A brief history of headland breakwaters for shore protection in Chesapeake Bay, USA

摘要

The first private headland breakwater system in Chesapeake Bay was built in 1985 at Drummond Field on the James River in James City County, Virginia. At that time, the Virginia Institute of Marine Science (VIMS) was researching stable pocket beaches where the embayed beach morphology emulates nature. This site provided an opportunity to apply those principles, including stable bay morphology. These principles were considered somewhat extreme since no extensive breakwater system existed on private properties in Virginia for the purpose of shore protection. In order to receive the appropriate permits, the rationale for the project was that state bottomlands would be exchanged for a stable beach with grass plantings. These provided natural habitats along the shore instead of the traditional stone revetments and bulkheads. The site has exceeded expectations, in that it experienced a severe storm just months after installation and has remained intact with little or no maintenance.rnSince that time, over 100 headland breakwater systemsrnhave been installed in Chesapeake Bay, both in Virginia and Maryland, thereby providing an extensive data set for assessing performance. The design of the system establishes the minimum protective beach width (B_m) and elevation desired in stable embayed beaches which will be held by the headland breakwaters. With B_m established, breakwater length (L_B), the breakwater gap (G_B) and the bay indentation distance (M_b) are determined from, in part, the wind/wave environment. The empirically derived relationships between these parameters offer guidelines for breakwater design along the sheltered coasts of Chesapeake Bay.rnConstructing stable headland/embayed beaches for long-term shore protection can be cost-effective. The procedures developed over the years to evaluate and design headland breakwaters have been effective. The installation of these systems over the last 20 years has created a unique database. This database continues to be updated as new sites are installed, thus providing verification of performance for headland systems as sites continue to mature.