WSP12246

• File Number: 8210.310
• Description: Colorado River Basin Organizations and Entities - Colorado River Water Conservation District
• State: CO
• Basin: Western Slope
• Date: 1/1/1996
• Author: David L Butler
• Title: Trend Analysis of Selected Water-Quality Data Associate 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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1978

STATION 09095500
STATION 09152500
STATION 09163500

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1984

1990

1992

1980

1982

1986

1994

1988

WATER YEAR

Figure 7. LOWESS smooth curves of flow-adjusted monthly dissolved-solids loads at stations 09095500
Colorado River near Cameo, 09152500 Gunnison River near Grand Junction, and 09163500 Colorado River
near the Colorado-Utah State line, water years 1980-93.

Trend results on the seasonal loads for August
through October and November through February were
variable (table 5). None of the trends in unadjusted
seasonal loads for August through October were signif-
icant (alpha 0.05). Trends in flow-adjusted loads for
August through October were highly significant
(decreasing loads with time) for station 09095500
for water years 1986-93 and for station 09152500
for 1970-93 (table 5). Although the flow-adjusted
loads for August through October for the three test
periods indicated decreasing loads with time for
station 09163500, the p values of the trends were
not significant.
Trends in unadjusted dissolved-solids loads for
November through February (table 5) were variable,
and the most notable result is the highly significant
downward trend in loads at station 09095500 for water
years] 986-93. The trend in flow-adjusted load also
was highly significant and downward for 1986-93 for
station 09095500. The salinily-control projects in the
Grand Valley primarily are designed to decrease the
quantity of subsurface irrigation drainage, which is the

mechanism of transport of irrigation-induced salinity
to the Colorado River (Bureau of Reclamation, 1986).
During the low-flow period of the year, a decrease
in irrigation-drainage load from the Grand Valley
might cause a trend in dissolved-solids loads at
station 09 I 63500 during November through February.
Although the trend for the November through February
loads was downward for 1986-93 at station 09163500,
the trend was statistically not significant (table 5). As
discussed with annual loads, the small sample size
(eight values) for the seasonal data for ]986-93 make
>,
it more difficult to reject the null hypothesis of no
trend.

Grand Valley Dissolved-Solids Load

The Grand Valley dissolved-solids load is
the annual dissolved-solids load to the Colorado
River from the Grand Valley (fig. ]), and at least
95 percent of that load was irrigation induced (Bureau
of Reclamation, ] 986). The trends in annual Grand
Valley dissolved-solids load (table I) were downward

20 Trend Analysis 01 Selected Water-Quality Data Associated With Salinity-Control Prolectsln the Grend Valley,
In the lower Gunnison River Basin, and at Meeker Dome, Western Colofado