Abstract:
In this study, two important base flow characteristics, namely: the base flow recession constant (Kr)and the time from the flood peak to the end of surface runoff (N) during flood seasons (May toOctober) were analyzed for Khong, Chi, and Mun river basins. In addition, three models forestimating the value of base flow for synthesizing design flood hydrographs by unit hydrographmethod were proposed, namely: (1) the fixed average base flow model, (2) the time-varying baseflow model, and (3) the base flow model for the HEC-1 software package. The base flowcharacteristics (Kr and N) and the dimensionless parameters of three models were correlated withthe physical and soil parameters of the river basins by multiple regression equations.From the study results, the base flow recession constant (Kr) was found to vary between 0.739 to0.923 per day. The time from the flood peak to the end of surface runoff (N) was found to varybetween 1.59 to 5.11 days. By comparing the measured runoff hydrographs from given storms inthe study river basins with the total hydrographs using the base flows estimated by the three models,it was concluded that these models could be safely applied in the study river basins, but givingslightly higher flood peaks than the actual ones.