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<br /> <br /> <br />Sandban provide habilal for plants and <br />wildlife along the Colorado River in the <br />Grand Canyon and are commonly th(' <br />only flat areas among cliffs and boulders <br />where ri\er rafter<> can camp. A~ part of <br />Lhe Glen Canyon Environmental SlUdies. <br />funded and coordinated by the Bureau of <br />Reclamation. the U.S. Geological Survey <br />~_'\ moniloring the suppl)'. storage, and <br />~ '... movement of sand in Grand Canyon <br />',Natioml Park (fig. I). Before Glen <br />~ ovon Dam was built. an an'race of <br />'l.ab6~~6i.mi\Jion IOns of sedJmenl~"'cre <br />\ tr'..Il{~portedQY the Colorado River into the <br />'Ip"ark each vear:-B';i,\:lUSe the dam now <br />....... ~, <br />~_~k." ,the ',river. th ,only significant <br />SOl~(,S .of ~jment ~Or~park are <br />stre~s and ri\'e~ ~ownsU'eaf1i from the <br />dam, The aniountQ,[ $..,nd-tbek tTlB'Utmes <br />~upp]y ~ va~B'i:~a~Y"'fe>lll 'tear'td.}ear <br />... but av~r~ge~ about 2.9 miJtion tons per <br />t Year_ ,,\Y'~ilable ,datIl indicate that if dam <br />i"':~~leas~ \re, managed properly thi~ is <br />..,. <br /> <br />\., <br /> <br />\ <br />~, \ <br />-'..... <br />~ <br />~' l' <br />- \. <br /> <br />.Ill ~ <br />:'--!, <br /> <br /> <br />'~a <br /> <br />-Haj(,IIU <br /> <br />v <br /> <br />. <br />f'h"C'nh <br /> <br />'--~ \ <br />'I' <br /> <br />" <br /> <br />. <br />ll1non <br /> <br />'. <br />. <br /> <br />"- <br />, <br /> <br />measure the change:s in channel sand <br />storage cau..e:d by tributary l100ds and the <br />low releases from the dam in 1992 and <br />1993 (with dail} maximum releases <br />restricted to les~ than about ~O.OOO cubic <br />feet per !'econdJ. The dat;;! collected also <br />are being used to refine computer models <br />that can simulate the movement of sand <br />through reaches of the river. <br /> <br />Channel Sand Storage is <br />Monitored at More Than <br />100 Sites <br /> <br />The Paria and Little Colorado Rivers <br />(fig. I) comribute: mo..t of the sand thaI <br />enters Grand Canyon National Park: <br />therefore. 34 monitoring ~ites .....cre <br />estahli..hed in the 7-mile reach of the <br />Colorad{) River jusl below the mouth of <br />the Paria River and 32 lllonilOring site.. <br />were established ill the 7-mile re-;u:h <br />below the mouth of the lillIe Colorado <br /> <br />about sand movement after individual <br />tribUlary tloods. <br /> <br />Sand Accumulales Below <br />Tributary Mouths <br /> <br />When the Paria and Little Colorado <br />Rivers 1100d, much of the sand they carry <br />quickly settles out in the main channel of <br />the Colorado River. With time the sand <br />moves downstream. The monilOring <br />network supplies de:taiJed information <br />about the areas of initial deposition and <br />the rate of sand movement through the <br />river. In August 1992. the Paria River <br />l100ded with a peak discharge of about <br />1.270 cubic feet per second. The: four sites <br />closest to the Paria River lfig. I) were <br />measured before and after the flood. <br />During the 1100d. discharge was measured <br />and seven suspended-sediment samples <br />were collected aUlOmatically at the Paria <br />River Qreaml1ow-gaging station 1.1 miles <br /> <br />113' l'T-,H 112' <br />" ARllo:;;-----------i--...."".. <br /> <br />, <br />\5 ~ILOI.lE~ERS <br /> <br />'- 3~' <br />"' Figure 1. Localion 01 study area and cross secllons. <br />.... \, <br />enough sand to maintain sandtlars and Ri\'er. Forty other sites are di~tributcd upstream from the mouth of the ri\'cr. The <br />_~~~~ ~posil.~ in. the park (Bureau of tletween lhese two rivers and farther Paria River 110wed thick with sedimenl <br />R~c1amatipn, 1994.'n.~50-5]). ~owustream. :\leasuremenlS are made at from about ~:OO p.m. on AU,2"ust 23 until <br />- r "-.. "" ,.. --:~-, <br />I - SaI;ld lf~..:~utarie.~~s !~rariJY L e;;1d1; ~e at th~e key Il~e~ dun~g the 9:00 a.m. the next day. The tota] <br />depo~jn me river chanlref during-tow ) ear. m, the .... mter, belore the spnng suspended sedimenl transported by the <br />.. tlo~'s ~uced~~lIed dam floods in ~b,?t2r~~: in blc spring or e;ul} llood wa,s cstlmated to be 5...\..4,000 IOns, of <br />releases. '\.J\ controlled flood of summer. after the 1l0('lh; and m lhe fall. which 330,000 ton,> was sand. :\tuch of <br />_ ~pprQprijte.)~in:: anif-dura~~ will scour. ~fter ~e ;'ummer th~derstorm '>eason, the sand was depo'>ited in the river <br />.-. -.....:.~d ~ rebuild ~so~ sandbars' ;ThL Some - SlIes may he 1ID:~~red more l-hannd Just belo.... the mouth of the Paria <br />~OlllloriD~ SU:d~lgne: t~ -f-~ to~~ecl det:U~~ m~~un Rl\er Sand accumulatt'd at all four of the <br />~~!'---> -- ~ ~- ::~~ <br />__ d--- -- ::;-~- ~ -=-'- ,"" - Fa" S~", p'onla~ <br />__ - ~ -=:0:- ... ,~~ 1!4.., ___ --.:,.,_ .' "~'.c~e,,~p'Il" <br /> <br />~ <br />