EFFECT OF MIXING ON TURBIDITY MAXIMUM MOVEMENT DURING SEMILUNAR TIDAL CYCLE IN THE CHIKUGO RIVER ESTUARY

Abstract

Spatial distribution and temporal variation of salinity and suspended sediment concentration (SSC) in the Chikugo river estuary, Japan, were measured for two weeks and investigated the effect of salinity mixing on the movement of the estuarine turbidity maximum (ETM). Vertically homogeneous salinity distribution and high SSC occurred during spring tide, and conversely, vertical stratification and clear water occurred during neap tide. Mixing, salinity intrusion, magnitude and location of ETM zone changed according to the semilunar tidal cycle. The flow ratio was determined using river discharge and the tidal prism, and a uniformly linear relationship was found between flow ratio and SSC. The relationship between salinity and SSC showed that SSC attained a peak in the region where salinity was 10 psu in lower estuary and region of 0.5 psu in the upper estuary. These indicate that the dominant factor determining SSC occurrence is the spring neap transition process and flow ratio.