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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INTRODUCTION

A.

STUDY AUTHORIZATION AND PARTICIPATION

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 (DF A
0055) watersheds. The study area is shown in Figure 1-1. A map showing the jurisdictional
boundaries within the area can be found in Map 5 of 24 in Appendix C ofthis report. Specific
project tasks for this study were performed in accordance with UOFCD Agreement Number 99-
03.09.

The overall study is divided into three components. The first eomponent (Phase I) discusses the
hydrological, hydraulic, and alternative evaluation aspects of the study. The Phase 1 report was
finalized on November 2000 (Reference 22). The second part (phase II) covers the preliminary
design of the selected alternative. This report is being prepared to complete the Phase Hcomponent
of the study. The final component is the Flood Hazard Area Delineation, which was submitted
September 2001 (Reference 23). In addition, the Hydrology Report (Reference 24), summarized in
this report, was finalized on February 2000.

Representatives of the project sponsors reviewed the progress of the study on a routine basis and
provided input and guidance throughout the study. The list of lead representatives is presented in the
Acknowledgements section at the front of this report.

PURPOSE AND OBJECTIVES

An Outfall Systems Master Plan (master plan) was prepared for First Creek and DFA 0055 in 1990
by Wright Water Engineers. In 1998, MartinIMartin revised the master plan in the Gateway area
from Picadilly Road to Buckley Road. The revised master plan proposed several smaller detention
basins in the Gateway area, in lieu of the Bald Eagle detention pond that was proposed in the
original master plan.

The purpose of this study is to update the master plan for the Lower First Creek watershed to reflect
anticipated development and to factor in the master plan revision that has been adopted upstream of
Pena Boulevard. Additionally, the intermediate goals that are required to complete the update are: to
analyze the existing and future drainage patterns in the lower First Creek watershed; identify
drainage problems; develop and evaluate alternatives to alleviate the problems; and prepare a
preliminary design for the alternative selected by the project sponsors.

The general scope of the Outfall Systems Planning Phase II part of the study is as follows:

1. Evaluate the alternative selected by the sponsors.

D.

2.

Update the hydrologic and hydraulic aspects of the drainage area to reflect the drainage
improvements selected by the project sponsors.

3.

Prepare a preliminary design of the selected drainage improvements including plans, profiles,
and details of said improvements.

4.

Prepare a detailed cost estimate for the selected drainage improvements.

5.

Provide a discussion on prioritization of the selected drainage improvements.

6.

Present in a written Phase II report, a summary of the study's analysis, discussions, results
and the improvements selected to address the drainage problems identified in the Phase 1
report.

C.

ACKNOWLEDGEMENT OF DESIGN CRITERIA

The Outfall Systems Planning and Flood Hazard Area Delineation were performed according to the
terms of the contract and the guidelines and criteria set forth in the Urban Storm Drainage Criteria
Manual (UDSDCM) (Reference 4). The storm drainage design and technical criteria of the various
project sponsors were also utilized.

A number ofUOFCD hydrologic evaluations have been completed for the First Creek watershed.
TC&B used these evaluations as the foundation to develop a complete hydrologic model for the
watershed. The previous evaluations were reviewed and the appropriate Colorado Urban
Hydrograph Procedure (CUHP) and Urban Drainage Stormwater Management Model (UDSWM)
computer models were obtained. TC&B used these models to develop the hydrology for the lower
First Creek watershed.

PROJECT HISTORY AND CORRESPONDENCE

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 project advisory committee was formed at the onset of the study. 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
District, 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.

A summary of the project meetings held during the Phase I part of the study was included in the
Alternatives Report (Reference 22). There were a total of five (5) progress meetings held after the

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