The presence of fish in rivers across Australia is affected by many factors, but a significant one is the presence of weirs and other structures that stop fish migrating up and down a river. There are several different designs to allow fish to navigate up or around a weir, and we had the pleasure of testing one of them with a physical model with the Australian Irrigation and Hydraulics Technology Centre at the University of South Australia recently.
In this blog we describe what a fish lock is, how it works, and what we learnt from building a scaled down physical version in the lab.
A fish lock operates in a similar fashion to a ship lock. However it requires a constant ‘attraction flow’ to be provided through the lock to attract fish into the entrance and out of the exit. The fish lock operates in four key phases:
Modelled fish lock (scale 1:10)
- Phase 1 - Attraction: provide attraction flow to lure fish into the lock chamber
- Phase 2 - Filling: the chamber is sealed and water level rises
- Phase 3 - Exit: the upstream gate is opened and the fish swim through to the weir pool
- Phase 4 - Emptying: the upstream gate is closed and the lock chamber is drained until the tailwater level of the fishway entrance is achieved
The fish lock system at Uni SA was built in two sections – the fishway (1:10) and the weir (1:15). Crucially, a number of key components of the model needed to be adjustable, including; the tailwater level, the baffle slot width, the upstream lay flat gate and the pipe diameters. We were lucky to have the opportunity to use fish during the testing, which allowed us to observe their actual behaviour in this environment and flow conditions.
We learnt several things in this process: the number of water level sensors that would be required, the optimal pipe diameter, the filling flow rate (during Phase 2), the location and configuration of the fishway entrance, and the height of the new apron weir for the plunge pool to facilitate downstream migration.
Modelled river/weir system (scale 1:15)
For this reason we believe that the physical model achieved its aim of optimising the design and therefore was a worthwhile part of our design process. The increased confidence in design should translate to a more economical outcome for our client.