FLOOD02900

• County: Adams
• Community: Commerce City
• Basin: South Platte
• Title: Lower First Creek and Direct Flow Area 0055 Major Drainageway Planning
• Date: 5/1/2002
• Prepared For: UDFDC
• Prepared By: Turner Collie & Braden Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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OUTFALL SYSTEMS PLANNING

The total First Creek watershed drains an area of 47.2 square miles. Its headwaters are
located in Arapahoe County, south of Interstate 70 (1-70) and east of E-470. Runoff from the
watershed flows in a northwesterly direction crossing Pena Boulevard just north of 56th Avenue and
then erosses through the northeastern portion of the RMA before crossing 96th Avenue at the
upstream limit of the study area. First Creek is a right-bank tributary of the South Platte River and
outfalls into the river at approximately 1 lOth Avenue. The average stream slope upstream ofRMA is
about 31 feet per mile, dropping to about 26 feet per mile downstream of Roeky Mountain Arsenal
(RMA) (Referenee 1).

LOWER FIRST CREEK and DIRECT FLOW AREA 0055

PRELIMINARY DESIGN AND FINAL REPORT

EXECUTIVE SUMMARY

DF A 0055 is a tributary watershed to lower First Creek. DF A 0055 did not originally have a
defined channel, however, several small channels have been constructed as the watershed began to
develop. These channels are Arsenal North Drainage, Rolla Tributary, Union Pacific Tributary, Elm
Drainage and Birch Run.

The Urban Drainage and Flood Control District (UDFCD), in joint sponsorship with Adams
County and Commerce City, contracted with Turner Collie & Braden Inc. (TC&B) for engineering
services for an Outfall Systems Planning Study for the Lower First Creek and Direct Flow Area
0055 (OF A 0055) watersheds. Specific project tasks for this study were performed in accordance
with UDFCD Agreement Nurnber 99-03.09.

The lower First Creek watershed is the study area and is located downstream from Pena
Boulevard and continues to the South Platte River. The study area is shown in Figure E-l. The
Lower First Creek watershed consists of irrigated farmland with pockets of light industrial and
residential properties. The existing land use for the First Creek watershed was identified using
Landiscor Aerial Photographs taken in 1998/1999 (Reference 2). Current development projects are
underway in the area. These developments, as well as anticipated future developments will affect
the drainage characteristics of the Lower First Creek and DFA 0055 watersheds. These issues are
discussed in more detail in the main text of this report.

A project advisory committee was formed at the onset of the study. Project meetings were held to
discuss various aspects of the study, to gather information and guidance from the sponsors, and to
present and discuss results developed during the process of completing the study. A complete listing
of meeting agendas and minutes can be found in Appendix A.

In addition to the project sponsors, the following organizations were notified of the project,
invited to public meetings, and received meeting minutes: Colorado Water Conservation Board,
Federal Emergency Management Agency, Colorado State Land Board, Central Colorado Water
Conservancy Distriet, Colorado Department of Transportation, Henrylyn Irrigation District, North
Front Range Water Quality Planning Association, Soil Conservation Service, Colorado Division of
Wildlife, U.S. Army Corps of Engineers, Colorado Water Quality Control Division, U.S.
Environmental Protection Agency, and Farmers Reservoir and Irrigation Company.

Several types of drainage problems exist along First Creek within the study area. These
problems can be summarized as: flooding created due to a lack of channel capacity; flooding created
upstream of channel crossings with inadequate conveyance facilities resulting in the potential
inundation of property upstream of these crossings; flooding of roads crossing the channel resulting
in traffic interruption and potential danger to drivers; washout of the Fulton Ditch, O'Brian Canal
and Burlington Ditch; and erosion of the channel and bridges.

Channel crossings determined to be inadequate to pass the frequent flood events are:

The purpose of the study is to update the drainageway plan for the Lower First Creek and .
DF A 0055 areas. The overall study is divided into three components:

. (phase I) - The hydrological, hydraulic, and alternative evaluation aspects of the study,
fmalized November 2000 (Reference 22).
. (Phase II) - The preliminary design of the selected alternative. This report is being
prepared to complete the Phase II component of the study.
. (phase Ill) - The Flood Hazard Area Delineation, which was submitted February 2002
(Reference 23).

. Fulton Ditch
. O'Brian Canal
. Burlington Ditch
. US-85
. 1-76
. SH-2
. Union Pacific and Burlington Northern Santa Fe railroads
. 96th Avenue

In addition, the Hydrology Report (Reference 24), summarized in this report, was finalized on
February 2000.

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