7761 



HYDROGRAPHIC MANUAL 



Page 730 



or positions controlling such abnormalities should always be verified before acceptance 

 as correct (see 353). 



Depth curves shall be penciled on the smooth sheet before it is transmitted to the 

 Office. The colors adopted to represent the various depth curves on hydrographic 

 surveys are listed in table 27. Depth curves on smooth sheets are only inked in the 

 Washington Office after the survey has been verified. 



Table 27. — Depth curves 



7761 . Selection of Depth Curves 



All of the applicable depth curves listed in table 27, except as modified under this 

 heading, shall be penciled on the smooth sheet. However, if the survey includes sig- 

 nificant submarine features which are not emphasized sufficiently by the use of the 

 curves listed, additional curves should be drawn. The nonstandard curves and the 

 reason for using them should be given in the Descriptive Report (see Si2J). 



Although they will ordinarily not bo inked (see 7763), the 4- and 6-fathom curves 

 shall always be penciled on the smooth sheet by the field party, and the )^-fathom curve 

 shall be added where it may bo useful in small-boat navigation. 



Occasionally some of the depth curves should be omitted for reasons of clarity. 

 On steep slopes the curves may be so closely adjacent as to be confusing; in such cases 

 the shoalest and the deepest curves are generally the most important and should be 

 shown, omitting the less important intermediate ones. Wliere rocks or steep shoals 

 rise suddenly from much greater depths one or more of the deeper depth curves should 

 frequently be omitted; for instance, if a 5-foot depth on a rock is surrounded by general 

 depths of 20 feet or more, the 6-foot curve must be drawn, but the 12- and 18-foot curves 

 may be omitted. In channels with steeply sloping sides, the curve which gives the 

 maximum through depth is the most important and should be shown at the expense of 

 some of the shoaler curves. Likewise, where islands, shoals, or reefs rise abruptly from 



