Federal and state officials will gather Monday to dedicate the new irrigation headworks for the Lower Yellowstone Project north of Glendive, at least five years in the making.
“We have tested the screens, gates and structure and it is working well,” said James Brower, project manager for the irrigation district.
A dry spring prompted the district to open up the headgates about two weeks earlier than usual. The main canal was flowing at 950 cubic feet per second on Thursday. At full flow, the headgate can divert 1,374 cfs.
The new canal headworks and canal extension were built by Ames Construction Inc. from Aurora, Colo., for $19.3 million, just over the originally projected cost of $18.2 million. The company broke ground in August 2010 under a contract with the Army Corps of Engineers.
“We had some modifications that took it above budget,” said John Hartley, civil works project manager for the Corps.
One of the highlights of the new structure is that it holds the promise of greatly reducing the number of fish trapped in the irrigation system’s canals. Previously, a study by Montana Fish, Wildlife and Parks found that more than 500,000 fish of 36 species were trapped in the canal system as it drew water from the Yellowstone River.
“The number of fish being entrained into that structure was pretty amazing,” said Mike Backes, fisheries manager for FWP in Miles City.
With the intake structure’s fish screens, Backes said the river system should keep more fish — including pallid sturgeon, an endangered species — to recruit to adulthood.
The screens are fitted with internal and external brushes as well as pressure sensors that allow them to automatically clean themselves when dirty, Brower said.
“I’ve never seen a fish-screening system designed this well,” he said.
The large screened drums used to keep fish out can be damaged by trash and trees that the Yellowstone River carries during high water during spring runoff. To protect the drums, the irrigation managers can raise them out of the water until the risk subsides — essentially circumventing the fish-screening capabilities of the new structure. What effect that may have on fish entrainment is unknown, Backes said.
What to do?
While celebrating success on the completion of the construction, the Army Corps of Engineers is still wrestling with the other half of its project at the same site — how to allow fish passage around Intake Dam, which diverts water to the irrigation canal.
The dam rises 12-feet high and extends 700 feet across the entire Yellowstone River. In its original plan, the corps wanted to add rock below the dam area to create a gradual climb to allow endangered pallid sturgeon and other native fish to swim upstream. Another $13.5 million was devoted to building the graduated rock ramp with $7.1 million set aside for environmental compliance, design and computer modeling and construction supervision and administration costs for both projects.
But last year the corps abandoned the rock ramp after coming to the conclusion that the Yellowstone River’s dynamic flows and ice jams would not allow the ramp to work as planned. Now the corps is considering constructing a sidechannel around the dam to allow fish passage. Hartley said the work is still in the conceptual stage and a new environmental assessment must be prepared. He added that there were no cost estimates as yet for the sidechannel, but he said that it should be cheaper than the rock ramp.
FWP’s Backes said his agency is skeptical about the sidechannel.
“Our concern is how do you make that sustainable at different flow rates, especially at high water like we had last year?” he said.
The original diversion dam and intake structure was completed in 1910 to divert water from the lower Yellowstone River into irrigation canals for roughly 54,300 acres of farmland that mainly raises sugar beets and corn. The canal annually diverts about 327,000 acre feet of water into 79 miles of main canal and 400 miles of maintained ditches.
The 2010 environmental assessment for the canal headgate rebuild pegged operation and maintenance costs for irrigators rising from $139,000 a year to $272,000 with the new headworks. The environmental assessment estimated the costs for the system’s roughly 500 irrigators rising from $2.38 per irrigated acre to $4.67.
Bower said there will be no direct cost to the irrigators initially, as the Bureau of Reclamation will take over operation of the system for the first seven to eight years. After that, the headworks would be turned over to the irrigation district.
“My understanding is there won’t be any additional costs to us,” Brower said.
The project was constructed under the 2007 Water Resources Development Act, which authorizes the corps to use funding from the Missouri River Recovery and Mitigation program.