Brewarrina Fishway
Recessed partial width (natural) rock ramp fishway with "V" shape profile to reduce debris collection
Duck Creek
Precast rock ramp with uniform concrete ridge elements
Kyogle Fishway
Precast rock ramp with "V" shape profile to reduce debris collection
Homestead Fishway (Toorale State Conservation Area)
Precast rock ramp with "V" shape profile to reduce debris collection
Downstream bed scour
A natural rock ramp fishway with scouring of the creek bed at the downstream entrance that limits fish movement into the fishway.
Debris collection
Plant debris can collect across the rocks and block fish passage
Natural rock ramp fishways
Early rock ramp fishway designs employed natural rock to form the ridges and pools, with natural rock seen as more aesthetically pleasing, and lower material costs. Natural rock ramp fishways used large rocks to form the ridges and outer lining of the channel, and smaller rock within the fishway pools.
A skilled machine operator is required to construct the fishway as each rock must be chosen carefully and interlocked with others to stabilise the structure. By nature, natural rock is variable in its shape and size, making it difficult to achieve consistent water velocities and turbulence throughout the fishway. The variability in shape and roughness of each rock also makes it easier for debris to catch and collect along fishway ridges, leading to blockages if the fishway is not maintained regularly.
Flooding flows and debris impact can also affect fishway structural stability. As individual rocks move, this affects surrounding rocks which are all interlocked with each other. This can then negatively affect flow patterns and reduce the ability for fish to successfully move through the fishway. To overcome this a V-shaped cross section has been incorporated into some designs, such as Brewarrina fishway.
Precast rock ramp fishways
These fishways consist of a series of pre-cast concrete baffle units that replace the use of natural rock to form the ridges within a fishway. The baffle units have become an innovative design as they provide a predictable hydraulic performance and greater structural stability than the natural rock design.
Baffle units are prefabricated off site and bolted together once installed. Their regular shape makes them easy to place on flat foundations, thereby significantly reducing construction time and contractor risk.
This design also incorporates a V-shaped cross-section that facilitates the downstream passage of floating debris which reduces hydraulic impacts and ongoing maintenance expenditure.
Additionally, ridges can be easily modified to address visual impact considerations (e.g. colour) and fish passage performance criteria.
Full width precast rock ramp fishway
These fishways consist of a series of pre-cast concrete baffle units with multiple ridges across the full channel width.
Ridges can be constructed from individual baffle elements or, depending on the width of the waterway, single-section precast ridge elements can be designed that extend across the width of the waterway.
Full width precast rock ramp fishways are generally the preferred option in NSW where technically and financially feasible as they provide excellent entrance conditions and a clear flow path along both banks for migrating fish. Kyogle fishway and Homestead fishway (Toorale State Conservation Area) are examples of this design.
Recessed partial width precast rock ramp fishway
Recessed partial width precast rock ramp fishways are designed to control flow within a portion of the channel width, with the downstream entrance located at the weir face and the remainder of the fishway within the weir pool.
This fishway has similar design elements and advantages to the full width precast rock ramp fishway but over a much smaller footprint. The selection of this design over the full width option is normally dependent on rock volume, availability and delivery costs, and weir design and headwater levels where integration of a full width design is problematic.
Brewarrina Weir fishway is an example of the recessed design but uses natural rock instead of prefabricated baffle units.
Conceptual layout of full width precast rock ramp fishway
Case Study – Homestead Weir fishway: Toorale State Conservation Area
The NSW Government worked with stakeholders to modify the 130-year-old Homestead Dam on the Toorale State Conservation Area. The old dams and levees limited environmental water flows and obstructed fish movement in the Warrego River. The works now make it easier for native fish to move between the Darling and Warrego Rivers, providing better access to waterholes, wetlands, food and breeding grounds. This project shows the success that can be achieved when Commonwealth and state agencies, first Nations, landholders, private industry and other stakeholders work together.
For full details of this and other projects, visit our Fish passage projects page.
Conceptual layout of recessed partial width precast rock ramp fishway
