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FLOOD04241
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Last modified
1/25/2010 6:45:42 PM
Creation date
10/5/2006 12:27:46 AM
Metadata
Fields
Template:
Floodplain Documents
County
Broomfield
Community
Broomfield
Stream Name
Nissen Res., City Park, Gay Res., West Lake Basins
Basin
South Platte
Title
Flood Hazard Area Delineation
Date
6/1/1979
Prepared For
UDFCD
Prepared By
Wright-McLaughlin Engineers
Contract/PO #
&&
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />Development in this area is presently confined to the mobile home park and <br /> <br /> <br />the nursery, although the City Park Basin, which interfaces the study basin <br /> <br /> <br />in this area, contains some industrial and commercial establ ishments nearby <br /> <br /> <br />along 120th Avenue, Construction plans have been prepared for the area <br /> <br /> <br />abutting the waste ponds south of the mobile home park and west of Perry <br /> <br /> <br />Street. An open channel with 100-year capacity has been designed to convey <br /> <br /> <br />flows to Perry Street; however, major flows can split upstream of the waste <br /> <br /> <br />ponds and flow across the ponds to overtop the embankment at the southeast <br /> <br /> <br />corner, thus circumvent i ng the proposed channe 1. In add it ion, sha llow <br /> <br />overbank flows from the City Park Basin enter the area from the west, <br /> <br /> <br />Other flows can overtop the mobile home park berm at the initial 90-degree <br /> <br /> <br />bend (Sheet 17) affecting those structures bordering the channel, <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />Between Perry Street and Lowell Boulevard (Sheet 18) major flows spread <br /> <br /> <br />out to partially inundate a drive-in-theater and then combine with flow <br /> <br /> <br />from the City Park Basin, The culverts at both Perry Street and Lowell <br /> <br /> <br />Boulevard are undersized, having less than a 2-year flow capacity, <br /> <br />I <br /> <br />I <br /> <br />I <br />I <br /> <br />The basin downstream of Lowell Boulevard (Sheet 19) lies entirely within <br /> <br /> <br />the City of Westminster and the immediate tributary area is undeveloped <br /> <br /> <br />at present, Major flows overtop the embankments of two existing ponds <br /> <br /> <br />and affect a few agricultural out-buildings before reaching Big Dry Creek, <br /> <br /> <br />Because of the steep basin and channel slopes, Big Dry Creek has little or <br /> <br />no backwater effect on the lJissen Reservoir Basin, <br /> <br />I <br /> <br />I <br /> <br />WINDMILL BASIN <br /> <br />I <br /> <br />There is no defined channel in the Windmill Basin and the topography is <br /> <br /> <br />extremely flat, as shown on Sheets 20 and 21, The 100-year flood flow <br /> <br /> <br />crosses Lowell Boulevard and is split by the irrigation ditch embankment, <br /> <br /> <br />Approximately 120 cfs flows to the south of' the irrigation ditch and rejoins <br /> <br /> <br />the main flow east of the windmill, The major flow proceeds eastward to the <br /> <br /> <br />sewage plant access road where the road is inundated along its lowest area. <br /> <br /> <br />The access road serves to spl it flows once again and approximate,ly half of <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />22 <br /> <br />the IOO-year discharge flows north of the road and the remainder flows along <br /> <br /> <br />the south side, The north flow proceeds east and partially inundates the <br /> <br /> <br />treatment plant before entering Big Dry Creek, The south flow enters <br /> <br /> <br />Big Dry Creek at a point south of the sewage treatment plant, <br /> <br />GAY RESERVOIR BASIN <br /> <br />The study of the Gay Reservoir Basin begins where the 100-year discharge <br /> <br /> <br />enters an agricultural pond just east of Sheridan Boulevard and south of <br /> <br /> <br />Carbon Road (Sheet 23), Flow overtops the pond embankment and proceeds <br /> <br /> <br />along a mild swale southeast to a point where it joins with a tributary <br /> <br /> <br />entering from the west (Sheet 24), The flat topography causes flood flow <br /> <br /> <br />to spread out in a wide floodplain, West tributary flow overtops a farm <br /> <br /> <br />pond east of Sheridan Boulevard and continues east in a well defined swale, <br /> <br />The combined flow of both tributaries (1,050 cfs) enters Gay Reservoir <br /> <br /> <br />(Sheet 25) and overflows to the east toward Lowell Boulevard, while a small <br /> <br /> <br />flow (< 10 cfs) exits via the south spillway. Approximately half of the <br /> <br /> <br />outflow (520 cfs) overtops Lowell Boulevard and flows southeast in a wide <br /> <br /> <br />shallow floodplain. The remaining flow (530 cfs) is directed toward the <br /> <br />intersection of Lowell Boulevard and West 128th Avenue (Sheet 26) where <br /> <br /> <br />it crosses the road and flows eastward, although a small amount of flow <br /> <br />is directed south along the ditches adjacent to Lowell Boulevard, <br /> <br />The total flow north and south of West 128th Avenue combines with flow from <br />the West Lake drainage basin at a point adjacent to the mobile home community <br />(Sheet 27), The combined flow of both drainage basins (1,820 cfs) continues <br />across the existing agricultural land and overtops a small farm pond before <br />entering Big Dry Creek (Sheet 28), <br /> <br />WEST LAKE BASIN <br /> <br />The West Lake Basin has two tributaries that combine at the lake, The <br /> <br /> <br />northernmost tributary flows eastward along Carbon Road, which effectively <br /> <br /> <br />limits the amount of flow reaching the lake, Flows to the north of Carbon <br /> <br /> <br />Road are unable to flow southward, thus only that flow which is to the south <br /> <br />
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