Hydrology and Water-Quality Characteristics
of Muddy Creek and Wolford Mountain
Reservoir near Kremmling, Colorado,
1990 through 2001
By Michael R. Stevens, and Lori A. Sprague
Available from the U.S. Geological Survey, Branch of Information Services,
Box 25286, Denver Federal Center, Denver, CO 80225, USGS Water-Resources
Investigations Report 03-4073, 82 p., 35 figs.
This document also is available in pdf format:
WRIR 03-4073.pdf (1.3 MB)
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Abstract
A water-quality monitoring program was begun in March 1985 on Muddy Creek
in anticipation of the construction of a reservoir water-storage project.
Wolford Mountain Reservoir was constructed by the Colorado River Water
Conservation District during 199294. The reservoir began to be filled
in 1995.
Water quality generally was good in Muddy Creek and Wolford Mountain
Reservoir throughout the period of record (collectively, 1990 through
2001), with low concentrations of nutrients (median total nitrogen less
than 0.6 and median total phosphorus less than 0.05 milligrams per liter)
and trace elements (median dissolved copper less than 2, median dissolved
lead less than 1, and median dissolved zinc less than 20 micrograms per
liter). Specific conductance ranged from 99 to 1,720 microsiemens per
centimeter. Cation compositions at Muddy Creek sites were mixed calcium-magnesium-sodium.
Anion compositions were primarily bicarbonate and sulfate. Suspended-sediment
concentrations ranged from less than 50 milligrams per liter during low-flow
periods to hundreds of milligrams per liter during snowmelt. Turbidity
in prereservoir Muddy Creek generally was measured at less than 10 nephelometric
turbidity units during low-flow periods and ranged to more than 360 nephelometric
turbidity units during snowmelt. Compared to prereservoir conditions,
turbidity in Muddy Creek downstream from the reservoir was substantially
reduced because the reservoir acted as a sediment trap.
During most years, peak flows were slightly reduced by the reservoir
or similar to peaks upstream from the reservoir. The upper first to fifteenth
percentiles of flows were decreased by operation of the reservoir compared
to prereservoir flows. Generally, the fifteenth to one-hundredth percentiles
of flow were increased by operation of the reservoir outflow compared
to prereservoir flows.
Nutrient transport in the inflow is proportional to the amount of inflow-water
discharge in a given year. Some nitrogen was stored in the water column
and gain/loss patterns for total nitrogen were somewhat related to reservoir
storage. Nitrogen tended to move through the reservoir, whereas phosphorus
was mostly trapped within the reservoir in bottom sediments. The reservoir
gained phosphorus every year (1996 2001) and, as a percentage, more phosphorus
was retained than nitrogen in years when both were retained in the reservoir
due to stronger phosphorus tendencies for adsorption, coprecipitation,
and settling. Only small amounts of phosphorus were available in the water
column at the outflow, and reservoir water-column storage did not influence
phosphorus outflowloading patterns as much as settling further upstream
in the reservoir.
From 1990 to 2001, upstream from the reservoir, concentrations and values
of dissolved solids, turbidity, some major ions, and dissolved iron increased
(p-value less than 0.10), and acid-neutralizing capacity decreased. From
1990 to 2001, there were no significant (p-value less than 0.10) trends
in nutrient concentrations upstream from the reservoir. From 1990 to 2001,
downstream from the reservoir, trends in concentrations and values of
dissolved solids, turbidity, major ions, total ammonia plus organic nitrogen,
dissolved and total-recoverable iron, and total-recoverable manganese
were downward.
Upstream and downstream water-quality constituents for the prereservoir
(1990 to 1995) period were compared. Concentrations and values of dissolved
solids, major ions, turbidity, and manganese were greater (p-value less
than 0.10) at the downstream site.
From 1995 to 2001 (postconstruction), upstream and downstream water-quality
constituents also were compared. Concentrations of specific conductance
and major ions increased at the downstream site when compared to the upstream
site (p-value less than 0.10), except for acid-neutralizing capacity and
silica, which decreased. Turbidity, concentrations of total-recoverable
and dissolved manganese, and total-recoverable iron also were smaller
downstream from the reservoir.
