Laserfiche WebLink
<br />'rf'i{-~ <br />.'W <br /> <br />:' <br />I;"~ <br />;. <br />i'; <br />~I <br />:1 <br />" <br /> <br />Under current operation., Plood aelea.e. will Occur <br />In About One Of Ivery Pour Year. <br /> <br />.1 <br />:~'I <br />')'.: <br />l:~ <br />10, <br /> <br />,. <br /> <br />Flood releases occur about one in four years due to <br />reservoir storage targets and errors in forecasted <br />runoff (among other variables). CUrrent data are <br />sufficient to show that this frequency of flooding <br />would be damaging to downstream resources, but are <br />insufficient to determine precisely the frequency of <br />flooding that resources can tolerate in the long-term. <br />Based on observations of the natural system in Grand <br />Canyon, flood releases should be avoided until a <br />tolerable frequency can be better defined. CUrrent <br />knowledge indicates that even a frequency as low as one <br />flood in twenty years will produce a net long-term loss <br />of camping beaches and substrate, although at a rate <br />reduced from that caused by current operations. <br /> <br />:~ <br />~ <br /> <br />";-i- <br />'.~ <br /> <br />- <br />Two methods of frequency analysis were used to arrive <br />at the one-in-four-year flood frequency. Operating <br />procedures and methods in place during the GeES study <br />period were used in calculating the frequency of <br />spills. <br /> <br />~<~ <br /> <br />,. <br /> <br />'." <br />,. <br /> <br />pluctuatinq aelea.e. Primarily Affect aecre.tion <br />and Aquatic ae.ource. <br /> <br />~ .~ <br />,. :~ <br />;:( <br /> <br />,"". <br /> <br />., <br />.;:. <br />:-:'. <br />.",. <br />~', ~. <br /> <br />Except during periods of very high runoff, the amount <br />of water released from Glen Canyon Dam is varied on an <br />hourly basis, often with two peaks and two troughs <br />daily. This is done to provide electrical power when <br />it is most needed during the day. These fluctuations <br />can cause the river level to change by up to 13 feet. <br />Fluctuating releases stay below 31,500 cfs and are <br />therefore not as detrimental as floods for terrestrial <br />resources. However, they have a deleterious effect on <br />recreation and aquatic resources. The quality of fish- <br />ing and white-water boating is reduced by approximately <br />15 percent under fluctuating releases as compared to <br />steady releases. <br /> <br />..... <br />":.~ <br />'....," <br />~~ <br />~.;;. <br />;~ <br />"~ : <br />:;:,." <br /> <br />?I'. <br />i'.~. <br />:"J <br />':1.. <br /> <br />Fluctuating releases have a greater impact on <br />than on terrestrial resources. Fluctuations <br /> <br />aquatic <br />at any <br />