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Show from Lake Powell ( USDI 1984). The bank storage from the reservoir ( water that percolates into the rock along the lakeshore) is estimated to be 10- 13 million acre- feet ( unpublished data, U. S. Bureau of Reclamation - Salt Lake City, 1987). A significant amount of water drains from the rocks back into the reservoir with any appreciable drop in lake level ( Jacoby et al. 1977). I I. C. 2. Springs and seeps. Springs in Glen Canyon NRA are often found in canyons where the surface intersects water- bearing strata or structural features. These springs can emerge from alluvial aquifers, from a zone of contact with an impermeable bedrock layer, or where a fracture zone drains local bedrock aquifers, particularly the Navajo Sandstone aquifer. Springs emerging from the alluvial aquifer fluctuate seasonally and in response to rainfall. Changes in hydrostatic head resulting from the filling of Lake Powell have created several new, large springs that flow from the lower canyon walls between Glen Canyon Dam and Lees Ferry. Seeps occur where a canyon cuts through an aquifer or a joint connecting to an aquifer. Seeps commonly are found in canyon walls that cut through Navajo Sandstone. I I. C. 3. Ground- water quality. Springs that discharge from the Navajo- Kayenta and Wingate Sandstone formations are generally of excellent quality except in places where the overlying Carmel Formation allows for the leaching of sulfate ions. In high concentrations, these sulfate ions act as a laxative, rendering the ground water unpotable. Local outcrops of other sandstones discharge water of good quality because the soluble salts have been leached out. In aquifers where ground water has accumulated soluble salts over longer geologic time, the water quality is poorer ( Hand 1979). Williamson ( 1985) profiled the trace element chemistry of several springs and seeps in the uplake canyons and found them to be relatively low in trace element concentrations. Saturated alluvium is generally a source of good water, although its original quality can be altered by evapotranspiration and calcium carbonate precipitation. Total dissolved solids ( TDS) in alluvial water in the Canyonlands National Park area in Utah are generally less than 400 milligrams per liter ( mg/ 1) ( Richter 1980). Alluvial waters in the recreation area have a similar origin and are probably of like quality. II. D Surface- Water Resources M. D. 1. Rivers, springs, seeps, and waterpockets. The principal sources of surface water in Glen Canyon NRA are five major rivers-- the Colorado, San Juan, Dirty Devil, Escalante, and Paria-- and Lake Powell. ( Lake Powell is described separately in Section I I. E.) In addition, most canyons are drained by ephemeral streams that flow in response to 11 |
