SEDIMENTATION ACCUMULATION PATTERNS IN THE DAMARISCOTTA RIVER ESTUARY

The Damariscotta River is a tidally dominated estuarine system located in the south-central compartment of the Maine coast. The narrow, elongate, north-south orientation of the estuary is characteristic of the indented shoreline in this region and is a consequence of the bedrock structural framework comprising high-grade metasedimentary rocks of Paleozoic age. The river basin has an overall relief of ~95 m. A series of pegmatite sills separate the estuary into seven distinct basins. The basins were sequentially isolated from the estuarine system during the fall to local relative lowstand of sea level after the retreat of the Laurentide ice sheet, and then gradually reincorporated into the marine environment during post-glacial sea-level rise. Sediment distribution within the system is typical of Maine estuaries, and can be separated into three distinct zones. The innermost zone has stable shorelines and is characterized by tidal flats, marshes and relatively rapid accumulation of sediment. Sediment sources consist primarily of reworked Holocene and Pleistocene deposits from within the estuary, as well as erosion of bluffs that border the middle zone. With fewer marshes and more tidal and subtidal flats, sediment accumulation is more transitory in the middle zone. The outer zone is the most exposed to waves and tidal currents that have largely stripped this zone of sediment, and Pleistocene and Holocene sediments are preserved only below wave base. Studies employing seismic reflection profiles, side-scan sonar and cores have led to a well-understood model of estuarine evolution. The present study, utilizing multibeam bathymetry, cores and grab samples, has resulted in high-resolution bathymetric and surficial sediment maps of the estuarine system and a better understanding of spatial and temporal variations in sediment accumulation within the estuary. This is particularly relevant in the context of historical and modern disturbances to the system, such as human land use and aquaculture.