FLOOD01823

• County: Garfield
• County: Mesa
• Community: Rifle, Parachute, DeBeque
• Stream Name: Colorado River
• Title: Floodplain Information Report Colorado River
• Date: 4/1/1996
• Prepared For: Garfield County / Mesa County
• Prepared By: CWCB
• Floodplain - Doc Type: Floodplain Report/Masterplan

I
t I
I el/
:; ~
~ ~
~~ ..<f~
I " (

12 .10 8-9
! GRAc"'D JUNcrJO.
I

o
"I~
" 0
C:1.....l
~18
1
I

,

, ,

4.3

Field Surveys and Cross-Section Prevaration

Since most of the scud)' reach on the Colorado River mainstem had already been studied by
dClalledmethods, and since the unstudied portions of the sIUdy reachfcJl into the "Narrow" or
"Canyon" categories, only one cfoss-section was actually field-surveyed. The selection of the
field-surveyed cross-section was based on the location of a series offish ponds at the Island
Acres State Park where the Colorado Division of Wildlife had an interest in some specific
floodplain infonnation. The availability of a benchmark, easy access and the ability to survey
the opposite bank dictated the specific location within the State Park. A field estimate was made
of the average water depth, but the channel bottom was nol surveyed. Estimates of the
Mannings'n'valuesweremadeatthesurveyedcross-sectionlocationduringthefIeldsurvey.

.
g
.
~

.f0-'/1v
C.fo..-

%. I "'0
"'" ....."
,_;-J_L '
, -
~ "
'\1\
/~ \ "
~--'-// : I
--( 0 // oJ....~~o"'f. \
\!Al'S~~o. 7\O'f.~0 ,~
---f{.'fl'< ,..-
, v- I ~
: ~~~r- I~
. ~, ,
:MON"O>< ,,-;- ~ T"s;-"o~ ~ ~

-.J ,_ .f'"t:
\M().~'TRo.~E <'".f'
C,\
r- ~ -\_\.
OURAYCO.-;' \
o.
'1', I
~\
"'
-.
,
,

Map-derived cross-sections were utilized for the remaining unstudied reaches. No adjusunents
were made to those cross-sections prior to performing the depth computations. Canyon reaches
on the Colorado River mainstem generally were not represented by cross-sections since the level
of detail obtained could not be shown on the base maps. One exception is noted below.

GARFIEW CO.

Since the majority of the study reach consisted of existing detailed infonnation or canyons (64
of the 93 miles are detalled. 24.5 miles are in canyons), only three cross-sections were used in
the hydraulic analysis. Two types of cross-sections were used in the unstudied reaches of the
Colorado River mainstem:

--'"
')
~

Type 1
Type 2

Field-surveyed cross-sections used only in the representative reach:
Map-derived cross-sections us<:d only in tlre represelltative reach.

By usiog these categories to idelltif'}" cross-section sources. 3 of the 12 reachcson the Colorado
River mainstcm were divided into the following groups:

Type 1 Cross-section.
Type 2 Cross-sections-

I reach
Zreaches

,
It
-P

One of the map-dcrived cross-sections (fype 2) was used for a canyon reach, Although thai
cross-section is included in this report, the flO<.X.lplaindelineationwas notsignifi cantlydifferent
thanitwouldhavebeensirnplyfollowingthecanyonwalltopography,aswasdoneintheother
3 canyon reaches.

,wn'''''1<E>
I,
\ .
, >
/ S
, .
, /
,I .$
, "
-+-.t'-
18

,
~ ...J
,
,

There were 9 additional reaches which were classified as follows: 3 canyon reaches for whieh
no cross-sections were developed (this excludes thc 4th canyon reach iorwhich a map-derived
cross-scclion was used): 6 reaches wheredetail<:d studies had already beenperfonned.

,

(-~~

-'

TableS identifies the cross-sections, the group type and flow values used to calculate the flood
depths. The cross-sections. with 50-)'car and loo-year flood hnes illustrated. are presented after
Section 4.4 in Figures 7A-7C.

FIGURE 6
LOCATION OF SlUDY RI;!ICHES
B~,in lIounda'1'
County Un. Slud)'R",,~h I
. Cil~
SCALI;: On. inch "'luals approximat.l)' Il>lIIil",

"

COI-ORAI)() RIV};R BASIN
COLORADO WATER CONSERVATION BOARD 31'15