CENTIMETER-LEVEL INTERTIDAL SEDIMENT DYNAMICS AT A SUBMERGED AND INTERTIDAL PREHISTORIC SITE IN NEW HAMPSHIRE

This paper details drone-based digital photogrammetric mapping at an Archaic to Terminal Archaic (4400- 3200 14CyBP) archaeological site in New Hampshire. The site is capped by 1-2 meters of salt marsh peat, exposed at a rapidly-eroding shoreline, and discontinuously preserved in a dynamic intertidal zone. Later Holocene and historical relative sea-level rise subsequently re-exposed portions of the site and intertidal processes now variably impact paleolandscape elements and the erosional escarpment at the shoreface. The dynamic intertidal zone was impossible to map in high resolution between tidal cycles, thus UAV-based digital photogrammetry was employed to capture a single ‘geomorphic moment in time’. Three years of intertidal UAV mapping and digital photogrammetry have generated sub-centimeter quality (6-8mm) DEMs and orthomosaics and allowed very high resolution assessments of shoreline retreat, sediment mobilization, and raster-based change-through-time analyses. This resulted in a replicable technique for mapping minute changes in dynamic environments, and facilitated quantification of sub-centimeter changes within a geospatial environment. Spatial monitoring at various spatial and temporal scales is now possible, and on-going research focuses on the interplay between mobile and static features as variables in intertidal landscape development. The ultimate goal is to understand the timing and nature of archaeological site submergence as part of a larger effort to model the preservation potential of undiscovered sub-marsh, intertidal, and submerged sites in the region.