Fish ladder being attached to smooth steel casing pipe.

Outlet to plunge pool.

Looking downstream fish ladder grouted in place and running full.

Under the auspices of the Natural Sciences and Engineering Research Council of Canada (NSERC), a small group of concerned industry colleagues has been collaborating on a project to design and test an innovative Corrugated Steel Pipe (CSP) ‘fish ladder’ that will enhance the safe passage of migrating fish over vertical barriers. Following the analytical /design stage of the project phase, the first prototype has now completed its first field trial. 

Throughout North America, perched culverts and similar hydraulic impasses represent a big problem for migrating fish. ‘Fish ladder’ is a term used to describe fishway conveyances intended to help alleviate this difficulty. They generally consist of a stepped series of sequentially elevated water pools, separated by weirs, or baffles. Most designs are quite basic and, although they do help somewhat, they are often relatively inefficient and have features that could potentially harm fish. Replacing a perched culvert is rarely an economically viable solution. And, despite the fact that these obstacles are widespread, there’s been little work done to scientifically analyze the performance of existing fish ladders in order to improve them. So, the problem has largely gone unaddressed. 

Overseeing this project are: Corrugated Steel Pipe Institute (CSPI) Executive Director Emeritus, Dave Penny; Civil Engineering PhD candidate at the University of Sherbrooke (UdeS), Jason Duguay; Jay Lacey, Associate Professor of Civil Engineering, UdeS; and Ken Hannaford, Environmental Scientist for the Government of Newfoundland and Labrador.

 “The whole idea for this research project came about at the university in 2012, during a discussion with Dave Penny, following his presentation on the advantages of using CSP,” explains Duguay. “During that chat, Dave described a concept that a contact of his in Newfoundland, Ken Hannaford, had for an innovative and better fish ladder. Dave had learned of this while showing Ken how using Polymer Coated Structural Plate Corrugated Steel Pipe (SPCSP) would offer the perfect base for fabricating these structures. And that’s when the concept began to germinate,” he adds.

Previous solutions have been devised to address the problem, including Denil fish ladders. Inside a Denil ladder are many metal fins which act as deflecting barriers to slow the water flow; but the fins have sharp edges and, if poorly configured, can create excessive turbulence in the pools. Moreover, they provide only small zones of calmer water, which fish need for resting, before proceeding to the next pool. Sharp baffle edges and excessive turbulence can injure or even kill fish – especially those that are exhausted from swimming against the combined forces of gravity and flowing water.

Unfortunately, many of these types of fish ladders are ineffective, non-permanent and non-portable devices, and are notorious for becoming plugged with debris, branches, etc.

Perched culverts are just one of many elevation obstacles that can stop the passage of fish migrating upstream. Many of the fish ladder designs currently in use are quite rudimentary and, although they may offer some benefit to migrating fish, most have proven to be both ineffective and inefficient. In fact, some designs even pose new threats to the safety of fish attempting to navigate them.

According to CSPI’s Dave Penny, it was great to finally have some colleagues on board who were also excited at the prospect of creating a better fish ladder. 

“After working with CSP products for decades, I knew that SPCSP would provide the perfect enclosure for any new fish ladder designs, as its corrugations naturally reduce the velocity of water flowing through it, particularly along the edges of the pipe; and in fact the deeper the corrugations, the greater the decrease in velocity. But, it offers other advantages, as well. CSP is lightweight, easy to transport and economical to install, even in very remote locations and/or in difficult terrain. A recent innovation to polymer coat the steel after fabrication meant we could provide more refined details and a very durable product,” adds Penny.

“The inefficiencies of current fish ladders and the dangers they pose to fish were the principal reasons why we wanted to design a better, affordable, portable or permanent solution for safe fish passage at vertical barriers such as perched culverts,” says Duguay.

Following their initial contact, the colleagues went ‘undercover’ for about a year, while fleshing out the idea and discussing the most prudent ways to initiate the design project. Next, Penny, Lacey and Duguay collaborated to secure funding from NSERC, which promotes and supports scientific innovation and collaboration among academic experts and industry. 

“We needed funds to support our work and purchase numerical modeling software to determine the effects of specific design changes on water velocities and turbulences within the fish ladder,” explains Duguay.

The team had to ensure that its new design could develop spatial distributions of water velocity and turbulence similar to those of other designs recommended by the Department of Fisheries and Oceans Canada (DFO). So, they employed a proven 3-D computational fluid dynamics program to analyze and design a baffle that would deliver equal or better results, while providing easier, safer fish passage over a wide range of flow rates.

Duguay is concurrently doing graduate work in civil engineering, specializing in hydraulic resources and fish passage at man-made structures; however, he volunteered to work on this fish ladder project on the side. Serendipitously, his thesis supervisor, Professor Jay Lacey, has a depth of experience in hydraulic engineering and fish habitats, and offered to help on the project to be certain the software was generating reasonable results.

“We wanted to ensure that our baffle would respect the minimum criteria laid out in the DFO recommendations and, hopefully, improve upon a few deficiencies that Hannaford saw in the DFO design,” explains Duguay. “First, the DFO design features aligned passages in the center of each baffle, which channel the flow straight down the center, creating excessive turbulence as the flow enters the next downstream pool. This effectively reduces the area of calm water available in the pool, where fish can rest before proceeding to swim or jump to the next pool. And a lack of effective resting areas can increase the chance of fatigue, injury and rates of mortality during ascent,” adds Duguay.

