Grain Size Distribution and Sediment
Transport Patterns Along Wallops Island, Virginia: Pre- and
Post-Beach Replenishment, and Post-Hurricane Sandy
Bond, T., Sergent, E.,Oakley, A., and
Cornell, S.R., 2013, Grain Size Distribution and Sediment
Transport Patterns Along Wallops Island, Virginia: Pre- and
Post-Beach Replenishment, and Post-Hurricane Sandy: Geological
Society of America Abstracts with Programs- 45 (1,) p. 93. GSA
Northeastern Section Annual Meeting.
Barrier Islands along the Mid-Atlantic coast are particularly
susceptible to damage from nor’easters and hurricanes, as
demonstrated recently by Hurricanes Irene (August 2011) and Sandy
(October 2012). Wallops Island (WI), a barrier island off Virginia’s
coast, 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 multi-billion dollar launch complex. WI is experiencing
significant accretion to the north and severe erosion, averaging 3.7
m/yr since 1857, on the south end of the island. Storm surge, waves,
and high winds often cause massive flooding and sand overwash and
threaten existing infrastructure. In response to these threats, the
beach was replenished in April-August 2012. Approximately 3.2
million cubic yards of sand were added, creating a 4.2-km long,
70-meter wide beach in front of the existing seawall. In order to
understand how beach replenishment affects sediment transport and
deposition on WI, we collected sediment samples from March
2011-April 2012 prior to replenishment activities, and during and
after replenishment. Our results pre-replenishment show a
south-north trend in grain size distribution, with coarser sand
(-1-2 phi) accumulating to the south and finer grained sand (2-4
phi) to the north. This south-north sediment transport trend is
reversed from regional mid-Atlantic transport. Our
post-replenishment samples (April-October 2012) show a significant
increase in mean grain size (1.75-0.5 phi), followed by evidence of
replenished sediment transport and deposition to the north. Two
months after the replenishment project, WI was hit indirectly by
Hurricane Sandy storm waves. Initial beach surveys post-Sandy showed
an overall retreat of the shoreline. More than 50 meters were lost
in some areas of the natural beach, but significantly lower
narrowing occurred on the replenished beach. Both areas showed
evidence of beach flattening via overwash, and longshore beach-berm
transport scoured erosional channels into both the new and natural
beach. We collected sediment samples post-Sandy to determine its
immediate effect on sediment distribution. Comparing post-Sandy data
to prior data may help us predict how long the replenishment will
last.
Grain Size Distribution and Sediment
Transport Patterns Along Wallops Island, Virginia: Pre- and
Post-Beach Replenishment, and Post-Hurricane Sandy