WSP03790

• File Number: 8220.101.13
• Description: Glen Canyon Dam/Lake Powell
• State: AZ
• Basin: Colorado Mainstem
• Date: 10/1/1998
• Author: Secretary of Inter
• Title: Report to Congress: Operations of the Glen canyon Dam Pursuant to the Grand Canyon Protection Act of 1992 ‎(Water Years 1997 and 1998)‎
• Water Supply Pro - Doc Type: Annual Report

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APPENDIX F

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IMP ACTS OF THE 3-5 NOVEMBER 1997 31,000 cfs TEST FLOW

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Introduction

The Bureau of Reclamation and the Grand Canyon Monitoring and Research Center conducted ,a test ofa
"Habitat Maintenance" style flow from Glen Canyon Dam on 3-5 November 1997, The flow peak reached
approximately 30,600 cfs for this 2-day test. This memo outlines the impacts of that flow event on resources
through Grand Canyon.

Phvsical Resource Impacts

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GCMRC coordinated pre- and post-event videography of the river corridor, and those images are being
examined for backwater habitat changes.

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Using the methods ofPamell et al. (1996), detailed topographic surveys of35 sand bar monitoring sites were
conducted immediately following the November 1997 test flow by members of the Northern Arizona University
Department of Geology sand bar studies office, Information gathered from these surveys is compared to
previous surveys conducted in August 1997 in order to quantify sand bar change. Based on this preliminary
date, the November test flow benefitted the sediment resources by depositing sediment at higher elevations. The
higher elevation areas of sand bars contain critical riparian habitats that AI.. of particular interest to management
agencies, Following the 199645,000 ft'ls test flow, erosion has steadily decreased the volume of sediment
contained in the upper elevations of sand bars, Preliminary results show that the November 1997 test flow
slightly increased the volume of sand bars (above the 20,000 ft'ls stage elevation), calculated as a percentage of
the pre-1996 test flow, from 87% to 91 %. High flows above powerplant capacity are the only means by which
the volume of the upper levels of sand bars can be maintained.

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The U,S, Geological Survey (G. Fisk, D. Topping, D. Rubin and S. Wiele) monitored mainstream streamflow
and suspended sediment at the Lee Ferry, Above Little Colorado River, Grand Canyon and Diamond Creek
gauges onelday before, during and after the flow event. Bedload sampling was condui=ted int he mainstream and
in eddies at selected sites following the high flow. Bar sedimentology, grain size, deposit thickness was
conducted with the NAU effort immediately following the high flow,

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Bioloiical Resource Impacts

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On November 6, 1997, the Arizona Game and Fish Department (AFFD) surveyed cobble bars in the Lee Ferry
reach to access rainbow trout stranding post downramp. AGFD evaluated stranding by dividing each cobble bar
examined into quadrants and obtaining a total count of stranded fish by examining total area of the bars. AGFD
also noted stranding of macro invertebrates, Cobble bars selected for evaluation were representative of this
habitat type in the Lee Ferry reach and were in areas which receive preferential use by fishing guides and trout
(6Omm) was observed to have been stranded and low concentrations of Gammarus were observed stranded in a
few shallow pools, no other stranded macroinvertebrates noted. At RM-8, two live rainbow trout (9Omm and
400-50Omm) were observed stranded in a large pool, Gammarus (~ 1,000) of diverse size range were observed
stranded in one small pool, and several thousand snails (Physidae) were observed stranded on two small sand
habitats associated with sedges nearshore. At RM-2.5, one dead adult flannelmouth sucker (catostomus
/atipinnis) was observed in approximately 3 ft. Of water just inside mouth of backwater. This was judged not to
be a stranding-related mortality.

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