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<br />To: Barry D. Gold, Chief, Grand Canyon Monitoring and Research Center <br /> <br />From: David M, ~u'ti{;f-and David J. Topping, U.S. Geological Survey <br />John C, Schmidt, Utah State University <br />Joe Hazel, Northern Arizona University <br /> <br />Re: Summary and Discussion of Recent Research Findings Related to Dam Operations and <br />Sand Bar Resources of the Colorado River Ecosystem <br /> <br />Back~round <br /> <br />Sand bars are an essential component of the Colorado River ecosystem downstream from Glen <br />Canyon Dam, They create habitat utilized by endangered fish; they contain and protect an array of <br />Native American cultural resources; they provide campsites used by recreational boaters; and they <br />are a distinctive attribute of the pre- and post-dam river landscape, Improving and maintaining sand <br />bars below the dam is a fundamental long-term management objective of the Grand Canyon <br />Protection Act, the Operation of Glen Canyon Dam Final Environmental Impact Statement, and the <br />Glen Canyon Dam Adaptive Management Program (See Attachment 1). <br /> <br />Sand bars and sandy banks of the Colorado River in Grand Canyon are maintained by the sand <br />that is transported through the canyon, The high-elevation parts of these sand bars (those parts at <br />elevations above peak power-plant discharge) can be constructed only by flows that exceed peak <br />power-plant discharge (i.e. flows greater than 31,000 cfs); in the absence of such high flows, these <br />high-elevation areas are eroded by lower flows or canyon winds or are rapidly colonized by both <br />native and exotic vegetation, Flows above peak power-plant discharge are necessary to maintain <br />these high-elevation sand bars, but are effective only when the river contains sufficient sand <br />resources, <br /> <br /> <br />lJur. I UI\ Iuun <br />INfORMATION <br />United States Department of dle Interior <br /> <br />US GEOLOGICAL SURVEY <br />Pacific Science Center <br />University of California at Santa Cruz <br />11 S6 High Street <br />Santa Cruz, CA 95064 <br /> <br />MEMORANDUM <br /> <br />August 29. 2000 <br /> <br /> -- <br />P;EI~;:\'/ED GCM~C <br />OFFICIAL FILE COpy <br />RESPONSE <br />RESP DATE J <br />CNTL # <br />FOLDER # <br />CLASS CODE <br />DATE TO INITIALS <br />'If':...irc I~;,,(L P1 I <br />1(;(; <br /> .. <br /> <br />, <br /> <br />,; <br /> <br />f.... <br /> <br />,.~';' <br />~~ <br />-, <br />....1 <br />,~. <br />~J <br /> <br />, -. <br />i/ <br />t-".;: <br />~::" <br /> <br />~>., <br /> <br />. -, <br /> <br />,..::.': <br />, .(::~. <br /> <br />';. ~ <br /> <br />;r~ <br /> <br />~ .: <br /> <br />Evaluating restoration and sustainability of sand resources is a complicated problem that <br />involves sand storage on the Colorado River's bed, tributary resupply of sand, sand deposition <br />induced by flows above peak power-plant discharge, erosion and transport of sand during normal <br />power-plant operations, and recolonization by vegetation, Improving or sustaining sand resources <br />is a difficult challenge because Glen Canyon Dam traps all of the sediment from the upper Colorado <br />River, resulting in an approximate 94% reduction (relative to pre-dam inputs) in the amount of sand <br />supplied to the Colorado River at the upstream boundary of Grand Canyon National Park. <br /> <br />With respect to restoration and sustainability of sand bars, the Secretary of the Interior's 1996 <br />Record-of-Decision (ROD) for operations of Glen Canyon Dam is based primarily on two <br />hypotheses: <br /> <br />(I) that much of the sand introduced to the Colorado River by tributaries downstream from <br />Glen Canyon Dam can accumulate in the channel over multiple years if dam releases do not exceed _, <br />average volume, and Grand C2~V.~C i'PY'.:("':.~ <br />:;:;.-._' n_._.r.-......... ~.-:.-~..:~..:-~ <br /> <br />i,I).; :l P 1'00:) <br /> <br />~~ <br />'=";<....; <br />