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<br />-'-'I <br />-{:" <br /> <br />.--,., <br />,>l~':, ':~ <br />"" <br />",' <br /> <br />measurements during the flood will not only be analyzed to test hypotheses but also to refine and <br />improve q10dels of river hydraulics and sediment transport. <br /> <br />I, a. Soatial Patterns of Bar Deoosition - reach scale <br />The purpose of this effort is to quantify the areal extent of newly formed bar deposits and <br />measure bar adjustment following flood recession. These data will be used to test hypotheses <br />regarding net change in bar area caused by the flood. Methods will be similar to those used by <br />Schmidt (1. C. Schmidt et al., 1994. Geomorphology of post-Glen Canyon Dam fine-grained <br />alluvial deposits of the Colorado River near Point Hansbrough and Saddle Canyon in Grand <br />Canyon National Park, Arizona, unpubl. report to GCES) in which surficial river-corridor <br />geology, based in part on aerial photographs, is mapped at 1 :2400 scale on base maps that depict <br />the river corridor in June 1990. Schmidt's maps also depict the status of sand bars depicted on <br />photographs taken in 1935, 1965, 1973, 1984, and 1990. Clark (1990) completed maps of <br />surficial geology for the reach near Nankoweap Creek for 4 additional years (1980, 1987, 1988, <br />1989). These maps are useful in predicting the elevation of the water surface and zones ofbar <br />deposition at discharges comparable to the magnitude proposed here. <br />In order to evaluate the area1 extent of deposition due to the planned flood, similar maps <br />will be made for selected reaches (initially in the established GIS reaches) based on <br />interpretation of aerial photos and field work (1) at low flow immediately prior to the flood, (2) <br />at low flow immediately following flood recession, and (3) at selected times that photos are <br />taken each year following flood recession. Maps made as part of this experiment will be entered <br />into the GCES GIS (Geographic Information System) data base and compared with predictions. <br /> <br />I, b. Soatial Patterns of Bar DeDOsition - site-snecific scale <br />Detailed patterns ofbar deposition, and characteristics ofbar deposits will be <br />determined from resurvey of geo-referenced topographic maps of 30 field sites. These sites have <br />been surveyed annually by the GCES program and are all part of the GCES GIS data base. <br />Using established protocols, detailed topographic surveys will be conducted immediately prior <br />to and after the flood. Comparisons of topographic change will be made using techniques <br />established by Beus and others (S. S. Beus et al., 1993. The influence of variable discharge <br />regimes on Colorado River sand bars below Glen Canyon Dam, unpUbl. report to Grand Canyon <br />National Park). Sedimentologic excavations and examinations will also be made at the survey <br />sites to test depositional sequences predictions for those locations. <br />These data will be used to evaluate detailed spatial characteristics of eddy deposition and <br />determine the volume of sediment deposited in specific eddies. These data will be lISed in <br />conjunction with area1 determinations of the extent of new deposits to estimate a reach-average <br />volume of newly deposited sediment <br /> <br />2, a. Main channel hvdraulics and sediment transDOrt <br />The primary data to be collected concerning the main channel are (1) velocity and <br />sediment concentration at 4 gaging stations (Lees Ferry, above the Little Colorado River, Grand <br />Canyon and Diamond Creek), (2) time of water travel based on measurements of dye <br />concentration, and (3) documentation of bed- sand-storage changes. Time-of-travel studies are <br /> <br />12 <br />