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<br />FIGURE 2 - LOCATION OF SURVEYED CROSS-SECTIONS
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<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 hut may e~ode
<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, etc. (per conversation "ith Charles Steele, i'lineral County Land
<br />Use Administr~tor).
<br />
<br />2. The
<br />of the channel
<br />channel.
<br />
<br />Corps cha<lnelW'as
<br />"as very good ~ith
<br />
<br />insp.,'Cted homend to end.
<br />no vegetation or cracks in
<br />
<br />The condition
<br />the masonry
<br />
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<br />Findings of tohe field investigation were combined "ith hydrolog1c
<br />findings and cross-section data from Corps flood control channel plans
<br />(see Ref. 12). IUl of the crc",~_section data vas inp\ltted into in the
<br />U.S. Army Corps of Engineers HEC-2 step-back"ater computer program. A
<br />starting water surface elevation of critical depth "as used at the
<br />entrance 1:0 the Corps channel since "ater in the Corps channel itself
<br />flo"s in supercritical no,,; thia type of flow regime could not be
<br />maintained upstream from the masonry channel due to the erodible type of
<br />streamlllaterial.
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<br />The hydraulic analysis usingtheHB:-2 cowputer model showed that,
<br />assum1ng a rigid (i.e. fixed) streambed, ALL of the floodwaters "ould
<br />enter the Corps channel, even at t.'leCorpschannel design flo"of 1800
<br />cfs. None of the flo" ~ould bypass the channel and flo" do"n Creede
<br />Avenue toward to..n. Thus at the lOO_yearpeakdischllrgeof1l20cfs,
<br />none of the tOloln would be f1ood~d if the channel "ere kept clear of
<br />debris.
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<br />Flooded Areas
<br />
<br />As determined by the hvdraulic:analysis of the study, none of the
<br />land in the town itself ..auld be flooded ~ith the lOO-year discharge.
<br />W,,~er ",,,.old "ntN" ann r..matn in th.. r"rp~ of Engineers noce!. control
<br />channel through town. The lOO-year flood IoIould, howf'ver flood a small
<br />are" just IJp:ltream from the Cor?s channel. Figur" '3 "~O"'>l this ar,,".
<br />Inror"'''-tion "ith. re;;srds to water surface elevation~ at various locations
<br />is ~ho~'n On the Plat as in Uli" r~po,t.
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