COMPARISON OF SEAWATER INTRUSION IN TWO RIVERS FLOWING INTO A SAME INNER BAY:FOR HABITAT EVALUATION OF RYUKYU-AYU

Abstract

Although the Sumiyo River has a similar size of basin and same inner bay to the Yakugachi River, it has smaller population of endangered freshwater fish called Ryukyu-Ayu, in Amami Oshima Is. Focusing on the upstream migration of the target species from inner bay, seawater intrusion measurement were conducted with GPS installed float, STD and ADCP. The result showed that the Yakugachi river has 6.9 times of total discharge from inner bay compared to the Sumiyo River from ebb tide to high tide. We speculated that the sill located on the entrance of the Sumiyo River is a blocking factor for seawater intrusion from inner bay.