Flood Details - 1973-04-01 - 1973-05-01

The winter of 1972-73 was one of above average snowfall in northern and central New Brunswick. By mid-April, the water equivalent of accumulated snow was as high as 12 inches [0.3m] in some areas and averaged 7.2 inches [180mm] in the Saint John River Basin above the Mactaquac Dam. Snowmelt and some rainfall from April 21 to April 24 caused river discharges of a magnitude greater than those associated with a normal spring freshet. Most rivers crested about April 24 or 25th and then began to recede as cooler temperatures reduced snowmelt rates. On April 27, an extra-tropical (frontal) storm moved into northern and central New Brunswick, bringing higher temperatures and rainfall averaging about three inches. Rivers rose rapidly, in many cases to levels higher than previously recorded, and peaked on April 29 and April 30. The most seriously affected part of the Province was the flood plain of the lower Saint John River in the Fredericton area and the agricultural lands a few miles downstream of Fredericton. Other areas seriously affected by the flood were the middle and upper parts of the Saint John River Basin, the Restigouche River Basin, the Miramichi River Basin, the Grand Lake area in the lower part of the Saint John River Basin and the St. Croix River Basin.

The Saint John River below Mactaquac Dam reached a maximum daily mean discharge of 393 000 cfs on April 30. Most rivers gradually receded after April 30, but the lower reach of the Saint John River between Fredericton and Saint John continued to rise until May 2. The magnitude of the flood in other areas varied from river to river, but at most stream gauging stations, the recorded discharges have estimated recurrence intervals within the range of 10 to 50 years. The April-May 1973 produced the highest water Fredericton ever recorded during an open water flood event. These water levels associated with this flood event were used to define the flood risk area from Mauguerville to Lower Jemseg as was depicted on flood risk maps produced under the Canada-New Brunswick Floood Reduction Program (1976-2000). The 1936 ice jam at Fredericton produced highest water levels at Fredericton, but the ice jam events at Fredericton are unlikely to occur due to the reduction of the supply of ice from upstream following construction of Mactaquac Dam.

The total economic cost of the flood was estimated to be $11.9 million [1923 dollars]. Of this, $10.8 million was attributed to the Saint John River Basin, about $1.0 million to the river basins in northeastern New Brunswick and less that $0.1 million to the southwestern basins. In terms of economic sectors, the Public Sector sustained the highest cost of $4.9 million, followed by the Personal Sector with $4.2 million, the Business Sector with $1.7 million, the agricultural sector with $0.7 million and the Organizational Sector with $0.3 million. Compensation was provided, by the federal and provincial governments, to the extent of 63 percent of the estimated total economic cost in the Province. The federal share of this compensation was about $5.3 million. Damages in the Fredericton area and in the agricultural area downstream of Fredericton accounted for about 60 percent of the total economic cost of the flood. During the 1973 flood, forecasting and emergency measures activities were successful in avoiding more serious personal hardship and greater economic losses. Warnings provided, through weather and streamflow forecasting, permitted some advance planning to react to the emergency, while the Emergency Measures Organization directed the disaster activities. In spite of this, the flood caused an estimated $2.5 million in damage to moveable property. Note: For further information on this flood, refer to the following publication prepared by Environment Canada, Inland Waters Directorate, Atlantic Region: New Brunswick Flood, April / May, 1973. Technical Bulletin No. 81