VI. SUMMARY 



A total of 815 profile line surveys were taken at 21 locations along the 

 13.2-kilometer south-facing shoreline of Holden Beach, North Carolina, from 

 November 19 70 to December 19 74. The average width of the narrow barrier 

 island is 250 meters, terminated at the east and west end by Lockwoods Folly 

 and Shallotte Inlets, respectively. The profile lii.es along the beach were 

 evenly spaced with minimum and maximum distances of 565 and 638 meters. 

 Average spacing was 610 meters. This spacing was convenient for calculating 

 total beach sand volume changes since profile distances did not have to be 

 weighted. 



The beach profile data were used to determine changes in above MSL sand 

 volume, changes in MSL shore, and profile envelopes. The parameters were 

 analyzed to determine beach changes during the survey period and those caused 

 by individual storms. Additional wave, wind and water level data were pro- 

 vided by visual observation, local wave gages, and from recording devices in 

 Wilmington, North Carolina. Fewer storms than average occurred during the study 

 period for this region, and recorded winds were more moderate. 



The beach face was divided into three reaches, based upon the variability 

 of the profile line changes during the study period. The two inlet reaches 

 each contained three profile lines with the remainder in the central reach. 

 The beach slope at MSL along the central reach increased from a value of 1:30 

 at the east end to 1:17 at the west end. The MSL intercept averaged across 

 the central reach varied from +8.99 meters (9 June 1972) to -13.17 meters 

 (3 December 1974). Linear regression analysis indicates the MSL shoreline 

 is advancing at a rate of 1.18 meters per year while the above MSL volume is 

 decreasing at 0.44 cubic meter per meter per year. The direction of change 

 is supported by analysis on an annual basis though the rates are an order of 

 magnitude different; 0.15 meter per year and 4.8 cubic meters per meter per 

 year, respectively. These estimates should be treated with caution since 

 short term variability is quite large and the coefficient of determination 

 calculated for linear regression is small. Empirical eigenfunction analysis 

 applied to the data did not indicate other systematic modes of variability. 



The profile lines in the inlet reaches showed the greatest variability 

 in all calculated parameters. The beach nourishment operation at profile 

 line 2 from 1971 to 1974 was intended to reduce the high erosion rate pre- 

 viously observed at the east end of the island. The approximately 280 000 

 cubic meters of sand placed on the beach during the study period contributed 

 to the net gains in volume and shoreline position along the Lockwoods Folly 

 reach and may have influenced the beach shape at the east end of the central 

 reach. The Shallotte reach showed even more substantial gains without the 

 benefit of artificial nourishment. 



A seasonal trend was evident in the change in above MSL sand volume. 

 Losses occurred during the autumn and winter, and gains were measured during 

 spring and summer. Volume losses along the central reach were greater than 

 gains while the reverse was true for both inlet reaches. The visual wave 

 observations were not complete enough to calculate the magnitude of littoral 

 transport. Estimates of alongshore energy flux suggest, however, that the 

 westward transport is two to three times greater than the eastward transport. 



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