Observation of Saline Wedge Behavior in Brackish Water Areas

In brackish water areas, where sea water and fresh water co-exist, accurately identifying the behavior of salt water is important for the fishing industry, and for studying environmental problems.
Laying an optical fiber temperature sensor along the bottom of a river or lake can provide continuous, wide-ranging detection of the boundaries between salt water and fresh water, based on temperature differences.
Combination with conventional salt meters and sonic probes allows extremely precise analysis of brackish water areas. The data gained helps to analyze sea level rises due to global warming and the impact of river construction works.

- Real application example

Optical fiber used in measuring temperature distribution

A two-core cable was folded back to make a loop connection.

Salt water wedge inflow was observed in the Gonokawa river (Shimane prefecture)

Salt water wedge inflow was observed in the Gono River, Shimane Prefecture

- Measurement data

Until 08:27 on 27th December, salt water (approx. 16 C) stopped downstream at the 330m point, with fresh water (approx 8 C) on the upstream side
At 08:27, the salt water moved upstream, and the river bed temperature distribution shifted upstream with the movement of the salt water wedge.

How water temperature changed with the entry of the salt water wedge
(diagram on the right)

Observation location: Gono River, Shimane Prefecture
Observation periods: December 1997 to January 1998

Development of a halocline (salt water wedge) dynamics observation system - Contribution against the problem of bodies of deoxygenated water in brackish water areas - Laguna (brackish water area research), 6.182-183