Fish passage: Fixing culverts is key to better stream habitat for salmon, other species
April 25, 2023
Barriers often stop fish from getting to stream habitat. Removing them to create connectivity is important to a river’s ecology.
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See that stream down there, flowing through that old culvert?
Driving at 60 miles per hour, you might not take much notice. You probably aren’t thinking about fish barriers or stream habitat. But that old culvert or bridge could be the equivalent of a brick wall for salmon or other aquatic animals trying to gain passage under your road and further upstream to critical spawning habitat.
Sure, water flows through them. But many culverts and bridges were installed decades ago. Back then, we didn’t fully understand how they create barriers to salmon restoration and problems for other species like trout, shad, and other aquatic animals.
Culverts that are too small or bridges that are too narrow can create water flows that are too shallow or too fast for fish to get past them. Have you seen a culvert perched over a stream that creates a small waterfall? It’s likely too high for fish to jump into it and swim past it.
These salmon are able to swim past this weir, but they often cannot get past culverts and bridges that are barriers to upstream habitat.
These barriers disrupt or prevent many fish species from completing their life cycles, especially the process of spawning and rearing baby fish. Even small aquatic animals, like minnows and aquatic insects, can be kept from getting upstream. That stream habitat becomes biologically barren without the fish and creatures that normally call it home.
Salmon and habitat restoration is a growing priority
Does fish passage and habitat restoration matter? Absolutely. Correcting it is a prominent issue that is gaining ground. In the state of Washington, 21 tribes asked a US District Court to rule that the state had to preserve fish runs under past treaties. In 2013, a federal court issued an injunction requiring the state to correct culverts that are barriers to salmon restoration and to steelhead (a sea-bound rainbow trout) within the injunction area in the western part of the state.
Other Western states are also racing to fix manmade river barriers to help restoration and recovery of salmon and other fish. Midwest and Eastern states are replacing bridges and culverts to improve passage for migratory sturgeon, salmon, steelhead, shad, herring, and other fish.
An example of a perched culvert that is a barrier to any aquatic animals trying to get upstream.
The problem isn’t just related to the design of culverts or bridges. Aging infrastructure and changes in watersheds can create barriers out of culverts and bridges that were once well-designed and passable to fish. A stream’s flow or path can change, making the culvert a barrier. The drainage area can increase or decrease, or fires, logging or other development can turn a culvert or bridge into a barrier.
Our Stantec team has helped our infrastructure clients correct stream-passage problems and focus on habitat restoration for decades. Our team of wildlife biologists, civil engineers, and hydrologists are skilled at evaluating fish barriers, designing to correct them, and monitoring them for long-term ecological success. Let’s dive into a recent example of this expertise in action.
Cedar Creek in Washington
Cedar Creek is in the City of Kirkland, Washington. Our project with the City started with fish passage issues due to a problem culvert. Over time, the project expanded beyond the culvert to the nearby habitat supporting the stream.
The original 36-inch concrete culvert was attached to an outdated storm-detention structure. It resulted in riverbank erosion and downstream flooding along the stream. The culvert’s outfall was perched 4 feet above the streambed, cutting off salmon and trout from their spawning habitat.
There were additional challenges for the Cedar Creek project. The creek had a degraded stream channel, invasive plants in the surrounding uplands, and an ongoing road-replacement project going over the stream.
This new culvert on Cedar Creek in Kirkland, Washington, was redesigned to allow for fish passage.
It took a diverse mix of designers to meet this complex challenge and return salmon and other fish to Cedar Creek. Our team included transportation, stormwater, and stream design engineers, along with hydrologists, biologists, and landscape architects.
The team also restored 1,200 feet of stream channel to Washington Department of Fish and Wildlife and tribal standards. Part of the project used native plants to restore vegetation to more than a half-acre of wetland and stream habitat.
Using woody debris to build resilience
Improving stream habitat goes way beyond just the culvert or bridge. We often use natural materials in our restoration projects to bolster habitat and build resilience to flooding and erosion. Once abundant in streams, woody material is often no longer available in stream corridors due to changes in historic land use. This causes streams to be starved of their woody habitat.
But large woody debris, such as root wads and logs, can be reused after construction projects. When it is strategically placed in channels and riverbanks, it helps to stabilize them and guard against scouring. Woody debris can provide fish refuges during high flows, protection from predators, and create and maintain deep-pool habitat.
Wood is also a great substrate for bolstering aquatic insect populations, which creates food sources for fish.
Does fish passage and habitat restoration matter? Absolutely. Correcting it is a prominent issue that is gaining ground.
Predicting debris flows and helping fish
How can technology come into play in mitigating fish barriers?
Climate change is leading to more wildfires and resulting landslides, which can cause natural barriers in rivers and streams to fish passage. Debris flows and sediment loads can also potentially turn older bridges and culverts in barriers and pose risks to redesigned fish passages.
Stantec has developed a tool called DebrisFlow Predictor. It can simulate and model debris flow hazards and address these potential barriers in rivers and streams.
Results from DebrisFlow Predicator show how debris flows could impact fish barrier sites or create new barriers. This technology revolutionizes how our teams design for and mitigate these hazards. We can use it not only for fish barriers but also for roads, bridges, and other linear infrastructure.
Does fish passage matter to communities?
It sure does.
If Washington’s salmon-restoration goals are realized, it will lead to healthy salmon and steelhead populations and increased access to the fish for tribes and other anglers. Washington Department of Transportation, which started a dedicated fish-passage program in 1991, says improving fish populations can contribute to the state’s economy through recreational and commercial fishing. It estimates the improvements will support 16,000 jobs and over $500 million in personal income.
Habitat above Cedar Creek was restored after a culvert was redesigned for fish passage.
The Biden Administration supports correcting fish passages. In a 2022 announcement for funding, it said fixing fish passages with Nature-based Solutions can help ecosystems and communities be more resilient to climate change and flooding.
“Across the country, millions of barriers block fish migration and put communities at higher risk of flooding,” said Deb Haaland, secretary of the US Department of Interior .
At Stantec, we understand that correcting a fish passage barrier is more than just a construction project. It’s a process that involves stakeholders and communities. Our commitment to the UN Decade on Ecosystem Restoration, partnerships with organizations like the Network for Engineering with Nature, and our knowledge of climate change position us perfectly to find holistic solutions to fish barriers.
See those salmon swimming down there? They’re heading upstream, past that new culvert, and toward a brighter, more resilient future.