shoreline with 0° to the left. Observations taken after 19 74 corresponded to 

 the LEO methodology (Szuwalski, 1970; Bruno and Hiipakka, 1974; Balsillie, 1975). 

 At 90° waves approaching from directly offshore would result in no net longshore 

 sand transport. Along Holden Beach, angles less than 90° are from the east 

 and greater than 90° from the west, producing transport westward and eastward, 

 respectively. 



The frequency of breaker approach indicates that net transport westward 

 predominates. Table 1 provides the relative magnitude of littoral transport 

 calculated for each month from 1971 to 1973. These values were determined 

 from the longshore energy flux relationship (U.S. Army, Corps of Engineers, 

 Coastal Engineering Research Center, 1977) and can be shown to be proportional 

 to wave height to the 5/2 power (H^' ^) . The breaker angle was included only 

 in the 1974 calculations, so the 1971-73 values and 1974 values should not 

 be compared. The computed parameters do not represent actual transport rates, 

 but provide relative rates and directions for each month. The estimates show 

 that net longshore sand transport is actually westward. The table also shows 

 that wave approach is predominantly from the east. There were several cases, 

 however, where waves from one direction were completely overpowered by large 

 breakers from the opposite direction. These are footnoted in Table 1. 



III. METHODS 



Profile Lines and Monumentation . 



Twenty-one profile lines extending from Lockwoods Folly Inlet to Shallotte 

 Inlet were surveyed along Holden Beach. The location and spacing of the pro- 

 file lines are shown in Figure 2. Except for a series of sandbag groins in- 

 stalled near the east end of the island between profile lines 1 and 3 during 

 1973-74, there were no erosion control structures placed along the beach dur- 

 ing the study period. Bulkheads in varying states of repair were present along 

 the beach at profile lines 2, 3, and 4. Their effectiveness was not specifi- 

 cally monitored during the study. The survey periods and number of surveys 

 per profile line are given in Table 2. 



a. Survey Procedures . The profile lines were relatively evenly spaced 

 along Holden Beach with distances varying from a minimum of 565.1 to 638.1 

 meters. The horizontal and vertical datums for each profile line were estab- 

 lished by the firm of Moorman and Little, Inc., Fayetteville, North Carolina, 

 for the Wilmington District. Actual profile line measurements were taken by 

 the firm of W. W. Blanchard, Inc., Wallace, North Carolina. Monuments con- 

 sisted of capped, galvanized pipes embedded in the dune or backshore area 

 with reference ties measured to local cultural features where possible with 

 third-order survey control providing the geodetic and state-plane coordinates 

 of the monument. Vertical control at each profile line consisted of a third- 

 order elevation of the top of the monument with respect to the National Geo- 

 detic Vertical Datum of 1929. Documentation of each profile line monument, 

 as well as ground photos of each site, is provided in Appendix A. 



Surveying crews measured each profile line, using a level and tape tech- 

 nique, and established a reference elevation at a fixed object such as the 

 top of a log barricade, the foot spike on a telephone pole, or nail markers 

 driven into the roadway. The survey proceeded seaward, approximately perpen- 

 dicular to the shoreline, from the reference along the preselected azimuth, 



22 



