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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NAU Sand Bar Studies

Final Report

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1997 ranked among the top 20% during the 75 years of gage record on the Paria River (Topping et ai"
2000b), This new sediment was the first significant input from the Paria River since the winter of
1995, and the largest since 1980, It is important to note that Paria River floods generally do not have a
significant effect on mainstem river stage because the water volumes are small relative to those in the
main stem and the duration of peak discharge is short, on the order of hours,

THE 1997 TEST FLOW

The 1997 Test Flow was the first attempt by the adaptive management program to implement a
flow release strategy for sediment redistribution following a tributary flood, The hydrograph of the test
flow, beginning on November 3, consisted of a rapid increase in discharge from 479 m3/s (16,909 fe/s)
to a steady flow of 878 m3/s (31,000 fels) for 48 hours, followed by a slow decrease to 480 m3/s on
November 6 (Fig, 2b), The maximum rate of up ramp was 68 m3/s (2,400 fe/s) per hour and the
maximum downramp rate was 39 m3/s (1,377 fe/s) per hour. Similar to the hydrograph for the 1996
Controlled Flood, the slower rate of downramp was designed to reduce erosion caused by dewatering
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of bank stored water in sand bars and to avoid stranding of trout in the tailwaters fishery upstream
from Lees Ferry, The release was approximately 93% of maximum power plant capacity,

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STUDY AREAS AND METHODS

Modeling Tributary Sand Inputs

A flow and sediment transport model for the Paria River was previously developed by Topping

(1997), The outputs from this model are the wetted reach-averaged cross-section geometry, the

discharge of water, the sand transport rate (in 10 size classes), and the silt and clay transport rate, The

model provides excellent agreement with the historical record for discharges, suspended-sediment

concentrations and hydraulic geometries for previous floods, In the future. model estimates may

provide cost-effective, real-time predictive capabilities for suspended-sediment yields to the Colorado

River,

To examine the rate at which sand inputs from the Paria River were transported downstream, we

compared model predicted sand loads (0,0625-2,0 mm) to measured bed changes below the mouth of

the Paria River (described below), Model loads were compared to deposit volume changes by

assuming a porosity of 35% for sand-sized sediment on the bed and 20% uncertainties associated with

the suspended-sand measurements [see Appendix B in Topping et ai, (2000a)],

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