Fairfax Tributaries Outfall Systems Plan (OSP)

The Fairfax Tributaries watershed is approximately 11 square miles and predominantly located in Commerce City with small portions in unincorporated Adams County, and the City and County of Denver. Significant urbanization of the watershed has occurred over the last few decades; the watershed is mostly developed and is a combination of commercial, industrial, and residential land uses. A portion of the watershed north of 72nd Avenue was studied by the Mile High Flood District in 1986 and no watershed level studies have been conducted thereafter.

The watershed has no regulatory floodplains within its limits and no discernable major drainageway.  However, the paved over drainageways in the watershed include undersized storm drains with significant overland/street flow leading to frequent shallow flooding. The watershed is in proximity to South Platte River and is bounded by South Platte River to the West, Sand Creek watershed to the South, and Irondale Gulch watershed to the East. The watershed has regional detention facilities including Fairfax Park and Dahlia Pond which attenuate some flows from the upstream sub-watersheds. There are various private best management practices (BMPs) throughout the watershed.

The primary goals of this Outfall Systems Plan (OSP) project are to perform a hydrologic analysis, identify existing drainage issues and non-regulatory flood hazards, develop alternatives and recommendations for stormwater infrastructure improvements for identified issues, and prepare conceptual level design and cost estimates for selected alternatives.

Work is expected to be completed by 3/18/2024.  The following deliverables are scheduled:

• Baseline Hydrology Report
• Alternative Analysis
• Concept Design Report

The anticipated schedule is shown below:

• Identify localized, non-regulatory flooding.
• Identify how drainage improvements completed since the 1980 Major Basin wide Planning have impacted drainage patterns.
• Identify and define direct flow areas (DFAs).
• Determine if the existing infrastructure has capacity for the 100-year event.
• Identify capital improvements to reduce flood hazards.

• Evaluate flood history in the watershed.
• Define design hydrology.
• Define current non-regulatory flood hazards.
• Identify flow capacity limits.
• Identify water quality opportunities.
• Integrate useable open space, trails, landscape improvements, natural areas, and water quality into stormwater management.
• Complete an Alternatives Analysis for outfall systems planning (OSP).
• Include public input regarding capital improvements in the watershed.
• Develop a Conceptual Design for the selected alternatives plan.

Drainage Outfall Systems Planning: Northern Commerce City and Irondale Area, McLaughlin Water Engineers, Ltd. April 1986.

Fairfax Park Drainage and Irrigation Improvements, Commerce City, Colorado, SEH, July 2008.

City and County of Denver Storm Drainage Master Plan, September 2014.

Drainage Outfall Systems Update: Northern Commerce City and Irondale Area, Icon Engineering, Inc. June 2017.

City and County of Denver Storm Drainage Master Plan, October 2019.

Final Drainage Report: Mile High Greyhound Park Commerce City, Colorado, Kimley Horn, May 2020.

Below is an interactive map of the project area. Click on the blue button in the upper left hand corner of the map to open the Map Layers, where each layer can be toggled on/off using the eye icon. The blue button to the right of that is the Legend, where the symbology of each visible layer is displayed.

A Technical Advisory Committee made up of the project sponsors and other stakeholders and agencies provided guidance during the study process. The Technical Advisory Committee met regularly during the project study.  Additional agencies and individuals were also involved during the planning process. Representatives who were directly involved with this study are listed below:

We need your input to develop the plan that best addresses community needs. If you would like to share storm drainage problems that you have observed within the project area or any solutions to solve them, please contact us. Also, if you would like to be invited to public meetings regarding this project, just let us know.

Please contact:

Pranay Sanadhya, P.E. Matrix Design Group, Inc. 707 17th Street, Suite 3150 Denver, CO 80202 Phone: (303) 226-7860 Email:  Pranay.Sanadhya@matrixdesigngroup.com