7425

• UCREFRP Catalog Number: 7425
• Author: Vandas, S. e. a.
• Title: Dolores River Instream Flow Assessment
• USFW Year: 1990.
• USFW - Doc Type: Project Report.
• Copyright Material: NO

initiated during this time. The runoff produced from
precipitation in the study area shows at the Bedrock
station, while the dam release remains constant. If
these runoff events are overlooked, it can be seen that
for June, July, and August, the Bedrock flows tend to
stabilize near 60 ft3/s. This equates to an 18 ft3/s
loss in flow between McPhee Dam and Bedrock. For
the most part, the summer of 1989 was drier and
warmer than average which would tend to maximize
the low-flow losses. It should also be noted that
during cooler months, when evapotranspiration rates
and irrigation withdrawals are lower, low-flow losses
would not be as great.
During the summer of 1989, BLM made several
discharge measurements on the Dolores River to
determine how and where the 18 ft3/s loss was
occurring. The average discharges measured at
selected points within the study area are shown in
Figure 14. The difference in discharge between sites
(i.e., water loss) correlates well with channel dis-
tance, especially if the "in use" water rights (see
Table 8) between sites are taken into consideration.
This indicates that most of the water loss is occurring
from evapotranspiration along the water course and

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from man-related water diversions. Water loss or
gain to or from ground water systems appears to be
insignificant. Also, water gains from tributary
inflows were minimal (e.g., Disappointment Creek, at
its confluence with the Dolores River, was ~ most
of June and July and flowing less than 0.10 ft Is in
August).
Table 9 shows how the 18 ft3/s loss would affect
the three bypass release flows (i.e., 78, 50, and 20 ft31
s) at selected points in the study area. A worst case
scenario is also presented which includes diversions
for all valid existing water rights with appropriation
dates prior to 1975 (see Table 9). Presently "in-use"
water rights are assumed to be part of the 18 ft3/s
loss, while inactive water rights are factored in,
continuously using their full ap~ropriation. As
previously mentioned, the 18 ft Is loss was deter-
mined during a summer release of 78 ft3/s. It is
possible that at the lower releases of 50 and 20 ft3/s
losses would be greater due to higher water tempera-
tures.
Based on river resource values analyzed in this
report, changes in water quality resulting from
operation of McPhee Reservoir are negligible.

2

-+- Bedrock

----- McPhee

:==:: Precipitation

1.5

Data Source: (USGS,
USBR, BLM), 1989

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July, 1989
Figure 11, Dolores River low flow - McPhee vs. Bedrock, June 1989.

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