1400 ‎(2)‎

• UCREFRP Catalog Number: 1400
• Author: Simons, D. B., et al., ed.
• Title: Proceedings
• USFW Year: 1980.
• USFW - Doc Type: Workshop on Downstream River Channel Changes Resulting From Diversions or Reservoir Construction.
• Copyright Material: NO

3.

Some reaches of the river are alluvial in nature. The bed is
armored with cobbles the size of which corresponds roughly to
the size for critical tractive force at bankfull discharge.

These gravel-armored reaches are relatively stable.

4.
S.

Small quantities of sand and fine gravel are available for
transport in the Yampa River above the Little Snake
confluence; these sediments move over the armored gravel bed
and accumulate in pools, on point bars, and in certain reaches
with mild slopes.

6. Much of the sediment transported to the Box Elder reach is
sand from the Little Snake River.

7. The reservo; rs wi 11 trap most of the sediment of the Yampa
River now passing the Maybell gage.

Much of the discussion centered around data needs. It was
generally agreed that the data provided were not adequate. In parti-
cular, it was pointed out that meander pattern and channel configuration
in the alluvial reaches of the river would likely depend on some
dominant or "channel forming" discharge that might occur only a few days
a year. The only information on reservoir releases were average monthly
flows, whereas specific operating rules were needed, along with infor-
mation on the outlet structures, their elevation, whether or not they
would release sediments, and so on. There al so was general concensus
that extensive bed samples and at least some general information on the
nature of the bank material were essential to any quantitative analysis.

One crit i ca 1 quest i on emerged. What would happen in the vi ci ni ty
and downstream of the confl uence of the Li tt 1 e Snake and Yampa Ri vers?
The little Snake River contributes heavy sediment loads. Would the
regulated flows be able to transport this sediment, or would there be
aggradation in the reach? Would the transport capacity of the sustained
sediment-free reservoir releases exceed the supply of sediment, result-
ing in degradation? Only one of the participants, Dr. R. J. Garde,
presented any calculations on transport capacities. He concluded that
there would be minor degradation and armoring at Deerlodge Park, and
that "once the surface is paved the material that comes in from the
little Snake River would be safely carried down the Yampa River." He
was careful to point out that his analysis was based on some "simplified
assumptions" and a careful reading of his paper will show that these
simplifications were necessary because of the lack of data.

It was generally agreed that more detailed flow and transport
calculations would be necessary to resolve the question of what would
happen in the vicintty of the confluence of the Little Snake River, and
that this would require the collection of field data to provide cross
sections and bed material size distributions. In addition, it was
stressed by Dr. Shen that future flows were stochastic processes; the
distribution of these flows would have to be determined and hydraulic
calculations should be carried out to cover that distribution. The
future conditions in the reach cannot be predicted preCisely; they
should be specified in terms of their probabilities of occurrence.

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