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Following impoundment, NHWZ vegetation cover increased by nearly 400% in GIS reach 5, despite a significant, flood-related decrease in vegetation cover in the early 1980s. This result indicates how productive riparian habitats can be in the absence of frequent flooding. The OHWZ in GIS reach 5 appears to exhibit a trend of increased vegetation cover in 1984, which may relate to the flood conditions that occurred during the early 1980s. High flows may have supplied mesquites with much-needed water for growth. Analysis of OHWZ patterns within the five other GIS reaches will help to determine if this trend is a larger-scale pattern of response throughout Grand Canyon. One of the environmental variables, depositional environment, may also influence vegetation cover along the Colorado River. Consistently less NHWZ vegetation cover was present in the mile below the Little Colorado River than in the mile above this tributary between 1965 and 1984; however, this pattern is reversed by 1992. Although vegetation cover increases both above and below this tributary from pre-dam times to the present, these data suggest that the rate of increase is greater below the Little Colorado River. A substantial influx of sediments from the Little Colorado River may be providing additional colonizable substrate for vegetation in this otherwise sediment-limited river system. We will measure vegetation patterns upstream and downstream from other tributaries, including the Paria River, Nankoweap Creek, and Tepeats Creek, to determine the extent of this preliminary finding. This research will also relate to the demography of one riparian species, Goodding willow, which may be negatively affected by river regulation, over the last 30 years. Currently, little evidence of recruitment in this species exists within Grand Canyon; most individuals are mature or decadent. Large populations have become established recently at the end of Grand Canyon on Lake Mead and represent an enormous recruitment event for Goodding willow. We will establish the timing and basis of this event'in the course of determining the age distribution of this species' populations through the canyon. Goodding willow's range is restricted to the southwestern United States. The Goodding willow - Fremont cottonwood association in Arizona is listed as threatened by the Nature Conservancy. A thorough analysis of riparian vegetation responses to river regulation will be provided by this study. As a result of this work, nearly 30 years of data on georeferenced vegetation cover will be available for 50% of all GCES/GIS reaches. This study will provide valuable insights into the impact of river regulation on riparian vegetation, will produce a permanent, quantitative record that can be included in all fixture research and monitoring efforts involving riparian vegetation along the Colorado River, and will serve as a comparison for other river systems. The fourth and final study to be included in this report was contributed by the U.S. Geological Survey and discusses how they are using existing GCES/GIS topographic and newly created bathymetric data to generate flow, sediment-transport, and bed-evolution models to predict sand accumulation or losses. 28