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TOPPING ET AL: COLORADO RIVER SEDIMENT TRANSPORT, 2 ''''''' 1200 { 1000 w " ~ < Ii eoo ~ Ci ~ w ~ ~ eoo ...~... LWRIAHWLECYMGIr.OI:D-T7lJJY'. SMtD -.- GfIAHl) CNfYOH GAGE ,.." IUSP. 6oIoHD .....-. aMHO CANYON OI.QE 1)-71""'. SNCl -"-12:l.wl.lEOOYO-nlllJSP8fDEl)&MIl) ___ NATIONAL CAH'/'ClH BADE ....II1U$P.1AHD --0- ClAANO CYN QAOE f'IrtE flEl*l1EHT0H.. """ 547 0." 050 0.45 0.40 0.35 0 . I 0.30 - 0.25 0.20 Q.t5 a) m~.1~1~2~3~4~6~8~7~+f 1400 1200 X lWFI MN8..E CYN o.771NCl + LWR lMRIlf CYN 0.17 aT" a..AY . QllWl)c:AHrClfNl11Wt:l 0 GRNClCYNI4I"T&Q..AY . QfWIO CNNtlH ll-n &fH) ~1000 () OIWlJ(:'I'ND-77....r.a..AV .. 122-*f:EDmD-74lWi1D 1. '" 1I2-M1J:EDClYD-745U&a..AY W . MATIOtW. C'l'N ..." SAHO " 0 M.II~CYl\IP'" 111.1 ..cu.y ~ < Ii eoo ~ I Ci ~ w !< ... !< I X 400 + 200 DA.Y, OAY3 DAY4 DAY 5 DAY6 DAV 7 b) 0.17 0.18 0.15 0.14 0.13 0.12 0.11 ~ o 0.10 m ~ a.OS! ~ 0.08 0 z 0.07 i 0.06 l 0." 0." 0.03 0.02 0.Q1 0.00 Figure 4. Sediment grain size and concentration during the 19% flood experiment. At all locations where measurements were made during the flood, the line sediment on the bed and suspended sand coarsened as the concentration of suspended sand decreased. (a) Hydrograph of the 1996 flood experiment (as measured at the Grand Canyon gage), spatially averaged median size of the line sediment on the bed, and spatially averaged median size of suspended sand measured at four sites. Error bars are 1 standard deviation. The travel time of the flood wave between the various sites has been removed in Figure 4a such thaI the beginning of day 1 al each site corresponds to the time of the beginning of steady high discharge at each site. At the Grand Canyon gage the samples collected with Ihe P-61 sampler were coarser than those collected with the 0-77 sampler because (I) the P-61 was only deployed at two verticals in the centra12/3 oflhe channel (see Figure 2), whereas the D-77 was deployed at five verticals across the entire channel, and (2) a P-6I sampler samples much closer to the bed Ihan a D-77 sampler. (b) Hydrograph of the 1996 flood experiment (as measured at the Grand Canyon gage) and spatially averaged concentrations of suspended sand and suspended silt and clay measured at four sites. Error bars are one standard deviation. tant issue is revisited in section 6.1. The maximum volume of sediment in the reach was attained on day 4 (Figure 6b), correlating fairly well with the time of maximum bed elevation at the cableway on days 4-5 (Figure 3). After day 4 of the flood. erosion of sand from the reach dominated (Figure 6b) as the bed at the cableway began to ,cour (Figure 3b), possibly driven by the measured depletion of the upstream supply of sand (Figure 4b). The grealest amount of erosion in the reach occurred during the receding limb of the 1996 flood not during the 7 days of high discbarse (Figure 6b). This erosion was due to the catastrophic failure of an eddy bar on river left in cross sections 3 and 4 beginning at 10:00 A.M. MST on ApriL 3