PROBLEMS FROM LAND OCCUPANCY 187 



of each drainage basin. Particularly in the West, a large pro- 

 portion of the water that falls as precipitation is returned to 

 the atmosphere without ever reaching the streams or ground- 

 water reservoirs. Vegetation sustained by this water might be 

 removed or replanted without affecting these net water re- 

 sources. The West has many barren areas, as well as forests, 

 which make their contributions to streams chiefly as the snow 

 melts and on which precipitation at other times may be dis- 

 sipated without benefit to man. 



A vegetative cover for prevention of erosion in these areas 

 might draw in large part on water that would not in any 

 case contribute to stream flow, just as the forests today subsist 

 in part on water that would return to the atmosphere and not 

 be available to the streams whether the forests were there or 

 not. On the other hand, the nonbeneficial vegetation alone 

 streams and the native plants that draw on ground water for 

 their supplies deplete the water resources that man might put 

 to better use. And by depleting the soil moisture in recharge 

 areas of ground-water reservoirs, other plants may reduce the 

 quantity of water available for ground-water replenishment. 



One of the major problems in the development of the river 

 basins of the West is the tributary drainage basin that con- 

 tributes large quantities of sediment but little water to the 

 main stream. The Colorado and the Rio Grande have dozens 

 of these tributary basins where nearly all the precipitation re- 

 turns to the atmosphere except after intense storms, and then 

 for a few days the main stream receives a veritable river of 

 mud. Research is needed to show to what extent the water 

 could be used within the tributary basin to prevent discharge 

 of sediment. For some tributary basins the value of the total 

 water contribution is negligible in comparison with the detri- 

 ment of the sediment load to the fully developed river system. 



ARTIFICIAL REPLENISHMENT OF GROUND-WATER RESERVOIRS 



The reduction of overland flow by effective land- 

 management practices generally increases the movement of 

 water into the soil, and thus the conservation of soil and the 



