FLOOD02883

• Designation Number: 266
• County: Broomfield
• Community: Broomfield
• Stream Name: Quail Creek & Tributaries & McKay Lake Basin
• Basin: South Platte
• Title: Flood Hazard Area Delineation - Quail Creek and Tributaries and McKay Lake Basin, Broomfield, Westminster
• Date: 7/1/1986
• Designation Date: 11/1/1986
• Floodplain - Doc Type: Floodplain Report/Masterplan

The study area for the McKay Lake basin begins just upstream of West l44th Avenue
and extends to the confluence of Big Dry Creek, a distance of about two miles,

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

BASIN DESCRIPTION

some flow is diverted south to Big Dry Creek along the east and west sides of the
Interstate-25 embankment. The small basin downstream of 1-25 drains to the
existing ditch along West 136th Avenue, which outfalls to Big Dry Creek,

Quail Creek
The Quail Creek basin generally drains to the north and south, at slopes ranging
from 1.0 to 5.0 percent, to Quail Creek which flows in an easterly direction.
The bas i n is bounded on the west and north by the Rock Creek and McKay Lake
basins, respectively, and on the south by Gay Reservoir, West Lake, and Big Dry
Creek basins (see Figure 1). The Quail Creek basin encompasses approximately
3,400 acres of drainage area, with elevations ranging from 5420 at its headwaters
near South 120th Street, to 5150 at the confluence with Big Dry Creek. There are
four small tributaries entering Quail Creek along the study reach that have been
labeled Tributaries A, B, C, and D.

The majority of the upper basin above West 136th Avenue is undeveloped agricul tural
land with the exception of the Sunny Side Estates development west of Lowell
Boulevard. Quail Creek is generally in its natural state through this portion of
the basin, except where the stream has been danmed for irrigation ponds, and
at street and ditch crossings. The stream falls at slopes ranging from 3.0 to
0.5 percent.

McKay Lake
The McKay Lake watershed covers an area of 2.8 square miles and has its confluence
with Big Dry Creek approximately one-quarter mile north of East 136th Avenue. The
headwaters of the McKay Lake basin originate at Lowell Boulevard at an elevation
of about 5460 feet. From its origin, the main drainageway runs generally southeast
and passes into McKay Lake, an irrigation reservoir which covers an area of
approximately 130 acres. At this point, the existing drainage channel terminates.
Downstream of McKay Lake, the basin is characterized by gently sloping agricultural
land with only small local drainage ditches paralleling roadways. Under existing
conditions, general flow directions can be identified from evaluation of topo-
graphic mapping. However flow in these pathways will occur primarily as shallow
sheet flow along and through cultivated or fallow agricultural fields.

The lower basin is rapidly approaching full development in the area south of West
136th Avenue and west of Huron Street. This area is characterized by single
family home, and dense mobile home developments. Quail Creek has been altered by
channel modifications for approximately one half mile through the Quail Crossing
Subdivision just west of Huron Street. The improved channel has a capacity of
approximately 650 cfs, but the undersized culvert crossings through the reach
limit the conveyance to approximately 170 cfs. This channel design is insufficient
for the peak flow of some 3700 cfs generated from the Quail Creek Basin at this
point during the 100-year event.

The entire McKay Lake basin is relatively undeveloped with land use being predom-
inantly agriculture. Residential dwellings are scattered throughout the basin on
small acreage lots.

The portion of the basin downstream of Huron Street is narrow with minimum
grades. The divide between the Quail Creek and McKay Lake basins is not well
defined in this area. Many years of cultivation of the land, along with construc-
tion of the Bull Canal and the Interstate Highway, have increased the problem of
identifying the historic drainage basins. A large portion of the Quail Creek
flows are presently lost to the McKay Lake basin above Interstate-25. Additionally,

Interstate-25 crosses the McKay Lake basin approximately 0.6 miles west of its
confluence with Big Dry Creek. There are no existing drainage crossings of 1-25
in the McKay Lake basin, consequently flows will be ponded behind the highway
embankment. In addition to ponding of flows at 1-25 on the McKay Lake basin,
similar conditions are also encountered in the adjoining Quail Creek basin.
Topography upstream of 1-25 is such that flows in the McKay Lake and Quail Creek
basins will be combined as water ponds along the upstream side of the highway
embankment. The hydraulics associated with this condition will be discussed in
more detail in a subsequent section.

2