Laserfiche WebLink
<br /> <br />Figure 17.--The remains of a large debris dam in the Roaring <br />River valley near river mile 3,21. <br /> <br />rapidly in Horseshoe Park to 0.7 percent (fig, 2); this decrease in slope <br />dramatically altered the flood-wave characteristics, The combination of the <br />small slope on the prehistoric glacial lakebed, flood-plain widths in excess <br />of 1,000 ft (table 4), and very dense brush (fig, 18) attenuated the flood <br />wave through Horseshoe Park (fig. 11), so that the leading edge was slowed to <br />2,1 milh and was no longer a wall of water (fig, 15), Peak discharge was <br />greatly reduced through Horseshoe Park (fig, 11), The water was very tran- <br />quil, as noted by the smooth water surface of the fl ood near its peak in <br />Horseshoe Park (fig, 19), The flow was subcritical in this segment. Peak <br />discharge decreased from an estimated 18,000 ft3/s (see "Dam-Break Modeling") <br />at Lawn Lake dam, to 7,210 ft3/s (Site 1) at the downstream end of Horseshoe <br />Park, The majority of this attenuation probably occurred in Horseshoe Park. <br />A 1 arge amount of organi c debri s from the Roari ng Ri ver was depos i ted or <br />trapped by the dense brush at the upstream end of Horseshoe Park, and the <br />majority of the sediment load was deposited in a large alluvial fan at the <br />base of Horseshoe Falls (fig, 1). Little debris or sediment was transported <br />by the flood wave in Horseshoe Park, <br /> <br />It was fortunate for the numerous peop 1 e in res i dences and commerci a 1 <br />estab 1 i shments downstream from Horseshoe Park that the park acted as an <br />efti ci ent fl ood- retardi ng bas in (fi g. 19), By s 1 owi ng the flood wave, the <br />time available for warning and evacuation was increased. Most other Front <br />Range valleys do not have large mountain meadows (that is, former glacial <br />lakebeds) such as Horseshoe Park; without Horseshoe Park, the flood peak and <br />resulting damages would have been much greater downstream, <br /> <br />40 <br />