IMPACT OF A MESH STRUCTURE ON SALINITY INTRUSION

The ecosystem in the tidal region of a river tends to be diverse because of seawater intrusion. Such an ecosystem is observed in the Abashiri River in eastern Hokkaido. The downstream end of Lake Abashiri is about 7 kilometers from the Abashiri river mouth. The lower layer of the lake is saline water that has flowed upstream from the sea. Dissolved nutrient salts from the saline water layer make the lake a good fishing ground. However, in recent years, the damage to fishery of blue tide happens frequently because the fresh water depth of the lake became shallow. One solution is based on the comb-shaped weir traps that are used for catching fish in Abashiri River. Mesh structures that simulate weir traps were used in laboratory experiments to study the relationship between mesh porosity and salinity intrusion velocity. The following findings were obtained: The salinity intrusion experiment showed that when the mesh porosity is low, the flow velocity decreases before the water reaches the structure, and that the flow velocity does not differ greatly between before and after passing through the structure.