Hither Creek Salt Marsh Overwash Monitoring

NCF is involved in many pilot research projects to examine how simple restoration techniques can help increase ecological health and provide increased coastal resilience and stability. One of these pilot restorations is a simple dune building and stabilization project in Madaket and coordinated with the Town of Nantucket Natural Resources Department with funding from the Madaket Conservation Association.

In October 2017, a significant storm that caused high storm surge and large surf on the southern shore of Nantucket caused erosion of a dune system at the southern end of Hither Creek, near Millie’s Bridge. The storm eroded the dunes, moving the sand into Hither Creek, drowning the head of the creek and smothering extensive shrub wetlands and salt marshes. Following the storm, a large smooth sand overwash area with very low dunes separating Hither Creek from the Atlantic ocean with no salt marsh remaining. 

Salt marshes typically respond well to small amounts of sand deposition (~1-2 inches) but little research has documented salt marsh vegetation response to large sand depositions. Starting in 2017, the Foundation monitored the depth of sand, elevation and extent of the sand washover, and colonizing vegetation communities to determine if the salt marsh would recover and what steps we could take to improve resilience. Over 2 meters of sand covered the wetlands in some places. A sand fence placed at the top of the low dune in 2018 began trapping sand.

Four years after the Halloween 2017 storm, the dune system elevation has increased dramatically and native dune plants have colonized the sand overwash, trapping more sand and naturally building up dune resilience. Salt marsh plants persisted only where shallow sand was deposited, with the majority of the area dramatically and permanently altered. This newly created habitat has been used by a wide variety of wildlife from shorebirds (including a piping plover pair), fiddler crabs, and mating, egg-laying horseshoe crabs. Even a state-listed plant of special concern has moved in.

Faced with the dramatic conversion of this habitat, the Foundation and the TON NRD decided to increase the resilience and stability of the developing dune field. In spring 2021, volunteers from island conservation groups planted ~5000 plugs of beach grass (Ammophila brevigulata) and 280 seedlings of native woody shrubs. These plants will grow deep roots to stabilize the developing dune field and will trap sand above ground, raising up the dune elevation. Foundation staff will track the survival of these plants and impact on dune elevation and development over the next few years. This work will help us understand dune development and how simple restoration projects can help protect our shorelines. Storms of this intensity and impact are predicted to increase in the future due to the impacts of climate change and projects like this will help conservation groups and private homeowners alike have tools to respond.