5. HYDROGRAPHY 



161 



been removed. In such cases, a new least 

 depth on each feature so affected must be 

 determined by hydrographic examination. 

 Rocks and obstructions supposed to have 

 been removed by blasting should be wire- 

 dragged, if possible. 



5-80 Aids to navigation. — The positions 

 and characteristics of all aids, to navigation 

 in the project area must be accurately de- 

 termined, and the dates of the determina- 

 tions given. The date of location is especially 

 important in connection with floating aids 

 for at the time of location the aid may have 

 been temporarily off station and subsequently 

 replaced on its correct station by the United 

 States Coast Guard. 



All fixed aids to navigation should be lo- 

 cated by triangulation (second or third or- 

 der) if their geodetic positions are not 

 already available or if the aid has been 

 moved or rebuilt since the date of the pre- 

 vious determination (see 1-50). The aids 

 may be located by photogrammetric meth- 

 ods when triangulation is impracticable or 

 too costly, but the determinations shall be 

 such that no appreciable error will result. 

 In projects where there are numerous minor 

 daybeacons whose positions are subject to 

 frequent change, these may be located by 

 topographic, photogrammetric, or occasion- 

 ally by hydrographic methods. 



The positions of all fixed aids located by 

 the survey party shall be reported on Form 

 567, Landmarks for Charts. The name and 

 description of each aid shall agree with the 

 data published in the most recent Light List, 

 or differences shall be explained in the re- 

 port (see 7-22). 



The positions of and the depths at all float- 

 ing aids to navigation in the project area 

 shall be determined during the hydrographic 

 survey (see 1-50). A floating aid should be 

 located by a fix at the aid, not by cuts from 

 shore stations, and a check angle should be 

 observed. Where a marker buoy is main- 

 tained near the aid, the positions of both 

 shall be determined. 



If a floating aid is found to be off station 

 by an amount which makes it unsuited to 

 mark the feature intended, the Commander 



of the nearest Coast Guard District should 

 be notified at once. Any recommendations, 

 based on the new hydrographic survey, for 

 additional aids to navigation or for more de- 

 sirable locations for existing aids, should be 

 reported to the Coast Guard and to the 

 Washington Office in writing and shall be 

 accompanied by a photostat or tracing of 

 the boat sheet. 



Reference shall be made in the descriptive 

 report to any reports which have been made 

 to the Coast Guard relative to floating aids 

 to navigation. 



Refer to 2-48 for instructions on prepara- 

 tion of a special chart to be furnished the 

 Coast Guard for use in locating floating aids 

 to navigation. 



The azimuth of all light and daybeacon 

 ranges maintained by the Coast Guard for 

 use in navigation in the project area must 

 be accurately determined. The ranges will 

 usually be located by triangulation or pho- 

 togrammetric methods. In the latter case the 

 hydrographer should verify the azimuth of 

 the range by observing one or more strong 

 sextant fixes with check angles some dis- 

 tance away from the front range. The azi- 

 muth of a range established for use in 

 crossing a bar shall be determined or veri- 

 fied by sextant fixes on or outside the bar. 



5-81 Nonfederal aids to navigation. — 



Aids to navigation which are established pri- 

 vately or by state or local governments shall 

 be located by the hydrographic party, and 

 their positions shall be shown on the boat 

 and smooth sheets. The status of these aids 

 shall be made clear on the sheet and in the 

 descriptive report. The report should state 

 the purpose of each unofl[icial aid, the date 

 of its establishment, the agency or person 

 who established it, and whether it is main- 

 tained, if these facts can be ascertained. 



5-82 Bridges and cable crossings. — 



Bridge and cable clearance data shown on 

 nautical charts and in Coast Pilots are usu- 

 ally furnished by the Corps of Engineers, 

 U.S. Army. Survey parties should refer to 

 the List of Bridges over the Navigable Wa- 

 ters of the United States, commonly referred 



