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. . Chapter 4. Hydrology of the Colorado Plateau Introduction Despite its many political subdivisions, the Colorado Plateau is a single hydrologic drainage basin and the suite of characteristics and processes affecting its hydrologic cycle are responsible for the distribution and quality of wetland habitats and the fitness of constituent wetland species. Research on Colorado Plateau hydrology has provided important insight into the dynamic interactions environmental and biological aspects of wetland ecology. This chapter discusses channel geomorphology, sediment deposition and transport, water supply, water quality, and related hydrological issues on the Colorado Plateau. Water Supply The Colorado Plateau is fed by snowmelt and the Colorado River receives most of its water supply from winter precipitation in peripheral mountain~. Iorns et al. (1965) estimated that approximately 114.4 km (92.739 maf) of water entered the upper Colorado River ~asin as precipitation annually (Fig. II). Of this amount, f.79 km (2.258 maf or 2.43%) were consumed or diverted, 15.71 km3 (12.733 maf or 13.73%) left via surface outflow, and 95.90 km (77.748 maf or 83.84%) were lost to evaporation and transpiration. Annual consumptive use had increased to 8.14 km3 (6.6 maf) by 1980 (U.S. Department of the Interior 1987), with more than 55% of the consumptive use going to transbasin diversions, 30% to agricultural use, 11.5% to evaporation in reservoirs and channels, 2.7% to municipal and industrial use, and none used for fish, wildlife or recreational uses on the Colorado Plateau (Iorns et al. 1965). Price and Arnow (1974) estimated that phreatophytes in the Colorado River basin consumed 3.08 km3 (2.5 maf) of ground and surface water annually, which is the equivalent of municipal and industrial consumption. Groundwater . . . . . . Thomas (1952) re-defined Meinzer's (1923) groundwater regions of the United States, placing the Colorado Plateau into a single groundwater region. Schlotthauer et al. (1981) described Utah's portion of the Colorado River basin as divided into three basins: a northern Uinta basin, a central Colorado Plateau region, and a Lower Colorado basin. Heath (1984) concluded that the Colorado Plateau groundwater region was characterized by complex, interbedded sequences of strata with multiply-layered aquifers. These strata (aquifers) consisted of generally insoluble sedimentary rock with low porosity and transmissivity. Recharge generally occurred in upland areas, with discharge through fractures and surface springs. . . 21 .