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<br /> <br />N <br />t.,; <br />W <br />~ <br /> <br />The Grand Valley dissolved-solids load is a salinity- <br />related variable that wOl,lid be most affected by salinity- <br />control projects in the Orand 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 Dlssolved-$o.nds 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 09163500 (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 1970--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 imflow-adjusted loads for <br />1970--93 at all three stalions occurred in the 1970's <br />before implementation of salinity-control projects in <br /> <br /> 0.10 <br />z- O.oa <br />0 <br />~ <br />a: 0.06 <br />I- <br />Z <br />w <br />o~ 0.04 <br />z_ <br />Oz <br />0::> <br />gs::; 0.02 <br />:ji!: <br />0- <br />Cl)a: 0 <br />,< <br />DC> <br />wo <br />>..J -0.02 <br />..J..J <br />~~ <br />-::> -0.04 <br />D!;( <br />DZ <br />wz -0.06 <br />!;;- <br />::> <br />i3 -0.08 <br />1= <br />~ -0.10 <br />"- <br /> -0.12 <br /> 1978 <br /> <br />/- <br />/ <br />/ <br />//" <br />// <br />" <br />// <br />/ <br />// <br /> <br />/ <br />./ <br /> <br />....... <br />.' <br />.' <br /> <br />................. <br /> <br />.' <br />................. <br /> <br />........... <br /> <br />1980 <br /> <br />1982 <br /> <br />1984 <br /> <br />western Colorado. In 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 />09163500 after 1986. The trend results (table 3) are <br />consistent 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 1980--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 1985 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 /> <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 />1986 <br />WATER YEAR <br /> <br />1988 <br /> <br />1994 <br /> <br />1990 <br /> <br />1992 <br /> <br />FIgure 5. LOWESS smooth curves of 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 FOR THE COLORADO AND GUNNISON RIVERS 17 <br />