Profile envelopes are useful in many aspects of coastal engineering 

 planning and design; e.g., in the siting and design of structures such as 

 groins or bulkheads on a beach, and in determining the depth to bury a cable 

 on an upper beach so that it will not be uncovered. Envelopes are also useful 

 in determining the range of erosion and the subsequent natural recovery expected 

 to restore a beach, and as an aid in determining the need to replenish a beach 

 at a given time. 



Upper and lower bounds of each envelope do not represent single surveyed 

 profiles. They are the resultant outline of the maximum and minimum elevations 

 as computed for all the profiles at fixed horizontal stations 10 feet apart. 

 A single line on the landward or seaward extremity of some envelopes may indi- 

 cate that only one profile contributed to the envelope at that location. This 

 occurs because some surveys do not extend as far seaward as others. Since many 

 of the Ludlam Beach surveys did not extend much below MSL, the subsequent analy- 

 sis of these envelopes only includes the area above MSL. 



Figures 42, 43, and 44 show profile envelopes constructed from the 10 years 

 of survey data collected between 1962 and 1972. Zero distance on the horizontal 

 axis references the shoreline position as established during the first survey 

 in October 1962. The lower envelope bound is MSL. For profile line 1, the 

 landward closure is approximately 1,600 feet landward of the zero distance 

 (Fig. 42) . Maximum horizontal and vertical excursions for profile lines during 

 the 10-year period are given in Table 8. The elevation of the maximum horizon- 

 tal distance was at MSL on all but two profile lines. 



Table 8. Horizontal and vertical 10-year excursion 



maximums for profile lines on Ludlam Beach. 



Profile 



Maximum 



Elevation 



Maximum 



Location 



line 



horizontal 



of maximum 



vertical 



of maximum 





range 



horizontal range 



range 



vertical range 





(ft) 



(ft) 



(ft) 



(ft) 



1 



930 







7 



-700 



2 



360 







15 



-250 



3 



275 







14 



-250 



4 



31-0 







10 



-300 



5 



250 







6 



-200 



6 



320 







6 



-175 



7 



225 



2 



5 



-125 



8 



300 







6 







9 



350 







6 







10 



320 







6 



-25 



11 



320 







7 



-150 



12 



200 







10 



-200 



13 



200 







8 



-225 



14 



250 







10 



-225 



15 



275 







13 



-225 



16 



275 







13 



-275 



17 



200 







6 



-200 



18 



175 







5 



-150 



19 



230 







7 



-375 



20 



500 



6 



11 



-150 



^As measured from the MSL shoreline position at the first 

 survey (see tick marks on Figs. 34, 35, and 36). 



56 



