9658

• UCREFRP Catalog Number: 9658
• Author: Schmidt, J. C. and K. L. Orchard.
• Title: Report A - Geomorphic Analysis In Support of a Channel-Maintenance Flow Recommendation for the White River Near Watson, Utah Draft Report.
• USFW Year: 2002.
• USFW - Doc Type: Logan, UT.
• Copyright Material: NO

(Fig. 28). Aggradation in the coarse bedded riffles occurred when adjacent pools
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scoured.

DISCUSSION

Channel Forming Flows

Several lines of evidence indicate that a high-flow component of an in-stream

flow should preserve most of the natural flow regime greater than approximately 40 m3/s

(-1300 ft3 Is). Flows of this magnitude are capable of scouring the bed near the cableway,

because the bed was never stable when the highest discharge between two discharge

measurements was more than about 41 m3 Is. Also, the bed never scoured when the

highest discharge between two discharge measurements was less than 37 m3/s. Thus,

I

flows greater than about 40 m3 Is are capable of transporting fine bed sediment. We

inferred that bedload movement occurred at 51 m3/s, because bedforms were detected on

fathometer traces at those cross-section with fine-grained bed material at this discharge.

The White River isa supply-limited stream, because much more suspended

sediment is carried on the rising limb of the annual snowm~lt hydro graph than on the

falling limb. Thus, some low flows might not be necessary to maintain an equilibrium

sediment mass balance wherein the entire load delivered to the stream is transported

downstream. A rule of thumb used in the federal government's reservation of in-stream

flows for the purpose of channel maintenance in Idaho has been to claim all flows greater

than the discharge above which 70% of the long-term annual load is transported. In the

case of the White River near Watson, that flow is about 40 m3/s. We assume that

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