Author(s): Sayed Ismail; J. L. Davis
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Abstract: The Saint John River, New Brunswick, has a history of frequent spring ice jam flooding at several locations. In late December 1990 a rare mid-winter ice jam was forrred in the Perth-Andover area, a village 14 miles (24 km) upstream of the Beechwood dam on the Saint John River. Over the winter months the ice in this jam froze together to fonn a consolidated mass. This created ice conditions which had the potential of causing severe ice jamming in the area during the coming spring. In order to determine the extent and significance of this consolidated mass relative to potential spring flooding, it was decided to try to measure the thickness of the jam. About 1.3 river miles (2 km) were surveyed using a Ground Penetrating Radar (GPR) system in attempt to determine the ice jam thickness. The GPR technique uses the changes in the electrical properties of different rredia, including different types of ice and water, to determine the ice thickness. The GPR technique was successful in detecting and measuring the thickness of both fragmented thermal ice, as well as slush ice, to depths up to 23 ft (7 m). The technique was also able to detect ice jam grounding. Subsequent to the GPR measurements a survey of the ice jam thickness prior to the spring breakup using conventinal technique was undertaken. This survey comprise a grid of exploratory boreholes covering the entire width of the river and 600 ft (180 m) long. The survey indicated that, except near the left bank, no apreciable ice depletion took place since the ice jam was forrmed in early winter. The results of the boreholes and the GPR ice thickness surveys compared favourably. This demonstrates that the GPR technique can be used to identify and estimate the thickness of slush and broken ice of ice jams.
Year: 1992