Development of Steel Folding Type Fishway and its Characteristics

Pool and weir type fishway is a kind of open channel with slope of constant gradient and connects a drop in a river. When this kind of fishway is built at high dam or debris barrier, it must inevitably be long and large, which induces high cost and long construction period. Recently, spiral fishway that is also a kind of pool and weir type but folded like a spiral has been developed to overcome the difficulties and installed to some high dams. It sometimes fail to dissipate energy and often slant its talwag outward, though it succeeds in cut-down of the cost and period according to some reports. Then, the spiral fishway is improved to be successive S shape channel with shallow pools and attached directly on the wall of barrier. At the same time the fishway that consists of several parts made of steel is built in a factory and the parts are assembled on the site, which cut the cost and period remarkably down. In the research its applicability are examined by hydraulic test and fish ascending test in a prototype experimental fishway. Results show that 1) flow is successfully decelerated throughout the fishway and approximately 28% of velocity is reduced at a folding pool, 2) flow at pools is slower than sustained speed of young Ayu (Plecoglossus altivelis) and Amago (Oncorhynchus masou ishikawae) and fastest flow seen at the slit of weir is less than their burst speed, 3) Roughly 90 % of ayu and amago ascend the fishway in 2 days. Consequently, the finshway is exptected to be of help to ascending fish at high dams and debris barriers.