Table. Calculation of profile approximation (example problem) 



(1) 



Distance 



offshore 



(ft) 



(2) 

 Depth 1st 

 below MLLW 

 (ft) 



(3) 

 approx. 



(ft) 



(4) 

 2d approx. 



(ft) 



(5) 

 3d approx. 



(ft) 





I >- + 37.5- 



+33.0 



-l| * +6 



70 . 5 



.0 1| - + 1 



76.5 









78.0 



200 



+ 4.0 



41.5 



47.5 



49.0 



400 



- 2.0 



35.5 



41.5 



43.0 



600 



- 6.0 



31.5 



37.5 



39.0 



800 



- 9.0 



28.5 



34.5 



37.0 



1,000 



-12.5 



25.0 



31.0 



32.5 



1,200 



-14.0 



23.5 



29.5 



31.0 



1,400 



-14.5 



23.0 



29.0 



30.5 



1,600 



-17.5 



20.0 



26.0 



27.5 



1,800 



-22.0 



15.5 



21.5 



23.0 



2,000 



-25.5 



12.0 



18.0 



19.5 



2,200 



-29.5 



8.0 



14.0 



15.5 



2,400 



-31.5 



6.0 



12.0 



13.5 



2,600 



-34.0 



3.5 



9.5 



11.0 



2,800 



-35.0 



2.5 



8.5 



10.0 



3,000 



-36.0 



1.5 



7.5 



9.0 



3,200 



-36.5 



1.0 



7.0 



8.5 



3,400 



-37.5 



0.0 



6.0 



7.5 



used since equation 3 is expressed in terms of e. Therefore, for the 

 example, equation 3 may be written 



y + 45.6 = 55.0e-°- 00056,+x . (5) 



IV. COMPUTATION OF LONG-TERM EROSION RATES 



To compute the long-term erosion rate from equation 2, the distance 

 from shore to the 55 -foot contour must be obtained from a hydrographic 

 chart and the long-term trend in sea level must be known. For the San 

 Francisco area, the long-term trend in sea level between 1898 and 1971 

 is a rise of 0.0064 foot (0.00195 meter) per year. The trend in the 

 more recent period from 1940 to 1971 has been 0.0054 foot (0.00165 meter) 

 per year. (See the App. which is reproduced from Hicks, 1973.) At 

 Ocean Beach, the distance offshore to the 55-foot contour varies, but is 

 approximately 32,600 feet (9,936 meters), thus B = 32,600. Solving 

 equation 2 , 



0.0054 (32,600) „„„,„.,„ 



Ax = = — =2.3 feet (0.701 meter) per year , 



(23.0 +55) 



