FLOOD04416

• Designation Number: 304
• County: Adams
• Community: Unincorporated Adams County
• Stream Name: Big Dry Creek, (ADCO), North area tributaries
• Basin: South Platte
• Title: Flood Hazard Area Delineation - Big Dry Creek, ADCO, North Area Tributaries
• Date: 7/1/1989
• Designation Date: 1/1/1990
• Floodplain - Doc Type: Floodplain Report/Masterplan

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SECTION II
STUDY AREA DESCRIPTION

The Union Pacific Railroad (UPRR) bisects the basin. The creek also
crosses two irrigation ditches, the Signal Ditch and the German Ditch.
The Signal Ditch is located in the headwater region and the German
Ditch crosses Wadley South Creek approximately 2,000 feet upstream from
its confluence with Big Dry Creek. The dilch crossings are nearly at
grade. Wadley Farms No. 2 irrigation reservoir is located on the main
channel a short distance upstream from the UPRR crossing.

A. INTRODUCTION
The drainage area for the project, shown on Figure II-I, was defined by
the contract and consists of the drainage basins tributary to Big Dry
Creek between 144th Avenue on the south and 168th Avenue (Baseline
Road) on the north. These basins drain an area of 18.7 square miles.
Nine tributary streams are included in this area, as shown in Figure
II-I. The drainage basins for each of the tributaries are described
individually in the following section.

Portions of the drainage area lie within the corporate limits of the
City of Broomfield, the City of Westminster, Adams County, and Weld
County. The portion of the basin within Weld County, north of 168th
Avenue, was included in the hydrologic analysis to define downstream
impacts on Adams County. However, floodplain delineation within Weld
County was excluded from Ihe scope of work.

Wadley NOJih Creek
This tributary is immediately north of the Wadley South Creek watershed
and drains an area of approximately 0.9 square miles. The main channel
is I. 9 miles in length with a typical slope of 1.5 to 3 percent. The
flow direction is 10 the nOJihwesl and closely parallels Wadley South
Creek. Much of the land in this basin is cultivated and the stream
channel is poorly detlned or absent in most reaches.

The UPRR and German Ditch
ponds - Wadley Reservoirs Nos.

cross Wadley North Creek. Two
and 3 - are also present in the basin.

irrigation

Wadley South Creek
The Wadley South Creek watershed lies in the southeastern portion of
the study area and drains approximately 0.9 square miles. The channel
is approximately 2.4 miles in length and slopes towards Big Dry Creek
at grades of 1.5 to 3 percent. Most of this basin is cultivated and
the stream channel is poorly defined or absent in much of the area.

Short Run
Short Run is the middle tributary of the five streams which are right
bank tributaries to Big Dry Creek. The drainage area of Short Run is
approximately 0.9 square miles with a main channel length of 1.5 miles.
This stream channel IS also relatively steep in that channel slopes
range from 1.3 percent to 3 percent. Although much of the basin is
devoted to agricultural use, the main channel IS usually located be-
tween cultivated areas and is better defined than the tributary streams
to the south.

B. TRIBUTARY DRAINAGE BASINS
The Union Pacific Railroad (UPRR) and Interstate 25 (I~25) embankments
at the crossings of the tributaries create areas of significant inad-
vertent detention; however, these detention areas were not included in
the hydrologic analysis.

The German Ditch and UPRR cross ShOJi Run with the UPRR bisecting the
basin.

II-I

11-2