Table 3-5. Summary of potential erosion of Profile Line R-7 by three selected storms. 



Storm Sequence 



Change of the 

 MHWL, ft 



Maximum Volume- 

 Loss Rate, cy/ft 



Initial 07/1 983 -Thanksgiving NE 11/1984 



-15.0 



-11.9 



Post-Thanksgiving NE 1 1/1984 - NE 03/1989 



-30.9 



-11.3 



Post NE 03/1989 -TS Gordon 11/1994 



-23.8 



-10.8 



Total Change of the MHWL, 

 07/1983 to 11/1994 (three storms) 



-69.7 



- 



For comparison, beach-profile change between September 1972 and December 30, 1993, 

 measured at R-7 and R-8 is plotted on Figure 3-9. Numerical calculations of beach-profile 

 change for the three storms, with survey data from R-7 as the initial condition, give recession and 

 erosion less than that documented by the surveys as described below. The magnitude of erosion 

 at R-8, located approximately 900 ft to the south of R-7, is less significant because the nearest 

 survey in time occurred on August 27, 1985. Comparison of the August 1985 surveys for both 

 R-monuments indicates similar beach dimensions relative to the position of the dune. 



3.4.4. Analysis of Storm-Induced Erosion at the Now Property 



Profile Line R-43 was selected to represent the condition of the beach and dune near the Noro 

 property. Remnants of a wooden bulkhead (apparently destroyed in the 1984 Thanksgiving Day 

 northeaster), sand-filled bags, and some stone rubble presently front this property. Therefore, the 

 dune behind these objects will be protected against mild storms, but not against severe storms. 



To conduct the calculations of dune erosion by multiple storms, the FDEP profile-survey data 



28 



at R-43 for May 1982 were selected to represent the beach and dune. This survey was made 

 just prior to the devastating 1984 Thanksgiving Day storm. Coverage for the survey extends 

 from landward of the dune crest to an elevation of -6.5 ft NGVD. To complete the profile so 

 that it could serve as a realistic initial condition for subjection to the three storms, the December 



29 



1993 survey data for R-43 were appended from elevation -7.5 to -32 ft NGVD. 



For the calculation, the stone revetment located at the dune on Survey Line R-43 was not included (although this is 

 possible in SBEACH) in order to calculate storm-induced erosion of a profile representative of that at the Noro property. 



29 



A point at -32-ft elevation was added to the profile some 4,000 ft offshore to extend the measured profile and allow 

 random storm waves to break beyond the limit of the actual survey data at elevation of about -25 ft. After the dune-erosion 

 calculation for each storm was completed, the resultant calculated profile, which was in equilibrium with the storm, was 

 replaced with data from the December 1 993 survey from the +4-ft elevation to the seaward limit of the survey data. This 

 combination of profiles provided a realistic and consistent profile shape to serve as the initial condition for the subsequent 

 storm. 



Chapter 3 Assessment of Coastal Change 



3-19 



