IMPACT OF HURRICANE ISABEL ON CHESAPEAKE BAY DUNE SYSTEMS

Bay dune systems of the Commonwealth of Virginia are considered a unique and valuable natural resource. They not only provide shore protection for upland properties but also habitat to a variety of coastal fauna and flora. The nature of dune systems around Chesapeake Bay is variable in terms of shoreline change and developmental pressures. Each documented dune has its own history of change -- both growth and decay. Dunes around Virginia’s Chesapeake Bay estuarine system encompass only about 1 percent of the total Bay coast making it a rare shore type.

A Bay-wide monitoring program of eight dune sites was established to characterize the seasonality of dune resources. Sites are located on the Western and Eastern Shore of the Bay as well as on the Rappahannock and Potomac Rivers. The beach surveying, sediment sampling, and ground and aerial photography program has defined, quantified, and delineated dunes as well as those adjacent ecosystems that complement functions of coastal primary dunes such as secondary dune fields biannually since 2000. These sites were surveyed after the passage of Hurricane Isabel in September 2003.

Prior to the passage of the Hurricane, storm events have been generally lacking in Chesapeake Bay since fall 1999. As such many of the dune monitoring sites had beach/dune sites that were accreting and, in fact, some primary dunes were developing foredune features that would have become the primary dune in the near future, relegating the existing primary dune to secondary dune status.

Large storm events can significantly alter coastal geomorphology. In addition to being in the "right front quadrant" of the advancing hurricane, the southern portion of Chesapeake Bay experienced winds from the northeast, east and east-south-east which accentuates storm surge. The magnitude of the storm surge, about 2 m, was close to that of the 1933 hurricane, the local "storm of record." In addition to the elevated water levels, many areas suffered the consequences of 2 m or higher waves. During the storm, this combination of waves and surge leveled the primary dune. However, there was little net volume change at the sites. Sand was transported alongshore and offshore but was not lost from the overall system and even began migrating back up onto the beach immediately following the storm.