Freshets

Freshets are sudden increases in the water level of rivers and streams caused by the rapid input of freshwater from melting snow, heavy rainfall, or flood releases from reservoirs. They most often occur in spring when accumulated snowpack melts quickly, but can also follow intense rain events in other seasons. The resulting rise in discharge can produce temporary floods along floodplains and near infrastructure.

Freshets are common in northern temperate regions with seasonal snow cover, including parts of Canada, the United States, and Europe. They may occur after periods of rapid warming or after long rainfall events, and can vary in duration from a few days to several weeks depending on hydrology and weather.

Impacts include inundation of agricultural land, roads, bridges, and properties close to rivers, as well as accelerated erosion and sediment transport. While freshets contribute to nutrient and sediment delivery to floodplains, they also pose risks to human safety and require monitoring and mitigation measures during high-water periods.

Forecasting relies on measurements of snowpack, rainfall, soil moisture, and river discharge, combined with weather forecasts and reservoir operations. Early warning systems, floodplain zoning, and controlled releases from dams are common management tools to reduce damage from freshets.