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<br />
<br />FIGURE 2 - LOCATION OF SURVEYED CROSS-SECTIONS
<br />
<br />,
<br />
<br />The second v~iIDary purpose
<br />determine the causes and history of
<br />upstream from the Corps channel.
<br />
<br />field
<br />of the
<br />
<br />.'as to
<br />material
<br />
<br />investigation
<br />loose rock
<br />
<br />of the
<br />erosion
<br />
<br />Other purposes of the field trip we~c to inspect the condition of
<br />the Corps channel and to dete~mine roughness coefficient,. (M"nn1-ng',. "n"
<br />values) Roughness coefficient for Willo,,;Creek upstream from the Corps
<br />channel was determined to be 0.040; for the Corps chann~l itself it was
<br />0.025.
<br />
<br />Field work yielded the following findings:
<br />
<br />1. The debris upstream from the channel is indeed migrating
<br />doW'nstred[ll; hoW'ever, th" debris is coming down gradually but may erode
<br />suddenly with high flows. It should be noted that the Public Works crew
<br />from the To"n of Creede annually clears debris upstream from the Corps
<br />channel. This practice must be continued in the future. In addition,
<br />d<Jring high spring runoff of snowmelt, there is a person put On 24 hour
<br />duty at the mines uvstream of to,,;n to insure that debris is cleared from
<br />cUlverts,eu. (per conversation Io'ith Charles Steele, Mineral County Land
<br />Use Administr~tor).
<br />
<br />2. The
<br />of the channel
<br />channel.
<br />
<br />Corps cha<lnelwas
<br />"as very good Io'ith
<br />
<br />insp.,cted horn end to end.
<br />no vegetation ar cracks in
<br />
<br />Theconditian
<br />the masonry
<br />
<br />Ii
<br />I
<br />"
<br />I,
<br />I
<br />I
<br />.
<br />,
<br />
<br />Findings of the field investigation were combined "ith hydrolagic
<br />findings and cross-section data from Carps flood control channel plans
<br />(see Ref. 12). 1U1 of the crc",~_section data vas inp\ltted into in the
<br />U.S. Army Corps of Engineers HEC-2 step-backlo'ater computer program. A
<br />starting water surface elevation of criticsl depth "as used at the
<br />entranco to the Corps channel since "ater in the Corps channel itself
<br />floW's in supercritical Ho",; this type of flow regime could not be
<br />maintained upstream from the masonry channel d<Jeto the erodible type of
<br />streamlllaterial.
<br />
<br />I
<br />,
<br />
<br />The hydraulic analysis usingtheHB:-2 cowputer model showed that,
<br />assuming a rigid (i.e. fixed) streambed, ALL of the floodwaters "ould
<br />enter the Corps channel, even at t.'",Corpschanne1 design flo"of 1800
<br />efa. None of the flo" would bypass the channel and flo" do"n Creede
<br />Avenue tOlo'ard tOlo'n. Thus at the lOO_yearpeakdisehargeof1l20cfa,
<br />none of the to"n W'ould be flooded if the channel "ere kept clear of
<br />debris.
<br />
<br />,
<br />Ii
<br />,
<br />,
<br />,.
<br />
<br />Flooded Areas
<br />
<br />As determined by the hvdraulic:analysis of the atudy, none of the
<br />land in the town itself "QuId be flooded with the lOO-year discharge.
<br />W,,~er ",,,.old pnt..r ann rf!matn in th.. rorl'~ of Engineers noce!. control
<br />channel through tOIo'n. The lOO-year flood "'<luld, how,"ver flood a small
<br />are" just IJp:!tream from the Cor?:! chann"l. Figur..'3showOlthtaar"".
<br />Inform"-tinn "i.th. re;;srds to water surface e1evacion~ at various locations
<br />is ~ho~'n On the Pbtos in Uli" r~po~t.
<br />
<br />,
<br />
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