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<br />
<br />Cover Photo.....;Upstream view of Imperial Dam, desilting works, Imperial Oasis Camp, Senator Wash Dam and Reservoir, and the
<br />lower portion 9f Imperial Reservoir. Note that one of the desilting basins has been dried up for mai~tenance activity.
<br />
<br />THE PROBLEM
<br />
<br />The Colorado River Basin encompass~ portions of
<br />seven states. The river flows over 1,400 Qliles from its
<br />headwaters in Colorado to its terminus in the Gulf of
<br />California in the Republic of Mexico, On. its journey, it
<br />joins with tributaries from Wyoming, Ut.h, arid New
<br />Mexico; flows through the Grand Canyon; and'provides
<br />state boundaries for Nevada, Arizona, arid California,
<br />The river's water, now and in future ytars, has been
<br />fully allocated through a long history of .ppropriations .
<br />and negotiations that include acts, compacts, decrees, and
<br />an international treaty, known collectively ~s "The L_aw of
<br />the River." .
<br />About half of th.e present salinity cOI1ceptration in the
<br />Colorado River at Hoover Dam near Las Vegas, Nevada,
<br />is attributed to natural sources. The remaining, half is
<br />man-induced as indicated in figure 1.
<br />High salinity concentrations result from two general
<br />processes: salt loading and salt concentra:tion, Salt
<br />loading increases the amount of salt add~d to a given
<br />amount of water, and salt concentration decreases th.e
<br />amount of dilution water available for a given amount of
<br />salt.
<br />Specifically, salt loading in the Colorad,o River system
<br />results iu the addition of mineral salts frdm natural and
<br />manmade soutces. Salt concentration results in (he rise in
<br />salinity through beneficial consumptive u~ of waters and
<br />
<br />",
<br />CJl
<br />~
<br />'..n
<br />
<br />A'total salt load of about 9 million toils annually
<br />entering Lake Mead in the Lower Colorapo Rivlir Basin
<br />adversely affects more than 18 million pcjople and 1
<br />million acres of irrigated farmland in the; United States.
<br />Damages in the amount of $580,000 (barkd on January
<br />1985 costs) are projected to occur for eaQh increase of
<br />1 mg/L at Imperial Dam (when salinity concentrations
<br />reach the 875 to 1225 mg/L range) as sho~ in figure 3.
<br />
<br />
<br />Figure 3. Total losses per mg/L increase.
<br />
<br />
<br />47% Natural Sources
<br />
<br />37% Irrigation
<br />
<br />12 % Reservoir
<br />Evaporation
<br />3 % Exports
<br />1% M&I
<br />
<br />'j
<br />-0
<br />
<br />record high flows have flushed and filled-the major
<br />reservoirs, resulting in significantly lowersalinity lovels at
<br />Imperial Dam-from an annual average i)f 826rng/L in
<br />1982 to 608 mg/L (provisional) in 1985. Without control
<br />measures, however, the concentration is projected to
<br />increase, following the overall rising trend shown in figure
<br />2, possibly reaching a level of 1005 mg/L* at Imperial
<br />Dam by about 2010,
<br />'" '{he current projection is from 1985 Evaluation'of
<br />Salinity Control Pro~ams in the Colora.do River Basin.
<br />
<br />;1
<br />
<br />Figure 1. Salt loading sources.
<br />
<br />'associated streamflow depletions in the Basin that
<br />concentrate the salt burden into a lesser _volume of water,
<br />'Generally, the application of irrigation water results in'
<br />increased salt loading because of salt leaching and the
<br />concentrating effects of consumptive use. The total salt
<br />concentration in the river fluctuates annually with the
<br />overall Basin water supply.
<br />The Colorado RiYer, at its headwaters in the mountains
<br />of north-central Colorado, has a salinity (dissolved,
<br />minerals) concentration' of only about 50 mg/L
<br />(milligraqts' per liter). The_salinity concentrations
<br />progressively increase as the river flows downstream as a'
<br />result of water diversion, evaporation from reservoirs,
<br />and salt contributions from a variety of sources, Recent
<br />
<br />The losses associated with municipal and industrial use
<br />occur primarily from increased water treatment costs,
<br />accelerated pipe deterioration and appliance wear,
<br />increased soap and detergent needs, and decreased water
<br />palatability. According to the EP A (Environmental
<br />Protection Agency) water standards, public drinking
<br />water-should ,contain no more than 500 mg/L of TDS
<br />(total dissolved solids),
<br />For irrigators, the higher salinity concentrations ca~e
<br />loWer crop yields, altered crop patterns, higher leaching
<br />and drainage requirements, and higher manl1-gemenf
<br />co~ts. Agricultural losses (either through lower yields or
<br />higher production/management costs) begin when
<br />.sali,?-ity levels of applied irrigatio~ water reach 100 to 850
<br />mgl L, depending upon soil conditions and type of crop
<br />,grown. A summary of .the effects is presented below:
<br />
<br />mg/L
<br />
<br />I;:ffect
<br />
<br />.
<br />:!
<br />
<br /><
<br />k
<br />.'1
<br />
<br />1200
<br />
<br />,
<br />j
<br />:,1
<br /><'~
<br />1
<br />"
<br />j
<br />
<br />.Below 500
<br />Abov~ 500
<br />70l}-:850 and
<br />above
<br />
<br />GQod drinking water
<br />Munil;ipal and industrial losses
<br />Agricultural losses
<br />
<br />1100
<br />
<br />_l-Jlsto,icol
<br />____nProjec1ed
<br />
<br />In the late 1960's and early 1970's, leaders at the
<br />regional and national levels began to recognize the
<br />problem and to seek solutions.
<br />
<br />...I 1000
<br />,
<br />,
<br />
<br />............
<br />/'
<br />
<br />~~~~~/'
<br />
<br />,"0
<br />'9~O
<br />
<br />19~ 'lg60
<br />
<br />1910 'SHO
<br />YEARS
<br />
<br />199(l 2000 2010
<br />
<br />Flow.w,;~M.d o""~, 0'""01 ,."mol..
<br />
<br />Figure 2. Historical and projectea salinity concen~
<br />trations at Imperial Dam.
<br />
<br />
<br />
<br />'Effect of salt on irrigated lands.
<br />
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