Development of Runoff Model Considering the Evapotranspiration Process in Forest Basins

摘要

We have developed a model to be applied to runoff analyses and flood prediction for dam basins. Taking the evapotranspiration process into consideration, we apply the snow melt theory to distinguish snowmelt from rainwater. Meteorological data is calculated from observed data provided by the Japan Meteorological Agency. The model is composed of three steps including the surface, the unsaturated layer and the underground layer. Heat flux is computed except for underground water. The model can predict snowmelt by a long-term runoff analysis for regions subject to heavy rainfall. This model was developed to predict discharge at dam basins for hydro-electric power stations. Since most hydro-electric power stations in Japan are located in heavily treed mountainous regions, the ability to estimate the amount of evapotranspiration involving forest vegetation is of considerable importance. Two cases were selected for study to represent divergent climate conditions. The 410km~2 Iwaki River basin in the northern snow region of Aomori Prefecture and the 510km~2 Kuma River basin in the heavy rain region of Kumamoto Prefecture in western Japan. Calculations were performed to determine the amount of evapotranspiration in wooded basins by age, season and tree type. Changes in discharge were explained by numerical experiments in cases involving greater changes in leaf volume rise of temperature.