落下流により発生する低周波音の低減対策工の提案

抄録

Weir waterfall generates sound of low frequency. In the conventional method, spoiler baffles are used at the levee crown to reduce the sound. However, this method is not effective for a low height weir. Recently, the surrounding space of small channel has become living space. Due to this trend, a new method to reduce the low frequency sound needs to be developed for residents near the area. The main objective of this research was to develop the method by organizing the characteristics of low frequency sound. In the research, the relationships between sounds and depths of different shape weirs were investigated. As the result, it was found that low frequency sound generated by weir waterfall was caused by the vibration of water film. In more detail, the sound source was the water film vibration near the discharge point. Considering this fact, the new method to reduce the vibration has been developed.

In this method, a gutter is installed on the downstream side at the levee crown to make water merge into some small sections flowing through weir. As the result, the low frequency sound is reduced to the level of 10dB or less. In the field test, the method also achieved a similar successful result.