FLOOD10080

• County: Mesa
• Community: Grand Junction
• Stream Name: Colorado River
• Basin: Colorado Mainstem
• Title: Flood Hazard Information
• Date: 11/1/1976
• Prepared For: Grand Junction, Mesa County
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Floodplain Report/Masterplan

VELOCITIES OF FLOW

DuringalOO.yaarflood,averagcvelocitics
of flow in main channel and overbank areas

would be as shown in Table 5

TABLE 5

AVERAGE VELOCITIES OF FLOW
100-YEAR FLOOO

Stream
Colorado River
Gunnison River
LeachCrcck
Horizon Drive Channel
Lewis Wash

I So o",'O'I","k no~.,

In sheet flow'aNas, velocities would rangc
from 1.3ketpersccond,ln somelocalizw
stream reaches, downstream from natural Or
manmade obstructions, for example,
vcl(l('itics of flow could significantl,' exc~cd
thme shown in Table 5_ Velocity of flow
durinl'( a SOO-year flood would be slightly
nigherthanciuringall)O.yearllood,
Wa~rflowingatarateof7f{'etper~erond

FLOODED AREAS
The areas that would b. inundated by the
100. and 500-j'~ar nood~ arc shelwn on Plates
2-57. As may be seen from those plates. the
lOO-yearflood on the Colorado and Gunnioon
Rivers would beeonlined to the immediately
adjacent overbank areas. Colorado River
f100dflows will inundate bottom lands along
the nelrth side of theriverandsandbarislands
immediately upstream from Grand Junction.
The commercially developed area near the

'R,.,."d..h.llowol'e,land no"'gen~,"1I;.I_\h""2r...ld."~.

Velocity
(Ieelpe.second)
Main Channel OVII.bankAreas

7.9
6.8
3.7
35
6

2.'
1
12
1

or greater will eau.c Beyere erosion of
streambanks and is capable of transporting
lan,e rocks. Streambanksanrl the fill around
brldJie abutments may be eroded and Jar!,:e
amelunt" of !,:ravel. sand, and silt may be
tranaporkd by water flowin!,: ata rate elf 5-7
feet per second. Waterflowinl<atabout2fe~t
per second or less wiil deposit ~and. silt, and
other d~bris.

Fifth Street bridges and the residential area
near Ri,'ersidePark would bethrea~ned by
the high flows of the Colorado River.
Floodflows can back into the Connecticut
Lakes area to the south of the river. as well as
into the lower reach of No Thelroughfare
Canyon, The higher flo~ on the Gunnison
River would flood agricultural areas
upstream from the mouth.

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11

Lewis Wash flocdnows would remain
immediate!)' adjacent to the channel
throughout its length. Flooding along Horizon
Drive Channel would closely parallel the
streamway. Leach C~k floodwater would
remain close to thechanneluntilabllut2,OOO
feet nelrth of U.S. Highway 6.50 where it
would spread easterly about 500 feet and
conlinuesoutherlyuntilpondingagainslthe
embankments of U.S. Highway 6.50 and the
Denyer and Rio Grande Western Railroad.
There wOllld be much sheet flow flooding on
both streams. Horizon Drive Channel sheet
flow would begin northwest of the in~rSC(tion
of 26 Road and F Road and conlinuewcsterly
adjacent to F Road in ll. narrow band about
1.300 feet long. Aboul 500 feet west of the
intersection,sheetflowwouldfanoutsouthof
FRoad foraboul 800 feet and extend to 25.l!,
Road, On Leach Creek, two small areas of
sheet flow would occur southeast of the
intersection of G and 25 Roads, and the

intersection of Gand24'l!,Road$. Floodwalers
would spread 0111 about 1,300 feet to the
southwest from G and 24.\j; Roads and extend
we;terly to 24 Road where they would turn
south along the east side of 24 Road in a
floodpath about 500 feet wide and 2.000 feet
long. North of U.S. Bighway6-50. floodwaters
would extend westerly ina path aboul2,OOO
feet long and SOO fect wide,
The 100-year noot! would inundate about
3.;00 acr<lS, of which about 2,300 aCres are
agricultural or open lands, 700 acres are
urbani~ed, 100 acres are rural residential,
lLnd 600 acres are streamway. The 500.year
flood would generlLlIj.follow the same pattern
llSthe lOO.year flood on the Colorado and
Gunnison Rivers and Lewis Wash. but would
be 50mewhalwider and deeper. Along Leach
Creek and Horizon DriveChannel,Jargelueas
of sheel flow and ponding would occur at
variouslelcationsduringa500-yearflood.

FLOOD DAMAGE',S

The major nood losses resulting from a 100.
or500-yearflood would comprise residential
and commercial danlage in Grand Junction
ami auhurban areM; agricultural damage;
and damage to bridges, culverts, railroad
embankment, !'(lads, andstreels.Residential
lo:;scswould inc1udedam"getofollndatiuns,
lower floors, walls, furnishings, appliances,
and lawns and gardens. Commercial loo;~
would include structural and equipment
damage,lossofinventory.andtcmporaryloss
of business. Agricultural losses would consist
of loss of crops, erooion, and costs of
rehabiliutingfields covered with debris and
silt. Streets and roads subject to inundation

could be damaged and made inaccessible for
extended Jl-eriods. Bridges and culverts could
be damaged or d,'stroyed. Strcambanks.
ehannel islands, and agricultural landsweluld
be subject to erosion. Flood fighting and
repair and restoration costs would bcexlen.
s"...
Damage would be greater during a 500-
year flood than during a lOO'yearflood due to
awiderfloodplain,grea~rdepthofflooding,
and higher velocit~' of flow.
The depth of flow in the various channels
and adjaeent flooded areas (excludingshect
flow areas) can be determined from the water
surface prolilesshown on Plates 58.74.