抄録
The comprehensive study on the landslide occurred in 2015 spring in the headwater area of Mt Hakusan was demonstrated a profound ecosystem relationship between water and biota. The vegetation established after BettoValley landslide in 1934 showed four distinctive types based on substratum condition, which indicates direction for future revegetation measure on 2015 landslide. A relation between the sediment distribution and the flow velocities in the sand settling channels was measured in Miyatake settling pond, then it is concluded that the settling pond has performed very well. The average percolation from all paddy fields was 12.4 mm/day in 2014 and 7.9 mm/day in 2016, indicating a significant decrease in percolation. The groundwater recharge from the paddy fields reduced by 36% and the total groundwater recharge reduced by 25%. Analysis of groundwater level in 2015 by the regression model using Random Forest showed irregular fluctuation particularly from May to July at both sites. Finally, a hydrologic model analyzed effects of the turbidity water on groundwater. These results showed that the water might decrease percolation from paddy fields and groundwater recharge from the Tedori River to cause the lowering of groundwater level in the alluvial fan. A grain analysis in paddy field and channel of Yamajima irrigation system showed that most of the fine sediments generated from the landslide were trapped within the alluvial fan of Tedori River. Monitoring of Pungitius sp.1 and the habitats was carried out in the Tedori River alluvial fan. Based on the monitoring results, emergency protection measures and medium- and long-term protection measures for Pungitius sp.1 were examined
