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HYDROGRAPHIC MANUAL 



dimensions be measured. A careful estima- 

 tion by eye is satisfactory. 



Table 10. — Sediments classified by size 



5-78 Description of bottom materials. — 



The nature of the bottom materials is indi- 

 cated by an adjective, such as soft, hard, 

 sticky, or the size, as coarse, fine, or medium. 

 When the consistency of the bottom is de- 

 termined by feeling with a leadline or pole 

 and without a visual examination, it shall 

 be described by an adjective unaccompanied 

 by a noun. The use of the term "rocky" is 

 to be avoided in this respect; the term 

 "hard" should be used instead in all cases 

 where applicable. The term rocky may be 

 used when it is known that the bottom is 

 bedrock or consists of material larger than 

 gravel but no speciman can be obtained for 

 examination. 



The color of the specimen should always 

 be noted while it is wet, as the color of some 

 sediments is different when dry. The terms 

 "dark" and "light" should never be used 

 alone; they are intended for use in quali- 

 fying the intensity of a color. 



5-79 Verification of charted features. — 



The data transferred to the boat sheet as 

 specified in 5-15 must be compared with the 

 results obtained by the survey. If the trans- 



ferred sounding is obscured by the new 

 soundings, there is a chance that it may be 

 overlooked and not properly investigated. 

 Each charted danger must be surveyed in 

 detail. If the hydrographer fails to find a 

 reported shoal or danger at its charted posi- 

 tion, the survey of the area must be so com- 

 plete that the cartographer is justified in 

 removing the feature from the chart. All 

 indications of shoals in the vicinity should 

 be meticulously examined as the positions of 

 reported dangers are often in error. A sound- 

 ing or charted danger cannot be removed 

 from the chart unless there is conclusive 

 evidence that the feature does not exist. 



It is not sufficient to merely prove the 

 existence of charted features ; their positions, 

 the least depth on submerged features, and 

 the elevations of the exposed ones must be 

 determined. If the new survey finds a least 

 depth which is greater than the charted 

 depth, the descriptive report must explain 

 the discrepancy and contain a positive rec- 

 ommendation as to which depth should be 

 charted, and why (see 7-4) . 



One of the most difficult problems en- 

 countered in hydrographic surveying is con- 

 cerned with charted piling. Submerged stubs 

 of broken piles are almost impossible to lo- 

 cate by any means other than dragging. 

 When there is no visible evidence of a 

 charted pile or dolphin, the hydrographer 

 should consult with local agencies as the 

 Corps of Engineers, Coast Guard, or owner 

 of the waterfront property to find out wheth- 

 er the piles have been removed. Lacking 

 conclusive evidence to this effect, the area 

 should be examined at the lowest tide, and 

 it may be necessary to use a small drag be- 

 fore a definite recommendation can be made. 



Where an adequate wire-drag survey has 

 been made in a nonchangeable area, the dan- 

 gers, shoals, and the least depths originating 

 with the wire-drag survey need not be veri- 

 fied unless required by the project instruc- 

 tions. In an area of considerable importance 

 to navigation, obstructions and dangers to 

 navigation may have been removed. The hy- 

 drographer must consult with the Corps of 

 Engineers to learn which obstructions have 



