A lumped runoff model named KWST Model III(Runoff Model III combined Kinematic Wave and Storage Tanks）is developed for analyzing both flood and low water runoff successively.
Evapotranspiration in the KWST Model III is evaluated by a procedure adopted in the Long and Short Terms Runoff Model(LST Model）proposed by Kadoya and Nagai. The upper zone of the model is composed of kinematic wave runoff model. The lower zone is the same with the LST Model. The runoff from upper zone of the model corresponds to a direct runoff component which is composed of surface flow and/or prompt subsurface runoff. The effect rainfall formed the direct runoff component is estimated by utilizing the model structure of lower zone in the LST Model. A base flow in a runoff cycle is divided into five stages and seven lower water runoff patterns are defined.
Next, a procedure of runoff analysis is described to direct and low water runoff components. The storage of tanks which change every second in KWST Model III are expressed by solving the linear storage differential equations. The runoff height of low water correspond to storage of tanks is evaluated at every calculating unit time. The direct runoff heightis estimated by kinematic wave runoff model which simulates surface runoff and/or prompt subsurface runoff.
Furthermore, indexes for a pattern of channel arrangement are defined, which substitute the arrangement structure of network for computer system. And it is shown that the indexes can be included in a runoff analysis and the lumped KWST Model III is possible to expand as a distributed one.