利根川河口堰下流部における貧酸素水塊の発生と流動

Abstract

A series of field observation were conducted to investigate the behavior of an oxygen deficit water mass in a reach of Tone River downstream from an estuary barrage. Vertical profiles of salinity, DO and velocity were measured along the deepest line. The data show that the anaerobic condition was frequently developed at the salt wedge front because of the oxygen supply restriction at the density interface and the oxygen consumption in a bottom layer. The data also show that the DO budget in the water mass is highly affected by DO transport due to an estuarine circulation.Numerical simulation by using a two-dimensional k-e model reproduces the phenomenon successfully. It also suggests that the DO consumption takes place not at the front part of the salt wedge but through the whole way that sea water is transported by the estuarine circulation from the river mouth to the salt edge front, and then that the residential time of salt water in the estuary is an essential factor for the development of the oxygen deficit water mass.