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<br />002353
<br />
<br />Table 3. Characteristics of the 5 reaches in Marble and upper Grand Canyons where fine-grain alluvium
<br />was mapped and analyzed in a GIS. The sixth reach was Glen Canyon.
<br />
<br /> Lees Redwall Point Tapeats Big Bend
<br /> Ferry Gorge Hansborough Gorge Reach
<br /> Reach Reach Reach Reach (RM 65-
<br /> (RM 0.8) (RM 29- (RM 42-50) (RM 6D- 72)
<br /> 35) 65)
<br />Reach length, in 14 10 10.8 8.0 12.1
<br />kilometers
<br />Total number of EDls all 37 56 81 57 56
<br /> > 1000 31 33 41 44 34
<br /> m2
<br />EDZ frequency, in all 2.6 5.6 7.5 7.1 4.6
<br />number per kilometer
<br /> > 1000 2.2 3.3 3.8 5.5 2.8
<br /> m2
<br />Total area of EDls, all 287,400 167,100 453,460 406,930 414,630
<br />in square meters > 1000 284,430 157,450 437,120 402,230 407,410
<br />m2
<br />Total EDZ area, all 20,500 16,700 42,000 50,900 34,300
<br />in square meters, > 1000 20,300 15,700 40,500 50,300 33,700
<br />per kilometer m2
<br />Mean size, in square all 7800 3000 5600 7100 7400
<br />meters > 1000 9200 4800 10,700 9100 12,000
<br /> m2
<br />Median size, in square all 3900 1400 1000 3000 1500
<br />meters > 1000 5900 3500 3600 7400 7100
<br /> m2
<br />Notabley large EDls 1.2R: 43.6L: 34,300 63.5L: 66.1L:
<br />(location in River Mile 67,000 44.5L: 34,400 33,300 34,500
<br />and size in square 47.1R: 43,300 64.4L: 68.2L:
<br />meters) 47.6R: 45,000 34,300 52,800
<br /> 71.3L:
<br /> 38,600
<br /> 71.7L:
<br /> 33,500
<br />
<br />~",
<br />
<br />The highest elevation parts of eddy bars
<br />sometimes merge downstream with linear
<br />banks of fine-sediment that resemble flood
<br />plains. These "channel-margin deposits"
<br />typically have levees of low relief and form by
<br />movement of suspended sediment away from
<br />the main flow, similar to that which occurs on
<br />the floodplains of alluvial rivers.
<br />A mid-channel, or bank-attached, cobble
<br />bar often exists downstream from the zone of
<br />flow recirculation. The debris on this bar has
<br />been eroded from the upstream debris fan
<br />(Grams and Schmidt, 1999; Pizzuto et aI.,
<br />1999; Webb et aI., 1999; Larsen et aI., 2004).
<br />At moderate and low discharge, flow typically
<br />passes around the margins of these bars and
<br />creates a riffle (Fig. 6B).
<br />
<br />3.2.1 Longitudinal Distribution of Eddy
<br />Deposition Zones
<br />
<br />The frequency and size of recirculation
<br />zones vary longitudinally due to differences in
<br />channel width, valley width, frequency of
<br />tributary debris fans, and shape and size of
<br />fans. We mapped the distribution of fme
<br />sediment in 80 kin of the study area (Fig. 1) on
<br />11 aerial photograph series. Mapping was
<br />conducted in Glen Canyon (Grams et aI.,
<br />2004), in the Lees Ferry Reach2 between Lees
<br />
<br />2 The reaches where mapping was conducted and
<br />analyzed within a GIS are referred to by specific name,
<br />i.e. Lees Ferry Reach and Big Bend Reach, to distin-
<br />guish them from geographic places, i.e. Lees Ferry and
<br />the Big Bend.
<br />
<br />3.0 The Valley of the Colorado River 15
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