The 2011 flood event in the Red River Basin: Causes, assessment and damages: Fid-Bau Portal

The 2011 flood event in the Red River Basin: Causes, assessment and damages

Stadnyk, Tricia

The 2011 Red River flood event was the third largest event since the operation of major flood control structures in the Province of Manitoba (exceeded by 1997 and 2009), and the fifth largest on record (including 1800s events). However, the flooding experienced on the Red River in 2011 has only an estimated 22-year (James Avenue) to 58-year (Grand Forks, ND) return period. Flooding in 2011 was the result of the second highest soil moisture index ever recorded (in 2010) prior to freeze up, lower-than-normal winter temperatures (causing significant frost penetration), high winter flows and above-average snow cover across the basin. The flood had the potential to be much more severe had it not been for favourable weather conditions within the basin during the spring of 2011. Below-normal precipitation, warm temperatures resulting in high evaporative losses from saturated soils, the non-coincident peak flows of the Red and Assiniboine Rivers, and lower-than-anticipated tributary inflows between Emerson, MB, and the City of Winnipeg mitigated the potential flood peak. The floodway had been expanded after the 1997 flood and further upgrades and maintenance following the 2009 flood allowed an additional 141.6 m 3 /s of flow to be diverted around the city, resulting in approximately a 0.38-m reduction in the James Avenue water level. The 2011 flood resulted in the fifth highest floodway peak on record, with flood control works in both the Red and Assiniboine systems estimated to have reduced James Avenue stage in the City of Winnipeg by 3.5 m. The majority of data presented in this paper have been taken from the Manitoba 2011 Flood Review Task Force Report and the Red River Floodway Operation Report.