An Analysis of the Massawippi Floods of 1982 and 1994

Abstract

Flood events in the Massawippi drainage basin of southern Quebec are a common phenomenon, usually occurring in the spring months. They are often relatively benign events causing low levels of inconvenience to the local populace, however on occasion floods can bring large-scale damage and disruption. Two of the largest floods on record for this basin occurred in April 1982 and April 1994. This study examines the meteorological and hydrological conditions present during both months with the goal of identifying any comparable or contrasting features of the flood events. The Massawippi drainage basin is one of the largest sub-basins in the Saint-Francois River basin, covering approximately 1670 km2. Its relatively large surface area, high frequency of streams, gentle slope and near-circular basin shape combine to create the geomorphological conditions suitable for frequent flood events. Abundant winter snowfalls, large spring precipitation events and river ice jams provide the necessary hydrometeorological conditions. In April 1982 a sudden, intense rainstorm created a flash flood type of situation. Rapidly rising river levels caused some of the worst infrastructure damages ever reported for the Massawippi basin. In contrast the April 1994 flood, which reached comparable river discharges, was created through a gradual rise of the basin’s rivers by a series of rainstorms and the melting of a deep snowcover over a two-week period. Thus, these two events, although comparable in magnitude, contrasted significantly in their character. The 1982 event, because of the sudden development of its peak flow, allowed little time for flood preparations and thus caused much more damage than the 1994 event.