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<br />330 SUMMARY AND SYNTHESIS OF GEOMORPHIC STUDIES <br /> <br />abundant. Thus, the flood was also a success in the sense <br />that new scientific insights were gained. <br />Some research findings implied (hat basic management <br />strategies utilized in the operations of Glen Canyon Dam <br />should be revised. Thus. the flood was also an importanl <br />step in learning!O manage the river "adaprjyely."' Managers <br />were reminded that Colorado River management policies <br />must be conlinually revised and refined in response to the <br />evolving scientific understanding of physical and <br />ecological processes. The purpose of this chapter is to <br />summarize and synthesize research findings that concern <br />geomorphic processes and !O discuss implications of Lhese <br />findings for the management of the Colorado River in <br />Grand Canyon. These research findings are also used to <br />estimate a sand budget for Ihe flood. <br /> <br />2. PHYSICAL RESOURCES OF THE COLORADO <br />RIVER IN GRAND CANYON <br /> <br />Many or the physical resources of the Colorado Riyer <br />have socieLal yaIue because of their use by the public, their <br />intrinsic landscape aLtributes. or their ecological function <br />[Webb e/ aI., this volume]. Campsites are those parts of sand <br />ban; large and high enough to be used by boating parties <br />without being inundated by the daily fluctualing dam <br />releases caused by producLion of hydroelectric power <br />(Figure J). The challenge of whitewater boating in Grand <br />Canyon is afforded by debris flows that deliyer boulders to <br />the riyer and by the Colorado River iLseIf. which redis. <br />tributes those boulders during flood. The size distribulion of <br />other tine-grained substrate determines !he composition of <br />riparian vegeLation [Stevens, 1989] and the composition and <br />abundance of benthic invertebrates [Brouder el al., Lhis <br />volume]. <br />Areas of stagnant flow that typically ..ist in the lee of <br />emergent realLachment bars that block recirculation into <br />formerly aClive eddy return.current channels are potential <br />nursery habilal for some nalive fishes. These habitats are <br />called backwalers by ecologisls working in Grand Canyon <br />[Brouder et at.. this yoIumel. The exislence and size of <br />these backwaters depends on Iwo morphometric allributes <br />of Ihe sand bar within an eddy: the !Opography of Ihe <br />re!Urn-currenl channel and Ihe !Opography of Ihe adjacent <br />reattachment bar. Deep relUm-curren1 channels are <br />inundated over a wider range of flows Ihan are shallow <br />channels, and higher reattachment bars block recirculation <br />over a wider range of flows than do low-elevation bars. <br />These "ecological" backwalers are difrerent phenomena <br />than are Ihe backwaters descrihed in hydraulics which are <br />areas of ponded flow upstream from channel constrictions. <br /> <br />3. UNDERLYING SCIENTIFIC QUESTIONS <br />ADDRESSED BY THE FLOOD <br /> <br />More than a decade of research in Grand Canyon, and <br />elsewhere, provided the basis for the underlying <br />geomorphic questions addressed in ~arious controlled-flood <br />research plans [Webb e( al., this volume; Schmidr el al., this <br />volume]. These questions were related to understanding the <br />processes that form and maintain the physical resources <br />described above. Thus, lhese questions concerned <br />entrainmem, Iranspofl, and deposilion of coarse and fine <br />sediment. Would large amounts of sand and finer sediment <br />be scoured from the river bed and be deposited in eddies <br />and elsewhere on Ihe banks? Would Ihe volume or newly- <br />deposited sediment be greater al sites further downstream <br />from the dam? Would net erosion or eddies and channel <br />banks occur at sites near the dam. especially upstream from <br />Lees Ferry? Whal would be the relalive proportion of fine <br />sediment deposiled in eddies and along the banks in <br />relalion 10 the amount transported to Lake Mead reseryoir? <br />Would the rate of fine.sediment deposition decrease with <br />time? Would lhe flood rework debris fan deposits, thereby <br />widening rapids? Was Ihe flood of su[ficient magnitude and <br />of appropriale duration 10 accomplish Ihese tasks? How <br />long would newIy.created deposits of fine sediment last <br />after the flood? <br /> <br />4. THE STATIlS OF PHYSiCAL RESOURCES IMMEDi- <br />ATELY AFfER THE R.OOD <br /> <br />The 1996 conLrolled flood caused widespread deposition <br />of sand at rel.lively high elevation on lhe river's banks at <br />eIeyations 3 to 5 m above the stage of the administrativeIy- <br />delermined minimum daylime dam release of 227 m3/s. <br />These new deposits Were as much as 2 m Lhick, exceeding <br />Ihe average thickness of any previous flood deposits since <br />1983 [Hazel el al.. this volume]. Much or Lhis sand was <br />deposited sufficiently high so thai il was exposed above the <br />stage of the typical maximum daytime dam release of 566 <br />m3/s. Hazel el al. [this volume I found that the average <br />increase in volume of high-elevation sand was 164%, the <br />average increase in area was 67%, and Ihe average increase <br />in Ihickness was 0.64 m. Schmidl e1 al. Ilhis volume] found <br />thai most of this sand was deposited in eddies except lhar <br />large amounts of sand were deposited as channel-margin <br />levees in reaches where debris fans are infrequent; they <br />determined (hat lhe (o[al area of new deposits was between <br />10.500 and 21,000 m2/km. <br />These new deposits increased the number and size of <br />campsiles throughout Grand Canyon. Kearsley el al. [this <br />volume 1 found that the number of bars usahIe as campsites <br /> <br />