By DAVID SMITH/ecoRI News contributor
WESTERLY, R.I. — The cofferdams, at the former White Rock Dam site on the Pawcatuck River, are scheduled to come down Oct. 13 and 14, signaling the closing weeks on a several-months-long dam removal project.
The downstream cofferdam, designed to keep water from flowing upstream into the work area, is scheduled to be removed Oct. 13 and the upstream cofferdam the following day.
Once that happens, the Pawcatuck River will flow freely in the area between Potter Hill and downtown Westerly. There had been a dam at the White Rock site since 1770. It was rebuilt several times over the centuries, and when the dam was washed away in the hurricane of 1938 it was rebuilt using concrete.
Work on preparing the riverbed below the former dam was completed last week by SumCo Eco-Contracting of Salem, Mass. A survey crew inspected the work Oct. 9.
The work remains on schedule and on budget, according to Scott Comings, an associate director with the Rhode Island Nature Conservancy, the leader of the project. The contract to remove 112-foot-wide concrete dam was awarded to SumCo in April for $710,869. A total of $1.9 million in federal Superstorm Sandy money was available for the project — $313,793 was spent on engineering the project and for a study regarding Bradford Dam, about six miles upstream.
The cofferdam was erected upriver of the old dam, to direct water down an adjacent sluiceway. That cofferdam dewatered the dam and allowed workers to sculpt the riverbed behind it. When the upstream cofferdam is removed, the water will flow into its newly sculpted riverbed and the water level will drop to its new level.
Work will then begin on building a berm across the entrance of the sluiceway that will be 16 feet higher than the river. The sluiceway will no longer have water running down it unless there is a flood.
When the old dam was removed, remnants of a “legacy” dam from 1888 were found, Comings said. The old timbers, which formed a crib filled with rocks to form the dam, were removed and washed. The Rhode Island Historic Preservation Commission measured and recorded the timbers and is going to compile a report about its findings.
As well as sculpting the riverbed, crews also will be working in the next few weeks on erosion control on each bank of the river. That work will include grading and placement of riprap and tree revetments.
White Rock is the fourth dam on the Pawcatuck River to be removed or modified. The effort is designed to improve fish passage on the 20-plus-mile waterway that stretches from Worden’s Pond in South Kingstown to Little Narragansett Bay in Westerly. The work also is expected to reduce flooding above the site.
About 15 miles upstream, the Kenyon Dam and Lower Shannock Falls Dam have been removed, while a fish ladder was built at historic Horseshoe Falls.