City of Boulder to begin construction of South Boulder Creek Flood Mitigation Project

The City of Boulder is preparing to begin construction of the South Boulder Creek Flood Mitigation project, the city’s top priority flood mitigation project. This project will provide protection from major floods and enhance safety for vulnerable community members in southeast Boulder. The construction approach will include both installation of flood infrastructure and floodplain restoration and protection, while also preserving access along US36 during a flood emergency.  

Construction on the project is expected to begin in early October 2026 and is projected to take between three to five years to complete. This work will require full closure of the CU Boulder South site to the community to prioritize the safety of community members and their pets and to minimize impacts on future protected open space during construction. The site will close fully to community access beginning the week of Oct. 5, 2026. Community members are encouraged to find alternative recreation locations through city parks and open space trails. 

Prior to the full site closure, community members may notice limited work as crews complete preparation work around the warehouse. This work must take place during a limited timeframe to meet environmental permitting requirements. 

Once complete, the project will provide flood protection for approximately 2,300 residents, 260 structures and key transportation corridors, including US36 and Foothills Parkway. The project is designed to preserve access along US36 during a major flood event, helping ensure emergency services and community members can safely travel into and out of Boulder. 

The project includes several major construction elements: 

• An earthen flood detention dam along the north and west edges of the CU Boulder South campus to store flood waters  
• A concrete spillway along US36  
• An outlet tunnel beneath US36  
• A groundwater management system  
• Removal of existing structures, including a warehouse and tennis courts  
• Reestablishment of South Loop Drive for future access after construction 
• Vegetation clearing and ecological restoration 

The flood detention dam will temporarily hold back floodwaters during major storm events, allowing flows to pass safely downstream. This design will help protect residential homes and critical infrastructure and facilities and prevent flooding like what occurred in 2013, when waters overtopped US36 and disrupted access to and from the city. 

In addition to reducing flood risk, the project supports environmental and climate resilience goals. Planned restoration work will help preserve and enhance wetlands and riparian habitat, protect species like the Preble’s meadow jumping mouse and Ute ladies’-tresses orchid, and restore more natural floodplain function. 

This project builds on more than a decade of planning and collaboration. Since City Council approval of the South Boulder Creek Flood Mitigation Plan in 2015, the city has worked with community partners, including Boulder Open Space and Mountain Parks, the University of Colorado Boulder, the Mile High Flood District and the Colorado Department of Transportation, to develop a comprehensive flood mitigation approach. 

The CU Boulder South annexation agreement, approved in 2021, brought the 308-acre site into Boulder city limits and established the framework for the university to transfer approximately 155 acres to the city, including 119 acres that will become new permanently protected open space. The agreement has also been voted on by the community several times since the early 2000s and each time voters have supported advancement of the flood project. This land supports both flood mitigation infrastructure and future open space use, while also enabling potential future university development, including recreational opportunities for the community. 

Construction of the project will be led by Concrete Express, Incorporated (CEI), selected in fall 2025. The total project cost is estimated at $76.5 million and will be funded using City Council-appropriated stormwater revenues in partnership with the Mile High Flood District. The city originally planned to fund the project through bond sales, which would have allowed the city to complete the project in three years, however litigation impacts the city’s ability to bond. Therefore, while the litigation is under way, the project will be funded on a year-to-year cash basis, extending the construction schedule from three years to five years and increasing the cost. If the lawsuit is resolved while the project is under construction, the city could bond for the remainder of the project costs and shorten the construction timeline and reduce overall costs.

Visit the project website and the project Frequently Asked Questions for more information and to clarify questions and misconceptions about the project.