FLOOD03713

• Designation Number: 173
• County: Boulder
• Community: Longmont
• Stream Name: Dry Creek No. 1
• Basin: South Platte
• Title: Floodplain Information, Flood Control and Drainage Plan - Dry Creek Number 1
• Date: 4/1/1980
• Designation Date: 2/1/1981
• Floodplain - Doc Type: Floodplain Report/Masterplan

TABLE-2
DRY CREEK NO. 1 DRAINAGE AREAS

Street. Figure-Ion page 3 more accurately defines the U..its of the
floodplain study. A total of 7.7 stream miles Were included in thc study,

Steele Lakes at 75th Street
Clover Basin at 75th Street

2.47
3.20

I
I
,
I
I
,

The ~aln Ory Cre~k No.1 channel SerVeS primarily as a waste channel
for surplus irrigation water. Base flows from this SOurCe are typically
5 to 20 cubic feet per second throughout the irrigation season. The
channel is relatively small with a bottom width of appro~imately 4 to 12
feet. Typical channel depths are J to 4 feet to the top of the defined
bank, The overbank or floodplain areas consist pri..arily of pasture and
cultivated land upstream from Hover Road. Urbanization is occurring
rapidly downstream from Hover Road, resulting in a much mOre confined
channel section. Photographs of typical conditions along the study reach,
tahn during August and October, are included on Pages17through 19.

LOCATIO:.

DRAINAGE AREA
(sqllaremiles)

Tributaries:

Dry Creek No.1,
75th Street
Below Clover Basin confluence
89th Street
95th Street (Hover Road)

Bowens Street

3.91
10.02
11.49
11.86
D.43
13.91
14.13
14.15

Road crossings are the primary obstruction to flood flows. Existing
culverts and bridges are too small to tonvey the lOO-year flood at almost
all crossings. The damming effects of the roads cause water to be
dlverted from its normal courSe at several locations in the study reach.
The effects of these obstructions are explained in the hydraulic analysis
portion of this study.

S.H.1l9

l07th Street (5. H. 287)
Mouth

Basin vegetation consists primarily of irrigated grass pasture and
agriclIltural land in the upper reaches. Approximately sixty percent of
the basin is irrigated presently. Typical crops in the lower basin are
cornand.ugarbeets.

C. Climate

B. Study Reach Descriptions

Official Weather Bureau monitoring stations are operating at BOlllder
and at Longmont. Over seventy years of weather records are available for
each station. The Longment station was considered most representative of
conditions in the Dry Creek No. 1 basin and data from the. station was
used to present the following general climate description.

The study reach for Dry Creek No.1 extends from 75th Street downstream
to tile eonUuencewlth St. VrsinCreel<. The Steele Lakcs tributary and the
Clover Basin tributary were also studied in the reaches downstr~a~ from 7Slh

The average annual precipitation at Longment is only 12.g inches.
However, the potential for excessive rainfall frOm a single thunderstorm
is relatively hl~h along the front Runge area. The greatest precipitation

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