Bypass fishway

Bypass fishway – Construction and operation

Select from the tabs below

• Overview
• Key considerations
• Planning and design
• Construction and operation
• Links and references

Please see general information for all fishway types.

Construction

For most bypass fishways (excluding where concrete is used, e.g. cone fishway), the commissioning process may allow a tolerance greater than 5% because of the unpredictable or imprecise nature of rock placement and earthworks compared with concrete. However, basic measurements such as head loss, water depth and slope should meet design specifications within the agreed level of tolerance.

Bypass construction is a specialist operation involving skill and patience. A close relationship is required between design, construction and supervision personnel, and advice should be obtained from a rock ramp construction specialist to ensure that the requirements for configuration and integrity of the structure are met.

Operation and maintenance

Bypass fishways tend to require little human intervention to operate, however optimal hydraulic operation and regular maintenance is crucial for the long-term passage of fish through rock ramp fishways. Rocks that move during high flows can eventually cause the hydraulics to become suboptimal and lead to functional failure of the fishway. A regular inspection schedule will ensure the fishway functions effectively in the long-term, however it is often hard to determine when maintenance is needed, and this aspect requires training for local operators

Examples of inspection and maintenance tasks for a bypass fishway:

• determine timing of operational reporting arrangements and inspection times (e.g. annually and after high flow events)
• visually inspect the entrance and exit for blockages and ensure it is trash (woody debris, flotsam etc.) free
• visually inspect head loss at each rock ridge to ensure it meets the design specifications
• inspect fishway for weed encroachment
• inspect fishway for sediment deposition
• after major flooding, check for any damage to the fishway (movement of rocks) and also to the bank armour[1].

References

1. ^ O’Connor, J, Stuart, I & Mallen-Cooper, M (2015), 'Performance, operation and maintenance guidelines for fishways and fish passage works', Trove. [online] Available at: https://nla.gov.au/nla.obj-480267623 [Accessed 10 November 2020].

Last updated: 10 May 2021