Quantitative Evaluation of Forest Influence for Soil and Water Conservation and Watershed Managemaent

本研究的目的是从径流机理出发，阐明森林的水土保持作用，并提出山地水土保持管理系统的方法。研究结果如下：1.（1）非均质土壤中雨水的流动路径：通过水力学试验和数值模拟，阐明了非均质土壤（如森林土壤）中雨水的流动路径，即雨水从大孔隙向小孔隙的流动主要依靠毛管势，而从小孔隙向大孔隙的流动主要依靠重力势。(2)山地森林植被蒸散量的估算：通过能量平衡波文比的测定，揭示了山地森林植被蒸散量的空间和季节变化规律，并建立了山地森林植被蒸散量估算模型。(3)火烧迹地小流域产流产沙特征火烧迹地植被恢复后，产流产沙量减少。但是，根据植被生长周期的季节变化被证明.森林影响的定量评价与流域管理系统的发展建立了评价森林影响的短期-长期径流模型（三层土壤模型），利用该模型可以用过程线的变化来表示土地利用变化的影响。该评价方法不仅可用于评价森林对流域的影响，还可用于尝试使流域管理系统最适合于流域。

The purpose of this study is to clarify the forest influence for soil and water conservation based on the mechanism of rainfall-runnoff, and to develop the method of manafement system on a mountainous waterahed. The result obtained from this study was as follows;1. Fundamental study on mechanism of rainfall-runoff(1) Flow paths of rainwater within heterogeneous soils: The flow paths in heterogeneous soils such as forest soils were clarified by hydraulic experiment and numerical simulation, that is, the rainwater movement from large pores to small pores is to depend on capillary potential and the reverse movement is to depend on gravity potential. (2) A estimation of evapotranspiration from a forested mountainsides: The spatial and seasonal variation of evapotranspiration was demonstrated by measurement based on energy balance Bowen ratio in a forested watershed and the estimation model was developed. (3) Characteristics of runoff and sediment yield from burned watershed; The runoff and sediment yield were decreased with recovering of vegetation in burned surface. But, the seasonal variation according to growth cycle of vegetation was demonstrated.2. Quantitative evaluation of influence of forest and development of watershed management system The short-long term runoff model (3-soil layer model) which is to evaluate the forest influence, was developed and by using this model, the effects of change of land uses can be represented by change of hydrograph. This evaluation method can not only use to evaluate the forest influence, but use to try to make the watershed management system most suitable.