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TABLE 2. Estimates of components involved in the sand budget of Ibe 1996 controlled 1l00d in Grand Canyon Componenl Length (km) Number of eddieslkm 1.2 Average eddy IIIC3 (m2) 1.2 TotallllC3 or eddies (m2) Areaofsigni~tl deposition (m lion) Change in thicmess3.4.1 of hign-elevatiOll sand (m) Increase in mass of high'.1 elevation sand (Mg) Change in thickness of'' sand to entire eddy (m) Change in mass of sand in' enlile eddy (Mg) Average new channell marzin depositlllC3 (m211on) Average thickness ot6 chaonOl mmgin deposita (m) Change in mass of channel' mugm deposits (Mg) Lees FelT}' to Little Colol1ldo River 102 4 6600 2.7'106 7000 lillIe Colorado to Grand Canyon gage 43 4 8000 1.4'106 8000 0.62 0.55 (0.51-0.73) (0.53-0.57) 0.76'106 0.3J-l06 (0.63-0.90' I 06) (0.31-0.34'106) -0.14 0.15 (-0.37 to +0.09) (-0.23 to +0.53) -0.6S"106 0.36'106 (-1.7 to 0.42'1O~ -0.55 to,I.J-lO~ 3500 6000 0.2 (0.1-0.3) 0.12'106 (0.06-0.18'106) 0.2 (0.1-0.3) 0.089'106 (0.04-0.13'106) I Data from Schmidt et aL, this volume. 2 Data from BlUOtJIl of Roc/omJJlion, ,1988, table A-3. 3 Data from Hazel et of., this volume. · Standard enor about the mean. S Assumes density is 2.65 Mglm3 and porosity is 0.35. 6 Assumed. 7 Only where deposition was significanl. on the banks. tn connasl, Ihe mass of sand deposited in eddies and on the banks in lhe 43 km downslream rrom the Lillie Colorado Riyer was approximalely 25% of lhe 10laI load Iransponed from the reach. The budgels also indicale Ihal lhe source of lhe sand deposiled along lhe channel banks differed in lhe Iwo reaches. More of this sand probably was eroded from low- eleyalion pans of eddies Ihan rrom Ihe channel bed between Lees Ferry and the lillIe Colorado River. More of Ihis sand probably was eroded from Ihe bed Ihan from Iow.eIeyalion paris of eddies funher downslream. These resullS are consislenl wilh lhe conceptual model of Rubin et al. 11994J, who proposed lhat eddies might be the primary sources of sand for redislribulion 10 high elevalion in upstream pans of Grand Canyon where Ihere is limited sedimenl resupply. SCHMIDT 339 There is insufficient data to accurately detennine the proponion of Ihe bed where significanl scollr occllrred, bUl an order of magnitude estimate can be made from bed scour dala of Hazel et af. [this yolllme]. The pllrpose of these eSlimales is 10 detennine if bed scour was likely to have been a widespread occllrrence. The proponion of Ihe bed scoured 10 a given depth was calculated as: r = m I (wdlY,n), (3) where r = the proponion of lhe bed where scour equal to the value d occurred; m = lhe mass of sand eSlimated to haye been scoured from Ihe bed, calculaled as shown in Tables 2 and 3; w = 100 m, an assumed average width of Lhe riyer; d = the mean depth of scour for the each reach; I = the lengLh of each reach: Ys = Ihe specific weight of sand (2.65 Mg/ m\ and n = lhe proponion of the lotal yolume which is solids, assumed to be 0.65. Hazel er at. [this yoIume] showed that the channel bed scoured at 15 of the 17 siles that they measured upstream from the Grand Canyon gage. The mean deplh of scour was 0.95 m upstream from Lhe LillIe Colorado River and 0.80 m further downstream. The proponion of lhe bed where significant scour occurred was probably small in bolh reaches. Only 5% of the channel between Lees Ferry and the Lillie Colorado River would have scoured 0.95 m to yield Lhe 920,000 Mg estimaled to haye been derived from the bed in Lhis reach (Table 3). Only 21% of the channel between the LillIe Colorado River and lhe Grand Canyon gage would have scoured 0.80 m to yield Ihe 1,250,000 Mg estimated to have been derived from the bed in this reach. These eSLimates of the proponion of Lhe bed where significant bed scour occurred are reasonable, because they are less lhan estimates or lhe proponion of lhe bed covered by sand. According to one eSlimate (J.D. Smith and S.M. Wiele, U.S. Geological Survey, wrillen commun., 1992), sand had to cover 13.28% of Ihe bed, depending on reach geometry, in order to maintain equilibrium sand transpon during research flows that were conducted in 1990 and 1991. The Bureau of Ree/amarioll [1988, Table A-26j estimaled that the proponion of the bed coyered by grayeI and finer sizes in 1984 was about 45% [Wilson, 1986]. 8. IMPLICATIONS FOR FUTURE RESEARCH The Glen Canyon Environmental Sludies program provided a wealth or new knowledge lhat led 10 lhis conlrolled flood. The flood was perrormed, in pan. as a river-managemenl demonstration with substantial confi- dence Ihat positive results were probable and thai damage was improbable. In Ihat respect, the flood was successful.