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

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ABSTRACT

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Flooding from the Paria River in August-September 1997, delivered an estimated 770,000 m3 (2,0

:t 0.4 million Mg) of sand to the Colorado River ecosystem below Glen Canyon Dam, The Glen

Canyon Dam adaptive management program implemented a 48 hr high flow of 878 m3/s on November

3, 1997, termed the 1997 Test Flow, to test the hypothesis that a short-duration, peak power plant

discharge could redistribute tributary-derived sand from the bed to the banks of the Colorado River, A

combination of field measurements and modeling were used to detennine the volume and distribution

of sand supplied by the Paria River, the rates of downstream redistribution of that sand, and the

effectiveness of the 1997 Test Flow at sand redistribution, Repeat surveys of the 3-km reach at the

head of Marble Canyon, immediately downstream from the Paria River, indicate that about 24 to 36%

of the Paria River sand inputs were immediately deposited in this reach, Approximately 50% of the

flood deposition in the 3.km reach was eroded within 37 days of flood cessation, Large increases in

suspended-sediment transport at the lower end of Marble Canyon were measured within 1-2 days of

these Paria River floods, suggesting that a measurable fraction of the supplied sand was transported

through Marble Canyon within days of input. Less than 10% of the sand delivered to the Colorado

River in August-September 1997, remained in the 3-krn reach at the end of the 1997 Test Flow, The

estimated sand export from Marble Canyon during the 2-day flow was 70,000 m3 (0,19 :!: 0,04 million

Mg), about 9% of the total Paria River sand input.

Despite the sand delivery to the Colorado River by the Paria River, the 1997 Test Flow did not

significantly aggrade sand bars at high-elevation, We conclude that stage elevations reached by the

1997 Test Flow were not sufficient to distribute sand to open depositional locations, In order to

redistribute sand to higher elevations, future controlled floods need to be of greater discharge than the

1997 Test Flow, Future high releases also need to be closely timed with tributary inputs, on the order

of weeks or months, to optimize sand storage and prolong the residence time of new sand supplied to

the Colorado River ecosystem,

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