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Index
 CSL Heron Squamish Operations
April-October 2017

2017 Seabed Morphological Change

John E.Hughes Clarke, Anand Hiroji, Liam Cahill Ian Church,  Angela Gillis
Center for Coastal and Ocean Mapping
University of New Hampshire, USA
 Ocean Mapping Group
University of New Brunswick, Canada

The South Channel

For all multibeam data collected along the south channel corridor, a standard rotated map is presented that aligns with the channel axis.  The following figures illustrate sequential surveys along the channel illustrating changes over monthly and/or daily time periods.

Monthly Changes:

The following images illustrate the long term changes over periods of months or weeks.
Over Winter Changes
bathy
change

Oct 2016
to
Apr 2017
 over winter
As can be seen, the 16-17 winter was a period of remarkably activity. This reflects the unusual amount of rainstorm events in the autumn period.
Note that this difference map utilizes survey data collected by GSC and NOC on board the CCGS Vector the previous October.

Spring low discharge inactivity.
bathy
change

April
to
May

low
discharge
 low discharge
As indicated by Environment Canada's discharge record, there was little likelyhood of major flow events in the first period. The ADCP, however, clearly showed that three flows did occur in this window, but with a maximum flow velocity of ~0.3m/s.

First flows of the year
bathy
change

May
to
June

increased
discharge		 may to june
In the next two weeks there was much more activity. Based on the ADCP data, while there were 9 flows, the seabed change was probably dominated by just two of them.


Daily Change :

While the previous three epochs show change that results from multiple flow events, for a one week period in June, we undertook daily surveys to see if we could catch a singular flow.

For the first day only we succeeded in exactly that. This was really rather lucky, and to put it in perspective, the day before we arrived, the fastest flow of the year happened. All this illustrates that it would be ideal to establish a long term monitoring scheme capable of maximum observations when one of these rare, irregularly time significant events happen.

The following set of figures illustrate the change and activity  - before/after singular flow on JD 159 ( June 8th) 2017:

Bathymetry Changes
bathy
before
 bathy before
bathy
after
 bathy after
bathy
difference
 bathy difference

Backscatter Changes
backscatter
before
 BS before
backscatter
after
 BS after
backscatter
difference
 BS change

Imagery During Flow Passage
backscatter
while
flowing
 BS of flow itself

This is a remarkable image and was only, honestly, acquired through blind luck.

After completion of the southern line, Heron turned to the north, crossing just behind the head of the flow and then proceeded to image the body of flow as the Heron steamed back to the west on the north side of the channel. The Heron is running at ~ 3m/s and the flow is moving at about 2m/s. About 3/4 of the way back along the channel, the Heron overtook the head of the flow.
A separate page is being prepared that shows the water column imaging as the body of the flow was examined.







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