Influence of high turbid water generated from a huge landslide occurred in the headwater

Abstract

A large-scale landslide occurred in May 2015 in headwaters of Tedori River at the foot of Mt. Hakusan. Highly turbid water has been generated from the landslide, which has had wider and seriously influences on the downstream area by such as rice paddy irrigation systems, ground water system, fresh water and coastal fisheries. Airborne LiDAR data and series of air photos were employed to analyze topographical features, this landslide occurred within the old landslide body. The suspended solids and sediments showed high pH and Ca concentrations, which gave the effects on the early growth stage of rice plant and the uptake of essential microelements. Miyatake settling basin has a role to prevent sediment from flowing into farmlands. Sediment heights of the sand settling channels were measured and the volume of total sediment was estimated, then it was concluded that the settling basin has performed very well. From May 2015 when the high turbid water occurred, the groundwater tables in the alluvial plane began to decrease seriously. So, it has been required to analyze the water balance in the aquifer and evaluate the influence of turbid water. A hydrologic model was developed for the analysis and evaluation. The model performance was very good and it is expected that the model will be available to predict the influence of the turbid water. Since the sharp decline of groundwater level has gave a serious damage to Pungitius sp.1, it is considered that the addition of spring-fed ponds with groundwater lifting pumps is urgently required for the future depletion of spring water.