Communications New Brunswick - River Watch - Flooding on the St. John River

Flooding on the St. John River

The St. John River, from its mouth to its headwaters in north-central Maine, is in excess of 730 kilometres in length.

The St. John River drains an area of 54,600 square kilometres. Fifty-one per-cent of the drainage area of the basin is situated in the Province of New Brunswick. The remaining areas are located in the State of Maine (36%) and the Province of Quebec (13%).

The basin generally experiences two marked increases in water level each spring. The first is associated with the break-up and movement of winter ice covers. Historically this break-up and its associated ice jam flooding has occurred in the first two weeks of April.

When high river coincides with an ice jam event, the result is a significant increase in water levels which far exceed the flood level caused exclusively by high river flows. Damages associated with such events are normally severe. This was the case during the 1976, 1987 and 1993 ice jam events along the St. John River.

The second annual high water event tends to occur later in the spring season and sees river flows reach their peak in late April or early May. These high water events are promoted when the spring melt occurs in conjuction with heavy spring rains.

The largest open water flooding event occurred on May 4, 1973. In that year, there was a 102 millimetre rainfall over portions of the basin during the peak of the spring runoff.