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Show 518 INTERSTATE ADJUDICATIONS The records of Colorado's consumption and ditch diversions, and the Colorado and Kansas exhibits showing the divertible and usable state line flow, rebut such an increase as Kansas asserts. Kansas' expert witness himself testified that the diversion records show no material change in Colorado diversions since 1905 and that if acreage in Colorado has expanded under the ditches on the main stem of the river, it has done so because of an improved duty of water; that, dur- ing the period, the river gains due to return flow have increased, the consumptive use of water has declined, and relatively the stream flows have improved. The Kansas ditches are capable of diverting water only up to 2,000 c. f. s. When the flow is greater the excess cannot be diverted and used. It is admitted that the character of the flow of the river in Colorado is variable from year to year, from season to season, and from day to day, and the main river below Canon City may be almost without water one day, run a flood the next day, and, on the following day, be in practically its original condition. Thus it appears that both in Colorado and in Kansas there may at one time be flood water unavailable for direct diversion and, at another, not enough water to supply the capacity of diversion ditches. The critical matter is the amount of divertible flow at times when water is most needed for irrigation. Calculations of average annual flow, which include flood flows, are, therefore, not helpful in ascertaining the dependable sup- ply of water usable for irrigation. That supply has, in Colorado, been supplemented by the extensive use of reservoirs for storage of flood waters and winter flows not usable or needed for irrigation. Though western Kansas affords sites for similar storage reservoirs, but one small basin has been constructed in that State. On the other hand, the storage in Colorado, and the release of stored water to sup- plement the natural flow of the stream in times of need, operates by seepage and return to the channel to stabilize and improve the flow at the state line and, to that extent, benefits irrigation in Kansas. Kansas relies heavily upon the increase of irrigated acreage in Colorado since our decision in 1907. The testimony in the earlier case was closed in 1905. The then latest available census-for 1902- reported 300,115 acres under irrigation in the Arkansas basin in Colorado. In its opinion the court referred to this figure. The next census-for 1909-gives the Colorado acreage as 464,236. The later reports disclose an addition of less than 5,000 acres between 1909 and 1939. Thus a total of about 170,000 additional acres has been put under irrigation since 1902. On its face this record would seem to indicate a large increase of consumptive use by Colorado, but the acreage under irrigation does not afford a reliable measure of actual consumption. When first turned in, the water is rapidly absorbed by the sub-soil with consequent high consumption. By continued irrigation the sub-soil becomes saturated, the water table rises, and water, in increasing quantities, flows back to the stream. Ultimately consumption falls well below diversion. The returned water again may be diverted and again supply return flows. Since the decision in the earlier case, studies of return flows have been made which indi- cate a steady reduction in the quantity of water consumed per acre of irrigated land. |
