2023 – The Telescopic Fishway: Case Study of an Innovative Approach to Downstream Fish Passage

Jack Bygott, Gabriel Giliomee, Ben Vickers, Frank Nitzsche

Downstream fish passage at dams and weirs is typically only provided during spillway overtopping and does not often cater for the diverse migratory behaviours exhibited by native fish species in Australia. The construction of dams and subsequent limited movements of species through watersheds has had a significant effect on native fish abundance and diversity in Australia. Further, without selective withdrawal facilities, reservoir impoundments can also affect downstream waterways due to cold water and anoxic pollution from low level releases. The telescopic intake can offer designers an alternative solution to both fish passage and multi-level offtakes. The telescopic fishway, a variation on the telescopic intake, was designed and built in 2021 to help improve fish movement at Paradise Dam by replacing the existing fish lock with a facility with an improved operating range. The design combines a floating skimmer with a telescopic standpipe to maintain a stream of attraction flows that lure fish into the chamber, where they are then gently released into the downstream approach channel, similar to the operation of a lock. The design was specifically targeted at the larger bodied Queensland lungfish. A unique advantage of this intake arrangement is that it passively follows the water level of the reservoir; reducing the number of chambers and hydraulic gates requiring regular maintenance and uses buoyancy rather than winches. It also gives operators the ability to fine tune both entrance depth and flow rate without making physical modifications. This paper presents a comprehensive case study on the design, construction, commissioning, and lessons learnt in developing a retrofitted telescopic fishway. The practical lessons learnt from this case study can be utilised by other designers wanting to implement a telescopic intake solution to provide downstream fish passage or multi-level offtake.

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