North Carolina's tidal inlets are fickle products 

 of an ever-changing coastline. They open, close, 

 widen, narrow and migrate — sometimes with no 

 warning at all. The impetus for change is often a 

 hurricane or similar storm. 



Coastal North Carolina now has 22 open inlets. 

 But there have been many others in the past. 

 Three inlets, Cape Hatteras, Oregon and Ocracoke 

 Inlets, are now open on the Cape Hatteras Nat- 

 ional Seashore. According to the National Park 

 Service, eight other inlets have opened and closed 

 along the seashore (some of them several times) 

 since the earliest records in 1585. Tubbs Inlet in 

 Brunswick County migrated a total of 3400 feet 

 between 1938 and 1969. In fact, of the inlets now 

 open, only Cape Fear and Barden Inlets and the 

 west side of Beaufort Inlet appear to be relatively 

 stable. 



In spite of their fluid natures, tidal inlets play 

 crucial roles in the coastal environment. They con- 

 nect rivers and estuaries w r ith the ocean and so con- 



Aerial photograph shows migration ol inlet. 



trol the circulation of water and sediment in the 

 whole estuarine system. They affect pollution con- 

 trol, navigation, recreation, flood discharge and 

 fish migration. 



Inlet changes sometimes affect man very drama- 

 tically. If a storm opens a new inlet, it may flood 

 private property and destroy communities. But 

 in recent years man has had a growing effect on 

 inlets. Two of North Carolina's inlets — Drum In- 

 let and Carolina Beach Inlet — are man-made. 



As is often the case when man tinkers with 

 natural forces, unexpected things happen. The 

 case of Drum Inlet is an example of the kinds of 

 difficulties that can ensue. In 1971 the U.S. Army 

 Corps of Engineers blasted open Drum Inlet in 

 Core Banks, just off the coast of Carteret County. 

 The inlet was opened to increase the salinity of 

 Core Sound and to give fishermen a passageway to 

 the ocean. Old Drum Inlet, which was located two 

 miles north, had previously filled with sand. 



The new inlet was expected to widen to about 

 1500 to 2000 feet. Erosion continued at an unex- 

 pected rate, though, until the inlet was 3350 feet 

 wide. Residents of the area complained that the 

 widened inlet exposed them to increased danger 

 from storm waves. In 1974 the Corps of Engineers 

 stopped maintenance dredging and the inlet open- 

 ing has narrowed to about 2000 feet. The corps is 

 now considering several alternatives designed to 

 break the force of storm waves and to decrease 

 erosion south of the inlet. One plan calls for build- 

 ing man-made islands at the mouth of the inlet. 



This year UNC Sea Grant is sponsoring research 

 which is aimed at predicting the effects of man- 

 made changes on flow dynamics and sediment 

 movement in tidal inlets. Jerry Machemehl of 

 NCSU has already developed a finite element flow 

 model for a typical barrier island inlet. The model 

 can be used by coastal engineers to assess the ef- 

 fects of inlet alterations on the shoreline and 

 estuaries. 



Machemehl is also studying the flow dynamics 

 of Carolina Beach Inlet, located 18 miles north of 

 the Cape Fear River in New Hanover County. The 

 Corps of Engineers is now considering altering the 

 inlet to improve navigation and to halt excessive 

 erosion on the beach south of the inlet. One alter- 

 native is to construct jetties with an excavated 

 channel or to excavate an entrance channel and use 

 frequent maintenance dredging. Machemehl will 

 be using the model he has developed to predict the 

 effects of proposed navigation improvements at 

 the inlet. 



UNC Sea Grant has recently published a booklet 

 which tells the stories of North Carolina's existing 

 inlets through photographs. The Citizen's Guide 

 to North Carolina's Shifting Inlets, was written 

 by Simon Baker of Sea Grant advisory services. 



Storms affect formation of dunes 



(Continued from p. 4) 



So far Hosier and Cleary have seen some definite 

 patterns emerge. The most chronic overwash ap- 

 pears to have occurred between Ocracoke and Cape 

 Lookout, and the area from Figure Eight Island 

 to Carolina Beach runs a close second. Hosier notes 

 that the land just north of all the capes seems to be 

 particularly vulnerable to overwash. He believes 

 that Bogue Banks, Bear Island and Browns Island 

 have never been overwashed. 



Areas of chronic overwash have a number of 

 characteristics in common, said Hosier. These 

 beaches generally have scattered individual stands 

 of salt meadow cord grass and individual clumps of 

 sea oats. They also may support ten to 15 species of 

 annual or perennial plants, such as goldenrod or 

 dune spurge. There is little or no dune formation. 



If a barrier island has been overwashed about 

 every ten years, there will be a weakly developed 

 dune ridge, Hosier said. A single strand of shrub 

 thicket and a salt marsh will be behind the dunes. 



Areas that are seldom or never overwashed have 

 the classic barrier island features. Dunes form in 

 ridges or fields and slope gently to the beach. 

 There is a strand line, indicating that the beach is 

 not eroding. And there are shrub thickets and a 

 salt marsh behind the dunes. 



Hosier and Cleary are also finding that the 

 type of sand available in an area has a significant 

 effect on the stability of dunes. Because it can be 

 easily blown by the wind, fine-grained sand forms 

 into dunes more quickly than coarse-grained sand. 



Coarse sand tends to form smaller, broken lines of 

 dunes, called haystack dunes. Fine sand forms 

 ridges or fields of dunes which act as a better 

 barrier. 



Two of the islands near Wilmington which were 

 overwashed during the Ash Wednesday storm of 

 1972 clearly illustrate that point. On Masonboro 

 Island there is coarse sand and poor dune for- 

 mation, but on nearby Coke Island fine-grained 

 sand has formed stable dunes. 



Preliminary studies indicate that the difference 

 in sand may be responsible for the fact that beaches 

 along the southern portion of the coast are smaller 

 and less stable than those in the north. Cleary 

 conjectures that Hurricane Hazel of 1954 may 

 have caused a deficit of fine sand on southern 

 beaches. He believes that the storm may have 

 taken much of this dune building sand five to ten 

 miles out in the ocean. 



The University of North Carolina Sea Grant 

 College Newsletter is published monthly by the 

 University of North Carolina Sea Grant College 

 Program, 1235 Burlington Laboratories, Yarbor- 

 ough Drive, North Carolina State University, 

 Raleigh, N.C. 27607. Vol. 4, No. 6, June 1977. 

 Dr. B. J. Copeland, director. Written and edited 

 by Karen Jurgensen and Mary Day Mordecai. 

 Second-class postage paid at Raleigh, N.C. 27611. 



University of North Carolina 

 Sea Grant College Program 

 1235 Burlington Laboratories 

 North Carolina State University 

 Raleigh, N.C. 27607 



