A Learning Mindset: a collaboration between BGC and geography students at the University of Calgary

On November 14, 2021, an atmospheric river (AR) brought two days of intense rainfall to southwestern British Columbia (BC). This rainfall resulted in extreme flooding and extensive channel changes in watersheds across a large spatial extent in the lower Fraser River watershed, including the Coldwater River. In support of ongoing projects (e.g., floodplain mapping, highway risk assessments) and flood recovery, BGC was retained by several parties to estimate the design flood (i.e., 200-year flood) to inform mitigation design, hazard assessments, and floodplain mapping in the Coldwater River watershed at the town of Merritt, BC.

Using a statistical approach to flood analysis, BGC estimated the present-day and climate-adjusted design flood considering the historical and future climate (the next 75 years). The climate-adjusted design flood was estimated to increase by 65% compared to the present-day estimate. This substantial increase in the design flood based on statistical modelling required an assessment of the physical possibility in the Coldwater River watershed. Statistical hydrology relies on extrapolation beyond empirical data which is an important limitation especially when accounting for climate change.

BGC collaborated with students from the University of Calgary enrolled in Watershed System Science led by Dr. Tricia Stadnyk to gain insight. The students developed a calibrated HEC-HMS hydrological model, using data provided by BGC along with publicly available data, as part of their term projects. The hydrological model was used to answer the following questions:

1. How big was the November 15, 2021 flood?
2. What is the influence of watershed characteristics on the November 15, 2021 flood?
3. Does the 200-year rainfall (intensity-duration-frequency) correspond to the 200-year flood?
4. What is the probable maximum flood (PMF)?
5. Where does the water go when it floods?

This collaboration was a win-win for the students and BGC. This collaboration provided a valuable opportunity for the students to apply hydrological modelling to a real-world problem and BGC gained insight into the physical possibility of extreme floods in the Coldwater River. This project was made possible by the leadership of Dr. Tricia Stadnyk in her effort to merge the gap between research and real-world applications.