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<br />ROAD LOG <br /> <br />Leave SDR - 1 :00 pm (site elevation and approximate arrival times; US <br />Highway 34 mileage marker MM, ... = optional stop; dependent on <br />available time). <br /> <br />1. Big Thompson River at Mouth of Canyon 5,500', 1:15 pm, MM=83 <br />a. Discuss the 1976 rainstorm and flash flood in the Big Thompson <br />Canyon. The 1976 peak discharge was 31,200 cfs (drainage area is 305 <br />sq.mi. but 137 sq. mi., noncontributing, is upstream from Olympus Dam and <br />Lake Estes). How is flood discharge be determined and how do you think it <br />was determined for this flood? What do you think the Manning's n value <br />for channel flow resistance was during the 1976 flood, for today's flow <br />depth, and for "normal" high water (here and other sites)? What are some <br />problems and issues with making estimates of extreme floods? Should <br />1-D or 2-D hydraulics be used for estimating modeling river flow? What <br />type of flood warning might canyon residents and visitors have received? <br />Then versus today? In this canyon or other basins? -How effective do you <br />think the sign (on Hwy 34 in front of us) "In case of flash flood, climb to <br />higher ground?" What lessons might have been learned from the 1976 <br />flood? What ideas do you have to improve a flood-warning system in <br />flashy streams such as mountain canyons? Urban areas? Areaf; burned by <br />fire? The 100-year flood is used for flood-plain management regulation? <br />Is this an appropriate level of protection? What other criteria might be <br />used? Should criteria differ for infrastructure, high-hazard facilities <br />(such as dams or nuclear facilities of waste storage)? <br /> <br />b. Discuss the Colorado River - Big Thompson River Project. <br /> <br />Imagine you are in the canyon on July 31, 1976, the eve of Colorado's <br />Centennial anniversary. If you were in the area of heavy rain (after dark!), <br />or if you were downstream in areas without any (or much) rain, how do you <br />think you would react? Then versus today? In you vehicle? In your home? <br />2. '''Big Thompson River at the Narrows 5,600', MM=81.7. <br />Observe post-1976 flood design of highway 34 and mid-channel flood <br />bars. How deep do you think the 1976 flood waters were and the flood <br />velocity in various parts of the canyon (MaC, The Narrows, etc.)? What is <br />a flash flood, and how flashy is flash? <br /> <br />3 <br />