Marsh Explorer

 

 

What is the Marsh Explorer app?

 

 

The Marsh Explorer analyzes and ranks the restoration potential of New Jersey’s Atlantic coast back-bay marshes based on the amount and size of linear ditching, marsh edge erosion, unvegetated marsh, and unused dredged lagoons.

Main functions:

  • The goal of this mapping is to provide a screening level tool for future on-the-ground review of NJ back-bay salt marshes that could potentially benefit from restoration either through the beneficial use of dredge material or other methods.
    • User selects an area of interest based on county
    • User selects a location based on 1 square mile grid, to obtain information on the following attributes within the grid:
      • Total marsh acreage
      • Acres of dredged lagoon
      • Acres of linear ditching
      • Acres of edge erosion
      • Ratio of vegetated to unvegetated marsh
      • % of unvegetated marsh
    • The user can rank the marsh grid based on individual or combined indicators to see how each area compares to other marsh locations for potential need of restoration.
    • Additional information on location of federal navigation channels, as well as, composition, and distribution of sediment types can be added to the map. This info enables the user to explore the feasibility of beneficially using dredged materials for marsh restoration in the area of interest.

A salt marsh peninsula acts as a natural breakwater protecting homes in West Wildwood, NJ. Photo Credit: Jim Wright, LightHawk

Who should use it?

The target audience for the Marsh Explorer includes state and federal resource managers, as well as, local and municipal stakeholders along New Jersey’s Atlantic coast who may be interested in planning a marsh restoration project using beneficially used dredged materials.

How does it work?

The Marsh Explorer ranks the condition of back bay marshes on New Jersey’s Atlantic coast by analyzing several indicators of marsh health: acres of linear ditching, acres of manmade but undeveloped dredge lagoons or borrow pits, acres of unvegetated vs. vegetated marsh areas, and acres of edge erosion.

The final product for the marsh condition analysis is a 1-mile square grid covering the back-bay marshes of Cape May, Atlantic, Burlington, Ocean and Monmouth Counties, that displays which areas are potentially most in need of salt marsh restoration. The grid is symbolized to show areas that rank highest using the combined metrics and in turn, have the highest potential of being an impacted marsh. The four-ranked metrics were not weighted due to an inability to assess which metric should be of higher or lower priority. Final ranking was calculated for all possible combinations of metrics. This allows the user to find impacted marshes that meet the requirements for specific restoration project types. The information can be used to identify where more in-depth assessments of marsh vulnerability, degradation, and need for restoration should occur.

The Marsh Explorer visualizes areas of salt marsh that have eroded between 1977 and 2012, along with other factors that indicate potential need for restoration (map: Little Egg Harbor, NJ)

Details on how each of the marsh condition metrics were calculated are below:

  • Marsh edge erosion (acres)
    • Marsh edge erosion is computed using the extent of the NJ Bureau of Tidelands claim line (TCL) compared to the extent of the NJ 2012 Land use Land cover (LU/LC). Erosional areas are defined by the TCL exceeding the LU/LC extent and quantified in total acres of marsh loss.
  • Undeveloped dredged lagoons (acres)
    • The dredged lagoons layer is identified from the NJ 2012 LU/LC and categorized into ‘developed’ or ‘undeveloped’ based on whether they were within 50ft of an urban area. Undeveloped dredged lagoons present opportunities for restoration.
  • Mosquito ditching (miles)
    • The mosquito ditching layer was acquired using the USGS’s National Hydrography dataset (high resolution). This parameter quantifies the total length of linear ditching and the density of linear ditches within a selected area.
  • Unvegetated marsh coverage (acres unvegetated/total acres)
    • The non-vegetated data layer was created to present the ratio of vegetated to non-vegetated coastal marshes using high-resolution orthophotographs and supervised image classification to classify each image pixel as either vegetated or unvegetated. The results are presented in total unvegetated acreage, and the ratio of unvegetated to vegetated acreage in the selected area.

Additional project feasibility data are included on:

  • USACE Waterway Network – Federal navigational channels in New Jersey
    • These are channels managed by USACE that frequently require maintenance dredging and which could provide a needed supply of material for salt marsh restoration through beneficial use.
  • Sediment Core Sample Data (Source: Stockton U. CRC). Looks at % of sand, silt, and/or clay at sample sites across the back bays of New Jersey.
    • The composition of material needing to be dredged within navigable waterways is an important factor in determining what type of restoration technique might be possible.
  • Sediment Distribution (Source: Stockton U. CRC 2006) NJ Bay Floor Sediment Classification. Looks at the distribution of sediment within the back bays.)

More detailed information on the methods used can be found in the following document: http://maps.coastalresilience.org/newjersey/plugins/marsh-explorer/MarshExplorerMethods.pdf

Where is it being used?

The Marsh Explorer is new and the New Jersey team is in the process of doing engagement with the community of coastal management stakeholders who we hope will utilize the tool. Their goal is to create a process for local planning of beneficial use projects that includes the Marsh Explorer as a first step in helping communities examine the condition of their marshes. It’s important to get communities thinking about the health of the marsh as a first step in determining the necessity and feasibility of these complex multi-year projects.

Who helped develop it?

Project partners include: