Posted on July 9, 2019
The failed Sesuit Creek restoration project provides a sobering reminder of what can go wrong with a Cape Cod salt marsh restoration. Not only did the project produce serious and costly downstream sedimentation problems, but it also degraded upstream wetlands.
In 2008, the “Sesuit Creek-Bridge Street Habitat Restoration Project” replaced a collapsing culvert with two 12-foot box culverts to permit free flow of seawater to the Sesuit Creek marsh upstream. Two years later, the Woods Hole Group prepared a waterways assets master plan for the town of Dennis, which reported that the town “raised concerns over shoaling and reduced navigability in the inner harbor area of Sesuit Harbor, especially in the vicinity of the public marina facilities.”
This concern was amplified by Paula and David Miller, longtime owners of a slip in the Sesuit inner harbor, who chronicled in a 2017 Cape Cod Times opinion piece that “within a few years of the ‘restoration’ we started to notice clogging mats of dead vegetation, accompanied by shallower depths and eroded banks.” “Boaters have suffered damage in the form of loss of services, worth tens of thousands of dollars, not to mention damage to hulls, engines and props,” the Millers said.
Bathymetry (water depth measurement) studies in 2004 and 2009, before and immediately after replacement of the Bridge Street culvert, showed depths similar to those in 1958, when dredging originally created the navigable inner harbor. However, sedimentation problems began to appear a couple of years after the new culverts were installed.
Eventually, in May 2018 the town of Dennis voted to appropriate more than $4 million to dredge Sesuit Harbor in its entirety. This project would include the inner harbor, which had not required dredging for 50 years before the Sesuit Creek tidal restoration. So Dennis taxpayers are now paying to mitigate harm resulting from this project.
Additional bad news has been heaped on ecological optimists who anticipated great things from increasing tidal flow in the Sesuit Creek floodplain. In 2008, celebrants at events marking completion of the Bridge Street culvert project spoke glowingly about restoring black ducks, short-tail sparrows, herring, rainbow smelt and American eels to Sesuit Creek.
However, once Mother Nature took over from human project managers, a very different reality emerged. The Millers observed in their 2017 newspaper narrative that “the salt marsh has not been able to restore itself.” “After nine years, the area is the picture of death,” they wrote. “Dead trees, denuded soil, eroded banks. The restoration has failed.”
Indeed, ecologists have been unable to figure out why saltwater flora has not replaced the freshwater vegetation that was killed off by the twice-daily inundation of salt water flowing through the Bridge Street culverts. Ecologists associated with the Association to Preserve Cape Cod have planted experimental plots of salt-tolerant marsh grass in the muck without much success.
Eleven years after completion of the 2008 Sesuit Creek “restoration,” ugly mudflats dominate the floodplain upstream from Bridge Street. Instead of restoring the salt marsh, the Sesuit Creek/Bridge Street project has degraded the wetlands, in addition to fouling the waterway downstream.
The area of wetlands affected by the failed Sesuit Creek salt marsh restoration is 57 acres, while that of the first phase of the proposed Herring River restoration project is about 570 acres. If so much could go so wrong with the relatively simple Sesuit Creek tidal restoration, prudent observers should ponder what harm could result from the proposed Herring River restoration project, which is 10 times as large and orders of magnitude more complex.
Source: capecodtimes.com
