5. MSL Position and Unit Volume . 



The distance-elevation coordinates of the MSL contour intercept with 

 the initial survey on each profile line were defined as the origin (0, 0) 

 of a new coordinate system, to which all subsequent surveys were refer- 

 enced (Fig. 20) . Negative distances indicate stations landward of the 

 MSL intercept with the initial profile; positive distances indicate sea- 

 ward stations. 



Later Survey 



-50 -40 -30\^^-20 -10 

 Distance ( ft ) 



Figure 20. Profile coordinate system. 



Unit volume was obtained from the area under the profile. Beach and 

 nearshore cross-sectional areas were computed (in square feet) under each 

 surveyed profile. These areas are bounded by four lines: the vertical 

 line projected from the landwardmost station, the MSL elevation, the 

 -12-foot elevation, and by the surveyed profile (Fig. 21). The total area 

 is defined as that area bounded by the vertical line through the landward- 

 most station, the -12-foot elevation, and the surveyed profile. The beach 

 area is that part of the total area above the MSL elevation. The nearshore 

 area is the difference between the total area and the beach area. The 

 beach area was computed by summing 1-foot horizontal slices (Fig. 21, a) 

 and the total krea was computed by summing vertical slices (Fig. 21, b). 

 Area change between successive surveys was then computed by subtracting 

 the area under the second survey from the area under the first (Fig. 22). 

 These cross-sectional areas were then converted to the volumetric notation, 

 termed "unit volume," of cubic yards per linear foot of beach. 



36 



