Innovative Fishways – Manipulating turbulence in the vertical slot design to improve performance and reduce cost.
Mallen-Cooper M, Zampatti B, Stuart I and Baumgartner L (2008) Innovative Fishways – Manipulating turbulence in the vertical slot design to improve performance and reduce cost. A report to the Murray Darling Basin Commission, Fishway Consulting Services, Sydney. 19pp.
|Innovative Fishways – Manipulating turbulence in the vertical slot design to improve performance and reduce cost.
Fishways are often constructed to provide migration pathways for fish obstructed by a dam or weir. These structures are currently constructed to provide passage for a wide range of size classes of fish (40 – 1000mm). This requires the construction on low slopes to reduce water quality and turbulence so that small fish can ascend. Fishways constructed on steeper slopes are still successful, but only large fish are able to ascend as water flow and turbulence is much greater.
Low slope fishways require a long channel to achieve fish-friendly flow conditions. This has the major disadvantage of increasing cost which can limit the potential for widespread application. The efficiency of steep fishways could be theoretically improved by modifying design aspects of steep fishways to create ‘fish-friendly’ flow through the structure. Modifying steep fishways would be much cheaper than constructing fishways on low-slopes but no such research has ever been conducted in Australia to determine the potential of these solutions to pass small-bodied fish.
The present study tested two methods of improving fish passage in steep fishways by reducing turbulence and flow within the fishway pools. The team improved reduced turbulence by roughening the fishway walls to create a ‘barrier’ of low flow along the channel wall. Total flow through the fishway was also reduced by constructing sills placed in each fishway baffle. The sills were 250mm high and were placed into the middle of each fishway baffle to limit the amount of water entering each cell. A study was then undertaken to assess the success of each technique at improving the passage of small-bodied fish (< 60 mm long) known to have poor swimming abilities.
Both wall roughness and middle sills greatly improved small-bodied fish passage (25 – 55 mm long) and hundreds were able to ascend the fishway in less than 30 minutes. However, up to 13 times more small fish ascended the fishway with middle sills compared with an unmodified fishway. Middle sills appeared to be slightly more effective than wall roughness and are a simple solution to significantly improving fish passage.
The experiments demonstrated that fishway modifications can greatly improve fish passage of small-bodied species. This is a major advance in our understanding of fishway design and has broad-scale application across the Murray-Darling Basin. The results have already led to new fishways with improved functionality at lower cost in the Basin and have major potential to improve the a number of steep fishways that have previously been constructed.