FLOOD10152

• County: Boulder
• County: Adams
• County: Jefferson
• Community: Broomfield, Westminster
• Stream Name: Big Dry Creek Tributaries
• Basin: South Platte
• Title: FHAD - Broomfield Area
• Date: 6/1/1979
• Prepared For: Broomfield, Westminster
• Prepared By: UDFCD
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Development in this area is presently confined to the "~bile home park and

the nursery, although the City Park Basin, which interfaces the study basin

in this area, contains some industrial and commercial establishments nearby

along 120th Avenue. Construction plans have been prepared for the area

abutting the waste ponds south of the mobile home park and west of Perry

Street, An open channel with 100-year capacity has been designed to convey

flows to Perry Street; however, major flows can split upstream of the waste

ponds and flow across the ponds to overtop the embankment at the southeast

corner, thus circumventing the proposed channel. In addition, shallow

overbank flows from the City Park Basin enter the area from the west,

Other flows can overtop the mobile home park berm at the initial 90-degree

bend (Sheet 17) affecting those structures bordering the channel.

the IOO-year discharge flows north of the road and the remainder flows along

the south side, The north flow proceeds east and partially inundates the

treatment plant before entering Big Dry Creek. The south flow enters

Big Dry Creek at a point south of the sewage treatment plant,

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GAY RESERVOIR BASIN

The study of the Gay Reservoir Basin begins where the 100-year discharge

enters an agricultural pond just east of Sheridan Boulevard and south of

Carbon Road (Sheet 23). Flow overtops the pond embankment and proceeds

along a mild swale southeast to a point where it joins with a tributary

entering from the west (Sheet 24). The flat topography causes flood flow

to spread out in a wide floodplain. West tributary flow overtops a farm

pond east of Sheridan Boulevard and continues east in a well defined swale.

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Between Perry Street and Lowell Boulevard (Sheet 18) major flows spread

out to partially inundate a drive-in-theater and then combine with flow

from the City Park Basin. The culverts at both Perry Street and Lowell

Boulevard are undersized, having less than a 2-year flow capacity,

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The basin downstream of Lowell Boulevard (Sheet 19) lies entirely within

the City of Westminster and the immediate tributary area is undeveloped

at present. Major flows overtop the embankments of two existing ponds

and affect a few agricultural out-buildings before reaching Big Dry Creek.

Because of the steep basin and channel slopes, Big Dry Creek has little or

no backwater effect on the tJissen Reservoir Basin,

The combined flow of both tributaries (1,050 cfs) enters Gay Reservoir

(Sheet 25) and overflows to the east toward Lowell Boulevard, while a small

flow (< 10 cfs) exits via the south spillway. Approximately half of the

outflow (520 cfs) overtops Lowell Boulevard and flows southeast in a wide

shallow floodplain. The remaining flow (530 cfs) is directed toward the

intersection of Lowell Boulevard and West 128th Avenue (Sheet 26) where

it crosses the road and flows eastward, although a small amount of flow

is directed south along the ditches adjacent to Lowell Boulevard.

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There is no defined channel in the Windmill Basin and the topography is

extremely flat, as shown on Sheets 20 and 21, The 100-year flood flow

crosses Lowell Boulevard and is split by the irrigation ditch embankment.

Approximately 120 cfs flows to the south of the irrigation ditch and rejoins

the main flow east of the windmill, The major flow proceeds eastward to the

sewage plant access road where the road is inundated along its lowest area,

The access road serves to spl it flows once again and approximately half of

The total flow north and south of West 128th Avenue combines with flow from

the West Lake drainage basin at a point adjacent to the mobile home community

(Sheet 27), The combined flow of both drainage basins (1,820 cfs) continues

across the existing agricultural land and overtops a small farm pond before

entering Big Dry Creek (Sheet 28).

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WINDMILL BASIN

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WEST LAKE BASltJ

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The West Lake Basin has two tributaries that combine at the lake, The

northernmost tributary flows eastward along Carbon Road, which effectively

limits the amount of flow reaching the lake, Flows to the north of Carbon

Road are unable to flow southward, thus only that flow which is to the south

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