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By Joe Block 

Two-year construction project begins at Prairie du Sac Dam


June 28, 2018

Joe Block

The Prairie du Sac Dam releases water after heavy rains last week. The two-year construction project will begin by closing the gates in the foreground. Temporary dams will be installed and each gate will be lifted.

Alliant Energy has plans to update the Prairie du Sac dam with a project expected to be completed by the fall of 2020.

The dam sits on a foundation of several thousand wood pilings, driven into the sandy river bottom. The wood pilings have proven to be extremely durable through the 107-year history of the dam. However, times of low water expose the uppermost part of the pilings to the air. As long as the pilings remain submerged, they won't rot. When periodically exposed to air, they can weaken.

There is jo short-term issue with the pilings. Alliant is looking into the future to maintain the integrity of the pilings.

The upgrade is focused on the spillway's foundation. Roughly ten gates will be closed per summer. Workers from Nicholson Construction will work from barges anchored over the spillway and on the spillway structure. They will be installing roughly 1,000 micropiles, 7-inch diameter high-capacity deep foundation elements. They are composed of high-strength steel casing, rebar, and grout. Piles will be driven vertically into the downstream part of the spillway, diagonally into the structure, and vertically just below the gates.

Worker will install temporary structures to hold back water during construction. This will allow them to lift the affected gates to access the full spillway.

Joe Block

Inside and outside the 100-year powerhouse at the Prairie du Sac Dam

The construction won't affect residents, except for a temporary closure of the access road for a few days each spring and fall to bring in the construction barges. Construction will be limited to the daylight hours.

Amanda Blank, site manager for the Prairie du Sac and Kilbourn dam, provided a tour of the dam and powerhouse to those present, and explained the project. The dam has been updated with new technology over the years to meet energy needs. "We need to keep the Lake Wisconsin with 7 inches of a certain level," she explained. The gates are raised and lowered with a crane, which rolls on railroad tracks on the spillway. She provided a walkthrough of the powerhouse, which stays warm due to the operation of the turbines and generators.

Alliant provides electric service to 470,000 customers in central and southern Wisconsin. More information about the project can be found at alliantenergy/PDSprojects.


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