|The tank model which was proposed by M. Sugawara (1961) is widely applied in Asia areas and gets highly assessment. The most evident characteristic of tank model is to simulate watershed runoff by the way of separating runoff into three parts, namely: surface runoff, interflow, and groundwater.
Firstly, the runoff simulation theory of the tank model is discussed in this study. From the infiltration point of view, the infiltration rates of tank model, under instantaneous rainfall condition and continuous rainfall condition, were examined and analyzed respectively. Secondly, by the theory of system engineering, a series of cascade tanks are transformed into a series of linear reservoirs in parallel and cascade. It provides an evidence that the good simulated performance of tank model is not due to the effect of separating runoff into three parts, but due to the effect of continuous damping and lagging.
Finally, a modified computational procedure of tank model is proposed, which is based on a traditional infiltration equation to match the original concept of the tank model. The modified model was verified by runoff records of Shihmen Reservoir Watershed and a profound result was obtained.