Hydraulic Characteristics and Effectiveness of the Terrace Type Fishway

Mabuchi Kazumi, Hiramatsu Ken, Itagaki Hiroshi

doi:10.7132/jrcsa.kj00000795222

The terrace type fisliway is a hybrid fishway of the pooi type and the stream type, which has been developed and constructed at a groundsill of River Neo in 2000 by the Upper-Kisogawa construction bureau of the Japanese government and Yamatatsu Construction Company where one of the authors is working. The terrace type fishway is named for its shape that resembles a terrace paddy in a mountainous area. This fishway is equipped with several devices; a) There are many slits on the walls that are surrounding the pools, because the walls are made of the fieldstones around the groundsill. The fishes can pass through the slits without jumping. b) The mouth of the fishway opens widely for fishes to find their routes easily. In addition, the slope for the lateral direction is set steeper than that for the stream direction to gather the river water along the walls, which assures the minimum water depth required for passing even in the drought period. c) The depth of the pools is shallow enough to flush the soil and sands during the flood, which makes the fishway maintenance-free. d) The roughness with small rocks on the slits and bottom of the pool effectively reduces the velocity in the fishway. e) The rapid velocity at the upstream mouth of fishway is reduced by raising the position of the mouth. The hydraulic characteristics and effectiveness of the fishway from the viewpoint of passage of the aquatic habitats are examined by the follow-up surveys during these 3 years. As a result, it proves that the terrace type fishway can be an alternative to the conventional ones and further it is superior to them in many aspects.

Hydraulic Characteristics and Effectiveness of the Terrace Type Fishway

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