WSP05649 - Laserfiche WebLink

Home Browse Search

TOPPING ET AL.: COLORADO RIVER SEDIMENT TRANSPORT, 1 519 1.0 ~_ 0.9 ~ B' 0.8 ~S i!; I 0.7 !i:" 0.8 ",E m,g 0.5 ;:;l! 0.' >' "'I 0.3 :5E 0.2 w- II: 0.1 0.0 0.0 0.1 0.2 0.3 0.' 0.6 0.6 0.7 0.6 0.9 1.0 1.1 1.2 1.3 1.' 1.5 1.6 SILT & CLAy CONTENT /SILT & CLAy CONTENT AT BASE OF DEPOSIT 1.0 t:: 0.9 ~i 0.6 wS! ~ I 0.7 ~.ll 0.6 m~ 0.6 PI ::: ~_ 0.2 a: Q.1 0.0 0.9 __AMI -+- AM 2 -o-AM11 -0- AM19-BEDl __RMI9-BED2 -<>- RM48.BED 1 -+- AM48-BED2 -"l- AM 170. BED 1 ____ AM 170. BED 2 1.1 1.2 1.3 1.. 1.5 SAND D../SAND D..AT BASE OF DEPOSIT FIgure 3. Vertieal trends in the silt and clay content and the median size of sand in predam flood deposits in Marble and Grand Canyons. Both the silt and clay content and the median size of sand are norma1ized by the values me8Sured near the base. The beds coanened upward in probable response to depletion of the finer sediment during floods. "RM" stands for river mile. 1.0 yon. The style of coupled hysteresis in suspended-sediment concentration, suspended-sediment grain size, and bed eleva- tion documented during the 1954 snowmelt flood suggests that the predam river W8S supply-limited with respect to fine sedi- ment (i.e., sand and finer material). The fact that this behavior W8S observed during the annual flood suggests that the time- scale over which this supply limitation occurred was a year or less. Furthermore, the observation that predam flood deposits coarsen upward in the majority of Marble and Grand Canyons, Figure 2. (Opposite) (a) The 1954 mean-daily discharge rerord from the Orand Canyon gage showing the seasonal separation between tnbutary sediment-input events and the annual snowmelt flood. Tributary rivers that contributed to the observed discharge peaks are indicated. Cross-hatched region indicates the period from April 28, 1954, through June 14, 1954, during which the data ShOWD in Figures 2b-2d were collected. (b) Hysteresis in the concentration of suspended silt and clay Bod suspended sand; arrows indicate the sequence of measurements. Progressive d~ple[ion of the finer sediment caused the concentrations (for a given discharge) to be lower on the receding limb than on the rising limb. (c) Hysteresis in the median grain size of the suspended sand. The suspended sand was coarser (for a given discharge) on the receding limb th~n on the rising limb. (d) Hysteresis in mean bed elevation. Stage is relative to gage datum. 1.6 suggesting a depletion of fines during floods, lends further support to this supply-limited interpretation. s. Evidence for Predam Differences in the Degrl!e of Sediment Supply limitation in Grand and Glen Canyons The hydraulic geometry of the predam Colorado River in Marble and Grand Canyons was very different from that in Glen Canyon. Though the mean depths of the predam river in Glen, Marble, and Grand Canyons were comparable, the river was generally narrower (by about a factor of 1.5~2) and steeper (by a factor of 3-5) in Marble and Grand Canyons than it was in Glen Canyon. Because of this difference in hydraulic geom- etry, the reach-averaged boundary shear stress, and hence the transport capacity for a given supply of sediment, would prob- ably have been lower in Glen Canyon. Predam USGS sediment records collected at the Lees Ferry and Grand Canyon gages indicate that most of the sediment that passed the Grand Canyon gage first passed through Glen Canyon. Therefore, though the predam river in Marble and Grand Canyons was probably annually supply-limited with respect to fine sediment by virtue of the difference in hydraulic geometry, the river in Glen Canyon may not have been. Howard and Dolan [1981] first suggested that because of the differences in hydraulic geometry, bed elevation in the predam river in Marble and