Abstract
We made investigation due to conservation of Corbicula japonica resources in the Teshio river basin(Tshio river, Sarobetsu river, Panke swamp), where the northern limit of fishing grounds in Japan. Attention to salinity environment, it was cleared that salt water intrusion formed two-layer structure of fresh-salt water in the Teshio river. We proposed a method to estimate the fresh-salt boundary elevation by fresh water flow rate. Salinity environment in the basin was revealed to be limit by main river flow. Salinity environment is degraded by an increase in river flow caused by rainfall increased in Teshio river basin, freshwater clam catch has been suggested to decrease.
As adaptation of salinity environment for the flow rate increase, it was examined for the effect of the shelf-like terrain in the numerical model. As a result, it was found that the saltwater intrusion distance and fresh-salt boundary elevation increases as the flow rate per width of fresh water reduced. Thus, it is suggested to be effective that the widening of the river width where fresh water flowing, and construction of the shelf-like terrain.
