FLOOD09884

• County: Crowley
• Community: Ordway
• Stream Name: Arkansas River
• Basin: Arkansas
• Title: Drainage and Street Design Manual for the Town of Ordway
• Date: 1/1/1987
• Prepared For: Ordway
• Prepared By: Simons Li & Associates Inc.
• Floodplain - Doc Type: Project

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L
ti =_+ 10
100

(1.4)

Vme t i = init:i.al or over 1.aIKI flow tine (minutes)
L = length of over1.aIKl f10w (feet)

Narmill y Fquati.on 2.4 will govern th! init:i.al tine in urJ=i """ b3sins.

'Ire travel tine (~ ) portim of th! tine of coocentration shall be canputed using th!
hydraulic ptu!"=' Ues of th! ditch, channel. curb and gutter, or
storm sewer. 'Ire travel tine for grassed watenays, shallow gutter flow, and slEet flOli over
jBved areas my also be ca1cu1ated using Qmt 1.9. th! min:ImJn t shall be five minutes.

Rainfall Intensity (I)

'Ire intensity, I, is th! average rate in :ioches per Iwr for th! period of ua,,;mlTl rainfall
of a given frequency having a duration equal to the tine of cm:entration. After the design
storm frequency has been se1a:ted. th! rainfall intensity shall be obtained fran Omt 1.1.

nmgn Storns

'Ire rainfall for th! init:i.al design storm shall be a S-ymr frequency, ooe-mur duration
event. The rainfall for th! mjor design storm shall be a 100-year frequeocy, <re-hcm- duration
event.

Rmoff Coefficient (C)

'Ire runoff coefficient (C) lepzesez,ts the integrated effa:ts of infiltration, evaporation,
retentim. flow rooting, and intercepti.oo, all10hich effa:t th! tine distribution and peak rate
of nIlOff. Table 1.2 presents the recaIJ16llled values of C for th! various recurreoce frequency
storms. The values are presented for different surface charocteristics as l>'ell as for different
storm frequencies. 'lre coefficients far th! various surface areas can be used to develop a
rl'tlqXJSite value for different land uses 10hich my exist within the w.itershed area. As an
alternate to th! above coefficients or far areas not specifically listed above (planned building
groups, shopping center, trailer parks. etc.) canposite runoff coefficients my be used. 'lre
canposite runoff coefficient is iBsed m th! percentage of th! different types of surfaces
involved .

'lre canposite runoff coefficient (C) shall be <,,,lrnl,,rPd using

Cc=l((;h + C:h+ C:h+...) (1.5)
At
Vme C c = CDJllOSite runoff coefficient
C l'C 2 = :iIKli vidual runoff coefficient correspoming to the specific type of surface
A 1,A 2 = area of each different type of surfaces to be cmsidered
At = total drainage area involved for which the canposite coefficient is applicable

It should be noted that the units of AI' A2> A 3 are imIBterial as 1mg as they are th! sane.

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