Analysis of Lake Champlain/Richelieu River's historical 2011 flood

Lake Champlain and its natural outlet, the Richelieu River, underwent an historical flooding event in 2011, exceeding by a wide margin all other extreme events in over 100 years of monitoring records. In Quebec, hundreds of homes were flooded for up to 2 months, requiring waves of evacuation and military involvement to support the effort. This paper examines the causes of this exceptional flood, performs a statistical analysis of important variables and compares the 2011 event to three other large floods. The results show that the return period of the 2011 spring flood exceeded 700 years and was caused by the combination of extreme precipitation over the spring season (500 years recurrence) and an important snowpack (15 years recurrence). Hydrological modeling of past extreme events over the Lake Champlain watershed indicates that liquid precipitation during snowmelt is the key factor in triggering large spring floods. The combination of the 2011 April and May precipitation with the large 2008 snowpack in a hypothetical meteorological scenario shows simulated discharges and lake levels much higher than the ones seen in 2011.