WSP05649

• File Number: 8220.101.10.D
• Description: Glen Canyon Dam/Lake Powell
• State: AZ
• Basin: Colorado Mainstem
• Date: 2/1/2000
• Author: Topping et al.
• Title: Colorado River Sediment Transport
• Water Supply Pro - Doc Type: Report/Study

526

TOPPING ET AL: COLORADO RIVER SEDIMENT TRANSPORT, 1

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Figure 6, Relationships between water-surface stage, bed stage, and changes in the upstream sand supply
during the average predam year at the Grand Canyon and upper Lees FeTTY cableways. Depletion of the
upstream supply of sand played a greater role in the response of the bed topography at the Grand Canyon
cableway. (a) Water-surface stage, mean bed stage, and minimum bed stage in 2-week bins during the average
predam year and the load-weighted normalized occurrence (in 2-week bins) of the four types of sand-supply
events at the Grand Canyon cableway. Analysis is conducted on aU the 1944-1962 discharge measurements
and on the suspended-sand data presented in Figure 4; stage error bars are 1 standard deviation. (b)
Water-surface stage, mean bed stage, and minimum bed stage in 2-week bins during the average predam. year
and the load-weighted nonnalized OCCUrrence (in 2-week bins) of the four types of sand-supply events at the
Lees FeTTY gage. Analysis is conducted on all the 1949-1962 discharge measurements made at the upper Lees
FeTTY cableway and on the suspended-sand data presented in Figure 4; stage error baTS are 1 standard
deviation. The lower Lees Ferry cableway was not included in this analysis because the channel at that location
was almost twice as wide as at the upper cableway, and relatively few discharge measurements were made
there. The cofferdam at the Glen Canyon Dam site (23 km upstream from the upper cableway) was completed
on February 11, 19591Martin, 1989J, and immediately began to trap some of the upstream supply of sediment
IPemberton, 1976J. Though the bed at the upper cableway began to scour in 1959 in probable response to this
partial trapping of the upstream sediment supply, the magnitude of this scour was much smaller lhan the
magnitude of the natural seasonal scour and fill at the upper cableway. Thus inclusion of the period 1959-1962
did not greatly affect this analysis, as indicated by the slight difference between the values of mean bed stage
for 1949-1962 and 1949-1958. The number of minimum bed-stage measurements in Figures 6a and 6b is less
than the number afwater-stage and mean bed-stage measurements because Burkham [1986] analyzed a subset
of the USGS discharge measurements.

a rearrangement of the gravel bars at the mouth of the Pacia
River that fonn the hydraulic control for the Lees FeTTY gage.
Second,'a large Pari a River flood caused backwater in the
Colorado River at the Lees Ferry gage on August 2,1929, and

rearranged the hydraulic control for the gage again. shifting
the stage-discharge relationship back to its pre-April 1923 state
(Figure 7d). Third, a large rock slide on December 19, 1944.
fell on the right end of the upper cableway (unpublished USGS