FLOOD01374

• Designation Number: 521
• County: Weld
• Community: Erie, Firestone, Dacono
• Stream Name: Tri-town drainageway, Godding Hollow Basin
• Title: South Weld I-25 Corridor Master Drainage Plan
• Date: 9/8/1999
• Prepared For: Weld County
• Prepared By: Anderson Consulting Engineers, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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drainage channel exists through portions of the basin. Several reaches of the major drainage path
~ave been altered by man-made activities, These activities include levee construction,'
channelization, urban development (buildings and streets), and modifications resulting from
farming and ranching operations. In general, stormwater runoff generated within the basin flows
into the Tri-Town Drainageway and is conveyed in a northerly direction toward the Saint Vrain
River.

The major drainageway for the Tri- Town Basin originates in the vicinity of the City of
Dacono. Stormwater runoff generated south of Dacono is combined with runoff from the
urbanized area and through the residential streets, ultimately concentrating east of the Birch
Street/8th Street intersection. At this location, stormwater runoff is conveyed across 8th Street and
State Highway 52 via a cluster of corrugated metal pipes (CMPs), typically less than 4 feet in
diameter. A channel/drainage swale conveys stormwater northward across an open field to a man-
made channel/berm which directs the runoff in a channel located west of the Towns of Frederick
and Firestone. The channel can be typically described as trapezoidal in configuration, bottom,
widths vary from four feet to six feet, maximum channel depth ranges from six to twelve feet with
IH: I V sideslopes, This channel conveys runoff west along the south side of the Town of
Frederick and beneath Main Street in a 6'H x 8'W reinforced concrete box (RCB) culvert. The
outlet of the Main Street culvert directs the flow contained in the channel north toward WCR 16
where the major drainageway conveys the runoff via a 6'H x 10'W RCB, The channel continues
north for approximately one mile along the west side of the Town of Firestone. Near Firestone,
the main channel alignment makes three sharp bends, crossing over the Coalridge Ditch siphon
and cutting through the abandoned railroad embankment prior to crossing WCR 13 through a 50-
foot wide steel and concrete bridge, Immediately after crossing WCR 13, the channel crosses
under WCR 18 through a 17.5-foot steel and timber bridge, Just prior to crossing WCR 20,
stormwater runoff conveyed in the major drainageway converges with flow released from the Weld
County Tri-Area Sanitation District sewage treatment outfall. From this location, the main
channel continues northward approximately one mile where it crosses a lateral from the Godding
Ditch before it traverses the Greggerson Dairy to WCR 24 in a series of open ditches and closed
conduits, The major drainageway is then carried by the Biederman Ditch north and east to its
confluence with the Last Chance Ditch, approximately three-quarters of a mile north of WCR 24,
During large flood events, Tri- Town Basin runoff will overflow the Biederman Ditch and combine
with out of bank Godding Hollow Basin runoff and proceed over land to the Saint Vrain River,
In summary, the major drainageway crosses one abandoned railroad embankment, seven county
and/or state roads, two canals, and numerous other minor roads and utilities,
Minor erosion of the major drainageway is evident at several locations; this erosion is
frequently associated with livestock watering and access. Erosion is also visible at several road

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Sepreml:Jt:r 8, 1999