In June 2018, Grand Forks experienced a record flood event, with historic snow accumulation, a widespread rain event, and significant spring heat resulting in record flows for the Kettle and Granby Rivers. Another major flood event occurred in 2017. In addition to flooding hazards, the municipality also experiences periodic extreme heat and drought events. Damage from the 2018 flood, which impacted about 240 hectares of the city and surrounding rural areas, was estimated at over $48M for the commercial, residential, and industrial core of the community. Thousands of hectares of land were impacted, disturbing agricultural areas, roads, and rural business sectors.
The 2018 flood occurred just days before the municipality had planned to update its floodplain hazard maps to better understand flood hazards and natural assets. Following the flood, an early-stage recovery plan was implemented, where community and municipal members investigated impacts on critical infrastructure and the surrounding ecosystem and initiated economic recovery.
Use of Climate Information
To increase resilience to riverine flooding, the municipality of Grand Forks examined hydrological modelling, driven by projected future climate data, to inform the flood mitigation and community dike plan. The open source hydrological model RAVEN was used, as modelling efforts on the Kettle River had previously used this tool. The model was calibrated using observed streamflow data and then used to estimate potential future streamflows on the Kettle and Granby Rivers. Two key points of interest at the City boundary were identified to provide streamflow datasets for input to a separate hydraulic model.
A historical dataset from the Pacific Climate Impacts Consortium (PCIC) and downscaled and bias-corrected output from six different Global Climate Models (GCMs) for the period 1950-2100, were used to drive the hydrological model.
Once the hydrological model was calibrated to match historical conditions, it was fed temperature and precipitation data from the six different GCMs for two different Representative Concentration Pathways (4.5 and 8.5). The model was then able to estimate future 1-in-100 year and 1-in-200 year peak flow return periods.
Following the hydrological modelling, it was recommended that the city enhance its flood protection to withstand peak flows 10% higher than the 2018 flood event. Ultimately, a design hydrograph was developed for both the Kettle and Granby Rivers, and this provided input for hydraulic modelling to determine the required dike design.