Development of Multistory Slope Tank Model Incorporated ET Submodel

Abstract

The authors developed evapotranspiration (ET) submodel in the last report. In the ET submodel, evapotranspiration ratio which is used in estimation of evapotranspiration value is decided corresponding to soil water content distribution. Hydraulic conductivity used in ET submodel is calculated using soil scaling method and is smaller than that of the actual watershed. In the calculation by the ET submodel using hydraulic conductivity obtained by the soil scaling method, percolation is smaller and evapotranspiration is bigger compared to the value calculated by water balance. In the soil, there are saturated-unsaturated flow part which is called matrix part and macro pore part in which saturated-throughflow is dominant and water flows rapidly. That is why hydraulic conductivity in the actual watershed is bigger. To incorporate the ET submodel in the runoff model, the runoff model has to be able to express that kind of inhomogeneity of soil. Therefore the multistory slope tank model is developed, in which the ET submodel corresponds to the matrix part of soil and the runoff tank corresponds to the macro pore part of soil.
In the application of the multistory slope tank model, the parameters values except for those obtained in the literature were calibrated and good results were gained. In the process of calibration of the parameters, some knowledges that distribution of hydraulic conductivity of runoff tank or step number of the tanks influence resultsof runoff analysis were obtained.