Integrated Studies of the New Hampshire Shoreline and Continental Shelf: An Important Step Towards Coastal Resiliency

TitleIntegrated Studies of the New Hampshire Shoreline and Continental Shelf: An Important Step Towards Coastal Resiliency
Publication TypeConference Abstract
AuthorsWard, LG, McAvoy, Z, Olsen, N, Vallee-Anziani, M, Chormann, F, McPherran, K, Nifong, K
Conference NameAmerican Shore and Beach Protection Association Annual Meeting
Conference LocationLong Branch, NJ
Conference DatesOctober 25-28
Keywordscoastal resiliency, continental shelf, new hampshire shoreline

The coast of New Hampshire (NH), like many paraglacial environments, is extremely heterogeneous ranging from bedrock outcrops, beaches interrupted by rocky headlands or remnant glacial features (e.g., drumlins), and barrier islands. The composition of the beaches reflects this extreme variability ranging from fine sand to cobbles with bimodal sediment populations being common. The NH shoreline to date has exhibited only small changes in position largely due to the low relative sea-level rise, bedrock outcrops, and extensive engineering structures. Changes in the location of the NH shoreline was determined from charts and orthophotography dating back to the late 1800s and more recent lidar surveys using the Digital Shoreline Analysis System (DSAS). Due to its relatively short length (~29 km), the entire coast was analyzed at a fine (50 m) spatial resolution. In general, the larger southern barrier beaches show a small net seaward movement (accretion), while the northern beaches show a small net shoreward movement (erosion). In contrast, the beaches have undergone larger vertical changes (volumetric) based on comparison of lidar surveys and seasonal beach profiling. Comparison of the lidar surveys from 2000 to 2014 showed large variability in trends, but most beaches appeared to have a net loss of sediment. However, the two largest beaches in the state (Hampton Beach and Seabrook Beach) show more gains than losses. To offset the vertical changes in elevation and to extend their widths, selected beaches have periodically been nourished. Although coastal erosion issues in NH have not been overwhelming, the expected acceleration in sea-level rise and the increase in storm severity will result in new challenges and requires building coastal resiliency. To address this expected need, offshore sources of suitable sand and gravel resources are being evaluated with significant support from Bureau of Ocean Energy Management, the New Hampshire Geological Survey, and the University of New Hampshire Center for Coastal and Ocean Mapping/Joint Hydrographic Center. Similar to the shoreline environment, the continental shelf of NH and vicinity is extremely heterogeneous and is composed of extensive bedrock outcrops, sand and gravel deposits, and muddier sediments. Depositional features are dominated by remnant glacial features (e.g., drumlins, eskers, moraines) that have been significantly modified by marine processes as sea level fluctuated following deglaciation. The glacial deposits have been eroded leaving very coarse lag deposits, while supplying sand to develop wave formed features (shoals). Many of these features have positive relief standing above the seafloor, lending evidence of their formation by waves and shallow water currents. Of particular interest is a large sand body that is ~3.2 km in length, ~1.3 km in width and has a maximum relief of ~7 m. As a result of the heterogeneity of the NH shelf, locating significant sand and gravel deposits is challenging. However, some of these modified glacial deposits and associated shoals, as well as some marine formed shoals, represent significant sand and gravel deposits that have the potential for future use for beach nourishment and other efforts to build coastal resiliency.