Spring floods in rivers

Spring floods come every year, and over time those living near a river have learned where it is the most likely to break its banks. A flood can nevertheless rise surprisingly fast.

A spring flood is the sum of many factors which may result in severe flooding when they all coincide.

The ultimate reason for a spring flood is snowmelt, and if the winter has brought a lot of snow, the spring will turn it into a high volume of water. If the weather warms up rapidly and it also rains, large amounts of water run into rivers over a short period. The channel does not have enough capacity for it all and the river breaks its banks, and large areas may be submerged in low-lying terrain.

The worst fluvial floods are caused when ice floes block a river and stop water from flowing smoothly. An ice jam can appear in a moment and raise the water level in a river by as much as one metre per hour. Stacks of ice can also be pushed out of the channel, causing more damage.

While spring floods can be predicted fairly reliably based on snow amounts and weather data, ice jams are difficult to anticipate. The risk of ice jams is the greatest when the snow is melting rapidly and the ice has not yet become fragile. In risk-prone river sections, the ice is sometimes cut up as a precaution. The pieces are washed downstream and the risk of an ice jam is avoided.