2013 Volume 19 Issue 1 Pages 37-43
A-weighted sound levels between 78 to 89 dB were observed immediately above the dropping point of nappe on the water surface in the stilling basin of drop structures of the Togashi main canal of the Shichika Irrigation District, Ishikawa, Japan. According to the noise distribution survey conducted at the noisiest drop structure of 89 dB, A-weighted sound pressure levels between 62 to 67 dB which exceeded the Japan's environmental quality standard were observed in the cross-section adjacent to ordinary houses located 25 m downstream of the drop. Therefore, the noise reduction experiments of gabion mattress, using the 1/8 scale-downed hydraulic model of the drop structure of water-cushion type, were conducted. The experiments showed significant reduction of sound levels in the cases of trapezoid-shaped and inverted trapezoid-shaped gabion mattress with single or double-slit. Then, the flow velocity measurement showed that the sound levels above the dropping point of nappe were positively correlated with the mean flow velocities in the stilling basin.
