A temporary dam, or cofferdam, holds back the Yahara River while workers make repairs to the Fourth Street Dam.
The multi-faceted rehabilitation project includes extensive concrete repair, replacing the gates which control the water levels and filling and reshaping the embankments.
Built during World War I, the Fourth Street Dam is undergoing a rehabilitation project designed to ensure the viability of the city landmark for generations to come.
Since mid-June, a construction crew from Marshfield-based Staab Construction has been working on the multi-faceted project, which includes replacing the two huge gates - called tainter gates - that control the water level behind the dam, replacing a third steel bulkhead or permanent gate in the dam and patching a significant amount of deteriorated concrete on and around the dam. The project also calls for extending a storm drain culvert adjacent to the dam, adding fill and reshaping the structure's embankments, and replacing the dam's old manual controls with motorized controls.
"The work has been going very, very well," project superintendent Troy Noth said last week. "As we got started, it was really obvious to us that this dam was definitely in need of repairs. A lot of the old concrete was weak and punky - we've replaced something like 400 square feet of concrete alone. It's a lot of work, but it's been going very well. I hope the public will be pleased when we're done."
Noth said although the project is a fair-sized job, it is not out of the ordinary for Staab, which has worked on much larger dam repair projects, including in Watertown and Necedah.
Although Staab's contract says the project does not have to be completed until October, Noth said the majority of the repair work will be completed by about Aug. 15. Refilling of the impoundment area behind the dam will begin shortly afterwards.
To prepare for the work, starting June 1 the gates holding back the water behind the Fourth Street Dam were opened to allow for a draw down of the approximately 82-acre impoundment area behind the dam, commonly known as the Mill Pond. The impoundment was drawn down at a rate of no more than six inches a day, so as not to create flooding downstream.
Owned by the City of Stoughton and located just upstream of the Fourth Street bridge, the project was approved last year by the Common Council following an inspection by the Mead and Hunt engineering firm in 2007. Mead and Hunt concluded that while the dam was in relatively good condition for its age, it still needed a number of repairs and upgrades to ensure its future viability.
After months of discussion, last year the city set aside up to $560,000 for dam repairs; 2009 was the earliest the city could put the money into its capital improvements budget.
Noth said so far his crew has not run into any major problems.
Of interest, he said, is the fact that for this job Staab is employing for the first time a new method of constructing a cofferdam, the watertight enclosure installed immediately upstream of the dam which exposes the bottom of the dam structure and allows for the repairs to be made.
For this job, he said, a subcontractor sunk a series of metal A-frame support structures perpendicular to and immediately behind the dam. After the A-frames were connected, a heavy rubber tarp was stretched across the A-frame and slowly lowered into the water to form a temporary dam.
"It saved us a lot of time and effort and it's held up really well," said Noth. "I think it's something we definitely will be looking at using again in the future."
Noth said the most difficult part of the project was "mucking out" the debris and sediment on the downstream side of the dam, where a large amount of new concrete was poured.
One of the more noticeable projects was the construction of a large new storm drain culvert on the south side of the dam. Previously, the storm drain emptied out into a long ditch that extended into the pool area immediately downstream of the dam. Over the years, storm water widened the ditch and eroded a large part of the embankment.
By extending the culvert and filling in the embankment, a large section of park-like area has been re-established south of the dam.
City officials believe the current dam was built about 1917. Before its construction, a series of earlier dams occupied the site, dating all the way back to 1847.
In the fall of that year, Stoughton founder Luke Stoughton built a small dam and sawmill on the site, one of the first steps he undertook in his efforts to give birth to the community that bears his name.
