Flood Mitigation along Gregory Canyon Creek

Several projects are ongoing along Gregory Canyon Creek.

Project Overview

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.

See below for ongoing and past projects, as well as mapping and mitigation information.

Flood Mitigation - Arapahoe Ave. to Pennsylvania Ave.

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 drawings.

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.

Project Status

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 in September 2021 to schedule individual meetings in October and November 2021.

Past Projects

Highland Bridge Project

In 2017, The City of Boulder completed the construction of a private access bridge to the historic Highland School property. The bridge replaced a 4-foot diameter culvert, increasing the capacity from less than 10 cubic feet per second (CFS) to over 800 CFS.

744 University House Relocation

The city purchased the property at 744 University to help accommodate flood mitigation improvements and remove a structure from the high hazard flood zone, the most dangerous area of the floodplain. The 100-year-old house structure was preserved and moved to Old Town Lafayette on December 21, 2018.

712 Pleasant Deconstruction

The City of Boulder purchased the property located at 712 Pleasant in 2019 as part of the city's property acquisition program for properties located within the High Hazard Flood Zone.

Project Status

The house has been removed and the site has been seeded with a native meadow mix to stabilize the soils.

In April 2020 the property underwent asbestos abatement in preparation for demolition of the structure. Abatement and demolition are complete. The city contracted Herron Enterprises to conduct the abatement and demolition as well as CTL Thompson as a third-party oversight consultant.

If you have any additional inquires on this project, please contact Laurel Olsen or call 303-441-3203.

Gregory Canyon Creek Mapping and Mitigation Information

Flood Mitigation Plan

The Gregory Canyon Creek Flood Mitigation Plan includes habitat improvements, culvert and channel improvements, a pedestrian bridge at Pennsylvania Avenue, sediment traps, roadway improvements and other features.

The Flood Mitigation Plan was accepted by City Council in December 2015. Capital improvements funds were allocated in 2018 for the design of culvert and channel improvements from Arapahoe Ave. to Pennsylvania Ave.

Gregory Floodplain Maps

The floodplain mapping for Gregory Canyon Creek was updated in 2010. As part of current design efforts, an updated flood risk analysis is currently underway. Updated flood risk information will be provided in the upcoming months. A regulatory floodplain mapping change is not anticipated until after flood mitigation improvements are constructed.