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<br />52 LAWN LAKE DAM AND CASCADE LAKE DAM FAILURES, COLORADO
<br /> TABLE 9.-Summary of darn-break model simulation
<br /> [First liDe is observed; seclmd line is model value]
<br /> Difference Pereentdif.
<br /> Difference . Difference fromob- ferencefrom
<br />DistaJ:Jce from olr Percent dif. ....moi> Percentdif. ""'''' observed
<br />dOWl:lstream P,ok served peak ference from Minimum served max- feranee from r...ding ~..... leading
<br />from Lawn discharge, in discharge, in observed Average g",uhd Maximum imum flood observed flood-wave Oood.weve flood-wave
<br />Lake dam, in cubic feet cubic feet .... floodeleva. elevation, flood depth, depth, maximum time, in time, in time, in
<br /> m.ilee per second per second discharge tion, in feet in fee~ in feet in feet flood depth h_ h_ h_
<br /> 0.0 "0
<br /> 18,000 "0
<br /> .55 (bl (bl (b) (bl (bl
<br /> 16,600 (bl (b)
<br /> 1.50 (hI (bl (b) (bl (bl
<br /> 15,200 (bl (b)
<br /> 3.83 (bl (bl (bl (bl (bl
<br /> 12,600 (bl Ib)
<br />c 4.73 0.75 0.05 -6,7
<br /> 11,800 8,556,1 ,80
<br /> 5.36 8,513,0 8,504.9 8,1 2.6 32.1
<br /> 10,600 8,515.6 10.7
<br /> 5.78 8,509,9 8,501.0 8.9 1.3 14.6
<br /> 7,500 8,511.2 10.2
<br />d 6.50 7,210 510 -6.9 8,492,6 8,482.6 10.0 .6 6.0
<br /> 6,700 8,493.2 10.6
<br />e 6.67 1.75 -0,15 -8.6
<br /> 16,000 1.60
<br />f 7.68 13,100 -3,200 -24.4 8,056.2 8,045.0 11.2 -1.3 -11.6
<br /> 9,900 8,054.9 9.9
<br /> 7.74 8,041.9 8,032.0 9.9 1.1 11.1
<br /> 9,700 8,043,0 11.0
<br /> 8.78 7,862,1 7,852.0 10.1 .7 6.9
<br /> 6,700 7,862.8 10.8
<br />g10.28 8,500 -2,300 -27.0 7,696,9 7,689.0 7.9 1.7 21.5
<br /> 6,200 7,698.6 9.6
<br />h11.45 6,550 -450 -6.9 7,579.1 7,573.0 6.1 1.2 19.3
<br /> 6,100 7,580.3 7.3
<br />i 12.50 5,500 600 10.9 7,502.9 7,492.5 10.4 .7 6.7 3.25 -.42 -12,9
<br /> 6,100 7,503.6 11.1 2.83
<br /> Average difference from observed maximum flood depth. in feet=l.O.
<br />Bclock time is 0530 Mountain Daylight Time.
<br />bSevere channel erosion; computations and comparisons are not applicable.
<br />cSynthetic cross section based 011 cross section at river mile 5.36.
<br />dgi"L
<br />eCascade Lake dam and Site 2.
<br />'Site 3.
<br />gSite 4.
<br />?Site 5.
<br />lSite 6; possible backwater from Dume.
<br />dimensions of the breach at the time of the peak. For 20,000 ftats to 16,000 ftats in that time frame. How-
<br />the actual breach dimensions, the model was able to ever, for Cascade Lake dam, the rate of change in peak
<br />evaluate the variation of time of full breach develop- discharge was much greater in the probable time of full
<br />ment on the magnitude of outflow discharges from the breach development of 30 s to 5 min (1 min was as-
<br />dams. Outflow discharge for various times to full breach sumed). The range of peak discharge from Cascade Lake
<br />development for both dams is shown in figure 47. This dam could have been 23,000 ftats to 9,000 ftats in that
<br />analysis indicates less change of discharge with time time frame. As the modeling demonstrated, because of
<br />occurred for the failure of Lawn Lake dam, and available the smaller capacity of Cascade Lake, greater attenua-
<br />information indicated a full breach-development time tion occurred downstream.
<br />of 10 min, with a probable range of 5 to 20 min. Hence, After the hydraulic-routing part of the model had
<br />discharge from Lawn Lake dam probably ranged from been calibrated, different simulation runs of conditions
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