CHATHAM – Addressing low-lying points at Outermost Harbor Marine and the adjacent Starfish Lane condominiums will provide the most effective flood protection for Little Beach, a new storm tide pathways study concludes.
“If you address those two, you've just tackled 78, 80 percent of your problem,” said the report's author, Mark Borrelli, a coastal geologist and director of the seafloor mapping program at the Center for Coastal Studies in Provincetown.
Four northeasters between January and March sent flood waters deep into the Little Beach neighborhood, the result of the opening of the Fool's Cut and the loss of protection previously provided by South Beach, Natural Resources Director Dr. Robert Duncanson told the board of selectmen Monday. While there was a lot of anecdotal evidence as to where the flooding was coming from, officials and neighborhood property owners wanted more specific information before pursuing potentially expensive mitigation. The Center for Coastal Studies completed a similar study of storm tide pathways in downtown Provincetown after flooding there, and town officials requested that Borrelli look at storm pathways at Little Beach as part of a wider, $250,000 study the Center is doing of coastal changes from Pleasant Bay to Morris Island.
Most of Little Beach is privately owned, and a newly formed property owners association is working on a comprehensive flood protection plan for the neighborhood, Duncanson said.
“Hopefully this will provide them with another tool they can use to really refine what their response may be,” he said.
Using three-dimensional and GIS mapping tools, Borrelli and his team found 36 storm tide pathways in the Little Beach area. The area from the southwest of the marina to the condos are where flooding occurs during less powerful storms, such as the northeaster two weeks ago. But once flood waters get to the 7.5 foot elevation, eight more locations begin to flood, inundating much of the neighborhood because of its relatively flat topography.
Addressing those areas immediately surrounding the marina “saves you the most,” Borrelli said. “You've got to attack those five or six locations and you're in better shape.”
According to the report, the flat topography may require a “micro-regional” approach that focuses on “potential solutions to multiple pathways of similar elevation over a broad area.” A similar approach is recommended for the northwest side of Little Beach, where floodwaters from Stage Harbor could follow a pathway through a culvert underneath Morris Island Road.
During the storm two weeks ago, a plastic “Muscle Wall” protected the marina's office building but there wasn't time to deploy it along the boat ramp, and that's where stormwater came in and flooded the low lying areas, Duncanson said.
“It just reinforces the fact that this is the critical place,” he said. The marina owner plans to place the barrier along the boat ramp during the winter. In concert with a rebuilt dune in front of the condos, which helped minimize flooding in the recent storm, that should keep flooding to a minimum during minor storms, Duncanson said. But if there are storm events like last winter, “all bets are off. That was a lot higher and a lot longer duration” than the recent storm, which only lasted one high tide.
The study looked at flooding up to elevation nine, but FEMA flood levels for the neighborhood are at elevation 13, and it may be necessary to build shoreline protection to that height to qualify for grants, Duncanson said. The Little Beach property owners will have to work together with the town to develop and permit protection for the area, “and it's not going to be cheap,” he said. The marina will also likely have to raise its bulkhead to meet the elevation of shoreline protection to the north and south.
“The marina is still going to be the proverbial hole in the dike,” said Duncanson. “You can't put 13-foot dunes on both sides and then have the marina sitting there at a much lower elevation. That's not going to solve the problem.”
Finding the most effective way to do that is part of the larger shoreline study, he said.
The Little Beach storm tide pathways study can be viewed on the town's website.