210 



HYDROGRAPHIC MANUAL 



legend "Rk" depending on the available in- 

 formation. Where several least depths are 

 obtained on a submerged reef, then the nota- 

 tion should be the abbreviation "rky," indi- 

 cating a rocky bottom. When the depth 

 has not been determined and the standard 

 symbol is used, a notation "breakers" shall 

 be added if so noted in the records. 



6-34 Coral. — Coral may be found as a 

 reef fringing the shoreline, as an atoll, or as 

 a detached coral "head" or pinnacle usually 

 submerged. A coral reef awash or uncover- 

 ing at the sounding datum shall be repre- 

 sented by the reef symbol with the legend 

 "coral." Pinnacles and small patches of coral 

 are represented by symbols for rocks with 

 the legend "coral," or the abbreviation "Co" 

 (Fig. 79). 



6-35 Rock elevations. — The elevations of 

 rocks or coral and of reefs and ledges are 

 referenced to low-water or high-water da- 

 tums as specified in 6-31 and 32. Elevations 

 above any datum should be given in feet to 

 the nearest whole foot. The values are al- 

 ways shown in slanting figures enclosed, in 

 parentheses, close to the feature. Elevations 

 referenced to a low-water datum shall be 

 underlined (Fig. 81). If the elevation of a 

 bare rock is transferred from a topographic 

 or photogrammetric survey, the value shall 

 be inked with red numerals about 2 mm 

 high, and for similarly transferred rocks 

 awash the values shall be shown in black ink. 

 All elevations determined by the hydro- 

 graphic party shall be shown in pencil on 

 the smooth sheet and will be inked in black 

 after office verification (see 5-67) . 



For rocks covered or exposed a half-foot 

 at the low-water datum, the elevation is 

 shown as zero, or the notation "awash at 

 MLW (or MLLW)" may be substituted to 

 emphasize the existence of a dangerous iso- 

 lated rock. For rocks awash which are 

 covered 1 foot (2 feet on Pacific Coast), the 

 notation "covered 1 ft. MLW (2 ft. MLLW)" 

 should be used in inland waters where the 

 rock is seldom exposed by rough water or 

 low tide. On an outer coast or in areas where 

 the rock is frequently exposed at low tide, 



then the zero value or awash notation should 

 be used. 



Where rocks are closely grouped, the ele- 

 vations should be omitted for those of les- 

 ser importance. The important values are at 

 the outer and highest rocks. Elevations shall 

 not be transferred from topographic surveys 

 beyond the general limits of the hydro- 

 graphic survey. 



6-36 Landmarks. — Each landmark that 

 is recommended for charting (see 7-18) that 

 is within the limits of a photogrammetric 

 or hydrographic survey must be plotted and 

 identified on one or the other of such sheets. 

 If the object has been used to control hy- 

 drography, it will be indicated by a station 

 symbol appropriate to the method of loca- 

 tion. To identify the object as a recom- 

 mended landmark, the landmark name as 

 reported on Form 567 shall be shown in 

 black ink and in parentheses after the sta- 

 tion name, and the word "landmark" in 

 black ink shall be placed in parentheses be- 

 low the station name, accompanied by the 

 elevations (also in black) of the landmark 

 above the ground and above mean high wa- 

 ter, if these are known (Fig. 79). 



The hydrographer may determine that cer- 

 tain structures, not recommended by the 

 photogrammetrist, are suitable landmarks. 

 If these have not been used as signals they 

 should be plotted on the smooth sheet, the 

 position of each being indicated by a black 

 circle 2 mm in diameter, accompanied by the 

 landmark name and other notations as above 

 and in black ink. 



6-37 Cables and bridges. — The locations 

 of overhead and submerged cables shall not 

 be transferred to the smooth sheet from 

 photogrammetric surveys. Terminal points, 

 such as towers or signs, used as signals shall 

 be identified and described by suitable notes 

 (Fig. 82). Cable and bridge clearances shall 

 be shown on the smooth sheet only when 

 measured in accordance with 5-82, and the 

 data shall be left in pencil until verified in 

 the office. When no positions for the towers 

 or signs are available, the inshore ends of 



