Pilot Shoreline Resilience Project at Piermont Marsh

To help prevent erosion at the edge of Piermont Marsh, we are piloting a stabilization project that will protect the shoreline from waves, boat wakes, and ice scour. 

Resilience at Piermont Marsh

Piermont Marsh is extremely unique among the Hudson River Estuary’s intertidal habitats. Encompassing 278 acres, it is the Hudson River Estuary’s largest brackish tidal marsh, which provides incredibly important habitat for a variety of native plants and wildlife that thrive at the confluence of freshwater and saltwater. Because of its proximity to the Village of Piermont, the Marsh also plays an important role in sheltering the neighboring community from storm waves and debris. Marsh managers and community residents have a strong shared interest in protecting and managing the marsh so that it exists well into the future.

What is Marsh Resilience?

Marsh resilience refers to a marsh’s ability to persist when faced with various stressors, like sea level rise, changing temperatures and salinities, and storms. Resilience is influenced by a complex interaction of various factors. We know that marshes are better able to adapt to changing conditions when they:

  • Are protected from erosion. Erosion caused by waves, boat wakes, and ice scour has the potential to degrade marsh edges.
  • Have adequate sediment supply. Healthy marshes are actually able to grow by accreting, or accumulating, sediment on the marsh surface over time. The ability of a marsh to accrete sediment can help compensate for losses due to sea level rise.
  • Have access to landward migration pathways. As climate change causes sea level rise, marshes adapt by migrating landward if there is room to do so. Since Piermont Marsh abuts the steep topography of Tallman Mountain, there is little opportunity for landward migration.

Obstacles to Resilience

Along the edge of Piermont Marsh, erosion caused by waves, boat wakes, and ice scour is eating away at the shoreline in a way that threatens its longevity.

How we know: Monitoring at the edge of Piermont Marsh

  •  Aerial photographs have revealed that the shoreline has retreated at least 50 feet since the 1920s.
  • On-the-ground measurements of erosion rates and vegetation changes has shown that the marsh has retreated about 10 inches from 2020-2021.
  • Light Detection and Ranging (LiDAR), which is used to study the three-dimensional shape of the shoreline, has identified areas where erosion appears to be more actively occurring.  For more information, see the LiDAR acquisition report linked here.
  • Modeling has been used to characterize wave energy along the marsh edge and identify areas subject to more intense wave action. See the report linked here. 

The Plan 

Because Piermont is such a critically important marsh, we developed a pilot project to be implemented in the summer of 2022 that aims to reduce erosion and marsh loss by:

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Reducing the wave energy reaching the shoreline

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Promoting sediment accretion

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Increasing critical lower marsh habitat to provide additional wave buffering for the Village

The pilot project involves installing two intertidal sills along a 275-foot stretch of particularly vulnerable shoreline. Made of marine-grade concrete oyster castles, these sills will help absorb wave energy coming towards the shoreline. The design will be supplemented with stabilizing coir logs, which are made of compressed coconut fiber. Additional plantings, focused on smooth cordgrass (Spartina alterniflora), will help expand important lower marsh habitat.

Interlocking oyster castles will be the building blocks for the intertidal sills. 

Coir logs made of compressed coconut fiber will provide structural support and substrate for native plant growth.

The root systems of Smooth cordgrass (Spartina alterniflora) will strengthen the shoreline over time.

Selecting a Site

Long-term monitoring efforts at Piermont identified one particularly vulnerable area along the marsh edge. This narrow stretch of shoreline separates an oxbow on the Crumkill Creek from the Hudson River. If this area were to erode away, the confluence of the Crumkill Creek and Hudson River would shift north. Such a drastic change to the flow pattern could destabilize the marsh and likely lead to even more extreme erosion. The pilot project aims to increase the stability of this area to prevent this chain of events.

Community Involvement

Piermont community residents are strong advocates for the Marsh, and their partnership has been crucial to the development of this pilot project. Click below to view recordings of community meetings pertaining to this project:

If you are interested in volunteering with us or have any questions, please contact us.

 

What’s Next?

After the project is completed, we will continue to closely monitor erosion rates, sediment accretion, vegetation, and the structural stability of the materials, to evaluate whether and how the project meets our objectives. The results will help us understand how we might expand to stabilize other sections of the shoreline at Piermont Marsh and other Hudson River marshes.