CO 



05 



1200 

 1000 



800 

 600 



c 



S 400 



00 ^ 200 



i' >. 



CO o- 



O -§--200 



E 



^ -400 



o 



^ -600 



'c 



^ -800 



-1000- 

 -1200 - 



r- 500- 





■500- 



■^ 



o o o 



I I I I 



I I I I I I 



100 



8 



200 



8 



Time Between Surveys (months) 



(bosedondota from Taney, 1961 o) 



Figure 4-27. Unit volume change versus time between surveys for profiles 

 on south shore of Long Island (data are from profiles extending from 

 MLW to about the -10-meter depth contour). 



nearshore profiles are usually much larger than net changes, even when the 

 interval between surveys is several years. These data show that care is 

 needed in measuring nearshore profiles if results are to be used in 

 engineering studies. The data also suggest the need for caution in 

 interpreting differences obtained in two surveys of the same profiles. 



The positions of beach profiles must be marked so that they can be 

 recovered during the life of the project. The profile monuments should be 

 tied in by survey to local permanent references. If there is a long-term use 

 for data at the profile positions, the monuments should be referenced by 

 survey to a state coordinate system or other reference system, so that the 

 exact position of the profile may be recovered in the future. Even if there is 

 no anticipated long-term need, future studies in any coastal region are likely 

 and will benefit greatly from accurately surveyed, retrievable bench marks. 



For coastal engineering, the accuracy of shelf profiles is usually less 

 critical than the accuracy of beach and nearshore profiles. Generally, 

 observed depth changes between successive surveys of the shelf do not exceed 



4-64 



