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provided an annual 1.5 million acre - <br />feet allocation to the Republic of <br />Mexico. <br />At the time, the river's average <br />annual flow was about 18 million acre - <br />feet; it is now known that the long- <br />term average is about 15 million acre - <br />feet, and closer to 13 million acre -feet <br />the past 30 years. Furthermore, records <br />from 1890 to today show that the <br />river's extreme variability in precipita- <br />tion and runoff may well be its only <br />constant. Yearly flows have fluctuated <br />from a low of 5 million acre -feet to <br />more than 24 million acre -feet during <br />its recorded history. "The river doesn't <br />spend much time in what you might <br />think of as the mean or average," Gray <br />said. "Instead what it tends to do is <br />switch back and forth between <br />predominantly wet and predominantly <br />dry conditions over time schedules of <br />10, 20 and 30 years." <br />The Law of the River <br />Six components are the focus of <br />today's efforts to address drought - <br />related issues: <br />• The Colorado River Compact of <br />1922, which divided the Colo- <br />rado River Basin into upper and <br />lower basins and apportioned <br />water between the two basins. <br />• The Boulder Canyon Project Act <br />of 1928, which ratified the <br />Colorado River Compact and <br />authorized construction of <br />Hoover Dam, its power plant and <br />the All - American Canal. The <br />act also authorized the Secretary <br />of the Interior to establish by <br />contract the basic apportion- <br />ments from the mainstem river <br />among the three Lower Basin <br />states. <br />• The Mexican Water Treaty of <br />1944, in which the United States <br />agreed to deliver 1.5 million <br />acre -feet of Colorado River water <br />to Mexico annually, except <br />under surplus or extraordinary <br />drought conditions, as defined by <br />the Treaty. <br />The Colorado River Storage <br />Project Act of 1956, which <br />authorized storage reservoirs and <br />dams, including Glen Canyon, in <br />the Upper Basin and on its <br />tributary rivers. <br />The Arizona v. California U.S. <br />Supreme Court Decree in 1964, <br />which affirmed the Lower Basin <br />mainstem apportionment among <br />Arizona, California and Nevada <br />and recognized under the 1928 <br />Boulder Canyon Project Act <br />American Indian water rights for <br />five tribes below Hoover Dam. <br />The Colorado River Basin <br />Project Act of 1968, which <br />authorized construction of CAP <br />and limited diversions to CAP <br />during shortages to assure <br />California's use of its annual 4.4 <br />million acre -feet apportionment. <br />Tree -ring based reconstruction <br />extends the hydrological records back <br />over 400 years. The rings of trees <br />growing in water - stressed locations are <br />typically narrow during years of low <br />precipitation. By comparing tree -ring <br />records in the Upper Colorado River <br />Basin with the annual precipitation <br />and flows of the Colorado River, <br />researchers discovered several in- <br />stances of prolonged droughts between <br />1500 and 1900. Examples include the <br />late 1700s and the mid- 1800s, along <br />with a particularly long period of low <br />flows in the late 1500s. <br />Based on the reconstructed <br />records, researchers say the current <br />Colorado River drought, which began <br />in 2000, is the seventh worst in the <br />last 500 years. From 2000 to 2005, <br />measured runoff into Lake Powell <br />ranged from 62 percent of average to <br />just 25 percent of average, reducing <br />the combined storage in Lake Powell <br />and Lake Mead to about 58 percent <br />today. Combined storage in 1999 was <br />94 percent of capacity. <br />Sharing Shortages <br />Developing a method to more equally <br />manage storage in Lake Powell and <br />Lake Mead became a major issue in <br />2005 as Upper Basin officials saw <br />Powell drop to just 33 percent of its <br />capacity, threatening the potential to <br />produce hydropower, with Mead still <br />at approximately 50 percent of <br />capacity. Developing a plan for <br />"coordinated operation" to better <br />balance storage between Lake Mead <br />and Lake Powell during times of low - <br />reservoir conditions was a major focal <br />point during the seven -state negotia- <br />tions. <br />Under current operations, Lake <br />Powell is mandated to release 8.23 <br />million acre -feet of water to Lake <br />Mead (and the Lower Basin) every <br />year — no matter what. (The 8.23 <br />million acre -feet includes the 7.5 <br />million acre -feet release to the Lower <br />Basin states plus half of the required <br />1.5 million acre -feet allocation to the <br />Republic of Mexico.) The preliminary <br />proposal by the seven states includes <br />WESTERN WATER <br />