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001361 Diversions ~ ~OutflOW J r M A ~A S 0 JI D-=- AVERAGE RETURN FLa-l EFFECTS FOR DRIER HALF OF YEARS IN DISTRICTS 14 & 17 The graph shows the definite effect of June diversions on the return flow which is available for diversion during August when the diver. ion. plus the outflow are equal to twice the inflow. This illustrates why we must be very cautious about restrictions on diversions. Generally, those water users who divert greatly excessive amounts of water durina the year have senior water rights and use them on land close to the river. If one of them who has historically diverted ten acre-feet per year is suddenly limited to three acre-feet per year, he will let most of his April, May and June water go by so that he can divert !DOst of his three acre-feet during July and August when it is needed !DOst. As a result, the downstream junior users will receive his exce.s water when it is least needed, but the return flow from his early diversions will no longer be available during the time when it is needed most. Therefore, it appears that water use should not be restrfcted unle.. provision is made for either storing or using the excess water up8tream from the point where it would have been diverted if the restriction had not been made. The poor t:iming of much of the return flow is also illustrated by the great an~unt of water diverted for direct use during the period of December through March. Much of this water is used because of the soil conditioning effect of freezing and thawing on wet soils. Some is stored for in-season use in heavy subsoils. Often this water is applied to leach salts and recharge the groundwater. EFFECT OF WELLS A few wells in the Arkansas Valley supply all irrigation water for . the land which they serve. Some of these intercept only return flow from other irrigated land while others draw much of their water directly from the river. In either case the entire net irrigation requirement for crOps produced is lost from the aquifer. This is an averaae of about 1.3 acre-feet per irrigated acre. Of course, surface diversions may not be reduced by this much if the pumping has resulted in a reduction in the amount of water used by phreatophytes or if some of the effect of the pumping on the river occurs during times when the water would not be diverted. The situation is entirely different for wells which are used to supple- ment surface rights. In this case, most of the net irrigation require- ment of the crop is usually met by surface water. Pumped water supplies the small additional amount which is needed during critical periods,