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<br />Webb (1996), and Webb and others (1999b), and
<br />their names will not be repeated here, The authors
<br />thank Bill Dietrich and Alan Howard for sharing
<br />ideas that led to some of the techniques used in this
<br />report, We also thank Grand Canyon Monitoring
<br />and Research Center and David Topping for
<br />laboratory analysis of streamflow sediment, and
<br />Waite Osterkamp, Richard Hereford, David
<br />Topping, and Jon Major for their reviews of the
<br />manuscript. We particularly thank Dave Wegner
<br />for his support of this project over the span of a
<br />decade,
<br />
<br />Units and Place Names
<br />
<br />In this report, we use metric units for all
<br />measures except river mile, which is used to
<br />describe the location of tributaries in Grand Canyon
<br />(Stevens, 1990), certain reference river discharges
<br />(e.g, , 10,000 ft3/s), and in equations that were
<br />originally developed for use in English units. Use of
<br />river mile has considerable historical precedent and
<br />provides a reproducible method of describing the
<br />location of tributaries with respect to the Colorado
<br />River, The locations of tributaries are described
<br />using river miles downstream from Lee's Ferry and
<br />a descriptor of"L" for confluences on river-left and
<br />"R" for river-right. The left and right sides of the
<br />Colorado River are determined as one faces
<br />downstream.
<br />
<br />We typically refer to "Grand Canyon" in broad
<br />reference to the Colorado River watershed between
<br />Glen Canyon Dam and the Grand Wash Cliffs,
<br />including Glen, Marble, and Grand Canyon proper.
<br />"Marble Canyon" is the canyon reach of the
<br />Colorado River between Lee's Ferry and the
<br />confluence with the Little Colorado River (river
<br />miles 0 to 61.5; fig, I); we refer to Marble Canyon
<br />only for specific tributaries in that reach. For our
<br />purposes, "Glen Canyon" is the canyon reach of the
<br />Colorado River between Glen Canyon Dam (mile-
<br />15) and Lee's Ferry (mile 0). Following Reilly
<br />(1999), we use an apostrophe in "Lee's Ferry,"
<br />despite the official Board of Geographic spelling of
<br />"Lees Ferry,"
<br />
<br />For sediment particle sizes, we use the standard
<br />unit 4>, defined as
<br />
<br />D=2-+,
<br />
<br />(I)
<br />
<br />where D = the diameter, in millimeters, of the
<br />intermediate axis, also known as the b-axis (Folk,
<br />1974).
<br />
<br />PREVIOUS STUDIES
<br />
<br />Definitions of Flow Types That Occur in
<br />Grand Canyon Tributaries
<br />
<br />Debris flows are an important sediment-
<br />transport process in a variety of geomorphic
<br />settings throughout the world. Costa (1984)
<br />described debris flows as water-based slurries of
<br />poorly sorted material ranging in size from clay to
<br />boulders. Debris flows occur in arid, semi-arid,
<br />tropical, and montane environments. In these
<br />settings, they are typically called mudflows, debris
<br />slides, and debris torrents, to name a few of the
<br />more common terms (Blackwelder, 1928; Sharp
<br />and Nobles, 1953; Johnson and Rodine, 1984;
<br />Pierson, 1984; Pierson and Costa, 1987), Debris
<br />flows can have devastating effects on populated
<br />areas (pierson and others, 1990), but damage can
<br />also be significant even in sparsely populated areas
<br />(Glancy and Harmsen, 1975; WoW and Pearthree,
<br />1991).
<br />Debris flows are slurries of clay- to boulder-
<br />sized sediment with volumetric water concen-
<br />tration ranges from about 10 to 30 percent (pierson
<br />and Costa, 1987; Major and Pierson, 1992). A
<br />variety of classifications has been proposed for
<br />distin-guishing debris flows, "hyperconcentrated
<br />flows," and streamflow (Beverage and Culbertson,
<br />J 964); recent work has focused on rheological
<br />properties (Pierson and Costa, 1987) and the
<br />interactions of fluid and solid forces (Iverson,
<br />1997). Debris flows are characterized by cohesive
<br />properties that are probably related to clay content,
<br />sand content, grain-particle interactions, and the
<br />ahility to transport large boulders (ROdine and
<br />Johnson, 1976; Johnson and Rodine, 1984; Costa,
<br />1984). Source lithologies strongly affect particle-
<br />size distributions and, therefore, flow rheology in
<br />debris flows. These lithologies vary greatly within
<br />and between individual drainages in Grand
<br />Canyon. Most debris-flow deposits have few or no
<br />
<br />4 Sediment Delivery by Ungaged Trlbutarle. of the Colorado River in Grand Canyon
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