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Study Plan— Biological Resource Responses to Fall <br />Steady Experimental Flows Released from Glen Canyon <br />Dam, 2009 -12 <br />Executive Summary <br />Experimental steady releases from Glen Canyon Dam in September and October 2008 through 2012 <br />(fall steady experimental flows, FSEF) were prescribed by a 2008 environmental assessment and an <br />associated biological opinion. The Grand Canyon Monitoring and Research Center (GCMRC) prepared <br />this science plan at the request of the Glen Canyon Dam Adaptive Management Work Group to examine <br />the effects of FSEF on downstream resources. Four ongoing projects are collecting data that will be <br />used to assess possible impacts of these flows on biological resources: (1) the nearshore ecology project, <br />(2) stock assessment of native fish populations, (3) aquatic food base monitoring, and (4) monitoring of <br />early life stages of rainbow trout. Given uncertainties regarding the extent and degree of nearshore <br />warming that will occur as the result of fall steady flow operations, we propose the collection of new <br />water temperature data in association with these flows. Physical and biological data will be integrated <br />and synthesized using an ecosystem model to evaluate whether this management action had impacts on <br />the ecosystem as a whole. A description of the sediment- monitoring program is not included in this <br />document. However, the effects of the discharge regime on sediment resources are well understood, and <br />the GCMRC Physical Sciences and Modeling Program could evaluate and report on the response of <br />sediment resources to fall steady flows, should it be of interest to managers. <br />The GCMRC also has been asked to recommend flow parameters because the environmental assessment <br />and biological opinion did not establish specific release rates for FSEF. Findings from recent studies <br />indicate that lower flows result in greater abundance of backwater habitats, which are thought to be used <br />by juvenile native fish, including the endangered humpback chub (Gila cypha). Thus, steady flows of <br />about 8,000 cubic feet per second (cfs) for the remainder of the experiment (20 10 through 2012) would <br />likely maximize backwater habitat in addition to maximizing the potential for nearshore warming, also <br />thought to benefit native fish. If water releases must be moved into other months of the year to <br />accommodate these steady flows, it is recommended that releases in July and August not be increased. <br />Daily peak discharges during July and August are already relatively high and further increases will <br />increase sediment transport and sandbar erosion, which are undesirable side effects. <br />