WSP09464

• File Number: 8220.101.10.D
• Description: Glen Canyon Dam/Lake Powell
• State: AZ
• Basin: Colorado Mainstem
• Date: 5/24/2000
• Author: Hazel et al.
• Title: Sand Deposition in the Colorado River Ecosystem from Flooding of the Paria River and the Effects of the Nov 1997 Glen Canyon Dam Test Flow
• Water Supply Pro - Doc Type: Report/Study

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NA U Sand Bar Studies

Final Report

The possibility that a shorter duration and lower magnitude release than the 1996 Controlled

Flood (i,e" a non-spill release) could achieve some level of sediment conservation was of interest to

the Glen Canyon Dam adaptive management program. Discharge beyond the 940 m3/s (33,200

ft3/s) power plant capacity requires use of the river outlet works (V,S. Department ofInterior, 1995),

Water and power interests in the adaptive management program were concerned about the loss of

power revenues and water storage, which increased the overall cost of the 1996 experiment

(Harpman, 1999), If similar results could be achieved without bypassing the power plant, the cost

would be considerably lowered and increased flexibility in implementing sediment-conserving dam

operations would be realized,

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The sediment supply is particularly limited in Marble Canyon (Topping et aI., 2000a), the 98-1an

reach between the Paria and Little Colorado Rivers, because of intermittent sediment delivery from

the Paria River and proximity to Glen Canyon Dam (Fig, I), Flooding on the Paria River in August

and September 1997, significantly replenished sand in the Colorado River downstream from the

confluence, Shortly after the sediment input, the adaptive management program recommended that a

short-duration, power plant capacity test flow be released from Glen Canyon Dam, Termed the 1997

Test Flow, the release occurred beginning November 3, 1997, and consisted of a constant flow of

878 m3/s (31,000 ft3/s) for 48 hours,

In this report, we evaluate the accumulation and transport of Paria River-supplied sand in the

Colorado River ecosystem and the effectiveness of the 1997 Test Flow at redistributing sand to the

channel margins, The focus of the report is the reach of Marble Canyon below the Paria River, a

portion of the ecosystem between river miles 1-61 (Ian 2-100), We used a combination of repeat

topographic and hydrographic surveys, suspended sediment and grain size measurements, and model

estimates of sediment inputs, Determining the distribution of sand added to the Colorado River

ecosystem and understanding the rates of downstream redistribution of that sand are important for

planning the timing, magnitude, and duration of dam releases intended for bar restoration purposes,

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PREVIOUS STUDIES

The Colorado River in Marble and Grand Canyons flows through a deeply incised channel
confined by bedrock and talus, Channel width is controlled by the erodibility of the bedrock exposed
at river level (Howard and Dolan, 1981; Schmidt and Graf, 1990; Melis, 1997), Transport and
deposition of fine-grained sediment in the channel is associated with a repeating pattern of long, low

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