Project Overview

The Gregory Canyon Creek Flood Mitigation project is dedicated to reducing flood risks, enhancing stream health, and improving public safety in the Gregory Canyon Creek watershed. This comprehensive initiative includes various measures to effectively manage and mitigate flooding, ensuring the safety and resilience of nearby communities. In addition to flood risk reduction, the project aims to preserve the natural environment.

Gregory Canyon Creek originates in City of Boulder Open Space. From the city limits at Flagstaff Road to its confluence with Boulder Creek, Gregory Canyon Creek is approximately 1.8 miles in length and the watershed associated with this creek is approximately 1.9 square miles.

The upper part of the watershed is south of the city limits. Upslope areas are covered with a variety of rock outcroppings, thick residual soils on bedrock, and thicker debris, alluvium, and slope wash deposits that are vegetated with grasses, trees, and shrubs. Deeper soils and wetland vegetation are found on alluvial deposits adjacent to streams. A well-defined channel is visible upstream of Flagstaff Road. The Gregory Canyon trail is located along this section of the creek.

Upcoming and Past Community Engagement Opportunities

Community Meeting

The purpose of the meeting was to update and inform the community about the progress of the Gregory Canyon Creek Flood Mitigation Project.

Phase I

Flood Mitigation - Arapahoe Ave. to Pennsylvania Ave.

The Vision

Make Gregory Canyon Creek a top-tier waterway, where both people and nature coexist, by reducing flood risks, enhancing stream function, and maximizing opportunities to restore features natural to the stream corridor.

How the creek flows

Gregory Canyon Creek originates in City of Boulder Open Space. The upper part of the watershed, located south of city limits, is covered with a variety of rock outcroppings, and vegetated with grasses, trees, and shrubs. From city limits at Flagstaff Road to its confluence with Boulder Creek, the creek is characterized as a narrow steep channel with dense residential development.


  • Protect life and property
  • Reduce the extents of the high hazard zone and 100-year floodplain
  • Provide variable natural features representative of the upstream natural watershed
  • Create resiliency for the future
  • Environmental education opportunities


  • Design to safely convey 10-year storm event without adverse impacts to regulatory 100-year floodplain.
  • Mimic the natural variability of the creek where feasible
  • Develop a unifying aesthetic along the creek corridor
  • Collaborate with the community on the use of the City of Boulder owned properties


  • 2013 Flood
  • Dec 2015 Mitigation plan Approved
  • 2017 Highland Bridge Installation
  • Fall 2023 - Spring 2025 Community Outreach, Design Development, Easement Aquisition (Community meeting/Collaborate with the community on the use of the City of Boulder owned properties)
  • Summer 2025 Construction starts

Project Outcomes

Incorporating natural channel restoration into flood mitigation projects can lead to a more vibrant, sustainable and resilient community and environment.

  • Flood Mitigation: Restored natural channels can absorb excess water during heavy rainfall, reducing the risk of flooding in neighborhoods.
  • Property Protection: Stabilized stream banks help prevent erosion, and protect homes and infrastructures located near streams.
  • Improved Water Quality: Natural channel restoration filters out pollutants and sediments, leading to cleaner water.
  • Educational Programs: These projects can serve as educational tools, promoting awareness about watershed health.
  • Community Engagement: Natural channel restoration projects offer opportunities for community members to get involved through volunteer efforts, workshops, and collaborative planning.
  • Climate Resilience: Restored natural channels are better equipped to handle impacts from climate change, providing a more resilient buffer against extreme weather events.
  • Wildlife Habitat: Restoring natural habitats can create homes for diverse wildlife species, enriching the local ecosystem and offering opportunities for wildlife observation.

Nature-Based Design

The city strives to help protect people, places, property, and ecosystems in a way that builds resilience and is consistent with community values.

The City of Boulder is partnering with the Mile High Flood District on the design of flood mitigation improvements for Gregory Canyon Creek between Arapahoe Avenue and Pennsylvania Avenue. In January of 2021, Jacobs Engineering completed the preliminary design.

The project includes new channel and roadway culvert structures. In order to build a larger channel and culverts, existing utilities in the area will need to be relocated, including the sanitary sewer and water distribution systems.

As part of the design process, a new flood risk analysis is being completed using updated topography and floodplain modeling techniques. A construction phasing plan is also being developed. Funding for construction is currently proposed in the city's 2023 Capital Improvement Program.

The Gregory Canyon Creek Arapahoe Ave. to Pennsylvania Ave. flood mitigation project has completed the Preliminary Design Drawings. Prior to advancing to Final Design, the project team would like to meet with property owners and residents to answer questions and discuss property acquisition needs.

Next Steps

The project team would like to meet with interested property owners and residents in the area. The project team anticipates reaching out to affected property owners between Fall 2021 and Spring 2025 to arrange individual meetings, conduct community outreach, progress through design development, and initiate easement acquisition. Construction is expected to commence around Summer 2025. Stay tuned for further updates and opportunities to get involved.

Frequently Asked Questions

What is an Easement? An easement allows the city use of a defined portion of your property for a specific purpose - in this case, construction of flood channel improvements and ongoing maintenance. Many properties have existing easements for maintenance of power, water, internet and other utilities. An easement does not transfer title to the land, and property owners retain ownership of the easement area. The size of the easement depends on the final project design. The Gregory Canyon Creek project will require both permanent and temporary easements along the creek. The temporary easement area is needed during construction and then expires, and the permanent easement will allow the city ongoing future access to maintain the improved floodway.

Will I be compensated for giving and easement? Yes. The city follows federal guidelines for acquiring easements and emphasizes respect for the property owner. Our goal is to fairly compensate property owners for easement interests by working with professional appraisers and through individual negotiations with property owners. The city covers the costs of property appraisals and discloses this information as part of the negotiation process.

What is eminent domain? Property owners often ask about eminent domain when discussing easements. In the rare case in which property owners and the city cannot reach a voluntary negotiated agreement eminent domain allows the city to order an easement on private property for just compensation. While it is a tool available to governments, the city has been successful in negotiating flood mitigation easements voluntarily with property owners and has not had to use it.

Will the floodplain be officially reevaluated by FEMA after the project is completed? Will this affect flood insurance? FEMA will officially re-evaluate the regulatory floodplain after the mitigation project is complete through a process called the Letter of Map Revision (LOMR). Some properties in the existing floodplain may experience improvements to their flood insurance after this review by FEMA is complete.

Will Pennsylvania Avenue be open to Flatirons Elementary School traffic? While the exact traffic impacts aren’t known yet, the team will make every effort to minimize traffic disruptions during construction and prioritize access to critical facilities, such as schools.

How can we provide our lived experience to inform the design? We want to hear community members’ experiences and know that hearing people’s stories enriches the project overall. Many of us lived through the 2013 flood ourselves and have heard community testimony of what people went through. We’d be happy to meet with people or receive emails about their experiences at

About the purchased property at 810 Marine Street, how will the area be maintained/managed? How will the nearby encampments be addressed? The future of the city-owned properties is one of the primary things that community input can shape as this project goes forward. Because of the drainage characteristics, there really aren’t a lot of options for flood protection besides doing some type of channel enhancements. But the purchased properties have more flexibility and are an area where the community can help us understand the associated desires and concerns. Regarding encampments specifically, the city’s Safe and Managed Spaces Program (SAMPS) focuses on addressing the impacts of unsanctioned camping in public spaces. More information on the SAMPS program.