32 Geological Impacts of Extreme Events on Land and Sea (Storms, Floods, Climate Variability, Tsunamis)

Friday, 28 March 2003
1:40 PM - 5:00 PM

IMPACTS OF THE AUGUST 2000 STORM ON THE CANADIAN BEAUFORT SEA COAST

Paper number: 32-9
Program: THEME SESSIONS
Time: 4:20 PM – 4:40 PM

Authors

Abstract

Infrequent, intense storms accompanied by NW winds of more than 25 m/s occur during the open-water season along the Beaufort Sea coast. These storms rapidly erode the unlithified, frozen cliffs, wetlands and deltas that characterise the region. Long-term erosion rates exceed 20 m per year in places and more than 100 m of retreat has occurred at the Hamlet of Tuktoyaktuk since 1947. Flooding also can be extensive in some low-lying locations. One of these severe events, which took place in August 2000, provided the opportunity to document some direct impacts of the storm at the Hamlet. Most of the infrastructure in Tuktoyaktuk is located on a narrow, north-south oriented peninsula of tundra facing to the west and backed by one of the best harbours in the region. The peninsula is flanked by sand and gravel spits which fine towards their distal ends. The 8 m-high tundra cliffs are composed of sand, sand and gravel fill and diamict with variable amounts of ground ice. The sandbag shore protection (installed in the late 1980s) was destroyed during a storm in 1993 and was replaced by the present structure composed of a concrete mat and riprap revetment in front of the cliffs and infrastructure.

The Y2K storm developed a maximum water level of 2.18 m (re: chart datum) at Tuktoyaktuk despite the proximity of pack ice in the region. Breaker heights were estimated to be 1.5 m high in water depths of less than 4 m; significant wave heights of 2 m were recorded in 50 m water depth. During the course of the storm, water levels remained close to their peak through 2 high tides resulting in prolonged washover of the flanking spits. The resulting landward migration ranged from 6-8 m at both spits. The presence of the shore protection and resulting decrease in sediment supply has contributed to a persistent decrease in the elevation of the proximal portions of the spits. The protection was mostly successful in limiting erosion of the tundra and fill cliffs although overtopping of the protection and erosion did occur at several locations. Tuktoyaktuk Island, which protects the mouth of the harbour is similar to the peninsula in setting and composed of sand, but is without any form of shore protection. It suffered severe erosion of more than 10 m, mostly by ice wedge polygon-defined block failures of cliff sediments.