In 2011, Lake Champlain and the Richelieu River suffered from a record flood. According to a new report, this was caused by warm, wet and windy spring weather that followed near-record winter snowpack, and human changes to the lake and river. The flooding damaged thousands of homes, eroded the shoreline and hurt wildlife.
The Lake Champlain-Richelieu River Study Board has released its “Causes and Impacts of Past Floods in the Lake Champlain-Richelieu River Basin” report. This report is part of the board’s work studying flooding in the region. In 2022, the board will provide final recommendations to the Canadian and US governments on ways they can mitigate future flood damages.
The board estimates that the 2011 floods caused more than US$86 million in damages to homes, farms and businesses, mostly in Quebec. The floods also altered habitat and disrupted the food web, and helped invasive species spread around the area.
The flooding started with extreme snowfall in the Adirondack and Green Mountains, which held 38-63 cm (15-25 inches) and 50-76 cm (20-30 inches) of water respectively as of March 15. With cold winter temperatures, this large amount of snow stayed through the winter months and into spring. Unfortunately, the spring brought record-breaking rain, with 51 cm (20 inches) falling between March and May. The warm spring temperatures and rain caused the snow in the mountains to melt quickly and flow into Lake Champlain.
Weather wasn’t the only issue that led to flooding. Lake Champlain flows into the narrow and often shallow Richelieu River. This means that high waters in the lake can quickly cause floods in the river that can take months to recede. And the water system isn’t entirely in a natural state.
The Chambly Canal was built alongside the Richelieu River and opened in 1843. When a section of it was widened into the river in the 1970s, water levels in Lake Champlain rose. Humans also have added piers and eel traps to the river that affect its flow.
Wetlands used to sit along the shores of Lake Champlain and the Richelieu River, reducing flooding impacts. Many of these were developed into farms and towns, and the streams feeding the lake were shifted and straightened, moving water more quickly to the river.
Towns built along the water also directly contribute to the amount and speed of water entering the lake, as rain and snow now land on concrete and other hard surfaces instead of being absorbed into the ground. With nowhere else to go, that water runs across the land or into sewer systems and eventually drains to the lake.
In 2011, water flooded homes, roads, marinas, other buildings and farmland. About 2,500 homes in Quebec and 1,310 in New York and Vermont were damaged due to floodwaters, leading to mold and unsafe drinking water. More than 7,740 hectares (19,000 acres) of farmland in the U.S. and 2,500 hectares (6,177 acres) in Quebec also were flooded.
Shorelines along the waterfront eroded due to floodwaters and powerful waves, powered by strong winds. Water quality in the lake was affected by sediment and nutrient runoff washed in by the floods. As floodwaters receded, fish became trapped in small pools and died, while invasive species like water chestnuts and Phragmites spread. The floods also altered and destroyed spawning grounds for fish and nesting sites for marsh birds and turtles.
Since water levels increased in Lake Champlain in the 1970s, more people have moved to the region. The area, meanwhile, is expected to get more frequent extreme rain events in the future, increasing the risk of future flooding.
While the study board hasn’t finished its work, it is still looking into ways that communities and individuals can prepare for future floods to minimize impacts. These include discouraging new development in areas at greater risk of flooding, restoring wetlands and building ponds to store floodwater before it enters the lake or river. New structures may help regulate the water, and improvements to flood forecasting and flood response plans can help communities prepare before the waters strike.