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'9: Page, ) Mexico. Ie Lower ,e of sub- ,e. It was m water at diver- e-feet are I yield of , subs tan- qcre-feet ,ndwater "as using Id place, lwed by e Lower "ial and A.rizona, : are sevp nia; and number .ibutaries 'e in the versy be- , arose m the main rict and, ;enerall y and spe- rn Cali- 'r A'!u_ !hi, sys- that are [iation and d Seu. 45 No,"ember '966] THE COLORADO RIVER 9 members of the Metropolitan Water District." In Nevada three munici- palities receive water from the main stream: Las Vegas, Henderson, and Boulder City. 3. Wata JUpply and principal storage works. As noted above, the only important source of main-stream water for the Lower Basin is the Upper Basin, and the /low is extremely erratic. Begin- ning with the year 1929, for example, We find a high /low of 19.2 million acre,feet, followed thc next year by 13.1 million acre-feet, then a low /low in 1931 of 6.4 million acre-feet, rising in 1932 to r5.3, in 1933 dropping to 9.7, and in 1934 reaching a record low of 4.4, only to rise again in 1935 to 9.!{-allligures being the measured, historic flow at Lee Ferry." For the pcriod rB9Il-r963 the average historic flow at Lee Ferry was r3.4 million acre,feet, and the reconstructed virgin Or undO! ':rted flow for the same period was 14.9 million acre-feeL" Both Hoover and Glen Canyon Dams were built to regulate and even out this variable supply. Glen Canyon Dam, besides generating power rev- enues to pay for the Upper Colorado River Storage Project, provides enough storage capacity to enable the Upper Basin to meter its water deliveries to the Lower Basin rather precisely, a practice that has already caused some friction between the two basins. Hoover Dam, with an active storage capacity of 27.2 million acre,feel, and a smaller regulating dam 67 miles downstream, Davis Dam, enable the Bureau of Reclamation, which oper- ates the river, to make weekly deliveries of water ro customers along the entire reach of the riva, including Mexico." For example, farmers in the Imperial Valley report their needs for the next week to an ollice in the dis- tricl. The ordas are totaled and transmitted to the Boulder City ollice of Ule Bureau (located at Hoover Dam), and in due course water is released at ule dam in time to reach each farmer in accordance with his order. Two other dams on the main stream, Parker and Imperial, serve re- 'l','clively as diversion structures for the Colorado River Aqueduct (leading 10 Los Angeles) and for the All-American Canal (serving Imperial and Coachella Valleys). The Colorado River Aqueduct is 242 miles long and is designed to transport 1.3 million acre-feet per year." Morelos Dam is the last structure on the main stream in the United States and was built unJer the Mexican water treaty of 1944 to serve as the diversion point for the Mexican irrigation works." 51. Set' gm"aJl)' MaJ/n'l F.eport 61-']1. 53. Id. at 117. 54. WAn.. Pu."-" III-I. 55. Aleu'"'J RtpOrl 31-33. 56. U. at 39. 57. Ii. at 36.