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in parts of the four study basins that are upstream from the irrigated areas (north of the Government Highline Canal in fig. I) could af~ect loads measured at out flow "-1 '. ....:! stations. However, on a long-term 1-.. basis. annual dissolved.solids c,.,,:> loads in the four study basins from areas upstream from irrigated land in the Grand Valley might not be a major component of the loads mea- sured at the outflow sites. Of the four study basins. the Salt Creek Basin has by far the largest drain- age-basin area outside of the irri. gated area. Data collected by the USGS on tributaries of Salt Creek during the 1970's and early 1980's (U .S. Geological Survcy. 1974-83) indicated that the annual dissolved. solids loads disch~lrging into Salt Creek from the drainage basin upstream from the Government Highline Canal are relatively small when compared to the load com. puted for the outnOw site near 1-70 (site SC in Jig. I). Another potential effect on dissolved-solids loads in strcams and washes draining the Grand Valley is conversion of agricultural land to residential and commercial development. Conversion of irri. oated Innd to other uses could b affect dissolved.solids loading in the Grand Valley. However. the effect of land.use changes on dis- solved-solids loads has not hcen documemed for the Grand Valley. Conversion or agricultural land has not been extensive in the Reed Wash and Salt Creek Basins during 1973-96. Some of the area around Fruita in the lower Big Salt Wash Basin has bcen affected by urban. ization. especially in the 1990's. and somc agricultural land in the Leach Crcck Basin was converted to other uses during the study period. Relation of Salinity-Control Projects to Dissolved-Solids Loads The previously discusscd analysis of dissolved-solids data collected by the USGS since 1973 indicated that annual dissolved. solids loads have decreased in four streams that drain irrigated areas in the western Grand Valley. In the Big Salt Wash. Reed Wash. and Salt Creek Basins. implementation of salinity-control projects by the BOR and the USDA was the most significant known change in these basi ns that could cause decreases in dissolved.solids loads. In those three drainagc basins. the projected decrcase in dissolved-solids loads fromtl,c BOR part (canal lining and piping of laterals) of the salin. ity.conlrol project was aboLlt 53,()OO tons per year (US Depart. mellt of the Interior. 1995~ Bureau of Reclamation. wrillen commun., 1997). The total projected decrease in dissolved.solids loads for the three basins would be greater than 53.000 tons per year if the salinity decreases from the USDA oll.farm salinity-control projects wcre included~ however, these decreases have not been determined for spe. cific drainage basins. Additional analysis of other water-quality and streamnow data tends to substantiate the dis- solved-solids-load decreases reported in this fact sheet. For example, review of the annual strearnllow data for the USGS gag. ing station on Reed Wash at site RW2 (fig. I) indicates a decrcase in annual mean streamflow after 1982 (fig. 3). The Stage I salinity.control project lined 6.8 miles of the Gov- ernment Highline Canal and placed 34.2 miles of open laterals in pipe ill the uppcr Reed Wash Basin from 1981 to early 1983 (Burcau of Rec. lamation, 1985). Some of the ground-water rechargL: rrom canal and lateral leakage in LIpper Reed Wash was eliminated. and the Stage I work should have decreased ground.water discharge MEA.N A.NNUAl STR~"MF\.OW, WATE: T"':~' - i .. , MEAN ANNUAL STREA.MFLOW, f " l WATER VEj"S "83-96 : , . t i. i . , : l . 1 , i ~ 0 i i 1 , 1 I. , , , ~ I , 6 , , 6 . , . i , ,. ., , . , '0 o 60 Z o u w " '" a: UJ D. 52 ,.. UJ UJ U. " u iii => u ;; ;0 o -' u. " '" UJ a: ,.. '" z '" w " -' '" => z z c:( 1914 1976 1978 19110 1982 1984 1986 1988 1990 1992 1994 1996 1998 WATER YEAR Figure 3. Annual mean stfedmllow for USGS gagmg slatlon on upper Reed Wash (sIte RW2 In fl9 I J. warer ye,lr r 916-96