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<br /> <br />I~ <br />Ii <br /> <br />~4lJ? <br /> <br />The Grand Valley dissolved-so]ids load is a salinity- <br />related variable that would be most affected by salinity- <br />control projects in the Grand Valley. The seasonal <br />loads and the Grand Valley dissolved-solids load were <br />tested for trends using the linear-regression method. <br /> <br />Monthly Dissolved-Solids Loads <br /> <br />All trends in unadjusted dissolved-solids loads <br />and flow-adjusted loads for the three time periods <br />tested for stations 09095500 (Colorado River near <br />Cameo; inflow station) and 09]63500 (Colorado <br />River near the State line; outflow station) were highly <br />significant and indicated decreasing loads with time <br />(table 3). For station 09152500 (Gunnison River <br />near Grand Junction; inflow station), the trends were <br />highly significant and loads were decreasing for water <br />years ] 970-93, but the trends were not significant or <br />were marginally significant for the two shorter periods. <br />The LOWESS curves (fig. 6) indicate that some of <br />the downward trends in flow-adjusted loads for <br />1970-93 at all three stations occurred in the 1970's <br />before implementation of salinity-control projects in <br /> <br />I <br />r <br />~ <br />l <br />I <br /> <br />r <br />I <br />I <br />I <br />! <br /> <br /> 0.10 <br /> ::i. 0.08 <br /> 0 <br />- ~ <br /> '" 0.06 <br /> ,.... <br /> Z <br /> w <br /> U'" 0.04 <br /> z"" <br /> Oz <br /> UOJ <br /> "'::; 0.02 <br /> OJ: <br /> ::JI-- <br /> 0- <br /> ",'" p <br /> ,"", <br /> oC> <br /> wO <br /> >-' .0.02 <br /> -'-, <br />...Jl~ <br /> _OJ .0.04 <br /> O~ <br /> Oz <br /> ~z -0.06 <br /> "'- <br /> OJ <br /> i3 -0.08 <br /> "'" <br /> ;:: <br />.- 0 -0.10 <br />-' <br /> lL. <br /> <br />/- <br />/ <br />/ <br />/ <br />/ <br />/ <br />/ <br />/ .' <br />/ .' <br /> <br />// //....../.. <br /> <br /> <br />..... <br /> <br /> <br />...... <br /> <br />-0.12 <br />1978 <br /> <br />1980 <br /> <br />1982 <br /> <br />1984 <br /> <br />western Colorado. ]n addition, the LOWESS curves in <br />figures 6 and 7 also seem to indicate decreasing flow- <br />adjusted monthly loads for stations 09095500 and <br />09]63500 after 1986. The trend results (table 3) are <br />consis~ent with the graphical information in figures 6 <br />and 7 because the trends for both stations for 1980-93 <br />and 1986-93 were highly significant with decreasing <br />flow-adjusted monthly dissolved-solids loads. By con- <br />trast, flow-adjusted monthly loads for] 980-93 and <br />1986-93 for station 09152500 on the Gunnison River <br />were increasing slightly, but the trend slopes were sta- <br />tistically not significant (table 3). <br /> <br />The highly variable streamflow during water <br />years 1980-93 might have masked some of the <br />trends in monthly dissolved-solids loads, as was <br />suspected with periodic dissolved-solids concentra- <br />tions for the same period. Information in table 3 and <br />figure 7 indicates highly significant, downward trends <br />in flow-adjusted monthly loads after] 985 or 1986 for <br />stations 09095500 and 09163500, which is the same <br />result as for the flow-adjusted concentrations (fig. 6; <br />table 2) for the two stations for 1986-93. <br /> <br />STATION 09095500 <br />STATION 09152500 <br />STATION 09163500 <br /> <br />...... <br /> <br />'. , <br />, <br />, <br />, <br />.....', <br />.....;\. <br />........":...... <br />..... ....................... <br />..... <br />..... <br />.......... <br />......... <br />..... <br />.....-- <br /> <br /> <br />1986 <br /> <br />1988 <br /> <br />1990 <br /> <br />1992 <br /> <br />1994 <br /> <br />WATER YEAR <br /> <br />Figure 5. LOWESS smooth curves ot flow-adjusted dissolved-solids concentrations for stations 09095500 <br />Colorado River near Cameo, 09152500 Gunnison River near Grand Junction, and 09163500 Colorado River <br />near the Colorado-Utah State line, water years 1980-93. <br /> <br />TREND ANALYSIS FDR THE COLDRADO AND GUNNISON RIVERS 17 <br />