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<br />o <br />o <br />(:;J <br />::--> <br />.- <br />.- <br /> <br />10 <br /> <br />Although the existing fish at these facilities range in total length from 150 mm to 300 mm, <br />and are thus smaller than the optimum size, the San Juan Recovery Implementation Program <br />could take possession of and stock these fish by fall 1997. A motion to stock these three <br />groups of fish in the San Juan River in 1997 was considered and passed by the San Juan <br />Recovery Implementation Program Biology Committee on 19 March 1997. <br /> <br />III. AFFECTED ENVIRONMENT <br /> <br />Based on the perceived range of environmental impacts resulting from the proposed <br />implementation of the preferred alternative, this EA incorporates as its analysis area the <br />immediate environs of the San Juan River and its permanent and ephemeral tributaries from <br />Navajo Dam downstream to Lake Powell. Baseline information concerning the delineated <br />affected environment is provided in the following discussions. The No Action Alternative sets <br />the environmental baseline (i.e., the affected environment) for comparison of the effects of the <br />proposed action. The environmental effects (changes from present baseline conditions) reflect <br />the identified major issues and other key elements of the environment. <br /> <br />A. CLIMATE, AIR QUALITY, GEOLOGY, AND SOILS <br /> <br />The San Juan Basin is typical basin and range topography with deep canyons, dry washes, <br />upland mesas, and hogback ridges with igneous dikes. Soils are derived from sandstones, <br />clays, and barren shales containing little organic matter. This area is classified as the Navajo <br />section of the Colorado Plateau physiographic province (Fenneman 1931). Elevation within <br />the basin varies from 1460 to 2100 meters (4790-6890 feet), <br /> <br />The climate and vegetation of the San Juan Basin is characteristic of the Great Basin, a cold- <br />temperature desertland. The Great Basin has cold, harsh winters, low precipitation scattered <br />throughout the year, with great extremes in both daily and seasonal temperatures (Brown <br />1982), Mean annual precipitation at Aztec, New Mexico is 242 mm or 9.53 inches. Winter <br />precipitation is dominant (more than 50 percent of the total precipitation falls during winter <br />months), although the Chihuahuan desert monsoon provides warm weather moisture during <br />summer months (Cully et al. 1987). <br /> <br />B. WATER <br /> <br />Flows in the San Juan River are dependent upon a number of factors. Climatic conditions, <br />water use demands for municipal, domestic, industrial, and agricultural activities, and release <br />of flows from Navajo Dam in response to the first two factors all influence the flow regime of <br />the river. These effects are attenuated as distance from the dam increases; the river reflects <br />more short term fluctuations from unregulated tributaries intersected en route to Lake Powell. <br /> <br />Prior to the construction of Navajo Dam, the hydrograph of the San Juan River was <br />characterized by large spring peaks and low base flow. Typically, spring runoff began in <br />March, peaked in midCMay to early June and ended by the first week of July. During the <br />remainder of the year, flow was characteristically low, punctuated by large, short duration <br />