FLOOD05191

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: Flood Characteristics of Urban Watersheds in the United States
• Date: 12/9/1983
• Prepared By: Sauer, Thomas, Stricker, and Wilson
• Floodplain - Doc Type: Flood Mitigation/Flood Warning/Watershed Restoration

..-.. Dra"
"" -..... , . mage Divide .........
, ~.._'.._..--...
.' Middle "
Third" Upper'
\ Third

/..
: \
/ '.
: I I
(Upper
Third
.
.

I
.-
.
\
.
.
r

.
',Or
q~
..
..~19
-,0.
"2-
c;.
. '"

r
.
.
---1

.
. .
'\ Lower /
Third /.,

oji/

A Long, narrow basin

\
.
'-
\

Lower
Third

.
.

\

.
.

..~.

.-.
/' ............ 0
. -(r~_
. Upper '.''1:
( .~
Third X 4;...
- - , .....Q!:

") -- "~

. "-

L- "\ "
__ Middle "
. '" .
. '" Third \ .
\ ~~;;r "'\ \
.

'\ \ \

I

"_" / I)
"""- . 4 _ I.
..~J.--""

.

\

.

I

Outlet

.
.

B Fan-shaped basin

-"
"

.
\

.
./

\
,y'

\
\ ,,-'
.J-..--"

Outlet

C Short, wide basin

Figure 2. Schematic of typical drainage basin shapes and subdivision into basin thirds. Note that
stream-channel distances within any given third of a basin in the examples are approximately equal,
but between basin thirds the distances are not equal, to compensate for relative basin width of the thirds.

Indices of Urbanization

Impervious area, lA, is a significant variable in
some of the regression equations, particularly for low
recurrence intervals. It is defined as the percentage of
the drainage basin occupied by impervious surfaces.
The IA variable was computed from the best available
maps or aerial photographs showing buildings, streets,
parking lots, and other impervious surfaces. Field inspec-
tions to supplement the maps were useful. Impervious

Several parameters were evaluated for each basin
in an attempt to measure the degree to which a basin
had been urbanized. Among these indices are percentage
of the basin occupied by impervious surfaces; population
and population density determined from Census Bureau
data for 1970; and basin response time, or lagtime.

Data Base 7