A cross-country road trip from Wyoming to Wisconsin last June gave plenty of windshield time for the mind to wander between “how much longer?” yelling from the backseat rider. As we crossed the Missouri River near Chamberlain, South Dakota, I recalled vivid stories from Lewis & Clark paddling and pulling their loaded boats up river in what looked drastically different 220 years ago from the four-lane highway and multiple bridge crossings that exist there today. While it was tough slogging for human navigation upstream in 1804, fish undoubtedly had it easier than today’s world where their routes have been dammed, fragmented, diverted and dried making passage up, down and around difficult — if not impossible. 

In simplest terms, fish passage allows the free movement of fish upstream and downstream to access spawning areas, thermal refuge, escape predation and meet other life cycle needs by removing or providing detours around barriers such as dams. Biologists have long recognized the potential limitations imposed by man-made, riverine structures on fish communities and have seen the effects of fish loss to diversions, However, only recently has there been widespread interest and ability to address fish passage issues. Wyoming has about 20,000 miles of perennial streams distributed among 14 major hydrologic basins, has 49 native fish species and 29 introduced fish species. For many fish species, long-term population viability depends on access and movement up and downstream.

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Construction of a rock ramp can be a solution for fish passage at irrigation diversions. (WGFD photo)

When one pictures fish passage they likely paint a scene with schools of salmon leaving the ocean to find small tributaries where they hatched years ago to leave their offspring. Wyoming also has fish that move many miles each year seeking small streams to lay their progeny, though skipping the ocean detour. Finding that perfect spawning habitat requires connectivity of streams. When connected, many trout species including cutthroat, rainbow and brown have been recorded moving at least 30-70 miles annually in Wyoming. Increasing movement opportunities is a key goal of the Wyoming Game and Fish Department’s Statewide Habitat Plan, and the department collaborates with multiple partners on various project types. 

Road crossing remedies

It does not take many miles of driving Wyoming’s roadways before you come across a stream crossing. Where bridges exist there is virtually zero impact on fish passage, but many culverts can be obstacles, especially undersized culverts.

Undersized culverts can convey water successfully under the roadway, but they neglect stream function and aquatic life. They operate like a fire hose at high flows causing extreme velocities within the culvert that leads to excessive erosion downstream of the outlet that frequently leaves the culvert perched above the stream. Fish struggle moving past such crossings, but solutions include replacing with a bridge or a larger structure that uses the natural streambed as the bottom, building a streambed within the culvert, installing baffles to retain sediment and slow water velocities or substitute a low-water crossing.

Diversion rehab

Agriculture in Wyoming depends on the countless miles of ditches, canals and extensive infrastructure used to provide water from rivers. Irrigation diversions use a variety of materials including concrete, rocks, telephone poles, old tires and other items. As these structures work to divert flows, however, they can deter fish passage. They also require constant maintenance and can alter stream function — potentially leading to instability of the channel and causing additional maintenance needs or loss of the diversion. 

Solutions at irrigation diversions have included fish ladders, grouted rock ramps, rock weirs, engineered riffles, a separate fish-way channel and other variations of these structures. Each site is unique and requires its own design in order to match the stream characteristics, and meet water-right demands and passage needs of the fish species. 

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Baffles with this culvert in the Hoback area in western Wyoming reduce water velocity and increase water depths through the structure. (WGFD photo)

Technical fish ladders are used at larger dams and use a sloping, concrete floor and series of pillars that provide resting pools and velocity breaks as fish make the climb. 

Bypass channel is a smaller channel that uses various sized rocks to connect the stream around a diversion structure. 

Rock ramps use concrete to secure rocks of various sizes in place at specific distances. These structures are typically steeper, yet stable and improve passage by removing vertical jumps, slowing water velocities and providing many small resting pools. 

Engineered riffle Large rocks are used to build several channel-spanning weirs to simulate a natural riffle and gradually step a stream down over several structures versus one large structure.

Roughened channel A roughened channel is a mix of concepts including rock ramp and engineered riffle that occupies the entire channel width at a specific length. These are less steep than rock ramps and use a specific mix of rock to lock itself together. Weirs are sometimes used at the upstream and downstream ends.

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Fish screens, like this one on Bear Creek in the Lander Region, keeps fish from entering areas of irrigation. (WGFD photo)

Fish screens

These keep fish from entering the irrigation ditch network and/or return them back to the river from irrigation infrastructure. Screens are usually placed in the irrigation ditch behind the headgate. Unlike other remedies that focus on upstream passage, screens typically assist with safe downstream passage. There are many types and configurations and Wyoming has close to 40 operating statewide. 

— Nick Scribner is the fish passage coordinator for the Wyoming Game and Fish Department.