Some Hydraulic Design Aspects of Nature-Like Fishways

Dams and other similar hydraulic structures constructed across streams result in obstruction to fish migration. As such, fish access to spawning grounds and other habitat areas, which provide for such life requisites as food and shelter, is prevented. In many cases, fish passage facilities have been constructed at the site of the obstruction. Most of these facilities have been constructed using a hard engineering approach. Recently, increasing attention is being given to the use of nature-like fishways for facilitating fish passage. Such fishways are based on the ecological principle of mimicking nature. There are at least two different types of nature-like fishway, namely the pool and riffle type and the rocky ramp type, both of which are primarily constructed of rock. This paper is focussed on the rocky ramp type of fishway. Particular attention is given to the spacing between the isolated roughness elements to form preferential flow paths along which fish may swim. The work is based on the results obtained from physical hydraulic models of three simple geometric flow obstructions (hemisphere, cylindrical column and square column). Experimental observations and results obtained from the model study are presented. Recommendations for the spacing of isolated roughness elements are provided, along with directions for further research.