Interactions between water, ice and sediment during spring breakup at the mouth of the Mackenzie River, Northwest Territories

Transcription

1 Interactions between water, ice and sediment during spring breakup at the mouth of the Mackenzie River, Northwest Territories Steven M. Solomon 1, Donald L. Forbes 1, Maxime Belanger 2, Dustin Whalen 1, Philip Marsh 3 1 Geological Survey of Canada, 2 University of Alberta, 3 Environment Canada

2 Acknowledgements Program for Energy Research and Development (PERD) Northern Energy Development MC Polar Continental Shelf Project Aurora Research Institute MGMEnergy, Shell Canada, Chevron Canada logistic support and data Partners and contractors: University of Calgary, University of Alberta, C-CORE, Aquatics Environmental, Tumichiat Outfitters Satellite imagery- ESA, CSA, University of Alaska GINA Canadian Helicopter Corporation

3 Issues and Objective Onshore gas production will lead to offshore exploration and exploitation of known offshore discoveries (pipelines) Assessment of risk to pipelines, navigation channels and infrastructure due to nearshore geohazards Ice-seabed interaction scours, shallow subsea permafrost Magnitude, extent and mechanisms of nearshore erosion and deposition Objective: Document river-mouth processes and river-ocean interactions during spring break-up.

4 Study Area

5 Winter-Spring Oceanographic Environment Freeze-up in mid-late October with formation of landfast and bottom-fast ice. Continuous discharge throughout winter Development of Lake Herlinveaux fresh water ponded behind stamuki (MacDonald and Carmack) Punctuated quiescence beneath winter ice - winter surges Early-mid-May: increased river discharge prior to sea ice melt Suspended sediment concentrations up to 4 g/l SPM load enters fresh water basin Sediment may be flocculated (Droppo et al 1998) Lake Herlinveaux Mackenzie at Arctic Red River After Hill et al 2001

6 Fluvial sediment delivery modes Hyperpycnal flows Require > 40 g/l if receiving water is salty, but < 1 g/l if fresh (e.g.mulder and Syvitski, 1995) Spring freshet TSS > 1g/l) plus ice constrained! Hypopycnal Homopycnal Boggs, S Principles of Sedimentology and Stratigraphy, 2nd edition, Prentice Hall Hyperpycnal

7 Methods Synthetic Aperture Radar (SAR) for mapping bottomfast ice MODIS imagery to monitor progression of breakup in near-real time Time lapse camera flood elevation and timing Water level gauges on-ice water levels Helicopter overflights and on-ice observations Sidescan sonar and depth sounding strudel scour mapping

8 Setting the stage: Winter Bottomfast Ice Development Ice Elevations ( -5.1 to -4.8 ( -5.4 to -5.1 ( -5.5 to -5.4 ( -5.6 to -5.5 ( -5.8 to -5.6 ( -6.8 to -5.8

9 Bottomfast ice controls on overflow and drainage End of Winter Early breakup Mid-breakup

10 BFI influence on water flow and channel incision

11 Nearshore BFI conditions prior to breakup

12 Spring breakup 2008 May 7, 18, 20, 22, 23, 24, 25, 30, June 4, 7, 11

13 Discharge and Overflow Timing Overflow precedes peak WL by several days to 2 weeks Overflow Initiation Overflow Max peak WL Inuvik 07- may May May May May Jun-07 Peak WL Outer delta 1-3 Jun-08 4-Jun May May May May May May May May Jun May May Jun-03

14 Overflow sediment concentration Overflow waters variable sediment concentrations Peak freshet concentration: Lesack data 2007 peak Suspended Sediment 2008 loads exiting delta in Aug /3 5/8 5/13 5/18 5/23 5/28 6/2 6/7 6/12 6/17 6/ Mackenzie at Arctic Red Middle Channel (MD) East Channel (MD) Middle Channel at Langley (OD) Reindeer Channel (OD) Napoiak Channel (OD) West Channel (OD) East Channel (OD) Arctic Red River Peel River Peel Channel (MD) Apr May-08 1-Jun Jun Jul Jul Aug-08 9-Sep-08 Mackenzie at Arctic Red Middle Channel at Langley (OD) East Channel (OD)

15 Initiation of Breakup Rising limb of the spring freshet Increased discharge from southern drainage basins Initiation of overflow, backwater effects Increased current velocity in ice-constrained channels? May 7, 18, 22, 2008 Local backwater effects?

16 Coastal well-site K30 looking north May 18 May 21 Backwater flooding May 31 June 3 Freshet Peak

17 Overflow water levels over ice Apr May 10-May 17-May 24-May 31-May 07-Jun 14-Jun BH4depth_corr Strudel_depth_corr Tuk_WL_24hMA

18 Overflow and upwelling May 21-22, 2008

19 Strudel Drainage l l l l f gg g f l g ff g ff ff f gg gg g gg f f gggg g lll f f ff f f f f f f f f 0 5 kilometres 10

20 Strudel Scours

21

22 Summary and Conclusions Upwelling, overflow and strudel drainage energetic but short-lived processes precede peak discharge by several days to two weeks locations are controlled by the distribution of BFI Backwater flooding and overflow are indicators of iceconstraints at distributary mouths Timing of overflow drainage indicates removal of constraints prior to peak discharge Flow perturbations at constraints are unknown Strudel scour is extensive locations appear to be predictable Infill may occur within a single season Future: What is happening to the dirt? Erosion at ice-constrained channel mouths Behaviour of suspended materials in plume Physical modelling of strudel drainage