Laserfiche WebLink
<br />. <br /> <br />PART II <br /> <br />DESCRIPTION OF BASIN <br /> <br />-' <br /> <br />pat terns of the rIVer. In add It Ion to the major reserVOirs, numer:ous <br />smaller reservoirs have been built on many uf the trlbutaru~s. Since <br />major storage began ....lth Lake !-lead In 1935, and concluded with the <br />flll1ng of Lake Powell In 1980, the Colorado River Bastn reserVOHS now <br />have a combined storage capaCity equal to approxImately four Urnes the <br />total average annual virgin (undepleted) flow of the ent He Colorado <br />River. <br /> <br />...... <br />UT <br />o <br /> <br />The Colorado River BaSin 15 an arid or semUlrld baSin compared to <br />others, such as the Columbia BaSin, wtl1ch dnllns approXimately the same <br />area but CarrH!S a comparat l.....ely larger flow, as sho'Jft In the follOWing <br />table. While the Colorado River 15 one of the major dr.<nnage baSins In <br />the contInental UnIted States, Its runoff IS about equal to that of the <br />Delaware, which drains a much smaller area. <br /> <br />River <br />baSin <br />Colorado <br />MISSISSippi <br />Columbia <br />Delaware <br /> <br />Comparison of <br />Drainage <br />area (1,000 <br />square mdes) <br />244 <br />1.234 <br />258 <br />12 <br /> <br />rIver baSins <br /> <br />Runoff <br />(MAF /year) <br />15 <br />440 <br />180 <br />14 <br /> <br />Runo ff per <br />unIt area <br />( Inches/years) <br />1. 15 <br />6,' <br />13.1 <br />20,9 <br /> <br />. <br /> <br />Silting and salInIty problems are more pronounced In the Colorado <br />BaSIn than elsewhere, as are IrregularitIes In flow. <br /> <br />The flow at various pOints In the Colorado River BaSin for the <br />1941-80 perIod IS gIven In Tables I through 20 at the end of thiS report. <br />The records of flow depIct charactenstlc WIde fluctuations month-to- <br />month and conSiderable variatIon ye:n-to-year. The storage reservoirs <br />now level out some of the fluctuat Ions In the reaches below the major <br />dams. <br /> <br />D. Geology and Salls <br /> <br />Rocks of all ages--from those of the oldest known geologIcal penod <br />to the recent allUVIal deposits, Including Igneous, sedimentary, and <br />metamorphic types--are found tn the Colorado RIver Basin. <br /> <br />Many of the sedimentary formations In the baSin were deposIted in <br />marine or brackish water envlr'onments, and therefore they frequently <br />contain salts of sodium chloride (halIte) and calCIum sulfate (gypsum). <br />The high salt content, low preCipItatIon, and the concentrating effects <br />of evaporation contribute to the high salinIty found III the Colorado <br />Rtver and Its trlbutat tes. <br /> <br />. <br /> <br />The salls of the Colorado River BaSin closely r..semble the geologiC <br />formations of theIr origin, since only In lImited areas at htgher eleva- <br />tions has the preCipitation been suffiCient to leach the SOil mass of ItS <br />soluble constItuents (salts), Over much of the area both reSidual and <br />transported sotls are alkaline and dtsplay "alkali" ac.;:umulatlon. <br /> <br />8 <br />