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Other information supported a small partial failure this early. l. V. Davis, the owner of Cascade Cottages at Cascade lake dam, reported flow was slightly higher than usual at 0700 MDT, before the main flood wave arrived at the dam at about 0715 MDT, Based on available information, it appears that lawn lake dam failure occurred about 0530 MDT, just before sunrise. Because campers along the Roaring River understandably were more concerned with fleeing the wall of water, their estimates of time may be only approximate. Observers along the remainder of the flood path were easily able to distinguish the leading edge of muddy floodwaters from the normally clear streamflow. Accord- i ng to Stephen Gi 11 ette, a truck dri ver for A-I Trash Servi ces, who was the first to report the flood at 0623 MDT, floodwaters reached Horseshoe Falls at about 0615 MDT and U. S. Hi ghway 34 in Horseshoe Park at 0634 MDT (fi g. 1). Accordi ng to Mr. Davi s, floodwaters reached Cascade lake dam at 0715 MDT, causing its failure at 0742 MDT. ~stes Park police reported that floodwaters reached Estes Park a little after 0830 MDT. Floodwaters reached 06733000 Big Thompson River at Estes Park streamflow-gaging station (Site 6) at 0835 MDT, and personnel of the U.S. Bureau of Reclamation reported that water levels started rising in lake Estes at 0841 MDT. It was more diffi cult to determi ne when the peak was occurri ng, as no distinctive hydraulic feature existed. Both Rann Schultz and Dan Davis of the National Park Service, as well as Stephen Gillette, provided information to estimate that the peak followed the leading edge by less than 40 min, or about 0700 MDT, at U.S. Highway 34 in Horseshoe Park (fig. 1). As the flood trav- eled only 0.6 mi through the flatter Horseshoe Park, this estimate appeared qui te long, cons I deri ng that the flood was a "wall of water" in the Roari ng River. Based on information provided by Rann Schultz, the peak followed the leading edge by about 25 min, or aPout 0748 MDT, at the Aspenglen Campground access road, located 0.4 mi downstream from Cascade lake dam, Dave Thomas, broadcasting the flood's progress from a KSIR radio mobile-transmitter station 1.2 mi upstream from Estes Park, indicated the peak followed the leading edge by 18 min, or at 0830 MDT. Based on a stage hydrograph reconstruction at 06733000 Big Thompson River at Estes Park streamflow-gaging station, just upstream from lake Estes, the peak fo 11 owed the 1 eadi ng edge by 30 mi n or at 0905 MDT, Inflow to lake Estes peaked between 0910 MDT and 0915 MDT (use 0912 MDT for the peak time), or 25 min after the lake began rising. Unfortunately, because of limited and approximate peak-time data, it is not possible to determi ne whether the peak was movi ng faster than the 1 eadi ng edge of the flood wave, as would be expected. A summary of .data related to time of flooding prepared by Graham and Brown (1983) is shown in table 6 and graphically summarized in figure 15. The lower line in figure 15 corresponds to the arrival time of the flood; the upper line in figure 15 corresponds .to the peak time of the flood. Traveltimes for the arrival time of the flood were summarized for three channel segments, based on fairly uniform reach traveltimes (fig. 15). The speed of the leading edge of the flood (and probably the peak) averaged 9.1 mi/h (miles per hour) in the Roaring River, 2.1 mi/h in the Fall River through Horseshoe Park, and 4.0 mi/h from Cascade lake dam on the Fall River to lake Estes, Overall the speed of the leading edge of the flood averaged 3,8 mi/h. Considering the high-gradient channels, these traveltimes were slow. Appar- ently, this slowness was because the channels were extremely rough, and tremendous amounts of debris in the water, particularly in the Roaring River, produced the slow speed of the flood wave. 31