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TitleCoastal and nearshore geohazards in the southern Beaufort Sea
AuthorWhalen, D; Solomon, S M; Forbes, D L; Craymer, M; Lavergne, J C; Marsh, P
Source36th annual Yellowknife Geoscience Forum abstracts of talks and posters; by Jackson, V; Irwin, D; Northwest Territories Geoscience Office, Yellowknife Geoscience Forum Abstracts Volume vol. 2008, 2008 p. 62-63 (Open Access)
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20080466
MeetingYellowknife Geoscience Forum; Yellowknife, NWT; CA; November 18-20, 2008
Mediapaper; on-line; digital
ProvinceNorthern offshore region
AreaBeaufort Sea; Mackenzie Delta
Subjectsmarine geology; coastal studies; coastal environment; coastal erosion; deltas; ice; ice movement; geological hazards; synthetic aperture radar surveys (SAR)
ProgramSecure Canadian Energy Supply
AbstractOngoing oil and gas exploration and development in the Mackenzie Delta and the southern Beaufort Sea continue to raise questions about geological conditions and potential hazards in the region. Recent investigations by the Geological Survey of Canada and partners provide new insights on sediment mobility, scour processes and distribution, coastal flooding and land subsidence in the area. The shallow, gently sloping, silt-dominated delta-front and nearshore region of the Mackenzie Delta is known to be dynamic due to the action of storms during the open water season. Investigations during the spring break-up period reveal that significant changes in seabed morphology occur during this transition from ice cover to open water.

Synthetic aperture radar (SAR) continues to be an invaluable tool for delineation of bottomfast ice. In addition to its role in maintaining and aggrading nearshore permafrost, we have confirmed that the distribution of bottomfast ice plays a critical role in the distribution of water overflow onto ice during spring breakup. As discharge increases due to melting in the south, the ice-choked distributary channel mouths force a portion of the spring melt waters over the ice surface as well as back onto the the delta top. The extent and volume of overflow has been documented over the last three field seasons using satellite imagery, helicopter surveys and in-situ measurements from time-lapse cameras and pressure sensors placed on land and over the ice during breakup. Overflow levels rise very rapidly (60 cm in 1 hour) and can exceed 1 metre, with dramatic effects on overland flooding extent in the low-elevation outer delta. Evidence of through-ice drainage was observed in 2006 and an active ‘strudel’ drainage field was documented during the 2007 and 2008 field seasons. The occurrence of circular strudel scour depressions as deep as 1.5 m into the seabed has also been confirmed through small-boat sonar surveys. In 2007 the scours persisted at least until August when the surveys were undertaken, whereas scours mapped in June 2008 had disappeared by August. The disappearance can be attributed to a moderate storm in late July. The observation that a storm of this magnitude can totally re-work the sediments in the nearshore environment will lead to a better understanding of the potential for seabed morphological change and sediment transport in this area. Direct measurements of waves, currents, turbidity, temperature and salinity made during the open water seasons in 2007 and 2008 provide additional information about the role of storms in controlling sediment movement in shallow delta front environment.

Impacts of marine processes on the delta (i.e. storm surge, ice-induced backwater effects) are influenced by the land surface elevation. Preliminary analysis of GPS data collected over stable monuments indicates that the delta is subsiding at a rate of 5-10 mm/yr. New GPS epoch stations have been installed on deep industry well heads in the past year as a further confirmation of the vertical crustal motion.