SQ Summer 2017 - ADCP results

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CSL Heron Squamish Operations
April-October 2017

ADCP Results - first deployment

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

ADCP Results.

The UNB 600 kHz ADCP was suspended beneath a surface buoy, anchored at two locations on either side of the channel floor. The ADCP was ~ 12m off the bottom at low tide (it would move up and and down ~3-5m with the tide). The system was configured to acquire 10 ping ensembles every 20 seconds. The bin size was 25cm.

The following plots have been generated by Liam Cahill using the data from the first 6 week deployment period.

Flow JD126: 6th May Peak ~ 0.4m/s
Flow JD131: 11th May Peak ~ 0.4m/s
Flow JD144: 24th May Peak ~ 0.4m/s
Flow JD147: 27th May Peak ~ 0.4m/s
Flow JD148: 28th May Peak ~ 0.2m/s
	The next three flows (JD150 - A, B C) all occurred within the same low water period within ~ 1.5 hours. (followed by another very weak one 3.5 hours after the first)
Flow JD150A: 30th May Peak - 3.5m/s The first major one of the year - 2048 - first of day...
Flow JD150B: 30th May Peak ~ 0.6m/s - 2135 - (47 minutes later)
Flow JD150C: 30th May Peak ~ 0.4m/s - 2213 - (38 minutes later)
this weak one is actually late on the same LLW.
Flow JD151: 31st May Peak ~ 0.25m/s - 0030 - (2 hours 15 minutes later)

Flow JD152: 1st June extremely weak, but clearly the remnant of an event.
Flow JD153: 2nd June Peak ~ 1.8m/s - 2235
Flow JD156: 5th June Peak ~ 0.7m/s neither a river surge (actually a drop) nor a spring LW.
	The next two flows (JD158 A and B) occurred within the same low water period within a half hour.
Flow JD158A: 7th June Peak ~ >2.0 m/s - 1650 - first of day...
Flow JD158B: 7th June Peak ~ > 4.0m/s the fastest so far. ~ 8 knots! Note that the suspended sediment concentration becomes so high that the ADCP backscatter is attenuated in the lower part of the flow. - 1718 - (28 minutes later)
and two more slow suspended sediment pulses at: 1910 and 1945 - possibly distal remnants of flow from the north or central channels?
	The next three flow (JD159 A, B and C) all occurred within the same low water period within 1.5 hours. As can be seen, the range to the seabed is moving up and down which implies that either the ADCP mooring is not stationary or the seabed is changing underneath the ADCP. In this case we were able to exactly locate the ADCP as we could see it in the 710 water column when we steamed by for the third flow. The ADCP is actually suspended over a bedform on the channel floor. Before the third flow, it was upstream of the crest, and after the flow the bedform had migrated upstream and thus the apparent seafloor dropped into the trough. Superimposed on this though is the possibility that the ADCP on its ~155m long tether is swinging gently when disturbed by a passing flow.
Flow JD159A: 8th June Peak ~ 1.5m/s - 1711 - first of day...
Flow JD159B: 8th June Peak ~ 1.5m/s - 1813 (one hour later)
Flow JD159C: 8th June Peak ~ 2.0m/s - 1838 (25 minutes later) This is the one that we chased down channel with the Heron.
On June the 8th at 2032 (well after the low water) the ADCP was lifted and the data downloaded and the battery replaced. It was subsequently redeployed on the early morning of the 9th of June, well before the following lower low water. There was no overnight bathymetric change.Thus no missing flow are suspected. Based on daily bathymetric surveys for the next 5 days, there were no further flow events. We have yet to recover the ADCP for the June 9th to July 11th period to see the subsequent activity.
	Subsequent Flows yet to be processed...

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