Creating a twisting, 3-mile-long channel around Intake Diversion Dam on the lower Yellowstone River to allow endangered pallid sturgeon and other native fish to swim around the dam would cost an estimated $58.9 million and the moving of more than a million cubic yards of dirt and gravel while adding hundreds of tons of rock to protect the work from flood waters, large chunks of ice and debris.
These details are found in the U.S. Army Corps of Engineers’ draft supplement to its 2010 environmental assessment released last week.
The funding would also include the construction of an $11 million concrete weir dam above the current rock structure to ensure the Lower Yellowstone Irrigation Project receives its required water allocation in its canals. It’s estimated the entire project would take two to three years to build.
Public comments are being accepted on the Corps’ proposal through May 1 and two meetings are scheduled later this month. A formal presentation is set for 6:30 p.m. followed by an open house on April 23 in Glendive at the Dawson County High School and on April 24 at Sidney High School.
The Corps had originally considered modifying the existing rock dam to allow fish passage, but the $90 million price tag proved prohibitive and engineers were worried that river ice would continually rearrange the structure. That’s when the Corps decided to pursue the side-channel option.
“From my perspective the Corps has done a pretty good job of tuning and tweaking their design to accommodate pallid sturgeon over a range of flows” in the bypass channel, said George Jordan, leader of the U.S. Fish and Wildlife Service’s pallid sturgeon recovery.
Jordan was one of several fisheries biologists working with the Corps’ engineers to try to design a side channel that would provide consistent yet slow enough water flows to lure the slow-swimming pallid sturgeon around the dam. Right now, the dam blocks the fish from moving further upstream.
Only 158 wild pallid sturgeon were estimated to still live in the Yellowstone and Missouri rivers above Lake Sakakawea in 2004.
Biologists believe that if pallid sturgeon can get upstream, the additional 165 miles of Yellowstone River habitat could ensure the fish’s larvae will survive. That’s something that hasn’t been documented since the Yellowstone and Missouri rivers were dammed in the early 1900s, leading to the fish’s decline. To ensure the fish doesn’t disappear, eggs have been taken from captured fish and hatched in captivity with the hatchery-born fish released into the river since 1998.
The pallid sturgeon is considered to be a relic of the dinosaur era. Fossils of the fish’s ancestors date back more than 70 million years.
“This supplemental EA results from an extensive, collaborative effort from the stakeholders and interested parties that have focused their energy on the goal of finding the most acceptable solution that will benefit the pallid sturgeon, the Lower Yellowstone Irrigation District and the local economy,” said Jerry Benock, Bureau of Reclamation project manager, in a statement.
Getting all of the state, federal and irrigation entities to come to an agreement on the work hasn’t been easy and most haven’t had a chance to review the 140-page document, including the Montana Department of Fish Wildlife and Parks.
“I’m glad to see the process moving ahead,” said Bruce Rich, fisheries chief for FWP.
The big question remaining, Jordan said, is whether Congress will approve funding for the project.
“Budget cuts and things like that make it hard to predict,” he said. “If they do make the appropriation, we could see something happen within the next five years.”
The side channel’s construction and the design that must be incorporated to make it appealing to pallid sturgeon is a first for the Corps of Engineers, making planning all the more difficult.
What the agency has proposed is excavating a winding side channel that would hold water year-round by diverting 10 to 17 percent of the main river’s flow. The entrance to the channel from downstream would be carved just below the dam through what’s known as Joe’s Island. Biologists believe building the downstream entrance closer to the dam would make it more appealing to fish moving upstream.
The bed of the bypass channel would be 40 feet wide, flaring out at the top to 150 to 250 feet wide. The slope of the channel bed would closely mimic the existing river. On the upstream end of the channel, the Corps is proposing the construction of a 6-foot thick concrete sill measuring 60 feet wide and 30 feet long to protect the inlet from erosion and ice damage.
Just to armor the bends in the side channel from erosion will require 65,000 tons of riprap. Another 64,000 tons of gravel 9 inches deep would be used to grade the channel’s slope to design requirements.
“They’ve put an impressive amount of financial resources and brainpower to account for a lot of these uncertainties,” Jordan said. “They’ve done a pretty stellar job.”
Because nothing quite like the bypass channel has been constructed, there are several unknowns.
One of the concerns is that there is no evidence of pallid sturgeon using such a long side channel. It’s also uncertain what toll the Yellowstone River will take on the structure during spring flooding and when large chunks of ice and debris are pushed into the channel.
The area below Intake Diversion Dam is a popular paddlefish spring snagging fishery. With the bypass channel, the fish may not stack up below the dam like they do now. The fish are a source of income for the Glendive Chamber of Commerce, which sells the paddlefish roe. But the congestion at the Intake fishing access site has created enforcement problems in the past.
On the positive side, if paddlefish do swim upstream, it would spread the fishery out and could even increase the paddlefish population if they find additional areas to spawn.
The channel would also provide a bypass for boaters around the dam.
Last year, irrigators expressed concerns that the new concrete weir dam could increase sedimentation and reduce the flow of water to the canal system, which supports a $26.5 million agricultural economy on nearly 400 area farms. The new dam would be built 40 feet upstream from the existing rock ramp and be raised about 1 foot higher.