|
<br />
<br />
<br />8urinQ flooa~, trees. ~ru$n J~d other vccctJtion qrcwinq
<br />alo~q the streJm banks or In the flood plain i~oede flood flews, thus
<br />c:reiltinq ~ckwilter and increilsed flooc1 heiqhts. Trees and other debris
<br />IYk'fV be washed away i1nd carried ~('wn;.trea'" to coll",ot On orid"e> and oth"r
<br />obstructions to flow. As flood flow increases. masses of debris break
<br />loose and a wall of wafer and debris surqes downstreilm until ~nother ob-
<br />
<br />structio" is encountered. Debris ""'v collect i1q" i nst a briane u~t i I the
<br />
<br /> .
<br /> ,
<br /> 2
<br /> .
<br /> ,
<br /> 0
<br /> .
<br />0 ,
<br /> 0 0
<br />. .
<br />, . <
<br /> . ,
<br />~ . ,
<br />, ,
<br /> . .
<br />0 0 .
<br />, " .
<br />. 0
<br />c ,
<br />. .
<br />- . ,
<br />. 0 c
<br />" 0 ,
<br />0
<br />.
<br />. "
<br />. ,
<br />. .
<br />" ,
<br /> ,
<br />. ~ .
<br />0 0
<br /> ,
<br />. 0 .
<br />, , 8
<br />,
<br />, . .
<br />> c 0 "
<br />< . . ,
<br /> - , ,
<br />0 . i
<br />, . ,
<br /> c c
<br />^ . -
<br /> .
<br />0 . .
<br />. . , ,
<br /> ,
<br />, " , .
<br />, , .
<br />c .
<br />c " . .
<br />.
<br />, " , ,
<br />0 . <
<br />, 0 . 0
<br /> , ,
<br />0 . "
<br />, > .
<br /> . 8
<br />. , !
<br />8 , ,
<br />" 8 "
<br />" 0
<br />. ,
<br />c .
<br />, ,
<br />0 ,
<br />" "
<br />
<br />10ild exerted upon It, bv the backwilter, exceeds Its structur~1 capacity
<br />and the brTdqe is destroyed. The limited capacity of obstructive brld~es
<br />Ciln retard fiood flows ~nd result in lloodTnq un"tre~M, ero~Ion ~round
<br />bridoe apor~ch embankMe~ts and posslbie damil~e to t~e overlylnq roadbed.
<br />In addition, erosion of culvert entra"ces a"d bridne anprOilch e~benk~ents
<br />Can occur with possible dilmiloe to the overlvinn roadbed.
<br />
<br />In qeneral, obstructions restrict flood flows and result in
<br />hiqher overbank flows and unpredlct~ble 3re~s of floodTno, destruction of or
<br />damdqe to brTdqes, and, ~n increased velocity of flow in the brldoe
<br />vicinity. it is impossible to predict the deoree or location of the ~ccu-
<br />mulation nf debris, therefore, for the purposes of this report It w~s
<br />neceSS~ry to assume that there would be no accumulation of debris to ciao
<br />any 01 t~e br idqe ope"inas in the development of the 1 iood rrof I 1.05.
<br />
<br />'Th",CachelaPoudre'livcr. inlh"sludvree<;i" issoannordl>v
<br />14 bridoes. ~onv of theso brldqe~ arc obstructive to flood flows.
<br />
<br />Flood damilqe reduction measures - T~ere are no flood control
<br />structures on the Cache la ~udre River in the study reec~. There i1re two
<br />dams on th", North ror~ ':"'che Ie roudre River. Th(> H~ II ioan (J"", "nd "ese~-
<br />voTr, located about 24 miles northl'est of Fort ("Allin;, was built in In10 tor
<br />Irrin~tion <;tnranp. IInd is owned bv the North Poudro I rr Icatlon Cornoanv.
<br />The Mi I ton Se""'~n [Jam i1nd ~eservoir, built bv the cltv o' t.rei.'lev in 1047
<br />for munic i pill wafer SUDol y. i s loc~ted about one mi Ie uostre",", from the
<br />'brth Fork confiuence wit~ the C~c~e la Poudre River. T~e flOOd control
<br />
<br />
<br />ef<ect 01 either ~a", i~ considered "eQI i<1iDI" in t~." ~t'Jd'/ re~"r,. '~" "It v af
<br />
<br />,
<br />
<br />"
<br />
|