Changes in properties of watershed and its conservation due to changes in land use in mountainous rural area

本项目针对山区农村的管理和发展进行了调查研究，山区农村人口减少和年轻人迁出是一个严重的问题。结果总结如下。（1）对该地区农田灾害的调查表明，与无农田灾害的地区相比，该地区农田灾害发生的规模较小，但发生的灾害较多。（2）由于农田和森林的破坏或为开发而开垦农田，改变了土地利用方式，改变了植被类型、土壤性质和排水系统，导致流域水文循环的组成部分如暴雨径流、枯水径流和蒸散量发生变化。（3）与森林集水区相比，开垦农田的洪峰流量和直接径流量增加。梯田集水区洪峰流量较大，而直接径流量与森林集水区相同。（4）丰水年的径流量比较表明，森林集水区的径流量大于农田集水区，而干旱年的径流量则小于农田集水区。这可能是由于土地利用方式的改变导致蒸散量减少所致。（5）研究了细沟网络的性质和细沟形成的机理，提出了防止土壤侵蚀和细沟形成的最佳坡长的确定方法，并对日本山地农村的管理和发展提出了建议。

In this project, investigations and researches have been carried out for the management and development of mountainous rural area, where reduction of population and moving out of the young people are serios problems. The results are summarised as follows.(1)The investigations of disasters on farm lands in such area showed that smaller but more disasters have occurred in comparison to the areas without such problems.(2)Changes of land use due to devastation of farm lands and forests, or reclamation of farm lands for the developments of the area, have changed the type of vegetation, soil properties and drainage systems, which leads to the changes in the components of hydrologic cycle in watersheds such as storm runoff, low-flow runoff and evapotranspiration.(3)Peak discharge and direct runoff from reclaimed farm lands were increased in comparison to the forest catchment. In the terraced paddy field catchment, peak discharge was greater, while direct runoff was as same as in the forest catchment.(4)Comparison of draft discharge for a wet year showed that the amount of discharge in the forest catchment was greater than in the farm land one, but it was decreased for a dry year. It might be caused by the reduction of evapotranspiration which was influenced due to the changes in land use.(5)The properties of rill network and mechanism of rill initiation have been investigated for land conservation and a routine to decide the optimum length of slope was developed to prevent the soil erosion and rill formation.Finally, we have proposed the ideas for the management and development of mountanious rural area in Japan.