Lake Champlain – Richelieu River Flood Study

The Lake Champlain-Richelieu River (LCRR) basin is a large international watershed located in southern Québec and northern New York and Vermont. It is a geographically diverse basin, with a deep lake surrounded by the Adirondack Mountains to the west and the Green Mountains to the east. The basin is very vulnerable to flooding, with major floods occurring in 1927, 1976, 1983, 1993, 1998 and 2011. A combination of topography and climate makes the LCRR basin naturally prone to extended periods of flooding. The steep mountain slopes of the upper basin, high winter snowfall amounts, the flow regime of the upper Richelieu River, strong winds and large waves, and the frequency of heavy spring rainfall are all key drivers of flooding in this basin. The spring snowmelt is the dominant hydrological event of the year, when nearly one-half of the annual streamflow can occur within an eight-week window. There are also instances of severe summer and fall floods, though these are more likely to be shorter flood events driven by individual storms or sets of storms rather than the longer-duration floods that occur in the spring.

In the spring of 2011, the region experienced flooding well beyond anything experienced in the almost 200 years that records have been maintained. Lake Champlain's water levels reached 102.46 ft above sea level, far exceeding the previous historical maximum level. The Richelieu River rose above flood stage for more than two months. Many farms, and an estimated 4,000 homes along the Richelieu River in Québec, and along the shoreline of Lake Champlain were damaged. More than 40 communities were directly affected, and thousands of residents needed to be evacuated. Flood damages were estimated at more than $80 million, with almost 80% of the damages occurring in Canada, and 20% in the U.S.

The catastrophic 2011 flood prompted the governments of Canada and the United States to investigate ways to mitigate the flooding issues. They worked through the International Joint Commission (IJC), which is responsible for approving projects that affect water levels and flows across the border between the U.S. and Canada, and for investigating transboundary issues and recommending solutions. The IJC formed the Lake Champlain – Richelieu River Study Board to support them in these efforts. The Board developed and implemented a plan of study for examining the causes and impacts of the 2011 flooding and to develop possible mitigation measures. Their work included activities such as collecting data, developing tools, and creating static floodplain maps.

A study framework was adopted that included consideration of a variety of structural and non-structural measures. The structural measures included: (1) reducing high water levels on the Richelieu River and Lake Champlain, and (2) impeding inflows through wetlands and temporary upstream storage of floodwaters. The non-structural measures included: (1) improved flood forecasting and emergency preparedness, and (2) enhancing floodplain management. This paper will describe the study process, the new models and tools that were developed to evaluate flood mitigation measures, and the key conclusions and recommendations.