long barrier island or spit of Assateague Island formed by coalescing of 

 smaller islands. They also concluded that the present-day barrier island 

 coast did not originate at its present location but rather migrated from 

 a former position at least 5 miles seaward on the shelf. The concept of 

 barrier islands migrating from the shelf during the Holocene to their 

 present position has been recently discussed in detail by Field and 

 Duane (1976) . They maintain that the inner shelf contains a sedimentary 

 record which shows the presence of barrier island environments and that 

 in view of this, many of the criteria developed to support hypotheses on 

 barrier island origin are not appropriate. Field and Duane further empha- 

 size that irrespective of its original mode of formation, a given barrier 

 may evolve through one or a combination of processes, such as submergence, 

 spit growth, and upward building. 



a. Erosion and Deposition on the Beach and Shoreface . Wind waves 

 that approach the shore at an angle produce longshore currents that may 

 transport sediment along the coastline. Bethany Beach, Delaware, is a 

 nodal point in the net littoral transport direction, such that sand is 

 transported by littoral currents away from the locale. Approximately 

 145,000 cubic meters (190,000 cubic yards) of sand is transported annually 

 along the coast between Bethany Beach and Indian River Inlet (Duane, et 

 al., 1972). On the north side of Ocean City Inlet accretion rates of sand 

 indicate 115,000 cubic meters (150,000 cubic yards) of material is annu- 

 ally transported southward. Historical profile data from the Ocean City- 

 Assateague barrier islands, compiled by the U.S. Army Engineer District, 

 Baltimore (1972), show an overall pattern of erosion of the coast. Major 

 exceptions to the general trend of recession are the shoreline just north 

 of Ocean City Inlet, just south of Indian River Inlet, the Fishing Hook 

 spit area of Assateague, and the Cape Henlopen spit. Photos of these 

 areas are shown in Figure 35, a to d. Between 1850 and 1929, the shore- 

 line along the Ocean City-Fenwick Island coast receded at rates of 1.5 

 to 7.1 meters per year; since 1929 recession rates have varied consider- 

 ably. The average retreat rate in Ocean City between 1850 and 1965 was 

 about 0.61 meter (2 feet) per year north of 10th Street. South of 10th 

 Street to the inlet accretion occurred rapidly after jetty construction 

 (0.91 to 6.4 meters or 3 to 21 feet per year) and has slowed in recent 

 years as sand filled in behind the jetty and began to bypass it. With 

 the hurricane opening of the Ocean City Inlet in 1933, and jetty stabil- 

 ization immediately thereafter, erosion increased on northern Assateague 

 to rates of 10.7 meters per year. Along central and southern Assateague, 

 accretion has occurred locally but the overall trend -has been recession. 

 Tree stumps and peat layers are periodically exposed on the beach face 

 after erosive events. As shown by Gawne (1966) and U.S. Army Engineer 

 District, Baltimore (1972), erosion is episodic and not continuous. 

 Major erosion is often associated with major hurricanes or winter storms 

 (northeasters) . The hurricane of 1933 and the storm of March 1962 are 

 two examples of storms which devastated the study area. 



If the long-term retreat rate averages about 0.61 meter per year 

 (in many places this is a minimum rate) , rough estimates of Holocene 

 retreat rates can be made. At this rate the barrier islands could have 



84 



