A study on the estimation of water-environmental change from urbanization and its preservation method using hydrological and water quality model

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This study evaluates the changes in water environment (in the aspect of discharge and water quality) from urbanization and to propose its preservation method. First, TOPMODEL (topography-based hydrological model) is a physically-based distributed type rainfall-runoff model which can represent not only river flow discharge but also distribution of variable source area. The model is applied to the Wajima-Yanagida catchment and the Yamada river basin. Next, the complex tank model, which is distributed model and includes the forest, paddy field, any city sub-tank model, is used in combination with LQ-equation (loading-discharge relationship of exponential style)determined from observed spatial water quality data. The results are as follows. 1. TOPMODEL shows good performance for estimating long- and short-term runoff and simulating distribution of variable source area. 2. The DEM is effective and useful for calculation of a topographic index used for application of the TOPMODEL.3. From LQ-equation, city and paddy field has a function of accumulation and flash of loading and its ability of supply of loading become smaller as compared as forest. 4. The model can evaluate water quality and discharge changes (loading) from land use ratio of catchment. 5. In current research area, effluent loading from unit area is bigger in order of paddy field, city, forest. 6. The model can evaluate the concentration rise of some nutrient in farming season.