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<br />Variations in Sand Storage Measured at Monumented Cross Sections <br />in the Colorado River Between Glen Canyon Dam and Lava Falls Rapid, <br />Northern Arizona, 1992-99 <br /> <br />BvMarilyn E. Flynn and Nancy J. Hornewer <br /> <br />Abstract <br /> <br />Bed elevations were measured at 131 monumented cross sections in the Colorado River between <br />Glen Canyon Dam and Lava Falls Rapid from June 1992 to September 1999 to provide data on <br />channel sand storage. This report documents the location of the 131 monumented cross sections, <br />dates of measurements for all cross sections, methods of data collection and processing, and <br />spatial and temporal variation and variability in changes in cross-sectional area for selected cross <br />sections. Additionally, data were analyzed to determine if changes in sediment storage could be <br />related to main channel flow conditions and tributary sediment inputs. Most of the cross sections <br />showed a limited capacity, both in terms of amount and residence time, to store sediment. Data for <br />83 of the 131 cross sections were comprehensive and complete, and were used for analyses in this <br />report. This data set is referred to as the primary data set. Of these 83 cross sections. 19 had a net <br />gain in stored sediment. 61 had a net loss of stored sediment, and 3 had no change in stored <br />sediment for the period of data collection, excluding data collected during the high release from <br />Glen Canyon Dam in 1996. A subset of the primary data set consisting of the sections downstream <br />from the Paria and Little Colorado Rivers with measurements made on or nearly on the same day, <br />referred to as the matching-date data set, was used to explore the effects of controlled flows and <br />tributary flows on the changes in cross-sectional area. The matching-date data set consists of data <br />from 57 cross sections. Of these 57 cross sections, I had a net gain in stored sediment. 55 had a net <br />loss of stored sediment, and I had no change in stored sediment. Results of the analysis did not show <br />that changes in cross-sectional area were strongly related to main channel flow conditions or tributary <br />sediment inputs. <br /> <br />INTRODUCTION <br /> <br />of monumented cross sections along the Colorado <br />River between Glen Canyon Dam and Lava Falls Rapid <br />(fig. 1) to measure changes in cross-sectional area. <br />These changes in cross-sectional area were intended to <br />be an indication of changes in sand stored on the <br />channel bottom. <br /> <br />Between 1992 and 1999. the u.s. Geological <br />Survey (USGS), initially in cooperation with Glen <br />Canyon Environmental Studies (GCES) and later in <br />cooperation with the Grand Canyon Monitoring and <br />Research Center (GCMRCl. established a network <br /> <br />~~~ <br /> <br />Abstract 1 <br />