WSP00601

• File Number: 8273.300
• Description: Colorado River Basin Salinity Control - Federal Agencies - USGS
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1996
• Author: USGS
• Title: Trend Analysis of Selected Water-Quality Data Associated with Salinity-Control Projects in the Grand Valley - in the Lower gunnison River Basin - and at Meeker Dome Western Colorado
• Water Supply Pro - Doc Type: Report/Study

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of decreasing dissolved-solids concentrations at
upstream station 09095500 on the Colorado River.
Climatic-induced changes in dissolved solids during
N the period of the salinity-control projects could mask
t\) or overwhelm the human-induced changes.
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Trends In Dissolved-Solids Loads

Trends also were examined by using ESTREND
on monthly dissolved-solids loads for the three gaging
stations on the Colorado and Gunnison Rivers in the
Grand Valley area. Monthly loads were computed by
the method described in the "Dissolved-Sol\ds Loads
in the Colorado and Gunnison Rivers" section of this
report. Using monthly dissolved-solids-load data has
an advantage when compared to periodic data because
the loads represent a uniform time series, and selection
of seasons is not a concern. However, the monthly
loads also are computed numbers, and various errors
are associated with the computations as described
previously in this report.

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Trend analysis also was done on annual
dissolved-solids loads using linear-regression analysis
instead of the seasonal Kendall test in ESTREND.
Seasonality is not a concern for annual data as it
is for periodic or monthly data. Normality tests indi-
cated that the annual loads approximated normal
distributions, and the data sets were not severely
skewed. Therefore, the parametric method was used
for the trend tests on annual loads.

In addition to trend tests on monthly and
annual dissolved-solids loads, loads for certain parts
of the year, or seasonal loads, were tested for mono-
tonic trends. 1\vo seasonal periods were tested:
August through October, which is the late irrigation
season in the Grand and Uncompahgre Valleys, and
November through February, which is a low-flow
period of the year. If the salinity-control projects
have decreased discharge of subsurface irrigation
drainage, then a trend in dissolved-solids loads during
November through February might be detectable. One
other time series of loads was tested for trends-the
annual Grand Valley dissolved-solids load (table 1).

STATION 09095500
STATION 09152500
STATION 09163500

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1968 1970 1972 1974 1976 1978 1980 1982 1984 1986 1966 1990 1992 1994
WATER YEAR

Figure 4. LOWESS 6mooth curves of f1ow-adju6ted dissolved-6olids concentrations for stations 09095500
Colorado River near Cameo, 09152500 Gunnison River near Grand Junction, and 09163500 Colorado River
near the Colorado-Utah State line, water years 1970-93.

16 Trend Analyals of Selected Water.Quallty Data Associated With Salinity-Control proJacts In tha Grand Valley,
In the Lower Gunnison River BasIn, and at Meeker Dome, Western Colorado