CLASSIFICATION IN BELATION TO WATER EESOXJECES. 173 



adopted. The detailed investigation consists of surveys to determine 

 river profiles, surveys of reservoir site, soundings at dam sites and 

 other places, and a more or less careful examination of the charac- 

 ter of the underlying formations that must serve as foundations, 

 especially for dams. In addition, it is necessary to establish river 

 gaging stations, if none have already been established, for the pur- 

 pose of determining, with a high degree of accuracy, the amount of 

 water discharged by the river, so that the economic capacity of the 

 reservoirs and power plants may be determined. 



The gaging stations are selected, equipped, and maintained ac- 

 cording to the standard methods followed by the United States 

 Geological Survey in its regular hydrometric work. The processes 

 are fully described in the annual progress reports on investigations 

 of stream flow published by the Survey. 



The investigation of dam sites for the purpose of determining 

 the security of the underlying formations that must serve as founda- 

 tions has, up to the present time, been based largely on general geo- 

 logic information concerning the holding qualities of the forma- 

 tions known to exist in the localities examined. Final work of this 

 character, none of which has been attempted in connection with the 

 classifieation of water-power sites, will consist of the usual soundings 

 and borings to determine the depth of the holding material, its 

 permeability, its strength, and all the other factors that enter into 

 its suitability for foundations. 



Special river surveys delineating the alinement and water-surface 

 contours of streams and the topography of the adjacent land are 

 made on a scale of 2 inches to the mile by the plane-table and stadia 

 method. The survey maps are accompanied by profiles showing 

 clearly the stream gradient. The contour interval on water surfaces 

 is usually taken as 5 feet but may be increased to 25 or even to 100 

 feet for sections of steep slope where the delineation of a lesser in- 

 terval could not be clearly made. The topography of the land adja- 

 cent to the stream is shown by a contour interval of 25 feet and in 

 general is carried to an elevation 100 feet above the stream by survey 

 and an additional 100 feet by sketching. General features of cul- 

 ture, gaging stations, existing hydraulic works, all lines of land sub- 

 divisions by public survey, and other relevant data are shown on 

 these maps. Promising reservoir and dam sites are shown with con- 

 tour intervals of 5 feet to an elevation equal to the height of the 

 possible dam. 



Engineers executing these surveys are instructed to obtain and 

 furnish to the Washington office all available data as to the water 

 resources involved, supplementing the data shown on the maps by 

 detailed description of existing or proposed developments. 



