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Show LARAMIE RIVER LITIGATION 681 varies considerably and there are no definite data on the subject. As respects irrigation on the Laramie Plains above the Wheatland diver- sion, the evidence satisfies us that the return water will certainly more than counter-balance the loss through evaporation and otherwise when the period of storage is not more than from one year to the next. What has now been said covers the substance of the evidence, as we regard it, bearing on the available supply at Woods and in that vicinity, that is to say, the supply remaining after the recognized Colorado appropriations are satisfied. We already have indicated that, as to such a stream as this, the average flow of all years, thigh and low, cannot be taken as a proper or reasonable measure of what is available for practical use. What then is the amount which is available here ? According to the general con- sensus of opinion among practical irrigators and experienced irriga- tion engineers, the lowest natural flow of the years is not the test. In practice they proceed on the view that within limits, financially and physically feasible, a fairly constant and dependable flow materially in excess of the lowest may generally be obtained by means of reser- voirs adapted to conserving and equalizing the natural flow; and we regard this view as reasonable. But Wyoming takes the position that she should not be required to provide storage facilities in order that Colorado may obtain a larger amount of water from the common supply than otherwise would be possible. In a sense this is true; but not to the extent of requiring that the lowest natural flow be taken as the test of the available supply. The question here is not what one State should do for the other, but how each should exercise her relative rights in the waters of this interstate stream. Both are interested in the stream and both have great need for the water. Both subscribe to the doctrine of appro- priation, and by that doctrine rights to water are measured by what is reasonably required and applied. Both States recognize that con- servation within practicable limits is essential in order that needless waste may be prevented and the largest feasible use may be secured. This comports with the all-pervading spirit of the doctrine of ap- propriation and takes appropriate heed of the natural necessities out of which it arose. We think that doctrine lays on each of these States a duty to exercise her right reasonably and in a manner cal- culated to conserve the common supply. Notwithstanding her pres- ent contention, Wyoming has in fact proceeded on this line, for, as the proof shows, her appropriators, with her sanction, have provided and have in service reservoir facilities which are adapted for the purpose and reasonably sufficient to meet its requirements. There is one respect, requiring mention, in which Colorado's situa- tion differs materially from that of Wyoming. The water to satisfy the Colorado appropriations is, and in the nature of things must be, diverted in Colorado at the head of the stream; and because of this those appropriations will not be affected by any variation in the yearly flow, but will receive their full measure of water in all years. On the other hand, the Wyoming appropriations will receive the water only after it passes down into that State and must bear what- ever of risk is incident to the variation in the natural How. Of course, this affords no reason for underestimating the available supply, but 94_497-69------44 |