Work to be conducted at the facility will include: dewatering of the surface and subsurface levels of the dam embankment foundation; excavating and placing of new dam embankment fill material; constructing 8016m of cement-bentonite cutoff wall to intercept seepage; and installing new foundation drains. The on-site work is expected to commence in June 2008 and be completed by November 2009.
In November 2006, USBR and Weber Basin Water Conservancy District (WBWCD) personnel observed between 100 and 150 gallons per minute of seepage just downstream of the dam. It was evident that a portion of the dam’s foundation had eroded, leaving a small number of sinkholes (0.6 to 1.5m in diameter) near the toe of the dam.
USBR, in cooperation with the WBWCD, acted immediately to stem the flow of soil and water from moving through the dam’s foundation. Sand, gravel, and other earthen materials were applied to key locations near the dam, and the reservoir was drawn down to a safe level.
USBR performed extensive geologic investigations at the dam throughout most of 2007, and in January 2008, a Corrective Action Study produced an alternative which called for the construction of a new five-mile cement/bentonite cutoff wall through a portion of the dam’s profile.
A.V. Watkins Dam is a U-shaped, zoned earth fill dam approximately 23km long with a structural height of 11m. The reservoir, named Willard Bay, has a capacity of 215,120 acre feet and a surface area of approximately 10,000 acres. Portions of the present embankment were constructed in 1955, 1964, and 1989, and were founded on compressible lakebed sediments of the Great Salt Lake.
‘Reclamation’s commitment to dam safety continues with the award of this contract as improvements to the dam embankment foundation and foundation drains will help to ensure the structural integrity and longevity of the A.V. Watkins Dam and Willard Bay storage facility,’ said Reclamation Commissioner Robert W. Johnson.
