52 THE U. S. GEOLOGICAL SURVEY 



viewed in the preceding chapter. The investigation of water 

 resources, however, was carried along on a small scale by- 

 special arrangements until 1894, when an appropriation au- 

 thorized its extension to the whole country, and since that 

 time the work has progressed steadily. The maintenance of 

 hydrographic work on its present scale is made possible in 

 large measure by substantial contributions made to the work 

 by many of the states. 



The operations embraced in the survey of water resources 

 may be grouped under three heads — the location of supplies, 

 the measurement of their quantity and the investigation of the 

 practicability of their utilization. These operations vary 

 essentially according as they deal with surface or ground 

 waters. 



Surface Waters. The location of streams and springs is 

 of course determined by the regular topographic surveys. 

 Their quantity is determined by measuring their flow through 

 a period of years sufficiently long to ascertain definitely the 

 limits of variation, by maintaining stream-gaging stations over 

 all the country, but particularly in the West. During the 

 year ending June 30, 191 7, nearly 1,200 such stations were 

 maintained, but only thirty-six of them by the Survey alone, 

 the others being maintained, in cooperation with the Survey, 

 by various bureaus of the government (the Reclamation 

 Service, the Forest Service, the Indian Service, the Weather 

 Bureau, and others) and by states, cities and private persons. 

 At these stations daily measurements of stream height are 

 made, and periodic measurements of the flow or discharge. 

 During the fiscal year 191 7 an average of over six measure- 

 ments of discharge were made per gaging station. 



In addition to the data thus collected to determine the quan- 

 tity of surface waters, analyses are made to determine their 

 suitability for domestic, irrigation, boiler and other uses. In 

 this work samples are usually taken from the stream daily for 

 one year, united in sets of ten consecutive samples and the 

 composite samples analyzed. The results of the analyses, 



