basins in the northernpart of Thailand (areas ranging from 426 - 730 square kilometers) were used in the analyses.Twenty five storms occurring in the flood seasons were selected for the study.Dimensionless unit hydrographs for Ping River Basin and for the Ping-Wang River Basinscombined were proposed, together with the regression equations relating the time-to-peak (tp) andpeak flow per unit area of the unit hydrograph (qp/A) with the physical parameters of the catchmentarea, namely : tp = 0.0001(LLc/?S)1.3625 and qp/A = 1.784 (tp)-1.0907 for Ping River Basin (alone), andtp = 0.0003(LLc/?S)1.2292 and qp/A = 1.777 (tp)-1.0876 ,for Ping-Wang River Basin combined. From theuncertainty analyses, it was found that the rising portion of the unit hydrograph was found to bemore uncertain than the recession part.It was suggested that the procedure for evaluating the unit hydrographs by the bootstrap method andthe regressive equations relating unit hydrograph properties with catchment physical parameters,and the dimensionless unit hydrograph developed in this study could be used as an alternative basisfor estimating design unit hydrographs for ungauged catchments in the northern part of Thailand,especially in the Ping and Wang River Basins.