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N t-...l f.... CDpurpose and Scope This report presents trend results for several water-quality variables for the Colorado, Gunnison, and White Rivers and relates these trends to salinity- control projects in the Grand Valley, in lower Gunnison River Basin, and at Meeker Dome in the White River Basin. The specific objectives are to: I. Estimate dissolved-solids loads for inflow and outflow stations for the Grand Valley Unit, which includes the outflow site for the Lower Gunnison Basin Unit. 2. Detennine trends in dissolved-solids concentra- tions and loads apd selected major-ion concen- trations for inflow and outflow stations for the Grand Valley Unit. 3. Determine if significant water-quality trends in the Colorado River are related to salinity-control projects. 4. Detennine trends in chloride and sodium concen- trations in the White River upstream and downstream from Meeker Dome. 5. Verify that the Meeker Dome Unit salinity-control project has remained effective since 1984. Monthly and annu.al dissolved-solids loads were computed for water years 1970-93 for the four USGS gaging stations s~own in figure I. The annual dissolved-solids load frOm the Grand Valley area also was computed. In the r~mainder of the report, data analysis is presented by water year unless otherwise noted. Dissolved-solids.loads at stations 09095500, 09105000, and 09152500 are the inflow loads into the Grand Valley Unit, ahd the dissolved-solids load at station 09163500 is the outflow load from the Grand Valley Unit. The station on the Gunnison River (09152500) also r~presents outflow from the Gunnison River Basin and is downstream from the Lower Gunnison Basin Unit. Monotonic trend analy- ses were done on periodic dissolved-solids, calcium, magnesium, sodium, and sulfate concentrations and on monthly, annual, and'seasonal dissolved-solids loads for the two stations on the Colorado River (stations 09095500 and (l9I63500) and the station on the Gunnison River (station 09152500) (fig. l). Trend analysis was done for three time periods: 1970-93, 1980-93. and 1986-93. The trend results were used with a graphical technique to detennine if the trends in concentrations or loads could be related to the salinity- control projects. Chloride and sodium data collected at three USGS gaging stations on the White River (fig. 2) from 1973 to early 1995 were analyzed to verify the effec- tiveness of the salinity-control project at Meeker Dome. Chloride and sodium concentrations were examined for the White River because those constitu- ents were most affected by the salinity-control work at Meeker Dome. DESCRIPTION OF SALINITY-CONTROL PROJECTS Grand Valley Unit The Grand Valley Unit is the irrigated area in the Grand Valley shown in figure 1. There are about 70,000 acres of irrigated land in the Grand Valley that contributed an estimated 580,000 tons/yr of salt to tlte Colorado River through deep percolation of water from canals, laterals, and on-farm irrigation (Bureau of Reclamation, 1983, 1985a). The salt load from the Grand Valley was about 7 percent of the salt load in the Colorado River at Imperial Dam, near Yuma, Arizona (U.S. Department of the Interior, 1993). In the Grand Valley, the salinity-control program consisted of two parts. In the first part, the BOR lined canals and placed laterals in pipes to decrease leakage from the water- distribution system. In the second part, the National Resources Conservation Service (fonnerly the Soil Conservation Service) initiated the USDA on-farm improvements, which involved upgrading fann irriga- tion systems and improving irrigation management. The USDA on-farm improvements included activities such as replacing ditches with underground pipelines or lining the ditches with concrete, land leveling, and installation of more efficient irrigation systems such as drip irrigation or surge irrigation systems. The BOR salinity-control program has been done in stages. Stage I involved lining 7 mi of canal and placing 34 mi of laterals in underground pipe during 1980-82 in the west end of the Grand Valley. Post construction monitoring indicated that Stage I had decreased annual dissolved-solids loading to the Colorado River by 19,900(ons (Bureau of RecIamation, 1985a, 1986). Construction on DESCRIPTION OF SALINITY-CONTROL PROJECTS 5