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Last modified
11/23/2009 10:51:04 AM
Creation date
10/4/2006 9:21:40 PM
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Floodplain Documents
County
Statewide
Title
Nature's Building Codes - Geology and Construction in Colorado
Date
8/1/1979
Prepared For
State of Colorado
Prepared By
DNR
Floodplain - Doc Type
Educational/Technical/Reference Information
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<br /> <br />Characteristics <br /> <br />In mdny stream valleys. the detH"ls f3ns. built up Over the <br />centuries at the mouth of the small tributaries. otter <br />attractive places for development. Frequently. In .!In effort <br />to dvold mdlnstrea~ flOOding. the debris fans are bur It upon <br />_rthout the realization that they, too, are subject to <br />periodic debris t10.5 ond flOOding. LJependlng on the climate <br />and geology. the tans may recover quiCkly fro'll the <br />destructive .ff.cts of a debris flo. event, ofterlng tittle <br />visual evidence of the active processes. In general, the <br />.xlstlng Channel on d debris fan cannot aCComodate the next <br />1""98 debris flo_, It cannot be assumad to be the only <br />hazardous location on a debris tan. The land form Is built <br />up Over the years as debris f10llls periOdIcally deposit <br />materials across the entire debris fan or portions of It. <br />During., I.,rge flolll a nelll Channel ,nay result from pluggIng <br />of the elllsting Ch4nnal IIIlth debris. Usually, the <br />destructl~e forces ot the debris flo_ decrease as one moves <br />from the narro.., steep apex ot the fan to the broader, <br />gentler slopes do..n gradient. ~orrespondlngly, the sIze of <br />the material deposited decreases as the debris tlo_ moves <br />across the fan. Debris f.,ns often "re ~egetated ..Ith <br />cottonwood or aspen trees, grasses and Shrubs In a distinct <br />contr"st to adjacent plant grO.th. Some debris fans in the <br />hl]h mountains also are Subject to a~alanches. <br /> <br />Consequences <br /> <br />Structures and Improvements on the ape II of the fan /IIay be <br />destroyed or badly dama~ed _hlle Improvements tarther dOllln <br />on tho fan liMy only experience ..ater and mud dam"ge. Erosion <br />and deposItion on an actl...e tan by successl...e debris flo..s Is <br />to be expected. <br /> <br />Aggravating Circumstances <br /> <br />/oldn's dctl ~Itl.s _hlch could Increase the natural hazards are <br />sImilar to those cited und.r debris f10. and mud flo_. In <br />addl t lon, ho..ev.r. sign I f I cant, shor t~term al ter.,t Ions to the <br />debris fan land torm can Increase the hazard on particular <br />areas on the fan. ''"'4sslve earth moving on the fan could <br />create an artificial diversIon or Channel ..hlch "ould c.,use <br />temporary preter.ntlal flo.. directions during" debris tlo_. <br /> <br />Mitigation <br /> <br />The best form ot ml t Ig"t I on Is b4sed upon an underst~nd I ng at <br />the natural processes ot a debris tan and locating and <br />constructing Improvements accordingly. ~I"'en the condition <br /> <br />ot a de...eloped debris fan, measures thdt c.,n be taken to <br />decre,ue the hazard Include building massl...e earth structures <br />on the uphill side ot houses or other l'lIpro~elnents to dl...ert <br />the flo.. to one side or the other, planting a dense ro_ of <br />tr.es, .rectlng retalnlhg ..ails, and Channelling th. stream. <br />These ~easures sh~uld be considered only atter a complete <br />understanding of the process Is obtaln~d b.cause In many <br />Instances tney could be of little ben.ttt and could ev.n <br />Increase the hal~rd to otner developed areas. <br /> <br />Land Use <br /> <br /> <br />Land uses on debris tans range tram open space to r.latl~ely <br />Intensl...e use. Intensive us. may be appropriate afrer a <br />thorough geologic study and understandlnJ of the debris t~n <br />Is Obtained. Some fans have ...ery deeply entrenched channels, <br />IncHcatlng that durIng recent ~eologlc time, th. dominant <br />process h"S be.n .roslon on the tan rather than d.posltlon. <br />SUCh a debris fan may be safe for d.....lopm.nt. until <br />determined other..lse, ho..e~er. bulldln; on a debris fan <br />snould be conslder.d halardous. <br /> <br />~;: <br />~.. <br />Dif:-""." <br /> <br /> <br />"" <br /> <br />I <br />I <br />I <br />._~ <br />... <br /> <br />~ <br /> <br />:. - <br />.. <br /> <br />- :\ <br />" <br /> <br />- ..... <br />:\ . <br />. <br />~ ' <br /> <br />A debris tlo... S'lldshed Into this G1en...ood Springs home In <br />1917. The hOuse Is a part of , residential cl.....lopm.nt <br />placed on a debris fdn _hlch had b.en built up o...er the <br />years. ~ote the hel'lht at the f 10.. as Indicated by the <br />..ater/mud /II~rk at second floor le~el. <br /> <br />" <br />
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