FLOOD08554

• County: Statewide
• Basin: Statewide
• Title: Application of the HEC-2 Split Flow Option
• Date: 4/1/1982
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

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l'lENERAL MOllELING CONSIDERATIONS

The soli t flow option requires that the cross section numhers (Xl card)

comtinually inerea~e in yalue from ~strpam to uDStream. It is rPCCm\ll~nde~

that statil'lft values in f~et or miles ....asu~ed along th~ main channel he us..n for

crosR section nu~rs. This is imoortant ~ause the REC-2 program uses the

cross section numbers sPecified on the split flow rpaehes to ~termine what

water surface or energy qrade line elevations to use in ~ptp.nftininq the amount

of flow 10At. Ear:h splil: flow reach is located based on cross section n'Jlllhers

at thl!! downstream and upstream ends of thl!! ~each.

If the downstream and

~stream split flow locations do not match a cross section number, the program

will linearly interpolate between cross s-.ction numbers to ~termine the water

surfaces or energy qrade tine eleyations. A wise practice would be to start and

end t~ split flow ~eaclles at cross section numbers that appear in the HBC-2

hydraulie model.

Split Flow Reaeh L.-nqth Consideration.

The overflow reaches should be kept as sbort as possible. TIle lon<ler th"

split flow reaehes, the less accurate will he tile split flows and bac~water

answers. The split flow problem can be compar..n to the integration of a curYe

by the Trapezoidal Rule, which is an approximate methoil of slJMiyiding the curyp

into a number of straioht line s~nts and ealculatinq the areall under eaeh

straiqht line seqm~nt and then addino up t~ subareas to calculate the total

area under the curve. The smaller th~ straiqht line segments an~ the larqer the

nllmber of s~ts, the II\Ore accurate will be the ealculateCl area. The same

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