These bars showed a strong indication of seasonal, shore-normal migration. 

 During the summer and winter months, the average distance of the bar from 

 shore was 137 meters (450 feet) and 290 meters (960 feet), respectively. The 

 total length of the bars ranged between 6.4 and 9.6 kilometers. The average 

 length of each proximal section was 1.2 kilometers, each body segment 7.2 

 kilometers, and each distal segment 1.4 kilometers. There was very little 

 indication of shore-parallel migration. Instead, there appeared to be a very 

 consistent location for the initiation of bar propagation from shore. 



7. Sediment Characteristics . 



a. Beach Material . As part of the BEP mentioned in Section III, a series 

 of 915 sand samples was collected quarterly from 14 transects along the beach, 

 above mean low water (MLW) between 1974 and January 1977 (Fig. 42). Headland 

 and DeWall (1979) reported on the analysis of these samples. Each sample con- 

 sisted of about 200 grams (7 ounces) taken by a specially constructed sampler 

 from the top 1 centimeter (0.4 inch) of the beach. The location and elevation 

 of each sample was carefully determined using tape and level techniques. Sam- 

 ples were collected from the landward side of the dune, the dune crest, the 

 dune toe, the berm, and the foreshore. 



Splits of the samples were analyzed on the CERC Rapid Sediment Analyzer 

 (RSA). Ten percent of the samples were also run at 0.5-phi intervals through 

 a standard sieve analysis for control. A subset of 60 foreshore samples col- 

 lected during 1976 was analyzed for carbonate content. The results were then 

 analyzed for variations in mean size as a function of (1) position along each 

 profile line, (2) position along the beach, (3) season, (4) percent carbonate, 

 and (5) foreshore slope. An average of all profile lines indicated the mean 

 grain size decreased landward from 0.52 millimeter (0.9 phi) on the foreshore 

 to 0.38 millimeter (1.4 phi) at the dune (Fig. 43). Profile lines to the 

 north show a much wider range of sizes than the lines in the vicinity of 

 Oregon Inlet, due to a secondary mode in the coarse fraction on the berm and 

 foreshore (Fig. 44). The mean size of the dune sand remains nearly constant 

 and ranges between 0.3 and 0.4 millimeter (1.7 and 1.3 phi). Figure 45 shows 

 the biraodal distribution for a sample taken from the foreshore at profile line 

 20 (south of the FRF). 



Figure 46 illustrates the change in average sample mean and standard devi- 

 ation alongshore and confirms a decrease in sand size from north to south. 

 The coarsest material occurs in the vicinity of the FRF (between lines 12 and 

 20) where the mean sand size on the foreshore averages 0.6 to 0.8 millimeter 

 (0.7 to 0.3 phi). 



Figure 47 summarize-s the seasonal mean sand size, averaged by position on 

 the profile line. Sand size on the dune remains generally unchanged, while 

 the foreshore laaterial (MllW to liSL) tends to become finer during the summer 

 months. Sand size on the berm is coarser during the summer than during the 

 rest of the year. Seasonal trends were not uniform from profile to profile. 



The carbonate fraction of the foreshore samples, which consists of whole 

 and broken shell material, ranges from to 20 percent of the sample by weight 

 (Fig. 48). The highest percentages occurred during the fall survey of profile 

 lines 35 to 41. Mean grain size was found to have a positive correlation 

 (0.4) with percent carbonate. 



69 



