Developing effective fishways: Emerging international trends

The good news is that recognition and acceptance of the importance of mitigating impacts on fish species has increased significantly, particularly during the last decade. Fisheries and environmental agencies worldwide consistently promote the important role of fish in our ecosystem. Fish provide good indications of water health, are beneficial to other forms of wildlife, and are a key link in the food chain.

However, while there is broad awareness of the impact of many instream barriers on fish, the challenge to protect them is likely to increase in line with the growing international focus on water security and renewable energy, which is likely to lead to large dams being constructed within some of the world’s most significant rivers.

With this shift imminent, careful planning and design of fishways to facilitate movement of fish across instream barriers is more critical than ever.

The performance of existing fishways indicates there is plenty of room for improvement in design. For example, it’s claimed that there are more than 6 million known instream barriers in the United States, and by some reports, just 10 percent have what scientists would consider high-quality fish passage. In Victoria, Australia, only 30% of fishways built to date are known to pass fish efficiently. 

Of course when it comes to fishway design, there are vastly different approaches in different parts of the world due to local variations in fish species and the maturity of legislation covering the design process. While it’s important that water infrastructure developers are aware of their local legislative requirements, including accounting for variables such as species, water flow and environment, there is scope to learn from other jurisdictions and share knowledge to collectively improve fishway design.

But what does good design look like?

Fishways themselves can vary substantially from relatively simple rock ramps through to highly complex mechanical lifts and locks. The success of a fishway at facilitating fish passage is dependent upon the development of site-specific design criteria and requires extensive collaboration between specialists from many disciplines during the design process, including fish biologists, fishway specialists, hydrologists, design engineers, permitting specialists and asset managers.

Effective approaches should also include the development of site-specific design criteria. For example, ecological design criteria may require consideration of fish size, their swimming ability including burst or sustain swimming speeds and the environmental conditions during migration. Engineering design criteria includes an extensive list of specifications including headwater and tailwater operating range, frequency and duration of operation, hydraulic and electrical requirements.

Australia and the United States have vastly different fish communities and legislative objectives underlying the fishway design process, which can lead to unique challenges and innovative design solutions for both. Some documented observations conclude that fish communities in Australian river systems have poor swimming ability compared to United States species. Further, while fish migration in the United States is generally seasonal, fish movement in Australia is often triggered by flows and can occur across all seasons.

In Australia, fishway design takes a broad approach in terms of accommodating a range of fish from large to small species across a range of swimming abilities. Whereas in the United States, while there are well-developed fishway design criteria in many parts of the country, solutions tend to favour strong swimmers and more commercially significant species, such as salmon and steelhead.

Pleasingly there are a growing number of case studies from around the world that illustrate best practice in fishway design.

For example, the Stillaguamish Adult Fish Passage Design project for the United States Corps of Engineers (USACE) Seattle District initially had poor fish passage design for the required migration times. This was due to poor hydraulic design and siltation issues that interrupted the design flows through the ladder that encourages fish to pass quickly over the weir. GHD was engaged to create a new design to minimize scour and maximize the weir design to have higher flows over a wider range of hydraulic conditions. The improvements to design are believed to deliver a longer approach to the weir along with a new sheet pile wall to capture flows into the new throat of the fishway exit. Overall it promotes higher attraction flows during the months that salmonids are migrating.

The Fitzroy Catchment, located in central Queensland, Australia, is the second largest catchment in Australia. GHD began working on the Rookwood Weir Project in this catchment more than 10 years ago. The ecological design criteria for the associated fishway included providing upstream and downstream movement for 34 fish species ranging in size from 15 – 800 millimetres with varying swimming abilities. Migrations in the river occur during all seasons and flows, with peak migrations during the first post-winter flow and on larger flow events during spring and summer. It is by understanding the fishes’ migration requirements that fish passage design solutions could be assessed and ecological benefits maximised.

Fishway and passage design is evolving at a rapid pace because of new developments in engineering technologies. While designing a fishway may seem straightforward in theory, designing one that achieves successful fish passage requires an in-depth understanding of ecological design criteria and specialised design solutions.

By adopting a holistic approach through collaboration and knowledge sharing, upfront planning and permitting, understanding the fish species and the natural hydrological profile of the river system, and learning from fishway projects around the world, designers and developers can deliver effective fishways together.

While regulators are often reluctant to accept fishway designs that are unproven, innovation usually evolves from modifications to existing designs to achieve site-specific design objectives.

It is also important to note that existing waterway barriers can be retrofitted with fishways to re-enable the migration of fish species and mitigate the environmental impact of critical water infrastructure to improve river system health.