FLOOD10479

• County: Statewide
• Basin: Statewide
• Title: Precipitaion - Frequency Maps for Colorado
• Date: 10/1/1967
• Prepared For: Engineering Division, Coil Conservation Service
• Prepared By: Special Studies Branch, Office of Hydrology
• Floodplain - Doc Type: Floodplain Report/Masterplan

!

,.

I:'

.
~
~
~
"0
o
~
I-l
o
Qj
lJ)
I-l
~
c:l.
lJ)
~
o
lJ)
~
o
~
tlO
Qj
I-l
~
....
lJ)
~
~
;j
o
m
~
o
Ti
..,
~
..,
....
c:l.
....
U
Cl
I-l
c:l.
I-l
;j
o
..c
I
...;t
N
I-l
~
Cl
~
I
o
o
.....
Qj
..c
..,
Qj
~
~
S
Ti
..,
lJ)
Qj
o
~
"d
Qj
".
:;
lJ)
~
o
Ti
..,
~
Qj
p::

.
M
Qj
.....
.0
~
~

...
(5
Ti
~
~
0-
>>.l

u
orf-
-a~
~~9'
.tll N'l f:l
.;:tob!>
r-fQ)orf
orf bO ft..l
~O~
U+Jorf
orf
r-fJotS
~~ 6
C(~i
ft..l
OfIJfIJ
Jot ~
~ Q) 0
O"orf
orf'S bO
bO,2 ~
~.:::.

.
. ~
I-l~
I-l Qj
o 0
uu

-
N
'-"
,"J
o
o
.
o
I
-
.....
~
'-"
.....
...;t
\0
N
+
N
0'\
...;t
.
o
I
II
>0

4-l
o
"'0
lJ)0
~o
Qj ~
.....
o -
"d '" 100
~ Qj -
I-l N
o Ti I-l
.......... ;j
o ~ 0
U I-l ..,
Q) ~
~ ~ 0
I-l Qj U
Q) co
~ ..,
lJ) Q) 0
~..c: 0
>>.l..,4-l

......
N
'-"
...;t
o
o
.
o
I
......
.....
:><
'-"
N
.....
N
.
N
+
...;t
co
...;t
.
o
II
>0

.....
~
.u _
i:::"'.....
QjQj-
~ N
..-l .... I-l
..,.....;j
~ ~ 0
o I-l ~
U Qj ~
~ 0
Qj Qj <J
..c tlO
.., ..,
o 0
4-l ~ 0-
o 4-l
Qj
~"Oo
lJ)..-l0
Qj:>O
I-l'''' ~
uO.....

N
co
.
o

0'\
00
.
o

^'
:;
o
..c
~......
N
~'-"
....
CIl lJ)
t\1 t\1
::l::l X
Q)
QjE-t
"0
~ ..
t\1 0
I-l lJ)
c.:> ~
P-o
o
Ti.....
~~

co
.....
.
o

-
N
'-"
M
o
o
.
o
I
......
.....
:><
'-"
.....
.....
\0
.
o
+
N
...;t
...;t
.
o
II
......
>0
'-"
tlO
o
...::I

......
N
'-"
,,~
o
o
.
o
+
......
.-f
~
'-"
M
M
.....
.
.....
+
...;t
LI')
N
.
o
II
>0

~ ......
o M
'^ -
..:i ~
~TiQj'"
~ lJ) U Qj
;jt\1~:>
c.:>~Q)Ti
;jp::
.. I-l .....
OQj4-lt\1
"':>~c:l.
t\1.... 0 e
I-l P:: U ill
.s: ~ Cl >0
01ll..cQj
UQj..,..c
I-l ..,
I-l c.:> ~
Qj o..c
c:l. "d ..... ..,
c:l. ~ Q)....
~t\1..c~

9

~
~
~ ......
... -+
,.::; ..:;,
"d
~ ~ lJ)
~ t\1 ~
tn ....
~ CIl
.. 0 ~
lJ) "d ~
~ ~ I-l
.... 0 Q)
..........:>
..... 0''''
.....up::
:3
Q) ~
....... ....
~ .., tlO
.......,I-l
Ti .... ..-l
c.:>...::I~

......
N
'-"
0'\
o
o
.
o

I

......
.....
:><
'-"
N
...;t
.....
.
.....

+

o
M
M
.
.....

II

>0

0'\
.....
.
o

o
co
.
o

......
N
'-"
o
N
o
.
o

+

......
.....
:><
'-"
0'\
M
M
.
.....

