Flood Graph from 1944 Report
Historical Erosion

History of Flooding on the Ganaraska River

Throughout history the Ganaraska River has experienced flooding at varying degrees Between 1848 and 1937, 34 flood events were recorded by local residents and the media. A relationship between forest cover in the watershed and the frequency and severity of floods has been noted. The principal factors  contributing to increases in the frequency of floods included deforestation within the watershed, and drainage and development for agricultural purposes. Reforestation of large areas was therefore proposed in The Ganaraska Watershed report to reduce the frequency of floods and improve summer flow conditions.

The vision of flood reduction coinciding with reforestation was slowly realized throughout the mid-1900s, as the forests in the headwaters began to augment surface water flows and groundwater infiltration. Flood control again increased in the province after Hurricane Hazel struck central Ontario in 1954, killing 81 people and leaving thousands homeless. Although devastating effects were felt in Toronto, Port Hope received little damage. However significant flooding still occurred through the 1950s, 1960s and 1970s.

On March 21, 1980, the flood of the century hit the Ganaraska River. It was caused by rainfall that was not particularly severe by yearly standards (5-year event), but which was relatively severe for the month of March (50-year event). Rainfall on frozen ground caused little or no infiltration, and it was concluded that the 1980 flood has a recurrence interval of 100 years. This event caused the Ganaraska River to experience a flow of 421 cubic metres/second, causing 66 acres of downtown Port Hope to be flooded with water depths to 1.5 meters (m) and velocities sufficient to knock down building walls.

In order to mitigate further flood events like what was experienced in 1980, channelization of the river through downtown Port Hope was proposed and constructed. The river was widened and deepened over a distance of approximately 1,000 metres to allow greater capacity of flow to move through the town. Since channelization has occurred, downtown has not experienced significant flood events, although localized seasonal flooding does occur throughout the watershed. Learn more about the 1980 Ganaraska River flood.