The causes, progression and magnitude of the 1826 red river flood in manitoba

In this paper we review historical and paleoenvironmental evidence related to the 1826 Red River flood in Manitoba. In 1825, significant spring flooding and persistently high water levels in early autumn filled natural storage in the Red and Assiniboine river basins to capacity. Although daily historical records do not suggest that the winter of 1825–26 was exceptionally cold or snowy, other comments note an unusually deep snow pack near the Red River Settlement and throughout the southern basin. Historical accounts and paleoclimatic data document a cold, snowy April and an exceptionally late spring throughout much of central North America. The 1826 flood was exacerbated by abundant rainfall during the rising phase and was, according to historical and dendrochronological evidence, the largest event since at least C.E. 1648. The estimated peak flow for 1826 is approximately 6,370 m3/s (40% greater than the 1997 flood), which exceeds the current design capacity of flood protection for Winnipeg. Historical accounts in western Manitoba and anatomical signatures in alluvial logs suggest that the lower Assiniboine (downstream of Brandon) produced an exceptional flow in 1826, equivalent to perhaps 20% of the Red River’s upstream discharge. Reports of extremely strong, persistent winds from the south coincident with peak stage suggest that wind set-up may be an important factor that should be considered in future hydraulic studies.