Quantitative evaluation of roles of farm land on water resource.

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It is very important to evaluate quantitatively roles of farm land on hydrologic cycle and water resource in regions. In this project, investigations and researches have been carried out in some experimental catchments and a alluvial plane to evaluate the roles.The results are summarised as follows for the catchments ;1. The analysis of evapotranspiration from the catchments revealed that evapotranspiration depends on wetness of the catchment and the dependency is more dominant in the upland filed.2. Rainfall loss is infuluenced by the initial condition of wetness and the percolation property. The comparison of estimated intensities of percolation in the catchment showed that the intensity is influenced by the type of soils and land use.3. A method was proposed to evaluate quantitatively the role of catchments on stream flow. A index of flow stabilization was defined and the values of the index were compared between the forest catchment and upland field catchment. It was shown that the forest keeps stream flow more stable than the upland field.The results for the alulvial area are ;4. The water budget analysis in the surface region showed that the groundwater recharge in irrigation periods is more than in non-irrigation ones and it means the importance of paddy field for the groundwater in the region.5. A lumped parametric model, which included the groundwater system, was developed to analyze the hydrologic cycle to evaluate the water balance in the region.