Collecting high resolution LiDAR to support engineering planning at eight salt marsh sites
On an early April morning, after all the snow had melted and before marsh grasses had started to grow, three people met. Sam from ARE, Stephan from UNH and Rachel, former Stewardship Coordinator at the Reserve got together to collect detailed elevation and aerial imagery data of the Philbrick’s Pond site in North Hampton. This was one of eight sites that had been selected by coordinating with partners including NH Coastal Program, PREP, and TNC to see where restoration projects were being planned.
Collecting aerial imaging data by drone. Photo Credit: Rachel Stevens
A good knowledge of elevation is critical to designing salt marsh restoration projects that include techniques such as runneling and restoration of tidal flow. It is also essential to designing projects that aim to adapt to erosion or sea level rise such as living shorelines or facilitating marsh migration by using techniques such as lowering the elevation of the adjacent upland or increasing tidal flow into the terrestrial border.
Ecotone boundaries, that is where two habitats interface, are determined by marsh surface height and consequently exposure to tidal flooding in salt marshes. An earlier study done by Great Bay NERR found that the entire high marsh occurred in an elevation range of just 4.3 inches. The high marsh is where saltmarsh sparrows nest and mummichogs, an important bait fish, feed. It is also important for reducing flooding of the adjacent upland and homes, being a nursery for recreational and commercial fisheries, and enhancing water quality.
Light Detection And Ranging, or LiDAR, technology uses laser payloads on aircraft or drones to measure elevation by timing how long an emitted pulse of light takes to reflect back to the sensor.
In this example of LiDAR from a salt marsh in great Bay, the detail is so great individual plow furrows can be detected in a neighboring field.
Detailed aerial imagery was also collected during the same flight as LiDAR was being gathered.
Below is an example of the results from the marsh next to Chapman’s Landing boat launch in Stratham. Cooler colors indicate lower areas and warmer higher elevations with bare area indicating standing water such as salt marsh pannes and pools.
LiDAR image by Katie Callahan, NH Fish and Game GIS Specialist.
Data can be downloaded at NOAA’s Digital Coast where compressed LiDAR files are available in .laz format.
A slide show about the project can be downloaded here.
Written by Rachel Stevens, former Stewardship Coordinator at Great Bay NERR and Principal at Birch Tree Conservation Consulting.
