245 HYDROGRAPHIC MANUAL PaGE 106 



245. Station Marks and Descriptions 



Stations located by hydrographic methods shall ordmarily not be permanently 

 marked, but if the frequency of the marked topographic stations is not sufficient for 

 the requirements of 235, selected hydrographic stations may be marked to supply the 

 deficiency where they are located by methods complying with the requirements for 

 topographic stations. Such stations shall be marked with topographic station marks 

 and be described on Form 524 just as if they were topographic stations (see 235 and 

 2351). 



246. Hydrographic Stations in Inaccessible Places 



The framework of a hydrographic survey must be provided by triangulation and 

 usually the control stations for the sounding are accurately located by the topographer, 

 but occasionally the configuration and the character of the coastline prevent the 

 topographic party from landing or traversing along the shore, or from it the main control 

 stations cannot be seen. Under such conditions along unimportant shorelines or 

 waterways the control may often have to be located by less accurate means. The 

 ingenuity of the experienced topographer or the hydrographer will practically always 

 discover a means of locating the control stations needed in such areas by methods 

 sufficiently accurate for the purpose. 



Under this heading a few unconventional methods which have been successfully 

 used in the past are described or mentioned merely as a guide to what may be accom- 

 plished under such circumstances. The list is not intended to be complete. Such 

 methods should be used only as a last resort. 



2461. Stations on a Precipitous Shore 



Occasionally a stretch of inaccessible shoreline at the base of steep cliffs is encoun- 

 tered which presents a special problem to the surveyor, especially on open coasts. It 

 is frequently impossible to make landings from small boats at such places or to traverse 

 the shoreline or to see the main control stations from the shore. 



In such cases small boats, in periods of flat calm, can generally be maneuvered 

 close enough to the base of the cliff's to place whitewash marks on them by the use of a 

 spray gun or by hurling glass bottles filled with whitewash against the cliffs, which, on 

 breaking, leave the spot whitewashed. The whitewashing should be done at high tide 

 and every effort should be made to place the signals on the cliffs as high above the high- 

 water line as possible in order to prevent their being washed away by the seas before 

 they have been used. 



When it is impracticable even to place whitewashes as described above, it is 

 often possible to identify natural objects such as rocks, discolored spots on the cliffs, 

 clumps of bushes, or trees which will serve for signals in lieu of anything more definite. 



The whitewashes or natural objects are then cut in by the method described in 

 2432. Figm*e 18 illustrates such a condition and the method used. 



Another method of establishing control for the inshore hydrography along an 

 inaccessible coast, provided the depths are not too great, is to anchor a series of buoys 

 comparatively close inshore. These are located in the same manner described above 

 for locating the shore stations. This method is described in 2551. 