Results indicate that concentrations of dissolved solids increased downstream
in Muddy Creek before the reservoir was constructed. This trend continued
after construction, but the difference between upstream and downstream
median concentrations of dissolved solids and major ion concentrations
was less than in the prereservoir period.
Spring runoff temperatures and fall temperatures in Muddy Creek were
lower than in the reservoir. Thus, inflows to the reservoir tended to
settle near the thermocline. In summer, inflow-water temperature was similar
to the surface layer, and flows were routed through the reservoir near
the surface.
In winter, Muddy Creek stream temperatures were near 0°C, and surface
water at the ice cover interface was 0°C, but the temperature in the reservoir
subsurface probably increased with depth to 4°C in the bottom waters (water
is most dense at about 4°C). Although no winter stratification measurements
were made under the ice, the reservoir was assumed to be similar to other
dimictic, montane reservoirs. Thus, inflow will tend to be routed just
under the ice. Flow patterns within the reservoir could be important because
residence time varies from season to season, and in the event of a chemical
spill upstream, knowledge of timing and probable vertical location of
the plume would be important for outflow gate configurations to manage
the spill.
Near-bottom samples of ammonia and nitrite plus nitrate generally had
larger concentrations than concurrent surface samples. Surface-sample
concentrations of nitrite plus nitrate were substantially depleted throughout
the growing season. Temporally, surface and bottom concentrations tended
to decrease and stabilize for ammonia plus organic nitrogen and ammonia
throughout the period of record. Nitrite plus nitrate seemed to increase
in bottom samples with time. Spatial variation in nutrient concentrations
from inflow to dam tended to decrease for total ammonia plus organic nitrogen
and total phosphorus in surface samples, whereas bottom-sample concentrations
of nitrite plus nitrate tended to increase from inflow to dam.
Spatially, total recoverable and dissolved iron and manganese and total
recoverable aluminum show decreasing median concentrations from inflow
to dam in surface samples. Bottomsample median concentrations of total
recoverable iron and aluminum decreased from inflow to dam. The spatial
increases in manganese along the reservoir axis probably are related to
redox reactions in the hypolimnion, which release manganese during periods
of hypoxia.
Bacteria counts were low to not detected in the reservoir samples. Bacteria
in Muddy Creek may be associated with suspended material that rapidly
settles out in the reservoir.
Trophic conditions generally were upper oligotrophic to mesotrophic from
1995 to 2001 in Wolford Mountain Reservoir based on available Secchi depth,
total phosphorus concentrations, and chlorophyll-a concentrations. Dissolved-oxygen
concentrations generally were in the range of 3 to 7 milligrams per liter
except in late summer when oxygen concentrations approached 1 milligram
per liter or less in the hypolimnion.
Constituent concentrations generally were acceptable and met Colorado
water-quality standards. Selenium concentrations exceeded chronic aquatic
standards twice in Muddy Creek at the Kremmling site (prereservoir, 198295).
Six selenium concentrations in near-bottom samples collected from the
reservoir near the dam during 199597 exceeded chronic aquatic standards.
Aquatic standards for iron and manganese were occasionally exceeded in
Muddy Creek and in near-bottom samples from Wolford Mountain Reservoir.
Contents
Abstract
Introduction
Purpose and Scope
Previous Studies
Description and Background Information of Study Area
Acknowledgments
Methods of Investigation
Field Methods
Data-Analysis Methods
Data-Set Construction
Hydrology
Water Quality
Streamwater Quality
Field Properties
Major Ions
Nutrients
Trace Elements
Biological Indicators
Suspended Sediment
Reservoir Water Quality
Field Properties
Major Ions
Nutrients
Trace Elements
Biological Indicators
Trophic Status
Water-Quality Standards
Summary and Conclusions
References Cited
Hydrologic and Water-Quality Data
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