Composite Loss Rate Model Combining Four Losses of Precipitation in a Watershed for Engineering Hydrology

Abstract

In engineering hydrology, a lumped rainfall-runoff model applied to a watershed often requires a calculation of the effective rainfall, which deducts the precipitation losses from the total rainfall contributing to the direct runoff. In the model, these loss elements vary individually with time during a rain storm on a watershed. An estimation of the loss elements or abstractions, such as infiltration, depression storage, evapotranspiration, and interception, for the calculation of the effective rainfall in a watershed presents a practical challenge. Previous research has estimated infiltration and other loss elements in a watershed individually in the case of a storm event. Moreover, to date, these other loss elements have been treated as minor. However, this study proposes a simple model that estimates precipitation losses not individually but by combining the loss components together. A composite loss rate model that combines four loss rates over time is derived as a lumped form of a continuous time function for a storm event. The loss rate model developed is an exponential model similar to Horton’s infiltration model, but its parameters have different meanings. In this model, the initial loss rate is related to antecedent precipitation amounts before a storm event, and the decay factor of the loss rate is a composite decay of four losses. As a case study, a method for estimating the parameters of this model is presented. In the case study, data sets from 10 rain storms observed at the Jeonjeokbigyo stage station in the experimental watershed of Selma-Cheon near Seoul in South Korea are used.