Salt marshes are important coastal wetlands that form transition zones between land and sea, freshwater and saltwater. On Cape Cod 38% of historical salt marshes have been lost or degraded by human activities such as agriculture, mosquito ditching, and development.
One way for salt marshes to adapt to SLR and continue to function, will be to migrate landward and form new salt marsh as older salt marsh becomes inundated by rising ocean water. The migration potential is, in turn, determined by available undeveloped floodplain landward of the salt marsh and man-made and natural barriers such as coastal armoring, roads, buildings and land elevation. If salt marshes susceptible to SLR are not identified and the area upon which they could migrate landward is not protected, salt marshes and the valuable ecosystem services they provide will be lost.
In 2009 APCC began a pilot project to map the boundaries of the salt marshes located at Quivett Creek, Stony Brook and Namskaket Creek in Brewster, Massachusetts. Mapping was done along the low-high marsh boundary and marsh-border boundary to determine and document the current salt marsh boundaries and to assess the potential for the marshes to migrate inland in response to rising sea level.
Since that time a new analytical tool has been made available for the coastal areas of the Northeast. Light Detection And Ranging (LiDAR) is a detection system that works on the premise of radar, but uses light instead of microwaves or radio waves. LiDAR uses ultraviolet, visible or near infrared light which, when projected through a narrow laser beam, can map physical features with very high resolution. LiDAR provides accurate, high-resolution image for objects on the ground, resulting in a one meter resolution bare-earth digital elevation model (DEM). A bare-earth DEM is a three dimensional representation of the earth’s surface without buildings or vegetation.
This study will coordinate the GPS data gathered during the 2009 mapping of the salt marsh boundaries with the LiDAR data to determine accurate elevations at marsh boundaries, and to identify areas where salt marshes have the capability to migrate landward, from which recommendations for salt marsh preservation can be made. Thus providing a tool that can be used to develop conservation plans, create and restore wetlands, restore and manage other coastal ecosystem and watershed resources, and analyze the threats to and opportunities for conservation of coastal wetlands.
In order for the LiDAR data to be used, manipulations, visualization and filters have to be added. Elevation data will need to be calculated from the LiDAR data. This is beyond our in-office capabilities with GIS.
Three maps of the three salt marsh sites, each will include high/low marsh boundaries and marsh border boundaries, elevation from LiDAR data, topographic data if appropriate, location of physical barriers to marsh migration, areas upon which marsh migration will be able to occur.
The final report will summarize the findings with maps, elevation, acreage, parcel locations of where salt marsh migration can occur.
The town of Brewster is currently working on its Integrated Water Resources Management Plan (IWRMP). This mapping project dovetails nicely with the goals of the towns IWRMP by helping to identify and protect coastal habitats through strategic acquisition of open space, as it will identify salt marshes that may be at risk and offer solutions for protecting this invaluable resource. For example, if the land area upon which a marsh could migrate is currently without obstructions, the information provided by APCC will enable the town to develop a plan for conservation or acquisition to ensure protection of this natural resource. The maps and procedure for this project will serve as a model for other towns to incorporate into strategic, long-term sustainable plans to evaluate and protect current and future water resources. The maps and reports will be made available on ArcGIS online, on our website and will be provided to the town of Brewster.
The Summer 2020 session has finished. Sign up for notifications about future opportunities.
