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TOPPING ET AL: COLORADO RIVER SEDIMENT TRANSPORT, 2 0.010 ~ (; 0.006 "- z 0 0.006 ;:: ~ 0.004 .... z w " z 0.002 0 U d) 0.000 SEPTEMBER 0.7 .... z 0.6 w ::;- - E fil .s 0.5 "'0 ~ ~ 0.4 U:z ~ 0 0.3 . 0.2 0 0.1 SEPTEMBER e) OE 35.0 illE 30.0 z"' O~ 25.0 ....0 m" 20.0 ::;"' i5~ WO 15.0 ",0 wZ 10.0 ZW -w :::~ 5.0 Ow ~m 0.0 f) SEPTEMBER 555 1__ 00625-0125 mm SAND I '''0", 0.25-2.0 mm SAND OCTOBER NOVEMBER DECEMBER --e- GRAND CANYON GAGE --0-- NATlONAl CNlYON GAGE --tr- ABOVE DIAMOND Q( GAGE OCTOBER OCTOBER Figure 10, (continued) the increase at the Grand Canyon gage, this increase in con- centration was also associated with fining of the suspended sand, with the median size decreasing from about 0.22 to 0.16 mm at this site (Figure IOc). At the Above Diamond Creek gage (222 km downstream from the mouth of the Lillie Col- orado River), suspended-sand concentration increased from about 0.003% to 0.02% (a factor of 6.7 increase) in response to the uttle Colorado River flood (Figure lOb). This increase in concentration was also associated with fining of the suspended sand, with the median size decreasing from about 0.20 to 0.11 mm at this site (Figure IOc). The fact that the suspended-sand concentration increased along 138 kIn of the Colorado River within 2 days of the peak of the Little Colorado River flood passing the LCR near Cameron gage suggests that some por- tion of the sand input during a tributary flood travels down- stream relatively quickly (at nearly the velocity of the water). In addition, the fact that the peak suspended-sand concentration decreased systematically in the downstream direction from about 0.1 I % at the Grand Canyon gage to 0.02% at the Above Diamond Creek gage indicates that some portion of this newly input sand was being deposited in the do.....nstream direction. Following the rapid increase at the three gages, suspended- sand concentrations decreased over 2 weeks as the Little Col- NOVEMBER DECEMBER NOVEMBER DECEMBER orado River flood receded (Figures lOa and lOb). By the mid- dle of October, suspended-sand concentration at all three gages had decreased to about 0.007%. This value was still higher, however, than the values measured before the begin- ning of the tributary flood. After recession of the Little Colo- rado River flood, suspended-sand concentrations continued to decrease more slowly from mid-October to mid- December (Figure lOb), and by the middle of December, suspended-sand concentrations were comparable to those measured in the Col- orado River before the uttle Colorado River flood. These decreases in suspended-sand concentrations were associated with coarsening of the suspended sand (Figure IOc). By the middle of December the median size of the suspended sand at each gage had increased back to a value comparable to that measured before the Little Colorado River flood. These observations of coupled changes in suspended-sand concentration and grain size suggest that sand supplied during a tributary flood travels down the Colorado River as an elon- gating sediment wave, with the finest sizes (because of their lower settling velocities) traveling the fastest. Because it is the farthest site downstream from the mouth of the Little Colo. rado River, this downstream segregation of grain sizes is shown best at the Above Diamond Creek gage. In Figure lOct a peak