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<br />3. Big Thompson River at Viestenz-Smith Mountain Park 5700'. 1 :30 pm, <br />MM=79.5 <br />This park was the site of a hydroelectric power plant (was 2-3 stories <br />tall), which was destroyed by the 1976 flood. Several types of flood <br />evidence remain. PSis are "old" high-water marks (HWMs) usually <br />consisting of tree (abrasion/corrasion) scars, woody debris, silt lines, <br />flood-deposited sediments, etc. What types can you identify? What do <br />such paleoflood indicators termed paleostage indicators (PSIS) "tell" us <br />about flood depth and discharge? <br /> <br />4. *** Pleistocene Flood Deposits 5,900', MM=78.1 <br />Roadcut on the left bank shows rounded cobbles and boulders clearly <br />imbricated (that are indicative of water-flood deposits) about 30-45 feet <br />above the present channel. Also, mid-channel boulder bars remain from <br />post-1976 floods. What is the interpretation of the depth and discharge <br />of the flood deposits (or PSis)? How might the channel have looked prior <br />to the 1976 flood? 100, 5,000, or 10,000 years ago? <br /> <br />5. *** Idlywilde Dam, 5,950', MM=77.2 <br />The 1976 flood overtopped (by about 5 feet) and destroyed the dam at <br />this site. - <br /> <br />6. Big Thompson River at Forks Park below Drake, 6,200', 2 pm, MM=75.9 <br />Indirect peak discharge measurements were made here/near here <br />following the 1976 flood. Peak discharge was 28,200 cis upstream from <br />Drake (189 sq. mi.), 8,710 cis in the North Fork Big Thompson River (85.1 <br />sq. mi.), and 30,100 cis here at Drake (276 sq. mi.). What criteria are used <br />for selecting difficulties with selection of n-values and with the <br />computation of peak discharge in mountain rivers? Discuss "state-of- <br />flow" for floods (sub-, critical, or super-critical flow) and what type <br />exists for extreme floods? Also, discuss 1976 stage indicators <br />(corrasion scars on trees) at this location. From the tree scars, how <br />might you infer flood depth and how reliable might such an estimate be? <br />In terms of flood depth or flood discharge? <br /> <br />4 <br />