783 HYDROGRAPHIC MANUAL PaGE 738 



differences in favor of the weightier evidence. Generally, the following rules will be 

 found applicable: 



a. Bare rocks. — Their locations and elevations should be accepted from the topographic survey 

 except where there is unmistakable evidence of incorrectness, or where it is obvious that the topo- 

 graphic location is weak. Where discrepancies between the two surveys result from the rules given 

 in 7823 for interpreting the sounding data, then the source that makes the rock a bare rock shall 

 govern. (See 7825a.) 



b. Rocks aivash. — The locations of such rocks should generally be accepted from the topographic 

 survey and should seldom be modified by the hydrographic survey. Their elevations above the sound- 

 ing datum should be taken from the hydrographic survey because of the more definite tidal information 

 available, and the closer proximity of the hydrographic party to such features. 



c. Sunken rocks and breakers. — The locations of sunken rocks and breakers, and notes relating 

 thereto should be accepted from the hydrographic survey, but it should first be determined that the 

 identical feature is involved. 



Changes in the character of rocks should not be made on the topographic survey 

 where the differences are consistent with the stage of tide at the time of survey, but an 

 explanatory note should be added to the topographic Descriptive Report. 



783. Bottom Characteristics 



After the soundings and depth curves have been penciled the bottom characteristics 

 should be penciled on the smooth sheet. Standard abbreviations have been adopted 

 for such information (see part "S" of Symbols and Abbreviations chart, fig. 189, 

 part XI) and these must be used on the smooth sheet, even if nonstandard abbreviatioiis 

 have inadvertently been entered in the Sounding Record. It should be noted that 

 low^er-case letters are used throughout for adjectives, to distinguish them from nouns 

 which all begin with capital letters. Periods must not be used after abbreviations, nor 

 are hyphens or other connecting symbols to be used between abbreviations, but there 

 should be a slight space between them. A standard bottom characteristic should 

 appear on the sm.ooth sheet thus: "hrd S Sh P". (See also 384.) Attention is called 

 to the fact that "rki/' is the abbreviation for rocky bottom, but tiie abbreviation "Rk" 

 is used only for a rock which rises from much greater surrounding depths, and not for 

 even rocky bottom (see 7823r). 



In placing the bottom characteristics on the smooth sheet a judicious selection 

 should be made. If a large number are recorded, as is usually the case in areas surveyed 

 by handlead or wire sounding, probably only part of those need be shown on the smooth 

 sheet. On the other hand, where echo sounding is used, comparatively few bottom 

 characteristics are obtained, and probably all obtained should be shown on the smooth 

 sheet, including those whose locations are somewhat indefinite. Bottom characteristics 

 obtained when anchoring and picking up buoys and when observing temperatures and 

 salinities should be shown on the smooth sheet, if an approximate location has been 

 given. 



Harbors, anchorages, and shoals are the areas where bottom characteristics are 

 most important. Each shoal must show a bottom characteristic, if one has been ob- 

 tained thereon. In harbors and anchorages, a sufficient number should be plotted to 

 show, particularly, where changes in the character of the bottom occur; but where there 

 is a monotonous sameness in the character and quality of the bottom, too many charac- 

 teristics should be avoided. (See 3842.) 



Bottom characteristics should, if practicable, be placed on the smooth sheet 

 reasonably close to and a little below and to the right of the soundings which they 