+

0'\
.....
M
.
o
I

II

>0

Q) Q)
... ...
"dO~
~..c
~~..c
..,
~ ~....
TiTi~
CIllJ) ......
t\1t\1QjLl')
rt:l::l::lU'-"
~
I-l I-l Q) I-l
Q) Qj ;j Q)
:>:>.....:>
'H 'i'14-l .....
P::~~~
o
~ l:l U ~
c:l. Qj Po.
~~]~
>ot..:)~>o

lJ)
Q)
.....
,.c
t\1
..-l
I-l
t\1
~
4-l
o
..,
lJ)
....
...:l

.
lJ)
Qj
..c
U
~
....
~
....
~
~
;j
o
~
I-l
::l
9
'"';"
~
N
I-l
~
Qj
~
I
o
o
.....
Qj
.:t::
~
lJ)
Ti

>0

.
lJ)
Qj
..c
U
~
....
~
....
..,
~
;j
o
e
t\1
I-l
::l
o
..c
I
...;t
N
I-l
~
Q)
~
I
N
Qj
..c
~
lJ)
....
.....
:><

.
..,
Qj
Qj
4-l
4-l
o
lJ)
"d
Q)
I-l
"d
~
::l
..c
...
.;:j
~
o
Ti
~
t\1
:>
GJ
.....
Q)
CIJ
..c
~
lJ)
....

N

10

Construction of the Precipitation- and Rainfall-Frequenc Maps. The
relationships shown in tables ~-5 were used to estimate the precipitation-
or rainfall-frequency values for a 5-minute latitude and longitude over
Colorado. The normal annual precipitation and normal May to September

Relations for Ma to October Season. Consideration of themeteorologi-
cal situations that produce large point values of precipitation in Colorado
in the May through October season indicate that a high proportion of them
result from thunderstorms, either air mass or frontal. During this season
the Gulf of Mexico is the primary moisture source for eastern Colorado. In
western Colorado, particularly for the southern-facing San Juan Mountains,
the Pacific Ocean remains a primary moisture source, but moisture coming
from the Gulf of Mexico during periods of southerly or southeasterly flow
becomes almost equally important. These considerations led to the conclusion
that the region should be separated along the Continental Divide and then
westward along the crest of the Sail Juan Mountains. East and south of this
line moist air is not lifted over massive orographic barriers, and moisture
from the Gulf of Mexico is either the primary source or equally as important
as the Pacific moisture source. North and west of this boundary moist air
from the Gulf of Mexico has to be lifted over barriers with average ele-
vations of over 10,000 feet and moisture from the Pacific Ocean has a long
overland trajectory. The western boundary of both of these regions is a
generalized crest line that extends along the ridge of the Wasatch Mountains
and Plateau. Table 5 shows the relations used to estimate rainfall-frequency
values in regions of sparse or no data for the 6- and 24-hour durations for
the 50 and 1 percent probability levels.

00
\0
.
o

The 100-year 6-hour amounts were first correlated with the 100-year
24-hour amounts for the same region used to develop the relation for the
2-year return period. Relations (table 4) developed for basins that were
primarily in Colorado, Utah and Nevada provided better results than those
which included basins in Arizona and New Mexico. For the basins along the
southern border of Colorado, San Juan, Rio Grande, etc., the relations de-
veloped for the Arizona and New Mexico frequency maps were used. This
equation is also shown in table 4.

lJ)
~
4-l 0
0-'"
..,
. t\1
o ..,
Ztn

CIJ lJ)
.=: Qj
~ ::l
.....
4-l co
0:>-
~ .
t\1 lJ)
^' ....
i5

0'\
.....
.....

M
.....
.
...;t

co
M

M
N
.
M

o
.....
.....

\0
N
.
M

M
LI')

.....
LI')
.
N

co
...;t
.....

00
0'\
.
M

.....
N

.....
...;t
.
N

Relations were also developed to estimate the 2- and 100-year 6-hour
amounts. Previous studies indicate relations between 6- and 24-hour amounts
to be fairly consistent over large regions. i.e.. they show little geographic
variation. A relationship to estimate the 2-year 6-hour precipitation was
developed previously from data for basins in Arizona, New Mexico, Colorado,
Utah, and Nevada. This same relation was used to develop the precipitation-
frequency maps already issued for New Mexico and Arizona and is shown in
table 4.

"d4-lCIJ
I-l 0 ..,
~ ~
"d I-l S
~O....
~ I-l ~
~ I-l lJ)
tI.l>>.lr-:l

N
LI')
.
o

M
...;t
.
o

C()
..;r
.
o

.....
M
o

0\
LI')
.
o

o
M
.
o

enabled the development of regional generalization based upon station data
When the maps for the longer return periods were developed the number of
stations with long records for which reasonably reliable 100-year values
could be computed was considerably less~ (Thirty-six percent of the stations
had less than 20 years of record.) It was considered advisable therefore,
to develop a relation (table 3) for this region to aid in interpolating
between stations.