SEDIMENT GRAIN SIZE TRENDS PRE- AND POST- BEACH REPLENISHMENT ALONG WALLOPS ISLAND, VIRGINIA FROM 2011-2017 AT MONTHLY AND SEASONAL RESOLUTION

Wallops Island (WI), a barrier island on the Eastern Shore of VA, has experienced severe erosion for more than a century. This erosion, combined with the highest rate of relative SLR on the East Coast, has caused the shoreline to retreat within meters of NASA’s Wallops Flight Facility (WFF). Longshore transport and overwash has caused significant long-term erosion averaging 3.7 m/yr since 1857 on the S end of WI (SWI). Due to 8+ decades of hard shoreline engineering, a localized S-N reversal of longshore transport, and a major 2012 beach replenishment, the N end of WI (NWI) has prograded seaward by ~1 km since 1930 (~11 m/year). Overall, WI is rotating clockwise (CW).

To understand the effects of beach replenishment on WI, sand samples were collected monthly (March 2011-Nov. 2012) at 31 sites along 7 km of beach prior to, during, and after replenishment. Our dataset includes samples from the artificial beach and seasonal samples (2012-2017) from site TN6, N of the beach replenishment area. Pre-replenishment average GS on SWI was 1.5-2 phi. Sediment fined northward to 2-3.5 phi on NWI. Beach replenishment added 3.2 million cubic yards of coarser (0.5-1 phi) sand to the system. Our sampling resolution allows us to track the replenished sand as it moved N through natural transport. GS at TN6 in 2017, 5 years after replenishment, is 1-3 phi.

Beach replenishment reduced the overall impact of Hurricane Sandy on WFF infrastructure and accentuated the CW rotation of WI as replenished sand moved both N and S of the hinge-point (near TN6). NWI is growing seaward and becoming more stabilized, while SWI continues to migrate landward. Increased permeability of the replenished beach system has resulted in a shallower, more extensive freshwater lens on NWI which has subsequently allowed growth of a vegetated dune-swale system, recently populated by Phragmites.

Trends in sediment transport and island morphology are observable in historical documents, but these data lack information about the physical properties of the beach system. Analysis of GS data provide insight into sediment transport, groundwater flow, and ecosystem processes. Our GS data analysis will provide WFF managers additional context and evidence to establish sustainable coastal management strategies.