FLOOD06904 - Laserfiche WebLink

Home Browse Search

30 LAWN LAKE DAM AND CASCADE LAKE DAM FAILURES, COLORADO FIGURE 20.-The entrance to Aspenglen Campground downstream from Cascade Lake dam through the campground area at river mile 7.01. Boulders moved by the relatively wide, shallow flow of water (resembling overland flow). 23 and 24 (taken at about the time of peak flow). Note in figures 23 and 24 that flow was very fast only in the main street of Estes Park (as indicated by the cross waves that imply supercritical flow); the majority of flow being impeded by the buildings was subcritical. Flood-wave attenuation continued, with peak dis- charges decreasing from 8,520 ft'ls (Site 4) at river mile 10.3 to 5,500 ft'ls (Site 6) at river mile 12.5. Orville Johnson, located about 0.5 mi downstream from the Estes Park powerplant was able to discern two flood surges. However, the surge associated with the failure of Cascade Lake dam rapidly attenuated, and it was not noticed by eyewitnesses farther downstream. Dave Thomas, observing the flood 1.2 mi upstream from Estes Park, indicated that at first the water was running clear. Then he saw debris and the floodwaters ", . .coming down the river. It just gradually began to swell-there was no wall of water." . As with the Roaring River, large amounts of debris affected the flow considerably. Bridges and culverts became filled with debris (fig. 49), and energy losses increased, resulting in high-flow resistance. These debris obstructions were noted throughout this channel reach during field work after the flood. Because of these obstructions and the limited channel capacity of the Fall River, the floodwaters went down the main street of Estes Park (figs. 23 and 24). The confluence of the Fall River with the Big Thomp- son River is in Estes Park (fig. 1). The Big Thompson River streamflow prior to the flood was 385 Wis. Note that the water re-entered the main channel before flowing into Lake Estes (upper right, fig. 24). The 06733000 Big Thompson River at Estes Park stream- flow-gaging station (Site 6) is shown at the arrival of the flood in figure 25A, and at the peak of the flood in figure 25B. Note the approaching muddy water, which supports eyewitness accounts that no wall of water oc- curred at this location (upper right-hand corner in fig- ure 25A). Patrick McLaughlin, located just up-stream from the streamflow-gaging station in Estes Park, described the initial arrival of the floodwaters as a mud- dy, "jellylike" muck preceding "a surge of water." GEOMORPHIC EFFECTS OF THE FLOOD For discussion of geomorphic changes, the flood between the Lawn Lake dam and Estes Park can be