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<br />,'.\ ~'~. r <br />j~~~i. <br /> <br />Trend Analysis of Selected Water-Quality Data <br />Associated With Salinity-Control Projects in the <br />Grand Valley, in the Lower Gunnison River Basin, <br />and at Meeker Dome, Western Colorado <br /> <br />ByDavid L. Butler <br /> <br />Abstract <br /> <br />To decrease salt loading to the Colorado <br />River from irrigatcd agriculture, salinity-control <br />projects have been under construction since <br />1979 by the Bureau of Reclamation and the <br />U.S. Department of Agriculture in the Grand <br />Valley and since 1988 in the lower Gunnison River <br />Basin of western Colorado. In 1980, a salinity- <br />control project was initiatcd at Meeker Dome, <br />which involved plugging three abandoned oil <br />wells that were discharging saline water to the <br />White River. Trend analysis was used to deter- <br />mine if the salinity-control projects had affected <br />salinity in the Colorado and White Rivers. <br /> <br />The mean annual dissolved-solids load <br />in the Colorado River near the Colorado-Utah <br />State line for water years 1970-93 was about <br />3.32 mil1ion tons. About 46 percent of that load <br />was from the Colorado River upstream from the <br />Grand Valley and about 38 percent was from <br />the Gunnison River. About 16 percent of the <br />dissolved-solids load in the Colorado River near <br />the State line was discharged from the Grand <br />Valley, and most of the Grand Valley dissolved- <br />solids load was from irrigation-induccd sources. <br /> <br />Monotonic trend analysis of dissolved- <br />solids and major-ion data for the Colorado <br />and Gunnison Rivers was used for determining <br />if salinity-control projects had affected salinity <br />(dissolved solids) in the Colorado River. Data col- <br />lected in water years 1970-93 at gaging stations on <br /> <br />\. <br /> <br />the Colorado River--one near Cameo and the <br />other near the Colorado-Utah State line, and at <br />the station on the Gunnison River near Grand <br />Junction-were analyzed for trends. A computer- <br />ized procedure developed by the U.S. Geological <br />Survey that uses the non parametric seasonal <br />Kendall test with adjustment for streamflow was <br />used for trend analysis of periodic and monthly <br />data. and linear regression was used for trend anal- <br />ysis of annual data. Three time periods were <br />tested. including periods that were concurrent with <br />work on salinity-control projects. Many of the <br />trends in unadjusted concentration and load data <br />were not statistically significant. There were <br />downward trends in flow-adjusted dissolved- <br />solids and major-ion concentrations and in <br />monthly dissolved-solids loads for all thrce sta- <br />tions in the 1970's, prior to the salinity-control <br />projects. The two stations on the Colorado Rivcr <br />also had significant downward trends in flow- <br />adjusted concentrations and loads for water <br />years 1986-93. The cumulative effects of salinity- <br />control projects in the Grand Valley and in thc <br />lower Gunnison River Basin on salinity in the <br />Colorado River would have become more substan- <br />tial after the mid-1980's. Part of the decrease in <br />dissolved solids in the Colorado River near the <br />State line probably was related to salinity-control <br />projects; however, there apparently arc other fac- <br />tors that are affecting dissolved solids in the upper <br />Colorado River in addition to salinity-control <br />projects. <br /> <br />Abstract <br />