9343 HYDHOGHAPHIC MANUAL PaGE 856 



veys are forwarded to the Office (see 381 and 7827). Those conflicts which are still found to exist 

 should be adjusted in accordance with 7827. 



The reviewer may, with discretion, alter the symbol of a rock or change the amount it bares on 

 a topographic sheet to bring it into agreement with a contemporary hydrographic sheet without 

 an accompanying notation. But he should not change the character of a rock on a topographic 

 survey, if the difference is consistent with the stage of tide at the time of the survey; an explanatory 

 note should be added to the review of the topographic survey. 



The smooth sheet should contain all information on the boat sheet when it is forwarded to 

 the Office (see 7912). Rocks and other hydrographic data inked on the boat sheet but not found 

 on the smooth sheet and having no other authority should usually be referred to the field party for 

 disposition, but where a satisfactory disposition cannot be made in this manner, they should, with 

 discretion, be transferred to the smooth sheet. 



e. Datum note. — The reviewer should check the correct application of the horizontal datum 

 note in Stamp No. 42 on the smooth sheet. 



Where the dms. and dps. of the reference station are found to agree with the values resulting 

 from adjusted office computations, the word "adjusted" should be added, and if they are from field 

 computations, the word "unadjusted" should be added. R.A.R. stations or buoj's cited as reference 

 stations should always be marked "unadjusted." 



9343. Comparison With Prior Surveys 



This is one of the most important phases of the review. Its purpose is to make 

 certain that the survey being reviewed is adequate to supersede the prior surveys, 

 and to carry forward to the new survey in colored ink any important data not verified 

 nor disproved by the new survey. After review it should be unnecessary for the 

 chart compiler to consult prior surveys of an area covered by a modern survey, except 

 as specificall}^ mentioned in the written review. 



Comprehensive evaluation of the material requires, among other considerations, 

 that the reviewer utilize his knowledge of the accuracy and limitations of both modern 

 and obsolete methods of surveying. Each prior survey must be individually com- 

 pared with the present survey. 



Important shoals and rocks on prior surveys shoidd be considered separately with 

 respect to the general character of the bottom, and where not reasonably verified in 

 position or depth by the new survey, their correctness should be verified by reference 

 to the original Sounding Kecords, with special regard to the type of sounding, reduc- 

 tion, plotting, and character of control. If found correct, the advisability of carrying 

 them forward on the new survey should be considered. Errors found on a prior hydro- 

 graphic or topographic survey, during the course of the review, shoidd not be corrected, 

 but the correct information should be indicated on the old sheet in red ink with a brief 

 explanatory note. (See also 9344.) 



a. Wire-drag surveys.- — Except where shoaler depths have been found by the new- 

 survey, all soundings and groundings on w^re-drag surveys shall be carried forward in 

 color on the new survey (see 7866). 



9344. Treatment of Rocks From Prior Surveys 



It will frequently be found that rocks sho\Mi on a prior survey have not been veri- 

 fied by the new survej' or have been located in a slightly different position, or are of a 

 somewhat different character. In the disposition of such cases all available information 

 should be consulted and the following rules should be followed: 



(a) Rocks shown on a prior h^-drographic survey that are not authenticated in the Sounding 

 Records or confirmed by other survej's should be considered as nonexistent and appropriately marked. 



