Lower Yellowstone Diversion


This federal contract was for construction of a new diversion dam and the first portion of the new intake structure designed to improve the existing irrigation system to protect endangered pallid sturgeons. The environmentally conscious project included construction of an earthen cofferdam to separate the work area from the river during normal river flow periods, and allowed crews to excavate down to the bottom of the footing for the new structure. The dam is founded on 247 caissons, with a sheet pile cutoff wall.

The massive concrete foundations required special procedures and monitoring to keep the fresh concrete within specific temperature limits for proper curing during the extreme hot and cold fluctuations of year-round construction. After a 35-day project suspension due to the rise in water level from record-breaking river flows, crews compensated for the delay by working 12-hour shifts six days a week, and re-sequencing work activities to conduct work simultaneously at multiple locations.

Once the cofferdam was removed, crews completed the remainder of canal excavation and placed riprap behind the new structure. The high-pressure sluice gates and programming for the master control unit for the fish screens was also completed, along with the final work of field tests for the fish screen level sensors, testing of the screen controls and endurance testing the entire system.