Page 299 



HYDROGRAPHY 



Form Lines 

 [COMPUTATION OF ELEVATIONS] 



383 



Observed data are entered in columns 1, 2, .3, 5, 11, and 12. 



Data entered in columns 4 and 8 are measured from the form-line sheet. 



Values in columns 6 and 10 are from tables 7 and 4, Topographic Manual. 



Values in column 9 are computed on hypsograph, or by using table .3, Topographic Manual, from values in columns 7 and 8. 



Values in column 13 are algebraic sums of columns 9, 10, 11, and 12. 



383; Aids to Navigation 



The positions and characteristics of all aids to navigation in the project area must 

 he accurately determined, and the dates of the determinations given. (See also 784.) 



It is important that the dates of location or visitation be a matter of record insofar 

 as the items under this heading are concerned. This is especially important in con- 

 nection w^ith floating aids to navigation for at the time of the location the aid may 

 have been temporarily off station and may have been replaced on its correct station by 

 the United States Coast Guard within a short time after it was located. 



Landmarks for charts are considered in 155, and the requirements for objects for 

 use in locating aids to navigation are given in 1551. 



3831. Fixed Aids to Navigation 



All fixed aids to navigation established by the United States Coast Guard should 

 be located by triangulation if their geodetic positions are not already available or if 

 the aid has been moved m position or rebuilt since the date of the previous determina- 

 tion. Wliere for any reason it is impracticable to locate one or more fixed aids by 

 triangulation, a substitute method shall be used, but the determinations shall be such 

 that no appreciable plottable error will result. In projects where there are numerous 

 minor beacons whose positions are subject to frequent change the project instructions 

 may specify that these may be located by methods other than triangulation. If 

 compliance with the instructions requires an apparently unjustified amount of work, 

 the Chief of Party should inform the Washington Office of the facts, recommending 

 an amendment to the instructions. (See also 7841.) 



The positions of all fLxed aids located should be reported on Form 567, Land- 

 marks for Charts. 



3832. Floating Aids to Navigation 



The positions of and depths at all floating aids to navigation in the project area 

 shall be determined during the hydrographic survey. Inshore floating aids should be 



