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

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Powell has not been this low since 1969 when it was initially filling. Lake Mead has not been this low since 1967, also during the filling of Lake Powell. Prior to that, Lake Mead's elevation was lower than at present for several years in the 1950s due to drought in that decade. Although the major reservoirs in the system were constructed for multiple purposes, providing water supply is foremost. In the past decade, the population of the seven basin states that rely on the waters of the river has grown by nearly I1 million, an increase of approximately 25 percent (Griles, 2004). Even with increased demand, most delivery obligations have been met throughout the basin despite the drought, primarily due to the relatively large inflows of the late 1990s, when significant amounts of water could be stored. Conservation efforts throughout the basin have also helped. For example, the Southern Nevada Water Authority (2005) estimates that Las Vegas area water use has decreased some 50,000 acre -feet since 2002, due to the implementation of a drought plan and the Water Smart Landscape program, which provides a $1 rebate per square foot of grass replaced by xeriscape. In some parts of the Upper Basin where shortages have occurred, confrontation has been avoided through shortage - sharing agreements. Such an agreement established on the Gunnison River requires water users to adopt plans to share shortages when reservoir storage at Blue Mesa Reservoir is below 400,000 acre - feet, as occurred during the particularly severe drought of 2002. Effect on Other Resources Declining reservoir levels have affected other resources, including power production and recreation. The amount of energy produced at a hydroelectric plant depends upon the rate of flow through the turbines and the height of the water behind the dam: as lake level declines, the capacity for generation decreases. At Hoover Dam, generation capacity has been reduced 20 percent since 1999. If lake See How Low ?, page 28 Lake • • • • Elevation •64 through Present 3700 Spillway Crest 3715 3650 % / 3600 Sept 1999 C 95% of Capacity 0 era 3550 a as W 3500 Dec 2004 36% of Capacity 3450 Lake Powell has not been this level since 1969 3400 0� 00 00 10 �'L �tx A% 1% 00 % 0� Al 00 00 0� O� 00 00 00 O`t' O� Ncs Ncs 1\01 Nlb .� �C Nch N% N% 1\% N% N% �� NCS -C Jan 1964 - Dec 2004 1225 1200 1175 LL- 1150 C yo 1125 ca 1100 W 1075 1050 1025 1000 Spillway Crest 1221 %999 apacity Dee 2004 1950's Filling of 54% of Capacity Drought Lake Powell Lake Mead has not been this level since 1967 3� 0 a� hti h� roti �� ti �� %ti w� A, a� oti Jan 1937 - Dec 2004 March /April 2005 • Southwest Hydrology • 17