FLOOD06904

• County: Larimer
• Basin: South Platte
• Title: Hydrology, Geomorphology, and Dam-Break Modeling of the July 15, 1982 Lawn Lake Dam and Cascade Lake Dam Failures, Larimer County
• Date: 1/1/1986
• Prepared For: Larimer County
• Prepared By: USGS
• Floodplain - Doc Type: Flood Documentation Report

IV

FIGURE 16-35.

38-43,

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46-48,

49-54.

LAWN LAKE DAM AND CASCADE LAKE DAM FAILURES, COLORADO

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Photographs showing:
16. The Roaring River. looking upstream from the Endovalley Road in 1978, and in 1982 after the flood, from
approximately the same location ... . . . . . . . . . . . , . . . . . . . . . - . . . . . . . . . . .
17. The remains of a large debris dam. in the Roaring River valley near river mile 3.21 ... . . . . . . . . . . . , . .
18. Surveyed cross section in Horseshoe Park showing topography of the flat glacial.lake floor. Looking down-
stream at man standing at cross section at river mile 5~36 ... ................ - . . . . . . . - . . . . . . .
19. The flood peak in the downstream end of Horseshoe Park. . . . . . . , . . . . . . . .. ..............
20. The entrance to Aspenglen Campground downstream from Cascade Lake dam through the campground area
at river mile 7.01 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21. The Fall River valley downstream from Aspenglen Campground (aerial). View is upvalley from about river
mile 8.5 ........ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22. View downstream at the indirect discharge measurement Site 4 on the Fall River above Estes Park . . . .
23. The Fall River looking upstream from the western end of Estes Park at river mile 11.9 (aerial) .......
24. Elkhorn Avenue, Estes Park, looking downstream from river mile 12.0 (aerial) ............. . . . . . . . . .
25. Aerial views upstream at the arrival of the floodwaters at the Big Thompson River at Estes Park gaging sta-
tion (Site 6), and downstream during the peak flow . . . . .. . .. .. . .. .. .. . . . .. . . . . . . .
26. Deeply scoured reach in the Roaring River valley below Lawn Lake dam at river mile 0.28
27. The Roaring River valley at river mile 1.14 (aerial) ...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28. View downstream at river mile 0.55 on the Roaring River valley in a scoured reach . . . . . . . . . . . . . . .
29. View across a mountain meadow at river mile 0.38, showing the accumulation of a thick boulder deposit in a
relatively flat reach in the Roaring River valley . . . . . . . . . . . . . . . . .
30. Imbricated structure in boulders deposited in the meadow shown in figure 29 . . . . . . . . . , . . .
31. Unusually thick sand waves deposited in the Roaring River valley on the inside of a sharp valley bend at river
mile 0.50 ........ .............. ..........
32. Horizontal laminations in sand deposits at the edge of flow in the Roaring River valley at river mile 3.41
33. Gently-inclined backset crossbeds, interpreted to be antidune structures in a sand splay 0.25 river mile down-
stream from Lawn Lake dam. ........ ................. ..............
34. The alluvial fan formed at the mouth of the Roaring River . . . . . . . . . . . . . . . . . . . . . .
35. Roaring River alluvial fan taken about 4 hours after the flood (vertical aerial) .........
Map showing contours of sediments in the Roaring River alluvial fan . . . . . . . . . . . . . . . . . .
Graph showing plot of largest particle measured in 3-foot radius every 50 feet down the major flow axis of the
dam-break flood on the Roaring River alluvial fan . . . . . . . . . . . . . . . . . . . . .
Photographs showing:
38. The single largest boulder thought to have been moved by the flood onto the Roaring River alluvial fan
39. The 17-acre lake formed in Horseshoe Park hy the damming of the Fall River (aerial), taken in August 1983
40. Horseshoe Park and the Fall River valley, looking down-valley . . . . . . . . . . . . .
41. Horseshoe Park taken 1 week after the flood, looking upstream from river mile 6.5 (aerial) ... . . .
42. The Fall River channel about 0.3 mile downstream from Cascade Lake dam, showing extensive channel scour
43, Photograph showing a well-developed boulder berm slong the right hank of the Roaring River and graph showing
particle-size analysis of matrix ... . . . . . . . . .
Photograph showing the front of one step-pool bedform in boulder deposits in the Fall River upstream from Aspenglen
Campground at river mile 7.01 .,. . . . . . . . .
Sketch showing dam-break model layout for the lakes-stream system . . . . . . . .
Graphs showing:
46. Selected modeled and observed hydrographs .".......... .. .. .. .. . " .. .. .. .
47. Outflow discharge for various times of breach development for Lawn Lake dam and Cascade Lake dam .
48. Outflow discharge for hypothetical breach width for Lawn Lake dam. assuming 104minute time of failure
Photographs showing:
49. Flood warning sign at the downstream entrance to the Big Thompson River Canyon near Loveland, Colo
50. About 0900 MDT on July 15, 1982, looking upstream at washed,out U.S. Highway 34 bridge in Rocky Moun-
tain National Park at river mile 5.3 . . . . . . . . .
Sl. The Ponderosa Lodge before the flood and after rehuilding . . . . . . . . . . . . . . . . . . . .
52. Debris jam on the upstream side of Elkhorn Avenue at river mile 11.8 along the Fall River in Estes Park
53. High-water lines on buildings along the Fall River at Estes Park . .
54. View upstream from Olympus dam. and Lake Estes, containing the floodwaters (aerial)

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