3122 HYDROGKAPHIC MANUAL PaGE 194 



3122. Inshore Limits on Open Coasts 



On open exposed coasts the hydrographic survey should extend as close to the 

 shore as possible without jeopardy to life or property. It is always desirable to have 

 the low-water line accurately delineated by the hydrographic survey, but on many 

 open coasts this is manifestly impossible — for example, in regions where the range of 

 tide is extremely small, as along the coast of the Gulf of Mexico. 



Along regular sandy beaches the lines should be run parallel to the shore and 

 advantage should be taken of periods of high tides and calm weather to run the lines 

 nearest to shore. Under such conditions where the range of tide permits, it should be 

 practicable to delineate the low-water line. In areas of extremely small range of tide 

 there may be a wide band of very shoal water offshore from the low-water line which 

 is difficult and uneconomic to develop. In such areas the inshore lines shall be run 

 as close as practicable to the shoal area, supplemented by a few widely spaced sound- 

 ings on the shoal area obtained by wading or from a pulling boat. 



On rocky coasts, especially where steep-to, it is frequently impracticable to delineate 

 the low-water line even in part and when it is dangerous to attempt this, the fact should 

 be stated in the Sounding Record. Where it is dangerous for the sounding launch to 

 enter a rocky area along the shore, or where kelp is so thick that the sounding boat 

 cannot navigate through it, the fact should be stated in the Sounding Record and the 

 area accurately outlined on the boat sheet. If the kelp area is of importance to navi- 

 gation a flat-bottomed skiff should be used in calm weather to investigate the area and 

 determine the least depth. 



Where the low-water line cannot be delmeated by the hydrographic survey, the 

 areas should be fully described in the Descriptive Reports with an explanation of the 

 conditions preventing the extension of the survey closer inshore. Copious notes should 

 be made in the Sounding Records in such cases to show clearly that the inshore Ime is 

 being run as close to the shore as safety permits, and estimated distances to the breakers 

 or to the shore should be frequently noted in the Record. From these data the line of 

 breakers, kelp, reefs, or other impedimenta should be sketched on the boat sheet in ink 



3123. Navigable Streams and Estuaries 



Within the project limits all streams shall be surveyed to the head of navigation 

 for small boats, and all tidal sloughs and estuaries to the same limit or until the low- 

 water line has been accurately delineated, unless the project instructions specify 

 otherwise. 



313. Project and Survey Junctions 



The project instructions will state specifically with what prior surveys junctions 

 are to be made. Photographic copies of these surveys will ordinarily be furnished with 

 the instructions (see 131). 



3131. Surveys of Other Organizations 



Where large-scale hydrographic surveys of other organizations exist in a project 

 area, such surveys shall not be duplicated if they are comparable in accuracy to the 

 surveys of this Bureau and can be utilized for charting. The United States Corps of 

 Engineers makes periodic surveys and examinations of dredged channels, and occasional 

 surveys of navigable streams and other inside waters. Such areas shall not be surveyed 

 by this Bureau when a suitable agreement in depths is found at the jmictions with the 



