SEMINAR: Can we decrease turbidity by constructing an artificial shallow area in a lake?

Lake Shinji is a brackish shallow lake in Japan. Its surface area is 86.8 km2 and the average water depth is 4.5 m. In 2001 the Japanese government (MLIT) started a project to construct an artificial shallow area around the shoreline where concrete embankments had been constructed and the water depth became deeper.

One of the main objectives of the project is to reduce wave energy and inhibit the suspension of bottom sediments, which is expected to decrease the turbidity in the lake. In order to reveal the effect of constructing an artificial shallow area on waves and turbidity, we performed field surveys of measuring waves, currents and turbidities at an artificial shallow area as well as an adjacent deeper area in the lake. Moreover wave analysis using a wave simulation model named SWAN was performed to evaluate the change of wave characteristics and bottom share stresses due to the water depth change.

The field survey showed that significant wave heights in the artificial shallow area became smaller than the deeper area. But there were no significant turbidity differences between two areas. Why? I will discuss the tricky part of the project.

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