THE SEDIMENTARY PROCESSES AND GEOMORPHIC HISTORY OF WRECK SHOAL, AN OYSTER REEF OF THE JAMES RIVER, VIRGINIA

• Main Author: DeAlteris, Joseph T.
• Format: Others
• Language: English
• Published: W&M ScholarWorks 1986
• Subjects: Geology
• Online Access: https://scholarworks.wm.edu/etd/1539616626; https://scholarworks.wm.edu/cgi/viewcontent.cgi?article=2193&context=etd

Wreck Shoal is a subtidal oyster reef area located in the James River, Virginia. Two significantly different types of oyster reefs are found in adjacent areas on Wreck Shoal. Hard-rock reefs are characterized by a relatively thick oyster shell layer, higher densities of live oysters, a coarser interstitial sediment, and a negligible sediment cover. In contrast, mud-shell reefs are characterized by a very thin osyter shell layer, considerably lower densities of live oysters, a finer interstitial sediment, and a 1-2 cm layer of very fine sediments covering the reef. The contemporary sedimentation processes operating on the hard-rock and mud-shell oyster reefs are distinctly different. The hard-rock oyster reefs are in shallower water, experience stronger bottom currents, and present a hydraulically rougher surface to the flow. The mud-shell oyster reefs are in deeper water, experience weaker bottom currents, and present a hydraulically smoother surface to the flow. These factors result in substantially different bottom shear stresses at the fluid-bed interface. The hard-rock oyster reef, with the high bottom shear stress is rarely depositional with respect to fine sediments. In contrast, the mud-shell oyster reef with the low bottom shear stresses is rarely erosional with respect to fine sediments. The James River estuary has evolved, moving upstream and landward in response to a rising sea level. The Wreck Shoal oyster reefs have developed on the ridge and swale topography of a point-bar formed during the late Pliestocene Epoch. From the 1550's to the 1850's the oyster reef developed vertically almost 1.5 m. From the 1850's to present the oyster reefs have lost more than 1.0 m of elevation due to intense harvesting activity. Conceptual models of subtidal oyster reef dynamics and development are proposed and verified based on field observations. The management implications of the results of the study are presented and recommendations are made for the rational exploitation and management of the resource.