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HYDROGRAPHIC MANUAL 



cept where shoaler soundings have been, 

 found by the hydrographic survey, verified 

 soundings, groundings, bottom characteris- 

 tics, and wreck or obstruction notations 

 shall be transferred from the wire-drag sur- 

 vey. They shall be inked in dark green ; and 

 the grounding circle shall be omitted. Any 

 conflicts between hydrographic-survey sound- 

 ings and wire-drag effective depth shall be 

 resolved. 



The notation "Soundings in green from 



H (19—) W.D." shall be inked in 



green slanting lettering in a marginal area 

 adjacent to the transferred soundings (Fig. 

 83). 



6-99 Prior survey comparison. — All prior 

 hydrographic surveys shall be carefully com- 

 pared with the new survey unless such com- 

 parison was made with the last previous 

 basic survey and fully discussed in a modern 

 review report. It is then necessary to com- 

 pare only the latest prior survey with the 

 current survey, in the common area. The 

 comprehensive comparisons and reviews 

 were initiated in 1932. 



This comparison serves two purposes. Pri- 

 marily, it is necessary to determine whether 

 the new survey is adequate to supersede the 

 prior surveys and to carry forward, in color, 

 any important data needed to supplement 

 the new survey. Also, the comparison will 

 reveal the stable or transient character of 

 the bottom as a matter of basic record and 

 will serve as a guide for scheduling future 

 revision surveys. 



6-100 Prior data evaluated. — In compar- 

 ing prior surveys with the new survey there 

 may be revealed differences in least depths, 

 spot depths, general hydrography, and other 

 detail. Some of these differences may be due 

 to natural or artificial changes, or to errors 

 in plotted data. Since each significant dif- 

 ference must be evaluated it is necessary that 

 the reviewer shall use competent judgment 

 before accepting or rejecting data from any 

 survey. He shall be familiar with procedures 

 and techniques used in hydrographic survey- 

 ing since the beginning of original surveys 

 in 1834. 



Before a significant prior sounding, rock, 

 or other critical detail is rejected or accepted 

 for transfer, the sounding record of the 

 prior survey must be inspected. After veri- 

 fying the reduction of a sounding, a hydro- 

 graphic position, or note, the reviewer shall 

 check-mark the recorded data in colored pen- 

 cil and append his initials. Reasons for re- 

 jections shall be noted therein unless they 

 are obvious. Rejected data on the prior 

 smooth sheet shall be neatly crossed with a 

 single colored line accompanied by a short 

 rejection notation, date, and reviewer's ini- 

 tials. Red ink shall generally be used. The 

 prior data shall not be erased as they are 

 recorded authorities for charted and other- 

 wise disseminated information. 



6-101 Retention of prior data. — Any im- 

 portant data on prior surveys which have 

 not been verified nor disproved by the new 

 survey shall be carried forward to the new 

 survey in colored ink (Fig. 83). A notation 



in the same color, usually red, "from H 



(year)" should be placed nearby, or in a 

 marginal area where a group notation should 

 read "Detached soundings in (color) from 



H (year)." Slant-line lettering shall be 



used. 



The locations of, and least depths on, all 

 important shoals, rocks, and other obstruc- 

 tions shall be compared. Where a differ- 

 ence in position is found for an identical 

 feature, the strength of the respective meth- 

 ods of location shall be evaluated and the 

 stronger one accepted. Where the least 

 depth on the feature is not verified nor dis- 

 proved by the new survey, the sounding 

 shall be transferred from the prior survey. 

 Both soundings should be shown, and each 

 shall be displaced slightly if necessary. It 

 may not be possible to plot both soundings 

 in a congested area, in which case only the 

 shoalest sounding shall be shown. 



Occasionally it is necessary to transfer a 

 group of soundings from a prior survey to 

 complete the hydrography in a gap or small 

 unsurveyed area of the new survey. Simi- 

 larly it may be necessary to supplement the 

 survey by transferring ledge, reef, or rock 

 delineations where both the new hydro- 



