22 Tropical Cyclone Impacts on Coastal Zones

Friday, 18 March 2005
1:00 PM - 4:40 PM

RECENT EVOLUTION OF A HURRICANE-IMPACTED RETROGRADING BARRIER ISLAND: MASONBORO ISLAND, NC

Paper number: 22-9
Program: THEME SESSIONS
Time: 3:40 PM – 4:00 PM

Authors

Abstract

The coastline in the vicinity of Cape Fear, NC consists of developed barriers that have been repeatedly renourished, and as a result, long-term recession rates and storm impacts are difficult to assess. However, exceptions exist and include undeveloped Masonboro Island, a 13 km long barrier located between Masonboro and Carolina Beach Inlets. Historically the island’s relatively high erosion rates and washover susceptibility appear to be attributable to a combination of variables including the storm climate and inlet modification. Data from digitized aerial photographs (1993-2003) and RTK survey data provide information on the event driven changes that occurred subsequent to the hurricane activity (1996-1999). The island’s low relief coupled with the hurricane-induced elevated water levels (2.5-3.4 m) during the late 1990’s has led to rapid shoreline translation along a significant portion of the barrier.

Shoreline recovery since Hurricane Floyd (1999) has been localized and confined to the 3.5 km long reach comprising the fillet of the south jetty at Masonboro Inlet. Since 1999 the remainder of the island to the south has continued to erode and translate landward at rapid rates. Landward translation has amounted to as much as 110 m along some segments. Along the southern part of the barrier, significant variation in shoreline translation has occurred due to the presence of a small interfluve that is composed of Pleistocene sandstone. Data indicate that the unit crops out on the upper shoreface, extends beneath the barrier and is intermittently exposed along the mainland. The influence of the antecedent topography has led to the development of a hinge zone that separates shoreline segments characterized by distinctly different retreat rates. Current annual erosion rates of this 1.0km long hinge zone approach 12 m while erosion rates of adjacent reaches immediately north and south of the interfluve average 22 m.