A Geotechnical Evaluation of Chesapeake Beach Shoal for Beach Quality Sand

Milligan, Donna A.; Hardaway, C. Scott; Cox, Mary C.; Wilcox, Christine A.

Publication

A Geotechnical Evaluation of Chesapeake Beach Shoal for Beach Quality Sand

Milligan, Donna A.
;
Hardaway, C. Scott
;
Cox, Mary C.
;
Wilcox, Christine A.

Abstract

Chesapeake Beach Shoal is located along the southern coast of Chesapeake Bay in Virginia Beach, Virginia (Figure 1-1). Chesapeake Beach, which is nearly adjacent, has a history of chronic beach erosion which threatens upland infrastructure. Beach nourishment occurs on Ocean Park Beach to the east from intermittent dredging of Lynnhaven Inlet (Figure 1-2), but the effects do not always translate westward to Chesapeake Beach. The general alongshore sand movement is east to west. The purpose of this project is to establish a reliable source of beach sand for Chesapeake Beach via the nearshore shoal. Many issues, including identifying the location and volume of suitable material, cost effectiveness, permitting requirements (marine habitat impacts) and impacts to the local wave climate, must be addressed before mining sand from offshore shoals. Permits for sand mining for beach nourishment in the Bay have been granted for the Buckroe and Factory Point areas, but extensive environmental assessments are required. First, the sand resource must be identified in order to develop a dredging/mining plan. A single core, taken by VIMS in 1981(Hobbs et al., 1981), showed that the first 20 feet of material in the subbottom was at least 97% sand (Figure 1-2). According to results from Hobbs et al. (1981), the surface sediments in Chesapeake Beach Shoal are mostly very fine grained silty-sands, grading to gray medium sand near the beach. The core shows a sand horizon starting at the beach which has an overburden of inorganic clays and silts that thickens to the north and west. However, a surface deposit has a thickness of between 7 and 20 ft and an estimated volume of material with an overfill ratio of less than 2.0 is about 3.0 million cubic yards (Hobbs et al., 1981). According to the Army Corps of Engineers (1990) the average mean grainsize of the beach sands along Ocean Park is 0.35 mm (medium-grained). This analysis is no doubt influenced by recent beach fill projects. Hobbs et al. (1992) found the sediments in the nearshore to be between 0.2 mm and 0.35 mm. This report focuses on the acquisition of short cores and site data in order to establish the extent of the sand resource and provide data for developing a sand-mining plan. Athena Technologies took 42 vibracores in August 2011. These were analyzed to determine grain size characteristics which would define the location and suitability of beach quality material in the nearshore off Chesapeake Beach. In addition, a selected storm wave was modeled to determine the effect of the proposed dredging in the nearshore.