WRRCTR No.15 Hydrological Data and Peak Discharge Determination of Small Hawaiian Watersheds: Island of Oahu

Abstract

Basic hydrological data including rainfall, runoff, historical flood, watershed characteristics, soil type, and land use of Hawaiian small watersheds on Oahu have been compiled and analyzed. Frequency analysis for annual peak discharge was made for 23 small watersheds on Oahu by using Gumbel's extreme value theory. A regional flood formula has been derived for Honolulu and between mountain ranges of the island of Oahu through the use of multiple regression. The regional flood formula expressing peak discharge as a function of watershed area, length and height and a precipitation index defined as 100-year, 24-hour rainfall in inches can be used to estimate peak discharges for ungaged areas. The rational formula which is currently used for drainage areas less than 100 acres has been evaluated through the study of overland flow.