22 



HYDROGRAPHIC MANUAL 



narily the project instructions will be divided 

 into and treat of the following subjects: 

 general, control, photogrammetry or topog- 

 raphy, hydrography, tides, currents, oceanog- 

 raphy, magnetics, and miscellaneous. A copy 

 of a chart of the area will be furnished on 

 which are shown: project limits, limits of 

 prior surveys, and proposed current, mag- 

 netic, and oceanographic stations. 



2-5 General instructions. — In the general 

 part of the instructions the limits of the 

 areas to be surveyed are specified, and prior 

 surveys with which junctions are required 

 are listed. A plan of operation will be stated 

 indicating the area in which operations are 

 to begin and the desired direction of prog- 

 ress. When two or more chiefs of party are 

 assigned to operate in the same area on the 

 same project, their respective areas of op- 

 eration and division of authority are defined. 



2-6 Instructions for geodetic control. — 



Copies of triangulation diagrams, lists of 

 geographic positions and descriptions of tri- 

 angulation stations will be furnished for the 

 project area. An index of control will also 

 be furnished when available. The project 

 instructions will ordinarily state whether 

 new triangulation is necessary, and, if so, 

 the requirements as to junctions and order 

 of accuracy. 



2-7 Instructions for photogrammetric 

 and topographic surveys. — Blackline impres- 

 sions, blueline tracings, and paper prints 

 of photogrammetric manuscripts, together 

 with field and office, copies of photographs, 

 will be furnished for most projects. Each 

 manuscript will be classified as preliminary, 

 incomplete, or advance (see 4-12). The in- 

 structions will state requirements, if any, for 

 identification of horizontal or vertical con- 

 trol and will specify areas where field inspec- 

 tion is necessary. Photogrammetric methods 

 should be used for location of signals wher- 

 ever practicable (see 4-18). Ground survey 

 methods shall be used to supplement the pho- 

 togrammetry where necessary or expedient. 



Instructions will state which areas are to 

 be surveyed by planetable methods and copies 

 of the most recent topographic surveys of 



such areas will be furnished for revision as 

 necessary. All planetable surveys shall be 

 made on aluminum-mounted sheets, unless 

 otherwise specified, and in accordance with 

 instructions contained in Topographic Man- 

 ual (Special Pub. No. 144) . (See 4-20) . 



2-8 Instructions for hydrography. — A 



presurvey review compiled by the Chart Di- 

 vision will usually be furnished on a large 

 scale chart of the project area. Charted fea- 

 tures which require investigation will be 

 indicated (see 6-108). The presurvey review 

 does not relieve the Chief of Party from his 

 responsibility to compare surveys with 

 charted data. Copies of the most recent hy- 

 drographic surveys in the project area will 

 be furnished for comparison or junction 

 purposes. 



The instructions for hydrography will ordi- 

 narily specify : 



(a) The scales to be used. The Chief of 

 Party is authorized to use larger scales in 

 small harbors if he so desires. 



(b) Maximum spacing of sounding lines 

 referred to certain areas or depths. 



(c) The percentage of crosslines to be run. 



(d) The required frequency of bottom 

 samples. 



(e) Sounding and positioning equipment 

 to be used. 



(f) Project limits and junctions to be 

 made. 



(g) Wire drag investigations required. 

 2-9 Instructions for tide stations. — 



Copies of the reports of tide stations pre- 

 viously established in the area, with the ele- 

 vations and descriptions of bench marks and 

 the heights of the datum planes at each, will 

 be furnished. The instructions will specify 

 what tide station is to be used as a standard 

 reference station for the project. An inspec- 

 tion of, and report on, an existing station 

 may be required. Supplemental tide stations 

 are usually required and the instructions will 

 usually specify how many are necessary and 

 the desired locations. A Chief of Party is 

 authorized to depart from a specified location 

 if, on examination, it appears impracticable 

 (see 1-46). 



