FLOOD03740

• County: Statewide
• Basin: Statewide
• Title: Adjustment of Peak Discharge Rates for Urbanization
• Date: 2/1/1979
• Prepared For: US
• Prepared By: COE
• Floodplain - Doc Type: Educational/Technical/Reference Information

By adjusting various parameters the calibrated data model can, in a representa.
tive way, simulate runoff from land-use conditions that existed in the basin
prior to 1970. This is accomplished by modifying the adopted parameters that
characterize the routing procedures, unit hydrographs, precipitation loss rate
functions, impervious surfaces, and contributing drainage areas. Adjustment
of routing criteria is dependent upon changes to the main channel system such
as the construction of concrete channels, flood control structures. etc. In the
Rahway study (3), unit hydrograph parameters [Clark method (2)J were modified

7,000

HEC-1 computed flood hydragJllphs
fO'lvent1

.,000

w
~
&
.
r
o
w
a

3,000

'-f

Land-UN conditions
1970
-1960
1950
1940

.
.

~.ooo

4,000

t2

18 2"1
TIME IHollnl

'"

FIG. 1.-Simulated Flood HVdrogr8pha for Various land-U.. Condition.

10,000

10.000

.
.
.
,
o
.
.
.

~E...rl(s.FI'll

~E""2
~b.n!~

- -
~E_II(s...F'OIJ

__---~E...12
~E_5
-,-----

,.,

'"

-----,RM~nl"""'......._....
_"''''_10.-4

1,000
lua 1940 I~ 1910 1110 IMO lfftO :eooo
n..EIY.....)

',~
193-0 lHO 1!t50 IKO 1170 1180 1910 2000
TlIlIEl.,...,.l

FIG. 2.-Effect of Urbanization on Peak Discharge Ratea

according to the following relationships based on a multiple regression analysis
of regional data:

7~~;: ~ (: : ~:~:~: )''' . . . . . . . . . . . . . . . . . . . . . . . . . . . (1)

(TC + R), (I + 0.031, )0..7 ........................ (2)

(TC + R), 1 + 0.031,

(Eqs. I and 2 relate the direct runoff hydrograph parameters, TC and R, to
an indice of urbanization, /, in which TC represents the time of concentration,
in hours; R represents the basin storage characteristics, in hours; and I is the
percentage of man.made impervious surface within a subbasin. Subscripts I

2