芦生演習林内トヒノ谷における地下水位、パイプ流量、流域流量の関係

Abstract

山地源流域の洪水流発生機構を明らかにすることを日的とし、降雨量、地下水位、パイプ流量、流域流量の観測を京都大学芦生演習林内の0次谷流域で行った。その結果、流出が生じる部位は降雨量の増大にともない変化し、以下のように雨水流出段階は3つに分類することができた。ステージ1 ; 流域末端の湧水点からのみ流出が見られ、地下水位の上下に従い流域流量の増減が生じ、地下水位―流城流量関係は直線的である。ステージ2 ; 湧水点と流域末端から6mの地点のパイプから流出が見られ、増水過程においては地下水位の変動が小さいにもかかわらず流域流量は増加し、減水過程では地下水位の低下にともない流域流量は減少する。ステージ3 ; 流域末端から10mの地点のパイプ群からも流出が生じ、流域末端から6mの地点のパイプ流量やパイプ群より下流側の地下水位の変動はほとんどないにもかかわらず、流域流量は大きく変動した。以上のことから、山地源流域の雨水流出現象は降雨量の増大にともない流出経路が段階的に増大し、その結果、流域流量がオーダーで変化し、洪水流発生機構も変化することがわかった。

In order to clarify the storm runoff process at headwater catchments, the measurements of precipitation, the amount of pipeflow, the discharge rate from catchment, and the groundwater levels were conducted at a headwater catchment in Kyoto University forest in Ashiu. Results showed that the storm runoff process can be classified into three stages based on the paths which contribute to the water discharge. 1. Water discharge occurs only at a perennial spring situated at the end of the catchment. The groundwater levels and the discharge rate from catchment had a linear correlation. 2. As a magnitude of rainfall increases, water comes out from a soil pipe (Pipe A) located at 6m upstream from the end of catchment. In the process of rising stream flow, even a slight change in groundwater level caused a large change in the discharge rate from catchment. On the other hand, in the recession process, the discharge rate from catchment decreased as the groundwater level dropped. 3. Under heaviest rainfall, the additional discharge occurs from a group of soil pipes (Pipe group B) located at 10m upstream from the end of catchment. In this stage, the groundwater levels which were measured between Pipe A and Pipe group B, and the discharge rate from Pipe A did not affect the change of the discharge rate from catchment. From these results, the change of the flowpath causes the change of the discharge rate from catchment and the change of the relationship between the groundwater and the discharge rate from catchment.