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Comparison of Dissolved- Solids Loads for Two Study Periods C\' -.J f-' CO Estimated dissolved-solids loads in Leach Creek. Big Sail Wash. Reed Wash. and Salt Cr~ek were lower in 1991-96 than In th~ earlier period (table 3; fig. 21 Only the dissolved-solids loads com. puted using the periodic method are compared for the earlier period and 1991-96. Decreases in the annual dissolved-solids loads ranged from about 13.3 to 20.6 percent in the four streallls. The largest decreases in annual dis- solved-solids loads were in Re~d Wash (27.600 tons) and Salt Cr~ek (27.000 tons). The changes in loads lor the four streams arc of sufficient Illa". . ~ nitude to indicate that dissolved. solids loading from the Grand Valley has d~creased over the LISt 23 years. The lar!:!csl sinole ~ nuwn . .... c ~rfcet on dissolved.solid, I"ad, in the Grand Valley was th~ imple. mentation of salinity.control projects In the Grand Valley. the BOR salinity-control projects began in late 1980 with the Stage 1 project in the Reed Wash Basin The Slage I project was completed 1C{).OOO 130,000 ~ 120.000 Z 0 ~ 110,000 ~ " 100,000 < ~ ".000 ~ 0 110.000 ~ 0 ~ 70,000 6 w 60,000 > . 0 ~ 50.000 ~ " 40,000 . < ~ ".000 z z < 20,000 10,000 0 BBII LOAD FOR EARLY PERIOD C!S lOAD fOR 1991-96 BIG SALT REED SALT WASH WASH CREEK Figure 2 Annual.dissolved'soli~s loads in .four streams m the Grand Vat/ey for two study peflods. Earfy penods are pnOf to Bureau of Reclamation s,ifmlty-con/rol projects and are' 973-17 for teach Creek and BIg Salt Wash. 1973-80 for Reed WaSh, and /973-83 for Salt Creok. In 1983. Because BaR salinity. control work was occurring in Reed Wash during 1981-83. the dissolved-sol ids load for the carl ier period was determined for 1973- 80 (table 3; lig. 2 \ instead of 1973- 83. In the S,lIt Creek Basin. the BaR did salilllty.control work from 1986to 1991. Decreases in dissolved solids resulting from BOR work in the Reed Wash and Salt Creek Basins would have occurred before the 1991-96 sampling period. In Big Salt Wash Basin. the BOR salinIty-control Table 3. Comparison of annual dissolved-solids loads for the 1973-83 and 1991-96 study periods I Annl];!1 JI"(ll\~tl-!-olid,, In,It!, Illr ~arll~'r pc:nods::rrc pnor It' Burl'all (II R.,:~'IJlll;illtm ,;!llnll~ .":lllll[(l1 rmj~C:b in Ihe h;blfl .:arlu::r periods are 197 \-77 1(lr l":;J..:h ere..:\'" anJ Big Salt Wa...h. IY7J-SO lor R':L'U W;I,h. and 1973-83 for Salt Cr~'<"\"'. h"ltl, tor hl.lh ,Iud~ pem-..h "<"rt' Cllll1rul~d u\ing f'l:=r11I1lIl' Inelhod. loads. in lon~ ~r ~e,lrl . Change in load, Annual load. Annual load 1991-96 to the Stream earlier period for 1991-96 early per;od. in Ions and percent Leach Crl::d 41.-100 J5.000 -6AOOH55<1'1 BIg 5:1lt Wash ~\ '00 72.100 -II.lOOI-L1 J%l Reed \\'a~h IJX.l.)!lO 111..'00 -:n.(l()() (-1l).917c) SaIl Crcl'~ 131.JOIl 104..100 -:7.0001-:06%) Tt"l(,t1 \1)-!.StllJ .r!:?.70{l -7:'..IOt.l (-I~ .,'}) work was started in 1991 and was completed by early 1993. Because of the overlap of the salinity-con- trol work with the 1991-96 sam. piing period in Big Salt Wash. the loads for Il)'! 1-90 might not com. pletely rdlcet elTects of salinity control. In the Leach Creek Basin. the 130R salinity work did not start until 1995. The second part of the Grand Valley salinity.eontrol project is the on-farm work done by the USDA. The USDA implemented the on. farm program in 1979. and work has been done at various farms throughoullhe Grand Valley since 1979. Because of the variable nature of the on.farm program. the effects oftllat salinity-control work arc cumulative since 1979. To doc. ument the full extent of the effects of the salinity-control projects on dissolved.solids loads in the four study baSinS. additional sampling would be needed after all salinity. control projects in the study basins are completed. Other factors. in addition to salinity.control projects. could affect dtssolved-sulids loads. Changes in dissolved.solids loads