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ABSTRACT BENEFIJS TO ENVIRONMENT GLEN CA~ON TO HOOVER DAMS 1 by Cecil Balt,ar Jacobson, 1 F. ASCE [Prepared for Amer~' an Society of Civil Engineers Annual and National nvironmental Engineering Meeting held on October 1 -22, 1972 at Houston, Texas] /. ~ .-, ~ ~ I . '_ ,. ~ ,I, -,.,:;-... .. t : ,"'.! y NO,; 0 ~ '", ' ./ .- 1972 (',., C C,"j.,'l I, , OIv3t.f.':~ -0. ._'-'~;~ER 0, '"J "". CO/1P.D " , I Beneficial changes in dpwnstream environment occur due to river regulation at Glen Canyon Daml: Excepting times of infrequent local thunder showers, the Colorado River bEjlow Glen Canyon Dam runs cool and clear. Rainbow trout are now caught b the thousands where only trash fish for- merly survived. To "whlte wat r" travelers the new river regimen is par- ticularly inviting. In 1971 nea ly 11,000 of these river runners sanely viewed the bottom sights of na ure's great wonder, the Grand Canyon of the Colorado River. Prior to c nstruction of Glen Canyon Dam, relatively few people risked travel down ~he rapids of the Grand Canyon. Now treacherous high water peaks ate stored to supplement low water flows. Thus, the river's rapids are nO\!l enjoyed year around with reasonable safety. Most spectacular, ho ever, are the changes effected at Lake Mead, whose useful life is bei g greatly extended by retention of sedi- ment in her sister, 27 million a re foot Lake Powell, formed 370 river miles upstream by Glen Canyon Dam. Cold water releases from the depths of Lake Powell for power gener tion at Glen Canyon Power Plant arrive at Lake Mead about 5 1/2 degrees I (Fahrenheit) cooler than the former unregu- lated flows. Annual rates of s~rface evaporation at Lake Mead are being reduced approximately 10 percept (8 inches in depth) with a substantial water savings of 75,000 to 100]' 000 acre feet annually. These positive benefits, incident to the funda ental purpose and operation of Glen Canyon Dam, improve for mankind the environment of the Colorado River system between Glen Canyon a d Hoover Dams. Such benefits are too otten overlooked by those criticis of the builders and operators of large dams. I I :1 :;1 ~ ~: r; r , .. c ,"j ;. i"; :~. " '. ~: , '.. ; .~ ~ " IProfessor of Civil Engineering, Brigham Young University, Provo, Utah, and President of Utah Sedtion ASCE.