43 The Science, Environmental Impacts, and Policy of Beach Nourishment (Posters)

Friday, 29 March 2019
1:00 PM - 5:00 PM
Carolina Ballroom

TRACKING TRENDS IN SAND GRAIN SIZE ALONG A BARRIER ISLAND AFTER A MAJOR BEACH REPLENISHMENT: WALLOPS ISLAND, EASTERN SHORE, VIRGINIA

Paper number: 43-2
Program: Theme Sessions
Time: 1:00 PM – 5:00 PM

Authors

Abstract

Wallops Island (WI) VA, has experienced century-long shoreline erosion to within meters of NASA’s Wallops Flight Facility (WFF). A localized S-N reversal of longshore transport (LST) and overwash have caused erosion averaging 3.7 m/yr since 1857 on south WI (SWI). Due to decades of engineering, dredging, and LST, north WI (NWI) has prograded seaward ~1 km since 1930 (~11 m/yr). WI has thus rotated clockwise (CW) at a hinge-point near the N end of a seawall.

To protect WFF infrastructure, NASA performed a major beach replenishment in 2012, creating a 6 km long, 70 m wide beach seaward of the seawall. To track changes in grain size (GS) distribution along WI post-replenishment, we established baseline conditions in 2011. Samples were collected monthly from the beach face and dune (March 2011-Nov. 2012) at 31 sites. Pre-replenishment average GS (beach face) on SWI was 1.2-2.4 phi. Sand fined northward to 1.8-3 phi on NWI. Completed August 2012, replenishment added 3.2x106 yd3 of coarser sand (0.5-1 phi). Seasonal and post-event sampling took place Nov. 2012-Oct. 2018. Our dataset allows us to track replenished sand as it redistributed naturally. In Oct. 2012, Hurricane Sandy removed ~50% of the new sand. By 2014, GS on SWI beach fined as replenished sand was buried by sand deposited by LST. On NWI, replenishment caused immediate coarsening to 1.4-1.6 phi. Six years after replenishment, GS at the hinge-point is 1-2 phi, NWI beach widened by as much as ~100 m, whereas the new beach has eroded to <20 m and storm surge reaches the seawall.

Replenishment reduced the impact of Hurricane Sandy on WI infrastructure and accentuated the CW rotation of the island as sand moved both N and S of the hinge. NWI continues to prograde but is stabilizing, while SWI continues to erode. Other effects of replenishment include increased permeability of the beach system (infiltration: 4-9 ml/s), lower densities of coquina clams, a pronounced shallow freshwater lens, expanded freshwater wetlands, and vegetated dune-swale systems colonized by Phragmites.

This region is experiencing SLR at twice the global average and NASA is planning for a second round of nourishment that may include relocating sand from NWI back to the south. Our data highlight the ephemeral nature of beach replenishment and a few of the unintended consequences of this short-term management solution.

Geological Society of America Abstracts with Programs. Vol. 51, No. 3

doi: 10.1130/abs/2019SE-327679

© Copyright 2019 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.