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<br />~. -- G. ,~:.ji ,"':":"';.!i.;'J;.;~--e.";,:.~t-j:t'.:.:.z{..~.r.P.~;~ . _......, 'U=.,......:.-i:;.;"': ~f.r';..t....:'h-.-.. ~~,_:#"l:~ <br /> <br />.~.. ;:J.....,.~~ <br /> <br />000917 <br /> <br />3.18 <br /> <br />3. Severe damage has occurred to the Portland Flume downstream of 2nd <br />Street. The side walls have been nearly destroyed and the bottom is <br />severely deteriorated. <br /> <br />4. <br /> <br />All the wooden bridges crossing Cascade Creek were destroyed in the 1982 <br />floods. The 2nd Street and 4th Street wooden bridges on Portland Creek <br />were destroyed in the 1982 flood. <br /> <br />,i <br />1 <br /> <br />5. <br /> <br />Patches to the flume walls have been made that project out abruptly <br />creating a condition that is more susceptible to flume blockage by <br />debris. <br /> <br />.; <br />, <br />~; <br /> <br />Figure 3.7 presents photographs depicting the current deteriorated con- <br /> <br />dition of the flumes. It is evident that the flume is in need of repair and <br /> <br /> <br />in SOme areas total replacement. As the flume progressively deteriorates, its <br /> <br />ability to transport debris will decrease and flood hazards will increase. <br /> <br />3.4 Flood History <br /> <br /> <br />Portland and Cascade Creeks have a well documented history of devastating <br /> <br /> <br />floods. Flooding on these blo adjacent tributaries to the Uncompahgre River <br /> <br />is often simultaneous and almost entirely triggered by cloudbursts associated <br /> <br /> <br />with intense mountain thunderstorms. <br /> <br />Unfortunately, flow records have not been kept to gage the relative <br /> <br /> <br />hydrologic magnitude of each event. The only measure of flooding intensity is <br /> <br /> <br />the often fragmentary damage estimates reported by the local newspapers. <br /> <br />However, the resultant damage is more often due to the unpredictable accumula- <br /> <br /> <br />tion of mud and rock debris than due to high water. <br /> <br /> <br />From a study of the past floods on these and other tributaries in the imme- <br /> <br />diate vicinity, the thunderstorm flood season appears to last about eight <br /> <br /> <br />weeks - from the first week in July through the first week in September. <br /> <br />Incidents of flooding have been repo=ted at least 14 times on Portland Creek <br /> <br /> <br />and 16 times on Cascade Creek since 1908. It is not unusual for.damaging <br /> <br /> <br />floods to occur on successive days as major weather systems are significantly <br /> <br />influenced by spectacular local toposraphy. The time of day of these events <br /> <br /> <br />is remarkably consistent, as almost all floods occur in the late afternoon or <br /> <br /> <br />evening. <br /> <br />The dates and times of the most significant floods on Portland and <br /> <br />Cascade Creeks are listed in Table <br />is illustrated in Figure 3.8. <br /> <br />- . <br />.:I..... <br /> <br />The path of the 1982 series of floods <br /> <br />