9568

• UCREFRP Catalog Number: 9568
• Author: Resource Consultants Inc.
• Title: Sediment Transport Studies of the Little Snake, Yampa, and Green River Systems.
• USFW Year: 1991.
• USFW - Doc Type: Fort Collins, CO.
• Copyright Material: NO

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All of the above discussion indicates that the reach between Deerlodge Park and Mathers Hole
cannot be shown to be either progressively aggrading or degrading. The canyon bound reach of the Yampa
River between Deerlodge and Mathers Hole is a supply limited channel. Under current conditions,
sediment deliveries from Deerlodge are readily transported through the Canyon. The above discussion
pertains solely to the overall tendencies of the study reach. As was noted in previous sections (see Section
5.1.2), it is probable that sediment is temporarily stored in pool reaches and in the lee of obstructions in the
channel during low flows and re-entrained at higher flows.

5.3 Effective Dischar~e

5.3.1 Definition and Procedure. Effective discharge is defined as the increment of discharge that
transports the largest fraction of the annual sediment load over a period of years (Andrews, 1980), and is a
definitive, readily calculated number. In contrast, the dominant discharge is more of a geomorphic concept
that attempts to define the "channel fonning" discharge. In alluvial stream channels the effective discharge
may be indicative of the dominant or channel fonning discharge. The bankfull discharge is also sometimes
considered indicative of the channel fonning or dominant discharge. As a result of its defInitive, numerical
basis the effective discharge is useful for evaluating or understanding potential sediment transport changes
resulting from changes in water or sediment transport.

Effective discharge computation is based on daily flow records and sediment rating curves. The
analysis can be completed by the flow duration curve method described by Miller (1951), or numerically by
dividing the daily flow record into equal class intervals and summing the total sediment transport by each
daily flow in each class interval. The mid-point of the interval with the greatest transport over the period of
record is then the effective discharge. The latter procedure was utilized in this report, utilizing 50 class
intervals.

5.3.2 Effective Discharee Results. The effective discharge was calculated for the Lily, Deerlodge
Park and Mathers Hole gages. The calculation was completed for historic conditions to establish baseline
conditions at each gage.

Table 5.4 Effective discharge results.

Gage EffQ
(cfs)
Lily 2,871
Deerlodge 10,166
Mathers 10,166
Jensen
(Pre-dam) 20,500*
(Post -dam) 11,500*

* From Andrews (1986).

The bias corrected rating curves for Deerlodge Park and Mathers Hole were utilized in the analysis.
Since these rating curves were developed for discharges greater than 2,000 cfs, only flows greater than 2,000
cfs were considered in the effective discharge analysis. To provide consistency in analysis the correction
factors for Deerlodge Park were applied to the Lily gage, on the assumption that both reaches are similar in
characteristics and would have similar correction factors. Therefore, the results for Lily, Deerlodge Park
and Mathers Hole may be readily compared. The results are summarized in Table 5.4. Detailed results are

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