The Improvement of SCS-CN Model and Its Application in Pengjiahetan Watershed

Simple methods of predicting runoffs from the watershed are important to project practice,particularly to flood forecasting and water-balance calculation.With the development of VSA hydrology,it is illustrated that the often used SCS runoff curve-number approach in its most elementary form can be derived from assuming that only the saturated areas contribute to direct runoffs.In the improved approach,the initial abstraction(the amount of water) for runoff starts is equal to air-filled pore space per unit area for the most shallow soil in the watershed.This SCS-CN method in Pengjiahetan Watershed is applied to plain lake areas of Hubei Province and dynamic initial abstraction Ia is defined.By plotting the effective rainfall defined as the amount of total rainfall minus the Ia against the observed runoff separate the base flow.It is found that the SCS curve-number equation in its elementary form fits the observed data well.