After 13 in. of rain fell on south-central Wisconsin in three days during early June, 2008, an embankment along Lake Delton gave way, unleashing a raging torrent of water that drained the 600-million-gallon lake dry in just a few hours.

Reconstruction of CTH A and Refilling of Lake Delton
Reconstruction of CTH A and Refilling of Lake Delton

Sauk County Hwy. A, which ran atop the failed embankment, was also washed away in the flood.

Tourism brings 1.5 million visitors and an estimated $1-billion to the Wisconsin Dells area each year. With the 2008 summer tourist season washed out, lakeside resorts and nearby businesses desperately needed the highway and lake to be back in shape by the summer of 2009.

Outstanding cooperation between the federal government, state agencies, local governments, engineering companies, and contractors enabled the team to get funding, design solutions, address environmental needs, get permits, build a stronger new embankment, replace the road, upgrade the dam that controls lake level, and start refilling Lake Delton in just 180 days—while meeting all regulatory requirements.

Shortly after the disaster happened in June, 2008, County Hwy. A was redesignated as a state highway so the project could use federal emergency funding.

By late July, the new embankment and highway were designed, and the Dell Creek Dam was being upgraded. By late August, contracts to build the new embankment and highway had been awarded.

Construction started in early September, and by early December the $5-million design-build project was complete, and Lake Delton was being refilled.

Lake Delton’s new embankment is the only water-retaining sand embankment of its kind in the state. Its waterproof bentonite slurry wall reaches down more than 120 ft and seals to the underlying sandstone, preventing lake-water seepage.

It has two different top elevations. The lake side is high enough to prevent water from overtopping. The side that carries the highway was reconstructed at its previous elevation to keep the road in line with adjacent properties and minimize road-reconstruction cost.

Key Players

Owner: Sauk County, Wis.; Village of Lake Delton, Wis.; Wisconsin Dept. of Transportation, Madison, Wis.
General Contractor: CTH A: Hoffman Construction, Black River Falls, Wis.; Dell Creek Dam: Staab Construction, Marshfield, Wis.
Design Firms: Mead & Hunt Inc., Madison, Wis.; MSA Professional Services, Baraboo, Wis.

Its slopes were restored by bringing in fill, and its sides were armored with heavy riprap.

Using locally available materials lowered costs, sped up construction, and produced a strong, low-maintenance embankment.

Improvements to the Dell Creek Dam’s base, sluiceway and spillways have made it more stable and boosted its discharge capacity from 1,500 cu ft per second to 6,100 cu ft per second. It can now handle an event twice the size of the one that caused the problem in 2008.