SHISHAMO SMELT SPAWNING SITES IN AZUMA RIVER AND IMPACTS OF SILT CONCENTRATION FROM LANDSLIDES

Abstract

 We investigated the physical parameters that suitable for Shishamo smelt spawning in the lower reaches of the Azuma River and the impacts of high suspended sediment concentration caused by the Hokkaido Eastern Iburi Earthquake by means of a statistic model and numerical simulation. The results of the statistical model showed that the most suitable spawning places were mainly determined by bottom velocity of 0.4 m/s. In the numerical simulation, the appropriate place (bottom velocity range 0.3 to 0.6 m/s) moved in the river according to the flow rate (about 5 m³/s), so there was no suitable place to cover from high to low flow rate. Silt, increased after the earthquake, was mainly deposited along riverbanks and less deposited in the low flow channel, suggesting that the effects of high silt concentration on the spawning sites in the river would be limited.