Although the existing Department of Fisheries and Oceans endorsed fish ladder design, above, helps fish navigate perched culverts and other elevation impasses, the development team on the project believes there are opportunities to improve its performance by slowing down the velocity of unimpeded water flowing directly through the collinear passages aligned along its center.

“The innovative, curved alternating baffle design was the key technical refinement of this design,” explains Duguay, “and that was Ken Hannaford’s brainchild. Ken came up with the concept of using curved forms, rather than angular ones, for some very good reasons. Also, by sequentially alternating the baffles on either side of the CSP pipe, I immediately saw its potential to relegate high velocities and reduce overall turbulence in each pool of the fish ladder, while the corrugated walls of the CSP also help to reduce flow velocities. 

“We were also concerned by numerous reports of debris blockages in the DFO design and believe that the curved form of the baffle can also limit debris snags and, ultimately, reduce maintenance costs, as well,” says Duguay. “Throughout the course of this development project, we continued to test, tweak and re-test the dimensions of simulated seasonal flow rates,” says Duguay, “and fine-tuned the attributes of the baffle curve, in order to optimize the efficacy of our fish ladder.”

Previous scientific studies demonstrate that increased passageway width in fish ladders directly improves jumping success rates. The new design, as illustrated above, offers fish a significantly larger primary passage, but also features a secondary one in each pool, which serves as an alternate passage for both fish and debris during periods of high flow rates.

Water cascading through primary and secondary passage.​

Duguay goes on to explain that one principal objective of the design study was to make the new fish ladder passable for as many kinds of fish as possible, which meant they needed to ensure fish had access to larger recirculation areas of relatively calm water and low velocities near the passageways. The DFO design recommends a minimum of 200 mm between the lowest part in the slot and the CSP corrugations, which results in little buildup of water depth in pools. That is a weakness, because deeper water will further reduce turbulence. Conversely, the innovative curves of this new, arched baffle produce significant increases in pool depths during higher flow rates, to minimize turbulence.

 “I would run simulations and send them to Ken,” explains Duguay, “Then we’d discuss the findings via email and proceed to suggest new refinements that might further improve the results we were getting. That was the iterative, collaborative process through which Ken and I developed the final design. Historically, other hydraulic simulations generated by the software have proved it to be a very accurate tool for predicting real-world measurements, so we’re pretty confident that our numbers are good; however we still want to compare results with a real world model,” he concludes.

As you can see in the diagram, above, the curved baffles of the new design provide a primary slot for fish passage, but also a smaller, secondary slot on the opposite side of the baffle. Primary and secondary slots are fixed on alternate sides of each successive baffle, so that flow moves through the primary passageway just above the secondary passageway of the next downstream baffle. In this fashion, the velocities through the pools are decreased, which translates into improved passage performance. Also, the primary passage (in the above line drawing) is wider, allowing more water to flow through, which in turn gives fish a larger opening through which they can jump. Previous scientific studies have shown that increased passageway width directly improves jumping success rates. The secondary passage serves as an alternative slot during high flow rates, not only for fish, but also for debris.

“As I mentioned earlier,” says Duguay, “the curved baffle is key to what makes this an improved fish ladder design. I suppose one could fashion it from any material, but corrugated steel pipe is a good choice for a variety of reasons, especially due to the fact that the corrugations naturally reduce the velocity of flowing water close to the pipe, which in turn complements the new baffle design by creating calmer rest areas for fish,” he adds.

To summarize, the fish ladder simulations were tested at typical seasonal flow rates of streams in which a number of important North American fish species – including Brown trout and Cutthroat, as well as Sockeye, Coho and Chinook salmon – are commonly observed. Results demonstrate that the new baffle design helps lower the global turbulence in each pool and confines the regions of high velocity to the side of the ladder – leaving a large portion of the pool free for fish to rest in before continuing upstream.

Above, the top illustration juxtaposes CFD renderings which predict lower surface velocities and larger rest areas in the new design vs. those of the DFO recommended fish ladder. The bottom illustration suggests that, even during periods of high velocity flow, the increased volume created by its curved baffle design will minimize turbulence and improve opportunities for safer passage.

Additionally, the high protruding arch of the baffle helps build pool depth as flow rates increase, thereby keeping turbulence and velocities within reasonable levels. The increased pool depths observed at higher flow rates also decreases the vertical drop fish need to overcome between adjacent pools. In some instances, fish may be able to swim directly between pools without resorting to jumping. The design still needs to be verified for its ability to pass smaller juvenile fish, as well as fish species with weaker swimming abilities. To this end, the team is currently expanding its research, in order to analyze, understand and address the additional needs of these types of fish.

The new design concept was initially presented to the industry at the 2013 TAC/ATC Conference in Winnipeg where Dave Penny challenged Canada’s Transportation Industry to seek out fish passage issues and fix them.  Jason Duguay gave a more detailed presentation at TAC/ATC 2014 in Montreal. 

In November 2014 at an Ontario Road Ecology Group (OREG), Canadian Parks and Wilderness Society (CPAWS), Royal Ontario Museum (ROM) conference in Ottawa the Ministry of Transportation Ontario (MTO) came forward with a culvert replacement/fish passage project under HWY 21, on Saugeen Ojibway Nation (SON) land. 

CSPI began work with the MTO design team that brought several new members and challenges to the collaboration. The HWY 21 project, completed in December 2015, has become part of our ongoing research and will be presented in detail at the 2016 Canadian Society of Civil Engineers (CSCE) Conference in London, Ontario, June 1-4.

Ray Wilcock
Director Corrugated Steel Pipe Institute