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Water-Quality Assessment of Elkhead Reservoir near Craig, Colorado

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Water-Quality Assessment of Elkhead Reservoir near Craig, Colorado

Study Area: Elkhead Reservoir, Routt County, Colorado
Period of Project: February 2002 - September 2002
Project Number: CO425
Project Chief: Gerhard Kuhn
Cooperator: Colorado River Water Conservation District

BACKGROUND:

In 1995, in anticipation of possible enlargement of Elkhead Reservoir, the U.S. Geological Survey (USGS), in cooperation with the Colorado River Water Conservation District (CRWCD), began a monitoring program on Elkhead Reservoir, and at inflow and outflow sites on Elkhead Creek. A site upstream of the proposed reservoir (Elkhead Creek above Long Gulch near Hayden, 09246200) and a downstream site (Elkhead Creek below Maynard Gulch near Craig, 09246400) were chosen to evaluate the effects of Elkhead Reservoir on Elkhead Creek.

Data collected at the stream sites included:

  • continuous measurement of streamflow,
  • water temperature and
  • specific conductance, and
  • periodic water-quality samples analyzed for major ions, nutrients, trace elements, and suspended sediment.

Three reservoir sampling locations were established and sampled approximately 3 times/year at the surface and just above the bottom at mid-lake and near the dam, and at a mid-water-column depth near the inflow to the reservoir. Depth profiles of water temperature, specific conductance, pH, and dissolved oxygen were collected at three points along a transect at each of the three sampling locations. Chemical constituents and nutrients were to be sampled at the surface and near the bottom of the reservoir and at the center of each transect at the three reservoir sites.

Enlargement of Elkhead Reservoir, and the potential effects on reservoir water quality, downstream water quality, and downstream effects on streamflow are of concern to many interest groups. When reservoir storage is changed, downstream flow can be affected, water quality can change, and different hydrologic conditions can be created in the reservoir. The nature and magnitude of potential changes is unknown, and indicates a need to characterize the current water-quality conditions in Elkhead reservoir and in Elkhead Creek. Compilation, analysis, and interpretation of these data are needed to increase understanding of the reservoir’s effects on water quality and streamflow in Elkhead Creek.

OBJECTIVES:

1. To collect continuous streamflow, specific conductance and water temperature data and monthly water-quality samples (major ions, nutrients and dissolved metals) at the Elkhead Creek above Long Gulch near Hayden, CO and the Elkhead Creek below maynard Gulch near Hayden, CO. And, to collect water-quality samples for low level nutrients, cholorphyll-a, and secchi-disk depth and water-quality profile data threes times per year at three sites in the Elkhead Reservoir.

2. To use summary statistics, flow-duration curves, boxplots, time series plots to describe streamflow and water-quality in Elkhead Creek and assess changes in streamflow and water quality that might be attributed to impoundment of Elkhead Reservoir.

3. To use field parameter profiles, reservoir level and bathymetric information, and periodic water-quality samples to describe stratification patterns, reservoir function, dissolved-oxygen dynamics, seasonal and spatial chemical gradients, time-series trend analysis, nutrient limitation, and trophic status indicators.

4. To compare chemical concentrations, dissolved oxygen, and pH data with Colorado water-quality standards.

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