WRRCTR No.30 Hydrograph Study and Peak Discharge Determination of Hawaiian Small Watersheds: Island of Oahu

Abstract

Hawaiian small watersheds are unique in watershed hydrology because of the high infiltration rate, small size, and mountainous topography. The flood hydrograph which has a short time to peak and small recession constant can be expressed as a steep triangular shape. A peak discharge equation is derived from the concept of a triangular hydrograph and a linear storage of recession flow. The peak discharge equation can be shown as a very simple form, Qp = CAR, where C is a coefficient and can be determined by the hydrograph time parameters, time to peak and recession constant, A is the watershed area, and R is surface runoff in inches. A linearity test between peak discharge and runoff has been made for Hawaiian small watersheds and a good linear relationship was found between peak discharge and surface runoff which is less than six inches not only for an individual small watershed but for watersheds of similar size.