“All those dams were built to power
mills during the Industrial Revolution, but the mills aren’t in operation any
more and the dams no longer serve an industrial function,” said Scott
Comings,
associate director of the Rhode Island office of The Nature Conservancy, which
is a partner in several dam removal projects. “Dam removal is beneficial for
flood abatement, it reduces the risk of dam failure, and reconnecting the river
is important for target fish species like river herring and shad.”
Bradford Dam prior to removal (Ayla Fox) |
The Pawcatuck River has been the
main focus of dam removal efforts in the region for several years. The White
Rock dam – the first obstruction that fish encounter as they try to make their
way upriver – was removed in 2015. The Potter Hill dam, a few miles further
upstream, was left in place, but improvements were made to its fish ladder in
2016 after sediment build-up around the ladder created what Comings called a
reverse eddy, which spun the fish around and directed them away from the
ladder.
The next dam on the Pawcatuck, the
Bradford dam, was removed last year in a six-month project that involved
construction of a temporary bypass channel to divert water around the dam,
demolition of the dam, and the repositioning of hundreds of boulders into the
river to create a series of step-like weirs and pools to enable fish to swim
upstream. It also allows canoes and kayaks to navigate the waterway safely without
portaging and reduces the risk of upstream flooding.
“Connectivity is the golden word in
this project,” Comings said. “By reconnecting the river, everything that
depends on the river will benefit – not just the fish, but freshwater mussels,
mammals, reptiles, birds and amphibians, too.”
The next dam to be removed in South
County is in North Kingstown adjacent to the Shady Lea Mill on the Mattatuxet
River. The former textile mill is now being used as artist studios. Following
the 2010 floods, the state inspected the dam and deemed it a high hazard, which
increased the liability on the dam’s owner and required preparation of an
emergency action plan. The owner ultimately decided to have the dam removed,
and she is working with Save the Bay to complete the project this year.
“We’re always looking for good
habitat restoration sites,” said Rachel Calabro, Save the Bay’s Riverkeeper and
the coordinator of the Shady Lea project. “There’s a large fish run just
downstream at the Gilbert Stuart Museum, and this will open up another half
mile of the river for herring, eels and trout.”
Work began last October, when a section in the
middle of the dam was removed to lower the water level behind the dam so the
sediments could dry out. It also allowed archaeologists to examine and
photograph the historic dam, which was found to have been originally
constructed of fieldstone in the 1800s and later capped with cement.
This spring and summer, contractors will remove
the sediments, which have already been tested and found to be free of
contaminants, and then the spillway will be dismantled.
“We can already see that the stones are really
loose, so I know when we go in to remove it, the dam will come down in a day,”
said Calabro. “Some of those stones will be placed in the channel below the dam
to create pools and make riffles in the stream for the fish to navigate. That’s
the finesse part of a habitat restoration project like this.”
Once the dam is removed, Calabro said that native
plants will sprout to revegetate the site.
“We’ll let the river naturally find its channel,
and we’ll end up with a nice stream running through a vegetated wetland,”
Calabro said.
Save the Bay will use this project as a showcase
of dam removal techniques to encourage other private dam owners to undertake
similar efforts to remove their liabilities and restore habitat.
“We’re not just interested in getting fish from
point A to point B,” Calabro said. “We want native species to be able to
migrate and also have better water quality, better dissolved oxygen, and the
other things that happen when you remove a dam. We’re always looking for
opportunities to improve stream health, which also improves resilience by
removing vulnerable infrastructure.”
Not every dam in the region can or
should be removed, however. Some deserve to be protected for their historic
attributes, for aesthetic reasons, or because there are alternatives to
removal.
“Every site is different,” said
Andres Aveledo, a conservation engineer for The Nature Conservancy and the
Rhode Island Department of Environmental Management. “The best conservation
alternative is through removal of the dam, but we sometimes select alternative
approaches because stakeholders want the impoundment to remain.”
The dam on the Saugatucket River
near Main Street in Wakefield, for instance, is on the state’s list of historic
places, and the town of South Kingstown did not want to lose its attractive
waterfall. Yet the site’s fish ladder, which was built in the 1960s, was not
working. So in 2016 the fish ladder was re-engineered to ensure more herring
make it over the dam and into Indian Lake.
A similar effort is planned this
year at the 12-foot dam at the Palisades Mill Complex in Peace Dale, enabling
fish to swim even further up the Saugatucket.
And in Charlestown, fish now have
better access to Factory Pond from Green Hill Pond and the Charlestown
Breachway, thanks to an aluminum device called a steep pass that was installed
in 2017 to help fish surmount the modest private dam on Factory Brook.
“That little run can now support
about 20,000 river herring,” said Aveledo. “That’s a lot of bang for our buck.”
No comments:
Post a Comment