Measurement of Density Current in River Bend with ADCP

The Lake Abashiri, located in the northeast of Hokkaido, has stratified layers of fresh and salt water. The biochemical pollution caused by inflowing load from the catchment area, and no oxygen state of the lower salt layer is becoming a serious problem. One of the important phenomena on this problem is the alternate directed density current of the Abasiri River, which goes into the Lake Abashiri. A 180 degree bend is existing in the Abashiri River at one km downstream of the lake, and this makes the hydraulics of the system more complicated. In this study, a series of field measurements on three dimensional flow field and density of river water were conducted in this bend in 1986. Two set of measurements in melting snow season and low flow season when the unidirected flow from the lake and the alternate directed stratified flow becomes dominant, respectively. ADCP (Acoustic Doppler Current Profilers) and STD (Salt Temparature and Depth) were used to collect the data continuously in a wide area within a short time. Collected data are compared with existing theory and the characteristics of the stratified density flow are discussed.