RELATIONS BETWEEN FLOW PATTERNS AND WATER QUALITY IN THE BANJO ESTUARY

In the Banjo River (Saiki, Oita), the population of clam drastically decreased after 1994 and has not been recovered yet. In order to make the reason clear some field surveys on water quality (: DO, salinity, water temperature, etc.), sediment quality and flow patterns were carried out from 2003 to 2004 in the Banjo estuary and Saiki Bay. Measurement results by ADCP showed the dominant flood current through the shorter navigation channel and the dominant ebb current through the longer one. In addition, water body tended to be stagnant in a neap tide and oxygen deficiency was measured in the longer channel. It was confirmed that temporal variation of DO concentration in the Banjo estuary depended on both flow patterns of tidal current and a redox conditions in the sediment.