The Mill Creek Flood Protection Project

Starting in 2020, the City of Kelowna began the Mill Creek Flood Protection Project to improve the Mill Creek corridor and reduce flooding potential throughout the City. Mill Creek is 35-kilometer in length and winds through farmland and alongside industrial areas before looping its way through some downtown residential neighbourhoods and then emptying into Okanagan Lake. Land use activities in the Mill Creek watershed include agriculture and urban development in the lower watershed, and forestry in the middle and upper portions of the watershed. Extreme weather events like floods are getting worse and more frequent in Kelowna. In Spring 2017, flooding along Kelowna’s Mill Creek caused by an ill-timed rainstorm on top of a higher-than-normal spring freshet swamped many properties, causing some apartment buildings to be evacuated. This event marked flood mitigation work along Mill Creek as a high priority by City officials and led to the Mill Creek Flood Protection Project. This multi-year, multi-million dollar initiative to improve the creek corridor and reduce flooding potential throughout the City, from the Kelowna Airport to Okanagan Lake. With a funding contribution of $22 million through the Disaster Mitigation and Adaptation Fund (DMAF), the Mill Creek Flood Protection project will better protect residents and businesses of Kelowna from future flooding events, and economic loss due to extreme weather.

Understanding and Assessing Impacts

Starting in 2020, the City of Kelowna began the Mill Creek Flood Protection Project to improve the Mill Creek corridor and reduce flooding potential throughout the City. Mill Creek is 35-kilometer in length and winds through farmland and alongside industrial areas before looping its way through some downtown residential neighbourhoods and then emptying into Okanagan Lake. Land use activities in the Mill Creek watershed include agriculture and urban development in the lower watershed, and forestry in the middle and upper portions of the watershed. Extreme weather events like floods are getting worse and more frequent in Kelowna. In Spring 2017, flooding along Kelowna’s Mill Creek caused by an ill-timed rainstorm on top of a higher-than-normal spring freshet swamped many properties, causing some apartment buildings to be evacuated. This event marked flood mitigation work along Mill Creek as a high priority by City officials and led to the Mill Creek Flood Protection Project. This multi-year, multi-million dollar initiative to improve the creek corridor and reduce flooding potential throughout the City, from the Kelowna Airport to Okanagan Lake. With a funding contribution of $22 million through the Disaster Mitigation and Adaptation Fund (DMAF), the Mill Creek Flood Protection project will better protect residents and businesses of Kelowna from future flooding events, and economic loss due to extreme weather.

Identifying Actions

Following the 2017 and 2018 flooding events, communication with the Okanagan Basin Water Board (OBWB) revealed that there were significant gaps in the type of information and data needed to properly evaluate the relationship between climate and creek/lake flooding events. The computer models used for studies in the past were becoming out of date and did not provide the level of precision necessary to properly address how and where infrastructure and emergency funding could be best applied. The City discovered that high quality and accurate data was available for rainfall, temperature, creek flows, creek temperature, snowfall, and other relevant factors; just not everywhere. They partnered with neighbouring communities, and initiated processes that provide a holistic approach that is now available to address the coordination of resources, expertise and budgets needed to effectively address flood and natural systems management. Data now produced are valuable inputs for such projects as the regional Emergency Operations Centre (EOC), environmental flow needs calculations, stormwater quality and development approvals in flood plains.

Implementation

The Mill Creek Flood Protection project will work to increase creek capacity through rehabilitating creek riverbanks, integrating increased drainage solutions, and adding new off-stream water storage areas. The City of Kelowna also plans to replace low bridges that cause debris blockages, make improvements to an existing diversionary channel, and begin construction of a new spillway. The city plans to improve the condition of a decades-old diversionary channel that feeds water from Mill Creek into Mission Creek through a tunnel near Leckie Road. In addition to the Mill Creek Flood Protection Projection, the City has been involved in many initiatives since the severe events in 2017 and 2018. These include:

  • Kelowna Flood Risk Assessment: The City was awarded $250,000 in Federal and Provincial funding from the National Disaster Mitigation Program (NDMP) Intake 4 to conduct a Major Systems Flood Risk Assessment. This led to the development of new computer hydraulic models which will be useful in future erosion and flood scenario development, as well as minimum building elevation needs.
  • Okanagan Mainstem Floodplain Mapping (OBWB): Comprehensive floodplain mapping for the Okanagan River from Penticton to the U.S. Border and the Okanagan mainstem lakes. The floodplain maps include flood inundation extent and flood hazard mapping for 20, 100, 200 and 500 year recurrence interval flooding.
  • The Okanagan Flood Story Web Portal (OBWB): This new website presents a single web portal for flood mapping, flood history, perspective and best management practices. The City will supply formatted data, mapping, photos and stories to this site on a regular basis.
  • Mill Creek Flood Mapping Project: New completed flood maps of Mill Creek using new LiDAR survey dataset. The work was funded from a $150k grant from UBCM – Community Emergency Preparedness Fund (CEPF). The new modern hydraulic model of Mill Creek (1D-2D HEC-RAS) will be used for future design and alternatives analysis for the Mill Creek Flood Protection Project.

Outcomes and Monitoring Progress

The Mill Creek Flood Protection project is expected to enhance the city’s ability to regulate water levels and protect homes and businesses from future flooding. It will also improve fish spawning areas and protect local wildlife and ecosystems.

Next Steps

Work on the Mill Creek Flood Protection Protection will occur in stages that began in 2020 and could take up to eight years before it’s all complete.

Resources

Link to Full Case Study:

Additional Resources: