Gregory Canyon Creek Flood Mitigation Projects

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 floodprojects@bouldercolorado.gov.

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.

How do we determine where to prioritize flood mitigation? The 2022 Comprehensive Flood and Stormwater (CFS) Plan developed a new prioritization framework based on community values and input to guide flood mitigation efforts for the 16 drainageways in Boulder. The framework encompasses key criteria with metrics which are used to assign a weighted value to each project. Commonly, and historically for Boulder, prioritization methods use a simple “losses avoided” approach to calculate project benefits, which frequently result in benefit/cost ratios that favor implementing projects in affluent areas with the highest property values as opposed to areas where the life safety risk and community needs are the highest. Incorporation of metrics like the Social Vulnerability Index into the new prioritization framework allows for prioritization of projects based on a consistent set of criteria that directly reflects community values and project benefits. Further discussion of project prioritization can be found in the September 15, 2022 memo to City Council.

Where does Gregory Canyon Creek join Boulder Creek? Gregory Canyon Creek joins Boulder Creek north of Arapahoe Avenue and west of 9th Street.

As Gregory Canyon Creek is rerouted, will the old creek bed be filled in/landscaped or remain a dry creek bed? Although not all portions of the creek will be realigned due to space constraints, where there is a change in alignment, the existing channel will be filled and landscaped.

What aesthetic considerations will be part of the design of bridge abutments at new concrete culverts? We are still working through the details of the design of the new concrete culverts. Aesthetic considerations will be addressed as part of this process, and we will provide more information once those details are finalized.

Do property owners have a say in the final design for segments affecting them? At this stage of the design, this is part of the negotiations. We aim to create a consistent appearance, so working with property owners is an important focus. This is a key element of our one-on-one meetings.

How will flood water that exceeds the design capacity be handled? Floodwater exceeding the design capacity is addressed through emergency preparedness. The capacity of Boulder’s 16 drainages varies based on designs for specific events, but extreme events can still occur. That's where preparedness is key. We offer resources on flood and disaster readiness through our city’s website.

For Gregory Canyon Creek, the current limitation is the culverts, which can handle 150 cubic feet per second (CFS)—equivalent to 150 basketballs passing through per second. For comparison, Boulder Creek’s peak flows reach 500-700 CFS during spring runoff. After Phase I, Gregory Canyon Creek will handle just under 600 CFS, nearly four times its current capacity. While extreme flooding may still exceed the channel's capacity, these enhancements will significantly reduce flooding impacts compared to what would have occurred without the improvements.

What is the flow rate in CFS of a 25-year event? The design flow is around 570 or just under 600 CFS.

Are you planning to underground utilities? We’re not at that level of detail yet. We’re working through our utility relocations.

Are you planning to add a bike path along the creek? No, I don’t see that as a possibility.

What is happening at the viewpoint of the trail and Anderson Ditch?
We are currently working through the design for this area. There is a crossing between Gregory Canyon Creek and Anderson Ditch, and we will collaborate with the ditch company throughout the process. We will ensure that construction in this area does not impact the ditch's operation, particularly during its active season. Any construction will be timed appropriately to avoid interfering with the ditch’s function. This area is part of the ongoing design effort.

How many trees will the project remove? Will this be like other projects where a lot of trees are removed?
Tree impacts are unfortunately a reality on all of our flood mitigation projects. However, we are working diligently to minimize tree removal as much as possible while still accommodating the project’s design and flow requirements. We are very conscious of this and will continue to prioritize minimizing tree impacts throughout the project. While we don’t have an exact tree count yet, that information will be finalized in the final design. Tree removal will be discussed with property owners who may be directly affected.

Is the project fully funded? Is it happening for sure? This is in the project funding that we’re planning for. In our minds, it is one of the priority projects that we’re bringing forward in the short-term capital improvement program. It is for sure happening.

What is the budgeted amount for this project? What we’re estimating now for Phase 1 is about $19 million.