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<br /> <br /> <br />To some limited e:(tent. flood control provided by reservoirs may also prevent the erosion of soils <br />and disso]Ulion of salts along the river corridor. Sediment is subject 10 mechanical degradalion in a <br />river em'irorunent. releasing salls bound in the matrix of the suspended sedimenl. Reservoirs <br />gready reduce floodmg of the river system and Its attendant erosion of saline soils. Whal little <br />erosion remains is quickly settled out in Ihe downslream reservoirs. <br /> <br /> <br />t' <br /> <br />c. <br />C) <br /> <br />Salimty Conditions <br /> <br />Chemica] preclpitatlon in reservoirs was found 10 have a negligible impact on salinity. This <br />potential loss in salinity was investigated by Reclamation for (he IWO largesl storage reservoirs in <br />the Colorado River Basin. lakes Powell and ~1ead. A Ihennal- hydrodynamics reservoir model. <br />which incorporated chemica] equilibria. was applied to each of the two reservoirs. <br /> <br />The eSlimated potential for calcite precipitation (the sail that precipitates from solution rlrst) was <br />found to be relatively small (abou( 20.(X)() tons per year for lake Powell and ..10.000 tons per year <br />for Lake ~tead). These eSllmates represent the upper limit of potential precipitation. as it assumes <br />Ihat there are sufficient nuclei for the calcium carbonate crystallization and that reaclion rate <br />kinetics do not limit the precipitation. The combined maximum preclpitalion is less than I percent <br />of the annual salt load passing Ihrough the reservoirs (aboul 9 million Ions per year) and is <br />slgnltlcant]y less than previous estimates which were based on inflow-outflow budgets using rather <br />incomplete or inadequate data. <br /> <br /> <br />Water Use by Agriculture and Municipal and Industrial Users <br /> <br />Salinity is directly influenced by the depletion (consumption) of water flowing in the river syslem <br />and by saIl loading. Agriculture increases salinity' by consuming Water Ihrough evapolfanspiration <br />and leaching of salts from saline soils. Municipa] and industrial (M&I) use increases salinity by the <br />consumplion of Ihe water: Ihus. redUCing the dilUlion of salis in the river. These Iwo Iypes of uses <br />are cmicalln predicting future salinity levels in the basin. <br /> <br />Reclamation cominues to monilor waler use and adjust its future salinity comrol needs as waler <br />development plans have been po:)tponed. delayed. or canceled. The depletion schedules used to <br />project salimi)' conditions have been updated so <br />that the implememation needs for the SalinilY <br />Control Program can be planned to offselthe <br />impacts of water developmem. Transbasin <br />diversions and increased reservoir evaporation <br />account for mo:)t of the increased water use; <br />however. no additional salt pid.-up or loading <br />occurred "-'ith these types of depletions. <br /> <br />The large quanmies of water e.'\pected to be <br />depleted for :)teampower generation. coal <br />gasification. oil shale. and mineral developmem <br />have not been realized in the past decade due to <br />the relatively low COSI of energ)'. The few <br /> <br />- <br /> <br />Upper Basin Uses <br /> <br />" <br /> <br />1987Pro;ection...........l <br />...... ..... <br /> <br />.--<::// ....~"~ <br />PI'Cl1edions <br />Hi$tonc Trend <br /> <br />i u. <br />~ <br />~ <br />.s <br />~ 45] <br />B <br />.. <br />~ <br />.! <br /> <br />". <br /> <br />4~' <br /> <br />". <br /> <br />,~ <br /> <br />'g10 <br /> <br />',", <br /> <br />'>>0 <br /> <br />"'" <br /> <br />"" <br /> <br />"" <br /> <br />Figure 13 --Companson 01 past and current <br />deplellon prOjections. <br /> <br />67 <br />