In the spring of 2011, Lake Champlain water levels rose to their highest on record, a result of a slow inundation of water from significant winter snowpack and intense rainfall in March, April and May. Scientists estimated such a severe event would only occur once every 200 to 1,000 years.
After the flood, the U.S. and Canadian governments asked the International Joint Commission, which regulates water bodies that cross the border between the two countries, to study ways to minimize damage from flooding. The resulting International Lake Champlain-Richelieu River Study Board, established in 2016, released its final report this month.
High water levels in the lake, which flows north, caused extensive flooding along the banks of the Richelieu River, which flows into the Saint Lawrence River in Canada. Flooding damaged 1,310 homes in New York and Vermont and more than 2,500 homes in Québec, and the flood lasted for weeks. Water in Lake Champlain rose to about 103 feet above sea level. The lake’s average annual water level is 96.5 feet, according to the Lake Champlain Basin Program.
“Here in the U.S. part of the basin, and all along the lakeshore, people whose homes were right at or right above 103 to 106 feet of sea level or so, they were experiencing flooded houses, flooded basements. People around the shore had logs crashing inside their houses,” said Eric Howe, program director at the Lake Champlain Basin Program, which was involved in the study.
The six-year, international study involved more than 100 people. It recommends ways to reduce extended periods of flooding.
On average, Vermont has already become wetter due to climate change, and that trend is likely to continue. Climate change could have a variety of impacts on flooding in Lake Champlain: Higher temperatures may decrease snowpack and increase evaporation from the lake, creating lower water levels, or additional rainfall in the spring could increase the chance of flooding. Winter rainfall could exacerbate flooding, too, according to the report.
The study board focused on the impacts and strategies to prevent inundation flooding, rather than extreme flash flooding that occurred later in 2011, when Tropical Storm Irene hit the state.
It recommended preserving wetlands, which both reduce the amount of water that flows into the lake and keep water levels more consistent during drought periods. It also recommended that U.S. and Canadian governments use updated forecasting, modeling and mapping tools to better predict and assess flood risks.
Because Lake Champlain drains into the Richelieu River, the spring 2011 flood hit Quebec harder than the United States, and areas remained flooded for nearly two months.
For that reason, the study group recommended selective excavation of the riverbed near Saint-Jean-sur-Richelieu, Quebec, combined with a new submerged weir, which would also help maintain water levels in Lake Champlain during dry years.
“Moderate structural measures alone cannot keep the waters of Lake Champlain and the Richelieu River within their shorelines under all conditions, but they can provide some relief under highflow events,” the report states.
A public comment period on the final report began on Aug. 19 and lasts until Sept. 30. Comments can be submitted on the International Joint Commission’s website.