WATER RESOURCES 191 
about 128 million acre-feet can be ultimately used for irrigation. 
Presently about 78 million acre-feet have been put to use. In many 
western streams, the entire water supply is fully used except for 
infrequent years of high flood runoff. 
In other words, about one-third of the total stream runoff can 
be used for irrigation, and we are now using only one-fifth of the 
total. But for the sake of progress toward the goal, it is essential 
that all efforts be made to irrigate the remaining 17 million acres, 
putting to work much of the remaining s0 million acre-feet of 
available water. In many cases this will necessitate diversions of 
water between major waterbeds. 
For streams such as the Columbia and Missouri Rivers, there 
is a large foreseeable flow that cannot be used for irrigation pur- 
poses. In such areas, plans are being formulated for the controlled 
and coordinated use of water for non-consumptive purposes such 
as navigation and power development. 
Problems of Long-Term Planning 
Whatever allocation of the water resource is made to whatever 
purposes, the greatest final benefit to all interests will necessitate 
adequate storage. Increasingly as years pass greater use will be 
made of both surface and ground water storage. I am not seeking 
an argument when I say that surface storage developed to its 
maximum is the prime means of developing and utilizing our sur- 
face water supplies. Some water should and will be put to work 
where it falls—head water, small dam storage has a proper place 
in planning full beneficial water development. The fact remains, 
however, that reservoirs, whether main stream or tributary, must 
be the principal basis for conserving the waters of our surface 
streams. 
Certain benefits of surface storage are so obvious as to need no 
recitation here. One benefit that I would like to bring out is that 
storage is a necessity to correct the variable characteristic of 
stream flow. Such variability is of a cyclic nature. It is marked by 
a tendency for high stream flow to occur in periods of from five 
to ten years, and for low flow to extend over periods of from five 
to twenty years. Capacities must be provided to retain water from 
