ABSTRACT: Geological conditions in the coastal-nearshore region of the Mackenzie Delta: implications for development.

CGRG Bibliography of Canadian Geomorphology
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Intensive new exploration and demand for natural gas has incited interest in the development of a pipeline from the Mackenzie Delta to southern markets. If this proceeds, construction activities are likely to occur on the coast and in the nearshore. An understanding of the processes which govern coastal stability and associated nearshore morphology, sediment properties and thermal regime is therefore essential for sound and safe development of hydrocarbon resources in the region. The coast and nearshore region in the vicinity of the Mackenzie Delta is characterized by extensive shallow water, large areas of which have never been sounded or investigated for physical properties. In addition, much of the delta front is erosional with maximum erosion rates exceeding 20 m per year. Geoscientific studies undertaken by the Geological Survey of Canada seek to quantify the coastal stability and nearshore sediment conditions.Water depths less than 2 m extend offshore from the low delta plain to nearly 20 km seaward of the delta front. The degree of ice bonding in the upper several metres of this zone is governed by subtle changes in bathymetry, which control the timing of bottomfast ice development. Surficial sediment properties established by very limited sampling indicate that the area is dominated by silt and very fine sand, but pockets of coarser material may be associated with seaward extensions of low-relief distributary channels. Subsurface information is also quite limited. Shallow onshore cores reveal high ice content in the form of lenses and layers down to at least 2 m below the delta surface. Ice lenses and veins are also found in nearshore cores in water depths out to 1 m. Depth of seasonal ice-bonding below the seabed (the subsea active layer) was found to be 1.9 m in one location. Sediments are characterized by an abundance of detrital organic material of fluvial origin.Coastal stability investigations have revealed high spatial variability in rates of retreat and progradation along the delta front. However long-term (decadal) retreat rates have been relatively consistent over time. Flooding due to storm surges is a common occurrence, increasing water depth at times of onshore wave activity and posing risks to infrastructure on the outer delta. The lack of detailed information on nearshore shallow bathymetry hampers our understanding of processes in the region. New techniques are being investigated to map the extent of bottomfast ice and nearshore permafrost development using satellite data and ground-penetrating radar. Application of technological advances in swath bathymetric mapping (interferometric sidescan sonar) is being considered.

Bibliography of Canadian Geomorphology