Surface runoff
With the water flow in the spring being six times the average rate, the valley has always been prone to flooding in the spring. Surface runoff from heavy rainfall is the main cause of flooding, and can be exacerbated by ice jams, high tides, and rapid snowmelt. Floods have been documented for more than 300 years. Flooding has occurred in Edmundston, Grand Falls, Perth-Andover, Hartland, and Woodstock, and most severely around Fredericton.