Southwest Hydrology: The Resource of Semi-Arid Hydrology Volume 4 Number 2

Home Browse Search

,; ; '�, .�i •7�! x �.•,: .� . .� ;fir• �'•''" • � `� � ' <` �� /�' .� -, .ice A Glen Canyon Dam and Lake Powell, December 2004. Photo by Howard Grahn. hen I first started working for the Colorado River Water modeling tools utilize the 1906 to 1995 period, with a mean Conservation District in 1981, Lake Powell had just undepleted flow at Lee Ferry of about 15 maf/year. A difference in finished its initial fill and there was ample water in the the mean of 1.5 maf/year may seem small, but at today's level of system. For the next 20 years, Colorado River Compact issues development on the Colorado River, its implications for water use were for the most part on the back burner. My district's focus, throughout the Colorado River Basin are enormous. and indeed the focus of the entire basin, was on the further development of Colorado River waters. Is the upper Basin Already at Capacity? Tipton concluded that if 13.5 maf/year is a more realistic flow, Today, after several years of below - average runoff, storage in Lake then the Upper Basin may already be approaching full usage Powell has dropped to levels not seen since the late 1960s. The of its portion of the river. If the Upper Basin's annual delivery latest 24 -month operations study by the Bureau of Reclamation obligation at Lee Ferry was 8.25 maf/year (the current but (Reclamation) shows Lake Powell is expected to reach a low of disputed minimum objective release level based on the Law of the around 8 million acre -feet (maf) of storage in April 2005, about 32 River), after deducting Colorado River Storage Project (CRSP) percent of active storage. Water managers and water policy boards reservoir evaporation, the Upper Basin states could develop and throughout the Colorado River Basin are now asking legitimate use only about 4.8 maf/year. Based on the latest Colorado River questions concerning the supply and reliability of their Colorado Consumptive Uses and Losses Report published by the Secretary River sources. In December 2004, U.S. Department of the Interior of the Interior and information from the states, the Upper Basin Secretary Gale Norton challenged the seven Colorado River Basin states are currently using about 4.3 maf/year (not counting CRSP states to develop a plan to address shortage and drought conditions evaporation). The unused capacity of existing projects and projects on the river. currently under construction could probably develop another 300,000 to 500,000 acre -feet per year; thus, the Upper Basin may 15 maf or 13.5 maf? already have the infrastructure in place to fully use 4.8 maf/year. Several studies from previous decades suggest we should not be surprised with current conditions on the river. In 1965, the Colorado engineering firm of Tipton and Kalmbach (Tipton) prepared a report for the Upper Colorado River Commission. The report examined the water supply available to Upper Basin (Colorado, New Mexico, Utah, and Wyoming) and Lower Basin (Arizona, California, and Nevada) states under a variety of assumptions. Tipton utilized a 1914 to 1964 period of record, but considered the 1930 to 1964 period to be the "firm yield" period. This 35 -year period had a mean undepleted flow at Lee Ferry in the range of 13.5 maf per year. A second significant study, published by Stockton and Jacoby in 1976, presented groundbreaking work estimating the long -term flow of the Colorado River system based on analysis of the tree ring record. They concluded that the long -term mean undepleted flow of the Colorado River at Lee Ferry is 13.5 f5 maf/year, similar to Tipton's results. In contrast to these estimates, Reclamation's current river 20 • March /April 2005 • Southwest Hydrology If we assume that the Upper Basin will continue to deliver 8.25 maf/year at Lee Ferry, one does not need a model to demonstrate the problems facing the basin: Available supply at Lee Ferry 13.5 maf/year Delivery to Lower Basin -8.25 maf/year CRSP reservoir evaporation - 500,000 to 700,000 af/year Available for use in Upper Basin 4.55 to 4.75 maf/year This amount is very close to the current level of development and is consistent with the Tipton report. Lower Basin Impact Consideration of conditions in the Lower Basin further illustrates the core problem of insufficient water in the system. If unlimited storage were available for the Upper Basin to store all excess water, and with a small amount of new development to utilize it, the Upper Basin would consistently deliver to the Lower Basin only the minimum required amount.