By DAVID SMITH/ecoRI News contributor
WESTERLY, R.I. — Work to remove the White Rock Dam on the Pawcatuck River and build a new 70- to 90-foot-wide river channel below it should begin in July 2015 and be completed by October.
Bids for the work are being sought this month and a contract should be awarded in early January, according to Scott Comings, associate director of the Rhode Island Chapter of The Nature Conservancy. His organization is overseeing the project, along with a host of partners.
The plan calls for removal of the 112-foot-wide dam deemed to be in poor condition and the creation of an almost 1,300-foot-long channel below it to reconnect the river. The waterway now flows down a granite-walled canal on the Rhode Island side of the river that once fed a nearby mill. The upstream mouth of that canal will be blocked and the canal will remain a dry river bed most of the year. Its granite walls, considered a historic fixture, will remain intact.
It will be designed so that a berm in front of the canal could be crested during flood conditions to allow more water downstream, to reduce the chance of upstream flooding. The height of that berm is still in the design phase.
The water level below the dam will remain unchanged, according to Fuss & O’Neill Engineering firm associate Nils Wiberg, but upstream levels will drop.
Wiberg spoke at a Dec. 2 public hearing. There were about 55 people in attendance who asked a variety of questions about the dam removal’s impact on the river and recreational boating.
The engineer told the group that because the level of the river is so flat in that area, the water levels will drop from 2.5-3 feet at the dam, from 1.5-3 feet upstream at the Boom Bridge Road Bridge and up to a half-foot at Potter Hill Dam, more than a mile upstream.
Wiberg said tests on the sediment behind the dam show the usual levels of volatile organic compounds (VOCs) and metals expected to be found in a river system dotted with mills, but he noted that the levels are all below exposure levels established by the state Department of Environmental Management. That means the sediment will stay on site and be used to form the new river channel or distributed in the old canal and capped with rock.
If the sediment had exceeded exposure levels, Comings and Wiberg said it would have meant a costly mitigation process.
White Rock would be the third dam on the Pawcatuck River earmarked either for removal or modification. 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.
A total of $1.9 million in federal Sandy money is available for the White Rock Dam project, according to Comings. He said that the engineering contract is for $313,793, and will cover three phases of the dam’s removal and the first phase of study regarding Bradford Dam, about 6 miles upstream.
The owner of the White Rock Dam is Griswold Textile Print, 84 White Rock Road, just downstream of the structure. Comings said The Nature Conservancy and a legal representative of the company are working out details of the project. The company makes high-end decorative fabrics and employs 18 people. It doesn’t currently use the dam.
The first dam at the site was built in 1770 and was timber and rock crib construction. Subsequent structures were built over the years, said Wiberg, until it was washed out in the flooding associated with the Hurricane of 1938. The existing cement dam was built in 1940, he said.
All of the structures were designed to hold back water to feed the granite-stoned sluiceway adjacent to it. The water flow was once used to power the historic mill. While Griswold Textile formed in 1937, the building it occupies is much older.
Wiberg said the canal suffered a breach in the 1960s, resulting in the water flowing back into the river below the dam. Otherwise the water would have just flowed along the canal and discharged further downstream. Aerial photos from the 1930s show the existence of a gate at the mouth of the canal and footbridge across it. Those features have been lost.
Comings said the goal of all these projects is for better river connectivity. Fish are sometimes unable to swim up the sluiceway/ “It is a barrier (to fish) the majority of the year,” he said.
Bradford Dam has a fish ladder that was improved several years ago. The entrance to the ladder was changed to enable fish to find it easier. But Comings said, “There are some things we could improve in Bradford.”
It’s because the dams in Bradford and Potter Hill have fish ladders that the White Rock Dam was given priority.
The state is currently raising and stocking herring in Worden’s Pond and Watchaug Pond in Charlestown. The hope is to imprint the fish born in those ponds. After they swim downstream to the sea to mature, it’s hoped they would return to spawn in 2016 and restart a cycle that was lost years ago because of damed-off waters.
During construction, access to White Rock Dam is expected to be via the Cherenzia Company’s property. Cofferdams will be built above and below the dam to dewater it. The canal will be used to carry the water around the site.
Wiberg said the new channel will not be straight, but will meander and have rock features to slow the water and provide resting places for fish as they move upstream.
Several people at the recent hearing questioned the impact on recreational boaters. Wiberg said a portage path will be available during construction to accommodate boaters. Details on how that will work haven’t been finalized.
While water levels will drop in the area, project officials say the flows should be adequate for fish migration during the spring.