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FLOOD01761
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FLOOD01761
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Last modified
11/23/2009 12:58:08 PM
Creation date
10/4/2006 10:20:25 PM
Metadata
Fields
Template:
Floodplain Documents
Designation Number
83
County
Larimer
Community
Unincorporated Larimer County
Stream Name
Big Thompson River
Title
Floodplain Information Report - Big Thompson River, Loveland to the Larimer-Weld County Line, CO, and the Little Thompson River, Boulder and Larimer Counties, CO
Date
6/1/1977
Designation Date
11/1/1977
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />the Littlo Thompson Rlve~ flood plain, ~espectTvely, a5 deserT bed <br />inthTsreport. InterstateHighway25presentsthelargestpoten_ <br />tia i fo~ obstructing f loodflows on tho BIg Thor>pson Rive~. County <br />roads at reference points 47, 59, 82, and 103, the Colorado and <br />Southern RaT Iway, and U. S. HTghway 287 p~esent the Largest f lood- <br />flo... obstruction potential on the Little Thompson River. <br /> <br />large dlstance between the two locations. Floodda.magesar-e <br />reduced to variouS extents. deoending upon the degree of pr-otec- <br />tlon provIded, by levees constructed by private interests along <br />the Big Thompson River in the study r-each. Unfortunately, the <br />presence of levees such as these orovide a false SenSe of securIty <br />since they do not provide adequate protection against floodS Such <br />as the 100-year tlood. <br /> <br />Manmade objects, such as buIldings, cars, and fences, as <br />woll as trees, brush, and other vegetatIon located on the flood <br />plain, Can also CauSe floodflow obstructIons. These Items, whIle <br />remaining 1n place, not only tond to create hIgher stages on the <br />flOOd plain because of r-educed flow area and flow blockage but may <br />also create hIgher iocalizedvelocitles as the floodwater-s flow <br />a~ound them. Flood stages may be lowered I n a local i led area, if <br />the floodflows are of sufficient magnitude to dislodge these flow <br />obstructions. The debris may then lodge at locations farther down- <br />stream, thus compounding problems. This floating debris commonly <br />lodges against bridge piers and bridge deCks; the flow area Is then <br />raducoo or the channel is completely blocked. The blockage can <br />produce sovore stJge and velocIty increases, offen accompanied by <br />bridge damage or complete failure. <br /> <br />FlOOd plain lonlng can be an effective method tor pre~ <br />venting future damages. To date, flood plain lonlng 1n Larimer- <br />and Boulder Counties bas been instituted where flood pialn informa- <br />tion is available. Any Federal related financial loans for bulld- <br />ingpurposesinthisspecllll floodhalardarearequirefloodinsur- <br />anceontheprOller-ty. <br /> <br />Ice effects have, historically, not been a prOblem on <br />the Big Thornpson and Little Thompson Rivers. IcejamS,however, <br />couid occur- in the futuro, lit though the chance ot occurr-ence of <br />suCh a phenomenon is guite ~omote. <br /> <br />Other factors and their impllcts - flood demllges are also <br />possible in the event of lar-goamountsofrunotftr-OtIlthenurr>erous <br />tributer-Ies and small drainageways flowing Into the Big Thompson <br />and Little Thompson RiVers. Cr-ops, roads, and farm buildings could <br />receive some damage from these smalf streams. Although the study <br />;Jrea is re:atlvelyclearof urban development, LarImer County has <br />been experiencing residential growth in the vicinity of both the <br />Little Thompson RIver valley and the 8ig Thompson River- yalley. <br />The flood damage potential In the Big Thompson River basin can be <br />r-educed by Implementing flood emergency plans and sound flOOd plain <br />management concepts. <br /> <br />FlOOd damage reduction measures - Olympus Dam, constructed <br />in 1949 by the ~ureau of Reclamation, is located near Estes Park in <br />tho upper 8ig Thompson River- basin. This structure, however, has <br />negligible effect in reducing flood damages on the reach of the <br />Big Thompson River studied In this reoort becaus~ of the relatively <br /> <br />FlOOd warnTng and forecasting - The National Oceanic and <br />Atmospheric Administration (NOAA), National Weather Service, sup- <br />plies weather forecasts at least twlC<;! daily for the area. Specllll <br />for-ecasts of sever-e storms, flood warnings, and snowmelt advl~aries <br />of a general nature are also issued 115 required. Radarobservation <br /> <br />13 <br /> <br />" <br />
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