5. HYDROGRAPHY 



135 



and inked in distinctive colors. Representa- 

 tive soundings in the area shall also be 

 transferred. It is desirable to transfer sec- 

 tions of depth curves which, with the sound- 

 ings, provide a direct comparison with pre- 

 vious surveys. 



The most recent print of the largest scale 

 nautical chart covering the area should be 

 examined and any additional dangers shown 

 thereon shall be transferred to the boat sheet 

 for verification as the survey progresses. 



A presurvey review (see 1-5 and 6-108) 

 will usually be furnished for each project. 

 Each feature marked on the chart shall be 

 transferred to a boat sheet and examined 

 during the survey. 



The positions of any locally reported shoals 

 or menaces to navigation should be plotted 

 on the boat sheet, so that their position may 

 be accurately determined or their existence 

 disproved. 



Soundings and other hydrographic data 

 transferred to the boat sheet may be oblit- 

 erated or obscured while surveys are in 

 progress. As an aid to daily inspection of 

 the survey, an overlay should be prepared on 

 tracing cloth showing all data transferred 

 to the boat sheet from the charts or prior 

 surveys (see 5-66) . As the survey progresses 

 critical data can be transferred to the over- 

 lay, as: least depths on shoals, locations of 

 rocks, breakers, obstructions, etc., with ap- 

 propriate notes for future reference. Used in 

 conjunction with the smooth sheet, the over- 

 lay provides a quick check on the complete- 

 ness of the plotted data. 



5-16 Junctions and overlaps. — To insure 

 satisfactory junctions in coverage and depths 

 with adjacent surveys, the soundings at the 

 limit of the latter shall be transferred to the 

 boat sheet prior to the beginning of a hy- 

 drographic survey. These soundings shall 

 appear in colored ink, using a different color 

 for each survey with which a junction is to 

 be made. These soundings may be from prior 

 surveys or surveys currently made on ad- 

 joining sheets of the same or different scales. 

 In areas where the Corps of Engineers, U.S. 

 Army, maintains dredged channels, .sound- 

 ings from the most recent Engineer survey 



may be transferred to the boat sheet, and, 

 if a satisfactory junction is made, the survey 

 of the channel need not be repeated (see 

 5-2). 



The source of soundings at junctions 

 should be noted on the boat sheet by ref- 

 erence to the field or registry number of 

 the survey, or the identifying number of the 

 Corps of Engineers survey. 



An overlap of at least one sounding line 

 shall be made with an adjacent survey (see 

 1-29) except where the survey is continuous 

 in the same year by the same method and 

 by the same survey vessel no overlap is re- 

 quired. If the depths at the junction are 

 not in agreement, the new survey shall be 

 extended into the old until agreement is 

 reached. If a reasonable extension fails of 

 agreement, a detailed report shall be sub- 

 mitted to the office with a request for fur- 

 ther instructions. 



The best evidence of a proper junction of 

 surveys is revealed by the continuity of the 

 depth curves in the overlap area (see 5-74). 



5-17 Inshore limits of surveys. — In pro- 

 tected waters the hydrographic survey shall 

 extend as close to the high-water line as 

 practicable. The low-water line should be 

 fully developed by the survey in all areas 

 where existing conditions permit. Sounding 

 lines should be run close to the shore during 

 periods of high tide and calm weather. Com- 

 plete development of extensive mud flats is 

 not required. A few sounding lines spaced 

 at 3 to 4 times the maximum spacing of 

 lines in the adjacent area will suffice. Sound- 

 ings are not required in areas which are 

 bare at low water. 



Within the project limit all streams shall 

 be surveyed to the head of navigation for 

 small boats, and all tidal sloughs and estu- 

 aries to the same limit or until the low-water 

 line has been accurately delineated, unless 

 the project instructions specify otherwise. 



On open exposed coasts the hydrography 

 should extend as close to the high-water line 

 as possible without undue risk to safety of 

 the boat and personnel. It is always desir- 

 able to develop the low-water line, but this is 

 impossible in many places. Along regular 



