1991 ice jamming along the Saint John River: a case study

Abstract

During April 1991, major and damaging ice jams formed on the Saint John River at Dickey, Maine, and at Sainte-Anne-de-Madawaska, New Brunswick. Field investigations included the measurement of five water surface profiles along the ice jam at Sainte-Anne-de-Madawaska and of shear wall heights at both Dickey and Sainte-Anne-de-Madawaska after the jams had released. These measurements were supplemented by considerable information from local observers and data collection agencies. Following a description of freeze-up and winter conditions, and a chronology of 1991 breakup events, the available data were analyzed according to current ice jam theory. Using a simplified equilibrium analysis and taking into account discharge and channel characteristics, the 1991 Dickey ice jam thickness and water level were calculated and were in general agreement with observed values. In the case of the Sainte-Anne-de-Madawaska jam, sufficient data were obtained for application and calibration of the numerical model RIVJAM which determines the configuration of a jam in nonequilibrium reaches. This resulted in successful reproduction of a measured water profile along the jam and approximate prediction of jam thickness. Implications of the calibrated model coefficients are discussed. Key words: ice jams, flooding, modelling, water level profiles.