FROM THE DUNES TO THE DEPTHS: IMAGING MAINE’S BEACHES TO UNDERSTAND SEDIMENT MOVEMENT AND FURTHER BEACH RESILIENCY

Beach nourishment and nearshore sand placement are two common beneficial uses of dredged material to increase beach and dune resiliency and improve habitat. In Maine, their use is generally limited to a few US Army Corps of Engineers (USACE) navigation dredging projects. In 2005, the USACE placed 62,730 m³ of dredged material from the Scarborough River navigation channel onto nearby Western Beach adjacent to a large ebb-tidal delta. Subsequent terrestrial RTK-GPS surveys conducted by the Maine Geological Survey (MGS) tracked sediment movement along the beach. In 2015, the USACE built a spring-tide berm at Western Beach using 90,000 m³ of dredged material; the design was optimized using MGS shoreline data. In 2016, MGS initiated additional monitoring using RTK-GPS surveys, nearshore bathymetric surveys (with the MGS Nearshore Survey System), and Unmanned Aerial Vehicle (UAV) imagery to monitor sediment movement within the entire beach-inlet system. Subsequent surveys were completed in 2017 and 2018. In 1996, 73,000 m³ of Scarborough River sand was transported 10 km and placed just offshore of Camp Ellis Beach in Saco for reintroduction into the longshore drift of Saco Bay for regional sediment management. We quantified slow dispersal of this mound using USACE SHOALS 1997 and 1998 bathymetric lidar and our own 2016, 2017, and 2018 marine and terrestrial surveys. UAV flights were added in 2018 and 2019. These data document storm reworking of December 2018 USACE beach nourishment of 75,000 m³ of sand from the Saco River at Camp Ellis Beach. June 2018 nearshore placement of 15,000 m³ of Webhannet River harbor sand at Wells Beach by the USACE was mapped pre-placement by USACE JALBTCX and post-placement with our methods and the addition of multibeam collected by the Maine Coastal Mapping Initiative. We will present how these data sources work together to create an assessment of sediment dynamics and effectiveness for resiliency in these three different beach settings.