9633

• UCREFRP Catalog Number: 9633
• Author: Schmidt, J. C. and J. B. Box
• Title: Application of a Dynamic Model to Assess Controls on Age-0 Colorado Pikeminnow Distribution in the Middle Green River, Colorado and Utah
• USFW Year: 2004
• USFW - Doc Type: Annals of the Association of American Geographers
• Copyright Material: NO

Colorado Pikeminnow Distribution

459

the southern Uinta Basin, 30 km downstream from the
confluence of the White and Green Rivers in north-
eastern Utah (Figure 1). We use the informal names
"upper" and "middle" Green River to refer to the Green
River upstream from our study area and within our study
area, respectively.
At their confluence, the upper Green and Yampa
Rivers have similar mean annual flows. Prior to dam
construction, the magnitude of the Yampa River's two-
year recurrence flood was about 18 percent larger than
that of the Green River (Table 1), and total runoff for the
flood and base flow seasons was approximately equal.
The post-dam hydrology of the middle Green River is
due to both the operations of Flaming Gorge Dam and
the unregulated hydrology of the Yampa River (Grams
and Schmidt 2002), where there are few dams or di-
versions. Thus, the influence of Flaming Gorge Dam on

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A

UINTA MOUNTAINS

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the middle Green River is not as obvious as in those
segments where tributary inflow is minor, such as the
Colorado River downstream from Glen Canyon Dam
(Topping, Schmidt, and Vierra 2003). Post-dam floods
on the middle Green River come from the Yampa River
because Flaming Gorge Dam has caused a 57 percent
decrease in the magnitude of the two-year recurrence
flood of the upper Green River. Between 1990 and 1995,
62 percent of the total stream flow of the middle Green
River during the snowmelt flood season between April 1
and July 31 came from the Yampa River; 2 percent came
from ungaged tributaries, and 36 percent was released
from Flaming Gorge Dam. In contrast, base flows came
primarily from Flaming Gorge Dam; 76 percent of the
base flow between August 1 and March 31, 1990-1995,
was released from Flaming Gorge Dam and 24 percent
came from the Yampa River.

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Figure 1. Map showing the study area, including reaches discussed in text. Circled numbers are U. S. Geological Survey gaging stations
referred to in the text: (1) Green River near Greendale, Utah (09234500), (2) Yampa River near Maybell, Colorado (09251000), (3) Little
Snake River near Lily, Colorado (09260000), (4) Yampa River at Deerlodge Park, Colorado (09260050), (5) Green River at Jensen, Utah
(09261000), (6) Duchesne River near Randlett, Utah (0930200), (7) White River near Watson, Utah (09306500), and (8) Green River near
Ouray, Utah (09307000).