Monitoring the erosion and accretion of a human-built living shoreline with drone technology

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Climate change is forcing coastal communities to adapt to rising sea levels and increased storm activity. Living shorelines are a new adaptation to reduce the resulting erosion and inundation. Living shorelines use a variety of salt-tolerant plants and other natural material to absorb the increased wave energy and sea levels along the coast while supporting an enlarged coastal habitat for a variety of plants and animals, improving coastal resiliency. In 2019 the coastal city of Salem Massachusetts (USA) received a grant of $216,550 to build a living shoreline (approximately 240 by 11.75 m) in a barren cove along its coastline. Drone technology was used to monitor the erosion and accretion of the new living shoreline. A dji Phantom 4 Pro with a normal color camera was flown in 2018 (before the living shoreline was established), 2019 (just after the living shoreline was created) and in 2020 (after almost 18 months of wave and tidal activity to the living shoreline). Each drone flight created three products: an orthographic mosaic, a Digital Terrain Model (DTM) and a Digital Surface Model (DSM). A ground survey was used to georeference the 2020 image and then the 2020 image was used to georeference the 2019 and 2018 images. The 2019 DTM minus the 2018 DTM accurately estimated the amount of fill used for the living shoreline within 3% of the actual amount of fill used. The 2020 DTM minus the 2019 DTM showed that 14.7% of the surface area of the living shoreline experienced erosion (24.35 m3) and 52.0% of the surface area experienced accretion (117.74 m3). Living shorelines can be widely used to protect coastal biodiversity and to adapt to rising seas and storm activity, providing a soft barrier instead of a hard barrier like sea walls.