The U.S. Army Corps of Engineers' schedule to reconstruct Intake Diversion Dam on the Yellowstone River has been delayed as the agency refines its design.

“We're trying to get the most benefit for the outlay of the taxpayers' dollars,” said John Hartley, project manager for the Corps.

The dam, located 16 miles downstream of Glendive, provides a popular spring fishery for paddlefish.

The project is meant to ensure the survival of pallid sturgeon, an endangered species that no longer naturally reproduces in the upper Missouri and Yellowstone rivers. Only 125 of the older native fish are found in the drainages, while others have been stocked to ensure the species' survival.

Corps' officials had hoped to begin work this fall on the north side of the dam by creating a rock ramp. To create the ramp, the old dam, built in 1905, would be left in place while an estimated 119,000 tons of large rock would be added to the riverbed to reduce the gradient of the stream, making it easier for pallid sturgeon and other fish to swim upstream.

The south side of the ramp would be the final phase of an estimated two-and-a-half-year project. The Corps projected the entire ramp's cost at $13.5 million. Hartley had no estimate of how that figure may change.

“Work continues and has not been halted on the project,” Robert Matya, chief of the Civil Works Branch at the Omaha District, said in a statement.

While the dam work has been delayed, construction that started this fall on a new headworks and fish screens on the Yellowstone Irrigation Project canal is progressing and on schedule for completion in March 2012, Hartley said.

The headworks and fish screens are the first phase of the $38.8 million project. That work alone is projected to cost $18.2 million.

The new screen and headworks should substantially cut the number of fish that die in the canal each year — estimated at more than a half-million.

The other $7.1 million was allocated for noncontract costs, which includes all planning such as environmental compliance, design and computer modeling and construction supervision and administration costs.

The old dam is a rock and timber structure that stretches 700 feet across the river and is 12 feet high.

By modifying the dam, fisheries biologists believe pallid sturgeon will use the additional 165 miles of the Yellowstone River above the dam for spawning. That extra distance may allow newly hatched pallid larva enough time to mature as they drift before entering Lake Sakakawea, where it is believed they now die in the stagnant water or are eaten by other fish.

The Corps is the lead agency for the project but is working with the Bureau of Reclamation, U.S. Fish and Wildlife Service, Environmental Protection Agency and the state of Montana.

“Despite the delay in the design for fish passage, the federal agencies remain committed to finding a solution that meets all federal laws and regulations and ensures the continued conveyance of water for Eastern Montana irrigators,” Matya said.

Contact Brett French at french@billingsgazette.com or at 657-1387.

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Contact Brett French at french@billingsgazette.com or at 657-1387.