Why it's so hard to design a fish ladder that works
The salmon look stressed. Behind the algae-streaked windows at Seattle’s Hiram Chittenden fish ladder they’re bumping heads, flipping in the current, and pointing their narrow jaws upstream.
To get to this point, they’ve already swum through the Straits of Juan de Fuca and the Puget Sound, and jumped through the first 17 steps of the ladder, which looks like a skinny set of concrete bleachers. Most fish passes aren’t as visible at the Seattle one, which has an observation deck where you can peer into the steps, but the way the fish have to work around a manmade barrier in the river is common. From here, the fish will keep following the current upstream to spawn in the stream where they were born. Anadramous fish are imprinted, Twilight style, in the rivers where they hatched, so depending on where they came from, they’ll still have several more dams to navigate.
There are more than 80,000 dams in the U.S. and nearly all of them have some kind of fish pass. They range from multi-step ladders like the Seattle one to elevators that suck the fish upstream to nature-like diversion canals. Some of them have been in place since the colonists started farming, and in 1890 the state of Washington passed a law that all dams, “wherever food fish are wont to ascend,” needed to include a fishway. The rest of the country eventually followed suit. Now, any new hydropower dam needs to get its fish ladder design cleared by the Federal Energy Regulatory Commission. But there aren’t a ton of new dams going in, and it’s becoming increasingly clear that just because a ladder exists it doesn’t mean that fish are going to figure out how to use it, or want to. (...)
All fish migrate to a degree, but dams have the biggest disrupting force on anadramous fish, like salmon or shad, which spawn in rivers but spend most of their lives in the ocean, and catadramous ones, like eel, which live in freshwater, but swim out into the ocean to do it.
There are other factors, like overfishing and climate change, which also hurt declining fish populations, but dams are the most obvious, and because of that, environmental engineers, dam operators, and fish biologists have been trying, with limited success, to design ways for fish to get past them.
In the middle of last century, dams were seen as the answer to a wide range of issues, from water supply to energy security. JFK boosted dam building in his campaign speeches. From the 1920s to the ‘70s, the Army Corps of Engineers built tens of thousands of dams, ones like the Columbia River’s Grand Coulee, which has cut off more access to fish habitat than any other structure in the world. That boom in dam building took a toll. “Many fishways were originally designed for adult salmon over 50 years ago, but we’ve recently found that they don’t work well for other species,” says USGS fish biologist Alexander Haro.
He’s trying to find ways to make them more appealing. At the Conte Anadramous Fish Branch, in Massachusetts, Haro sends fish through a respirometer to see how much energy they exert when they’re stressed, and through what he calls a “sprint swimming flume,” to see how fast they can swim and for how long. “It’s kind of like a high-speed treadmill for fish,” he says. He’ll use that data to try to design fishways that actually work.
The biggest issue, according to Jim Taurek, a NOAA restoration ecologist, is that different fish swim very differently. Some, like salmon, can jump high and sprint, while others — sturgeon for instance — mosey upstream. Alewife freak out in confined spaces and shad don’t like air bubbles.
Because of that, there are almost as many ways to design a passage as there are fish trying to swim through it. “In general, the lower the slope of a fishway, the easier fish can ascend, but that also means the fishway needs to be longer, and many fish will not stay in a fishway structure for very long,” Haro says. It’s possible to have a theoretically perfectly designed ladder that keeps fish stranded on the bottom, because they don’t like its style.
In addition to figuring out the size and shape of the structure you also need to design an appealing entrance, and to make sure the river flow points the fish in the right direction. Salmon can’t use an elevator if they can’t find the door. “Building fish ladders, even thought it’s engineering, it’s also art,” Waldman says.
Then you have to engineer the other side, for downstream fish migration. That’s simpler from a design perspective — the hardest part is teasing the fish out of the main current and into the fish pass — but it can be complicated from the financial side. Running water around the dam is the simplest solution, but utilities make their money on river flows, so they’re hesitant to spill a single drop.
by Heather Hansman, Medium | Read more:
Image: French Lake Dam fish ladder, Wichita Mountains Wildlife Refuge, Oklahoma. Flickr/lsmith2010
The salmon look stressed. Behind the algae-streaked windows at Seattle’s Hiram Chittenden fish ladder they’re bumping heads, flipping in the current, and pointing their narrow jaws upstream.
