FLOOD00254

• County: Statewide
• Title: Floodway Design Considerations
• Date: 9/1/1978
• Prepared For: US
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

;

FLOJD:I'.W yODEL (HEC- 2) COCiCEPTS

_ \.. is :-:e:eSS2.1-Y that the bc.sis and li-r.itations of the mathei-:12tic JT,odel
,'~-:=C- ='. ,,- '~::-.~:2Y;::;~OOC:' ::'. C'~-C2T to correc:'ly apply the flooGhay conceDt.

...:Y':- _ ::::. . :.~..:c -,

,;- _..~,- ~~.:

.. ~ ~ ','
..,,~ "'c_ ~-~. -,--~~',-L:

C:I1C cC:~~~3tions are graduall)' varisd

ste~::c:.>' ~l:',.:.

c ;:1c.': 13 CDe di-::er.,Si':Jr,21
o Pressure is hydrostatic
G Channel slope' is minor (less than 10 percent)
o O1"-,,,l'l ~oW1dar;, is rigid (e.g., no enlargl'ment fro:;] sedinent
tra:1sportation)

..,_ ~C-2 ?,o;r::L-;j \,,'as designed to detemine flood profiles for natural
channels ',,:i th \'<irying horizontal roughness and velocity. This model
.,-e.,-:'eCO:,,5 ,",e ~e5t ?....ai~a'::cle, l-:ork3.~le mathematical model for detennining
1':2:er S1..:rr2:e profiles.

During the cO:TIputation of water surface profi les and floodl,ay widths, many
co~ditions arise Ivhich require judgement. Among these are:

o Ccr.di t iO:1s h'r.ere the basic asswnptions don't hold
r U~-~rt"in-\' o~ o'o-a
_ ..Lt... c.... .1-. .L uL
o In2dequ2te data

The cO:lputatio:1S and data should be reviewed continually during the floodl.;ay
determination process. Thence, make adjustments by:

o .~,pplying SOUJld judgements
o Using HEC-2 cO:TIputations as a guide

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