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reservoir contents have declined in recent years and historical lows were recorded in <br />2002 for the Colorado River reservoir system. Indian tribe reserve rights remain an <br />important issue. <br />16 Great Basin Region —The Great Basin Region includes most of Nevada, most of <br />western Utah, and small portions of Oregon, Idaho, and Wyoming. The Great Basin is the <br />Nation's most and landscape, and is characterized by internal drainage, saline terminal <br />lakes, and vast desert playas. The climate has limited most development to the extreme <br />edges of the Great Basin, where snowmelt from the Rockies to the east and the Sierras to <br />the west have supported agriculture and population centers. Almost all the surface water <br />results from snowmelt, and because annual snowfall is extremely variable, there is a <br />critical need for an understanding of how short and long term climatic cycles will affect <br />the amount of available surface supply. Surface water throughout the region is fully or <br />over allocated, and competition between agricultural, municipal, Native American, and <br />ecological interests is intense. Future growth is dependent upon locating and developing <br />additional ground -water resources. Of particular interest is the vast regional carbonate <br />aquifer that underlies western Utah and eastern Nevada. Preliminary information <br />indicates that the carbonate aquifer contains many hundreds of millions of acre -feet of <br />ground water in storage, but recharge rates, flow paths, discharge to springs and playas, <br />and the potential impacts of development are not quantified. Mine dewatering of <br />carbonate units in central Nevada and long -term withdrawal tests in the carbonates in <br />southern Nevada are creating new stresses that are not well understood. <br />17 Pacific Northwest Region —The Pacific Northwest Region includes all of Washington, <br />most of Oregon and Idaho, portions of Montana and Wyoming, and a small part of <br />California. Most of the region drains to the Pacific Ocean and mainly lies within the <br />Columbia River Basin. The remaining part drains the western slopes of the Cascade <br />Range in Washington and Oregon, the Olympic Mountains in Washington, and the Coast <br />Range in Oregon and a small part of California. There is a smaller area that contains <br />topographically closed basins. The region is typified by a wet `Westside' and a dry <br />`Eastside', with annual precipitation ranging from 5 to 200 inches. The differences <br />between the location and timing of water input and water use has led to the development <br />of extensive reservoir systems on major rivers, and numerous small -to -large reservoirs on <br />the Westside and throughout the region. Surface water in the region is nearly fully <br />appropriated and the aquifer systems are nearing their sustainable yield. In some areas, <br />ground -water withdrawals have caused water -level declines of more than 200 feet and the <br />ability of aquifers to support current or future withdrawals is in jeopardy. The <br />withdrawals have caused decreases in streamflow and deterioration in water quality <br />throughout the region, and in some areas, such as the Snake River Plain Aquifer, these <br />decreases are impacting senior surface -water rights. There are extensive conflicts due to <br />competing needs for water, and include interstate and international boundary issues. <br />These conflicts have been compounded because of the need to supply water for <br />threatened or endangered species, especially anadromous salmon. Indian tribe reserve <br />rights remain an important issue. <br />22 <br />