7739

• UCREFRP Catalog Number: 7739
• Author: Muth, R. T. and T. P. Nesler.
• Title: Associations Among Flow and Temperature Regimes and Spawning Periods and Abundance of Young of Selected Fishes, Lower Yampa River, Colorado, 1980-1984 - Final Report.
• USFW Year: 1993.
• USFW - Doc Type: \
• Copyright Material: NO

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9

P :s: 0.05. Degree of association for correlations with non-significant coefficients was subjectively considered
strong if r values were within 0.001-0.1 from the lower limit of significance, moderate if r values were within
0.101 from the lower limit of significance to 0.500, and weak if r values were :s: 0.499.

RESULTS AND DISCUSSION

Flow an4 Temperature Regimes

Annual flow regimes of the lower Yampa River for April-July varied considerably among the five
years studied, encompassing a fuU range of flow conditions including extremes and averages (Figure 3;
Table 3). In increasing order, total discharge (m3) over these four months near MaybeU and at Deerlodge
Park, respectively, was about 5.7 and 8.1 x 1()8 in 1981, 1.4 and 2.0 x 1()9 in 1980, 1.5 and 2.1 x 1()9 in 1982,
1.6 and 2.5 x 1()9 in 1983, and 2.4 and 3.3 x 1()9 in 1984. Similarly, annual peak discharge (which, except
near MaybeU in 1981, occurred in May each year) was low in 1981, high in 1983 and especiaUy 1984, and
more moderate in 1980 and 1982. Even though annual peak discharge was higher in 1983 than in 1980 and
1982, values of daily mean and total discharge for April and May were greater in 1980 and 1982 than in
1983; in 1981 and 1984, these values were consistent with the respective lowest and highest annual peak
discharges. In 1983, unlike in the other four years, values of daily mean and total discharge for June were
substantiaUy greater than those for May; values of these discharge parameters for July were greater in 1983
than in the other four years (even greater than those in 1984). Rate of decrease in flows following annual
peak discharge to near baseline was fastest in 1981 and slowest in 1982 (Figure 3).
In historical perspective, extremely low-flow years like 1981 and extremely high-flow years like 1983
or 1984 occurred very infrequently. Values of annual peak discharge during 19~1984 were some of the
smallest and greatest recorded at the Maybell gage in 1934-1991. Peak discharge in 1984 was the highest
recorded during the 58-year period. In 1981, peak discharge had a percentile rank of 13 (i.e., only 13% of
annual peak-discharge values during 1934-1991 were lower than the value for 1981). Values of peak
discharge in 1980, 1982, and 1983 had respective percentile ranks of 79,57, and 89.
The water-temperature regime of the lower Yampa River during spring and summer in 1981-1984
differed among years (Table 4; Figure 4), and annual trends in monthly water-temperature parameters
were somewhat predictable given values of corresponding discharge parameters and the shape of yearly
hydrographs. Rate of warming per month (as represented by numbers of degree-days) was fastest in 1981
and slowest in 1983. In 1981, monthly means of maximum daily water temperatures for April-July were
about 3-6OC greater than the same values in 1982 and 1983 (compared to 1984 for May-July, monthly
means were 2-5OC greater in 1981). Comparing 1981 to each subsequent year of progressively increasing.
discharge, cumulative numbers of degree-days over the fIVe temperature thresholds for the April-July
period were 28-56% lower in 1982,49-65% lower in 1983, and 28-53% lower in 1984.