To get to this point, they’ve already swum through the Straits of Juan de Fuca and the Puget Sound, and jumped through the first 17 steps of the ladder, which looks like a skinny set of concrete bleachers. Most fish passes aren’t as visible at the Seattle one, which has an observation deck where you can peer into the steps, but the way the fish have to work around a manmade barrier in the river is common. From here, the fish will keep following the current upstream to spawn in the stream where they were born. Anadramous fish are imprinted, Twilight style, in the rivers where they hatched, so depending on where they came from, they’ll still have several more dams to navigate.There are more than 80,000 dams in the U.S. and nearly all of them have some kind of fish pass. They range from multi-step ladders like the Seattle one to elevators that suck the fish upstream to nature-like diversion canals. Some of them have been in place since the colonists started farming, and in 1890 the state of Washington passed a law that all dams, “wherever food fish are wont to ascend,” needed to include a fishway. The rest of the country eventually followed suit. Now, any new hydropower dam needs to get its fish ladder design cleared by the Federal Energy Regulatory Commission. But there aren’t a ton of new dams going in, and it’s becoming increasingly clear that just because a ladder exists it doesn’t mean that fish are going to figure out how to use it, or want to. (...)
All fish migrate to a degree, but dams have the biggest disrupting force on anadramous fish, like salmon or shad, which spawn in rivers but spend most of their lives in the ocean, and catadramous ones, like eel, which live in freshwater, but swim out into the ocean to do it.
There are other factors, like overfishing and climate change, which also hurt declining fish populations, but dams are the most obvious, and because of that, environmental engineers, dam operators, and fish biologists have been trying, with limited success, to design ways for fish to get past them.
In the middle of last century, dams were seen as the answer to a wide range of issues, from water supply to energy security. JFK boosted dam building in his campaign speeches. From the 1920s to the ‘70s, the Army Corps of Engineers built tens of thousands of dams, ones like the Columbia River’s Grand Coulee, which has cut off more access to fish habitat than any other structure in the world. That boom in dam building took a toll. “Many fishways were originally designed for adult salmon over 50 years ago, but we’ve recently found that they don’t work well for other species,” says USGS fish biologist Alexander Haro.
He’s trying to find ways to make them more appealing. At the Conte Anadramous Fish Branch, in Massachusetts, Haro sends fish through a respirometer to see how much energy they exert when they’re stressed, and through what he calls a “sprint swimming flume,” to see how fast they can swim and for how long. “It’s kind of like a high-speed treadmill for fish,” he says. He’ll use that data to try to design fishways that actually work.
The biggest issue, according to Jim Taurek, a NOAA restoration ecologist, is that different fish swim very differently. Some, like salmon, can jump high and sprint, while others — sturgeon for instance — mosey upstream. Alewife freak out in confined spaces and shad don’t like air bubbles.
Because of that, there are almost as many ways to design a passage as there are fish trying to swim through it. “In general, the lower the slope of a fishway, the easier fish can ascend, but that also means the fishway needs to be longer, and many fish will not stay in a fishway structure for very long,” Haro says. It’s possible to have a theoretically perfectly designed ladder that keeps fish stranded on the bottom, because they don’t like its style.
In addition to figuring out the size and shape of the structure you also need to design an appealing entrance, and to make sure the river flow points the fish in the right direction. Salmon can’t use an elevator if they can’t find the door. “Building fish ladders, even thought it’s engineering, it’s also art,” Waldman says.
Then you have to engineer the other side, for downstream fish migration. That’s simpler from a design perspective — the hardest part is teasing the fish out of the main current and into the fish pass — but it can be complicated from the financial side. Running water around the dam is the simplest solution, but utilities make their money on river flows, so they’re hesitant to spill a single drop.
by Heather Hansman, Medium | Read more:
Image: French Lake Dam fish ladder, Wichita Mountains Wildlife Refuge, Oklahoma. Flickr/lsmith2010
