SEASONAL VARIATION OF SAND SPIT AND ITS EFFECT ON FLUCTUATION CHARACTERISTICS OF WATER LEVEL AT THE MOUTH OF SH1RIBETSU RIVER

Distinct water level rise above tidal level has already been reported at several river mouths during the period of high waves. At Shiribetsu River mouth located in Hokkaido, Japan, a lot of cases of wave set-up are observed every year during the period from October to March, and it is found that the magnitude of water level rise increased with the development of sand spit at the river mouth. In order to find a relationship between wave set-up height and sand spit length at the river entrance, oblique photographs at the Shiribetsu River mouth, taken from a small mountain almost every week for these twenty years, are effectively utilized in this study.