MONITORING SEDIMENT TRANSPORT AND GRAIN SIZE DISTRIBUTION ALONG WALLOPS ISLAND, VIRGINIA, PRE AND POST-BEACH REPLENISHMENT

Wallops Island, a barrier island on the Eastern Shore of Virginia, has experienced severe erosion for more than a century. This erosion, combined with rising sea level, is causing the shoreline to retreat rapidly to within meters of NASA’s Wallops Flight Facility, a billion dollar complex. A narrowing beach, wind-driven wave activity and storm surge periodically cause massive flooding and sand overwash on the island and threaten existing infrastructure. In response to these threats, NASA began to replenish the beach in April 2012. Millions of cubic yards of sand from two shoals ~6-10 NM offshore are being added to the existing beach face and in front of the seawall to widen and elevate the beach. In order to understand how beach replenishment will affect sediment transport and deposition, as well as habitats for endangered species along the 12-km shoreline, we established baseline conditions pre-replenishment. We collected surface sediment samples along the dune and beach face from March 2011-April 2012 to determine sediment transport trends and grain size distribution. Our research also included rapid storm response and biotic surveys. Our pre-replenishment results show a south-north trend in grain size distribution with the coarsest sand (Phi = -2 to 2) dominating beaches to the south and the finest sand (Phi=3 to 4) north of the seawall. Severe erosion, averaging 3.7 m/yr since 1857, occurs on the southern portion of Wallops Island while significant accretion is occurring to the north. The observed south to north sediment transport trend is reversed from mid-Atlantic regional transport. This is in part caused by a local reversal in longshore current created by the interaction between tidal outflow from the Chincoteague Inlet and the geometry of Wallops Island and adjacent Assateague Island. Our project is ongoing and we are continuing to monitor post-replenishment grain size distributions along Wallops Island. We will use these data to compare pre-replenishment baseline conditions to post- replenishment conditions in order to determine how the addition of offshore sand will affect this barrier island system. Here we will present baseline conditions and the first few months of post-replenishment data.