Numerical study of wave-driven flooding on Lake Ontario

In this study, four high-resolution numerical models of nearshore wave propagation, runup, overtopping, and coastal flooding were developed using the open source XBeach model for three sites on the Canadian shore of Lake Ontario where flooding occurred in recent years. The models were qualitatively validated through comparison with photographs of flooding from these sites, and then used to model 24 to 48 combinations of water level and wave condition at each site. A set of flood metrics were developed and computed from the simulation output based on the potential impacts to waterfront buildings and roads. Relationships were established between the flood severity metrics, lake level, and incident wave conditions at each site. Results show that the flooded area, the number of flooded houses, and the length of flooded roads were influenced by both water levels and wave conditions, generally increasing with rising water level and increasing wave height. However, the rate of increase varied from site to site depending on local factors and conditions. Approximately linear relationships were found in some cases, whereas highly nonlinear relationships were identified in others. The study highlights the importance of wave action in initiating flooding at water levels below the threshold required to cause flooding under calm conditions, and exacerbating flooding at water levels above this threshold. This study was undertaken to support the International Joint Commission’s Great Lakes-St. Lawrence River Adaptive Management Committee and International Lake Ontario-St. Lawrence River Board in assessing strategies for regulating outflows from Lake Ontario into the St. Lawrence River.