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~~~ in Pueblo Reservoir began in January 1974, and the dam was completed in August 1975. Since impoundment, reservoir elevation, surface area, and storage have varied greatly because of inflow and demand for the stored water (fig. 3). Prior to 1983, after appreciable storage was attained, the reservoir contents varied from 22,680 acre-ft in November 1974 to 111,920 acre-ft in March 1982. Since early 1983, reservoir contents have been greater than 200,000 acre-ft as the result of greater than normal flows from the Arkansas River (fig. 3). During the 1985 water year, reservoir contents varied from 239,960 acre-ft (4,875-ft elevation) in October to 295,480 acre-ft (4,887-ft elevation) in February. Less seasonal fluctuation in reservoir contents occurred from 1983 through 1985 than in previous years (fig. 3). The reservoir inundates four large canyons and several small canyons. The canyon walls are composed of sedimentary rocks. The Fort Hayes Limestone Member of the Niobrara Formation of Cretaceous age lies at the top of the canyon walls surrounding the reservoir and is about 40 ft thick (Scott, 1972a). Underlying the Fort Hayes Limestone Member is the Carlile Shale which contains, from top to bottom, the Juana Lopez Member (2.5 ft thick), the Codell Sandstone Member (30 ft thick), the Blue Hill Shale Member (100 ft thick), and the Fairport Chalky Shale Member (100 ft thick) (Scott, 1964, 1969, 1972a, 1972b). The reservoir, at most stages, is in contact with the Blue Hill Shale Member, which is insoluble and relatively impermeable (Scott, 1969) and, therefore, inhibits lateral or vertical movement of water from the reservoir. The Codell Sandstone Member is permeable and, where inundated, could transmit water to and from the reservoir depending on reservoir eleva- tion. The Fort Hayes Limestone Member is not very permeable. However, water may flow at the contact between the shale and the limestone beds. If inun- dated, the Fort Hayes Limestone Member could transmit water to and from the reservoir. At all pool elevations, the reservoir is dendritic and the shoreline is very irregular. At minimum pool (30,355 acre-ft), the reservoir is about 3.5 mi long and varies in width from a few hundred feet to about 1.3 mi. During the 1985 reconnaissance study, the reservoir was near the top of the conservation pool (about 265,000 acre-ft or about 4,880 ft in elevation). At this pool elevation, the reservoir has a length of more than 9 mi, a width that varies from less than 0.3 to about 2.2 mi, a depth that varies from a few feet near the inflow to about 155 ft at the dam, and a shoreline of about 60 mi. Water is released from the reservoir through the river outlets, Bessemer Ditch outlet, south outlets, and the fish hatchery outlets. The river out- lets, which are located at an elevation of 4,766 ft, or about 114 ft below the reservoir surface during the 1985 data-collection period, release the majority of the water from the reservoir. Water released from the river outlets provides municipal and industrial water to Pueblo. The Bessemer Ditch, which is an irrigation canal, provides water to St. Charles Mesa via the Bessemer Ditch outlet. The Bessemer Ditch outlet is located at an elevation of about 4,780 ft or about 100 ft below the reservoir surface during the 1985 data-collection period. The south outlets deliver water to Pueblo West and the Fountain Valley conduit, which is a 45-mi-long pipeline that delivers water to the city of Colorado Springs and the communities of Stratmoor Hills, Widefield, Security, and Fountain (fig. 1). The south outlets release water from the reservoir through multilevel intake lines located at elevations of 9