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<br />r .... (.,:-,) <br />.;; ..,:.... <br /> <br />1 <br /> <br />(,.; <br /> <br />METHOI'OLlTAN WATER DISTRICT <br /> <br />occurs as surface discharge derived from seepage percolation below <br />Gene and Copper Basin resen"oirs and is mea:;:.ured by four weirs <br />at the points shown on the vicinity map, figure 5. For the water <br />year 1952, the return flow measured in the four wash channels <br />tributary to the Colorado River or Lake Havasu amounted to <br />5,124 acre-feet, the rate of flow varying from 7.6 cubic feet pel' <br />second in winter to 6.8 c.f.s. in late summer, showing moderate <br />evapo-transpiration effects along the wash banks. The weir meas- <br />urements are made when no flow from the rare desert rainstorms <br />is present. All of the washes formerly showed flow only during and <br />immediately after such infrequent storms but are now perennial <br />streams. Their seepage flow gradually increased for several years <br />after aqueduct pumping into the two reservoirs began in 1939, but <br />with restored stabilization of the loca! groundwater storage, their <br />flow has become very uniform during the last 6 years or more. <br />Records are not as yet secured to indicate in all cases the exaet <br />amount of beneficial consumptive use, defined as "diversions less <br />returns to the river" for the irrigated valleys adjacent to the lower <br />Colorado River. This is because the precise amount of such retul'll <br />flow, reentering the river at such points as to permit its beneficial <br />diversion and reuf.C by lower projects, is not now availahle or of nluch <br />practical impol'tance as long as these irrigated projects are only <br />partially developed and while large volumes of Colorado River water <br />continue to waste unused into the Gulf of California. This flow at <br />the mouth of the Colorado River, as yet of economic use only for <br />power development at Hoover, Davis, and Parker dams is, during <br />normal or above normal runoff years, mainly upper basin allocated <br />water, only temporarily available in the lower basin. To the extent <br />that return flows are not fully allowed for, however, the indicated <br />river loss is also too small by the same amount and the consump- <br />tive use likewise too large. Ultimately, of course, such river losses <br />will be greatly reduced, after completion of channelization work <br />now under way and when upper basin allocations are more com- <br />pletely in use above Lee Ferry. <br />In addition to the main Colorado River water uses listed in <br />table 14, recent U. S. Bureau of Reclamation reports indicate mis- <br />cellaneous present beneficial consumpti\'e uses averaging 170,000 <br />acre-feet annually on lower Lasin tributaries in Nevada, Utah, New <br />Mexico, and Arizona (except Gila River). On the basis of the <br />quoted consumptive use definition, considered properly applicable <br />in Arizona as in the remainder of the Colorado River basin, the <br />beneficial consumptive use in the Gila basin iu normal years has <br /> <br />j <br />