Repairs at A.V. Watkins Dam - Northern Utah

Current Status

A.V. Watkins Dam - cement-bentonite
cutoff wall construction

Reclamation performed extensive geologic investigations at the dam throughout most of 2007 to collect information and design a permanent fix. In January 2008, a Corrective Action Study outlined an alternative for constructing a five-mile cement-bentonite cutoff wall through a portion of the dam's profile. Once this alternative was cleared by the Office of Management and Budget in March 2008, a $17.4 million contract was awarded to Geo-Solutions Inc., of New Kensington, PA, for the repair work. Geo-Solutions, along with subcontractor Nordic Industries, began work on constructing the cement-bentonite wall on July 21, 2008. The work is expected to take 12-18 months to complete, with a final construction milestone target of November 2009.

The underground cutoff wall will extend below the dam to to intercept seepage and prevent it from moving under the dam. This cutoff wall will be constructed for the entire length of the southeast side of the dam and new foundation drains will be installed to ensure the long-term structural integrity of A.V. Watkins Dam. Once construction of the cutoff wall is complete, the reservoir will begin to refill.

Background

On the afternoon of November 13, 2006, a land-owner neighboring the 14.5-mile long A.V. Watkins Dam north of Ogden, Utah, made an interesting and important observation. Serious seepage was occurring on the south eastern side of the dam. A.V. Watkins Dam is a U-shaped, zoned earthfill dam approximately 36 feet high, that impounds Willard Bay Reservoir. Immediately after the problem was reported, senior dam safety specialists and managers from Reclamation and the Weber Basin Water Conservancy District (WBWCD) were on-site assessing the problem and temporary repair work began that evening.

The seepage, which was occurring at a rate of approximately 100 – 150 gallons per minute through the downstream toe of the dam, could have resulted in a significant uncontrolled release of water from the reservoir, constituting a failure of the dam. Prompt response by both Reclamation and WBWCD prevented this from happening and the immediate threat was eliminated. In addition, Reclamation and WBWCD immediately put into place an emergency action plan that allowed officials of both agencies to follow established processes including notification of Box Elder County and Weber County emergency officials.

The emergency remedial actions undertaken at the dam consist of construction of upstream and downstream berms, including a sand filter and gravel blanket on the downstream slope to prevent additional soil from being moved out of the foundation and to stabilize the area from further erosion. In addition, the reservoir level was drawn down and the area placed under continuous monitoring and evaluation.   

At the time the seepage was noticed, Willard Bay Reservoir was approximately 80 percent full, storing about 175,000 acre-feet of water. The reservoir level was lowered by releasing water through the outlet works into the Great Salt Lake and via pumps temporarily installed by Reclamation. Following the draw-down, engineers and geologists were able to inspect the face of the dam and seepage-prone areas.

Inspection of the dam revealed an initial area of concern approximately 150 feet wide where piping under the dam embankment resulted in erosion of foundation materials and numerous sinkholes. The sinkholes ranged from two to five feet in diameter and were located between the toe of the dam and the South Drain Canal.

05/28/08 news release
03/13/07 news release

For more information contact:

Brandt Demars
Bureau of Reclamation, Provo Area Office
302 East 1860 South
Provo, Utah 84606
801-379-1284
bdemars@uc.usbr.gov