FUTURE NEEDS FOR DEVELOPMENT 231 



tal agencies. Full utilization of ground-water reservoirs is de- 

 pendent also upon an understanding of the place of each 

 reservoir in the hydrologic cycle. Unfortunately the hydro- 

 logic cycle is not studied as a unit but by phases, and the 

 quantitative analysis of the movements of water through it is 

 dependent upon basic data collected by many governmental 

 and private agencies, and also upon data not yet being 

 collected because no satisfactory means have yet been de- 

 vised. 



In very few areas in the United States have hydrologic data 

 been collected and studied for a long enough period to point 

 the way toward a firm program for the fullest utilization of 

 the available water resources. For nearly all the country there 

 is great uncertainty as to the magnitude of the storage or 

 natural replenishment of water in the ground or the extent to 

 which man has modified or can modify the natural conditions. 

 A prerequisite for full development of water resources in these 

 areas is adequate technical information, including both the 

 basic data necessary for application of proved hydrologic prin- 

 ciples and research to provide more effective ways for meas- 

 urement of the water passing through each phase of the 

 hydrologic cycle. With adequate hydrologic data a reliable 

 determination can be made as to the quantity of water that 

 can be yielded perennially by a ground-water reservoir, or 

 more broadly, a drainage basin. Thus the technical data be- 

 come the basis for determining the full potential of develop- 

 ment that can be sustained. 



ADEQUATE INVENTORY OF WATER PASSING THROUGH THE 

 HYDROLOGIC CYCLE 



In every area where ground-water development has re- 

 sulted in declining yields, increasing lifts, or encroachment of 

 unusable water in wells, hydrologic data have been essential to 

 a diagnosis of the trouble, and to the development of corrective 

 measures in the areas which have faced critical problems in 

 the past. But the value of data concerning storage and move- 

 ment and inflow and outflow of water in ground-water reser- 



