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002598 United States Departrnent of the Interior GRAND CANYON MONITORING AND RESEARCH CENTER 2255 N. Gemini Dr., Room 341 Flagstaff, AZ 86001 520556-7094 IMPACTS OF THE 3-5 NOVEMBER 1997 31,000 cfs TEST FLOW Introduction The Bureau of Reclamation and the Grand Canyon Monitoring and Research Center conducted a test of a "Habitat Maintenance" style flow from Glen Canyon Dam on 3-5 November 1997. The flow peak reached approximately 30,600 cfs for this 2-day test. This memo outlines the impacts of that flow event on resources through Orand Canyon. Physical Resource Impacts OCMRC coordinated pre- and post-event videography of the river corridor, and those images are being examined for backwater habitat changes. Using the methods of Parnell et al. (1996), detailed topographic surveys of 35 sand bar monitoring sites were conducted immediately following the November 1997 test flow by members of the Northern Arizona University Department of Oeology sand bar studies office. Information gathered from these surveys is compared to previous surveys conducted in August 1997 in order to quantify sand bar change. Based on this preliminary data, the November test flow benefitted the sediment resources by depositing sediment at higher elevations. The higher elevation areas of sand bars contain critical riparian habitats that are of particular interest to management agencies. Following the 1996 45,000fe/s test flow, erosion has steadily decreased the volume of sediment contained in the upper elevations of sand bars. Preliminary results show that the November 1997 test flow slightly increased the volume of sand bars (above the 20,000 fe/s stage elevation), calculated as a percentage of the pre-1996 test flow, from 87 % to 91 %. High flows above powerplant capacity are the only means by which the volume of the upper levels of sand bars can be maintained. The U.S. Oeological survey (0. Fisk, D.Topping, D.Rubin and S.Weile) monitored mainstream streamflow and suspended sediment at the Lees Ferry, Above Little Colorado River, Orand Canyon and Diamond Creek gauges once/day before, during and after the flow event. Bedload sampling was conducted iil the mainstream and in eddies at selected sites following the high flow. Bar sedimentology, grain size, deposit thickness was conducted with the NAU effort immediately following the high flow. tC