by Mark Halverson (University of British Columbia)
The Fraser River reaches the ocean near Vancouver, and there the fresh water it carries mixes with ocean water to form a thin plume of buoyant brackish water, which according to one oceanographer is the “showpiece of the Strait of Georgia.”
Oceanographers have been studying the Fraser River plume since at least the 1960s, but more recently, VENUS has installed a radar system to measure the surface currents in this region. Furthermore, VENUS has also installed the Seakeeper seawater monitoring system on the BC Ferries MV Queen of Alberni to collect detailed information of water properties along the Duke Point – Tsawwassen ferry route which cuts through the plume eight times per day. These new observations, coupled with satellite imagery, are being used by UBC researchers Dr. Mark Halverson and Prof. Rich Pawlowicz to reveal the nature of the Fraser plume. The research is being carried out as part of the Marine Environmental Observation Prediction and Response Network (MEOPAR), which is tasked with improving Canada’s ability to respond to marine hazards.
In the early summer when the Fraser River carries high sediment loads, the plume is easy to distinguish from ocean water by its distinct light brown colour (Fig. 1). It can be highly reflective and opaque to sunlight, and because it is a mixture of river and ocean water, it can be quite “fresh.” A comparison of the measured surface currents to both surface water salinity and satellite imagery shows that a jet of swiftly flowing water can form near low tide (Fig. 2).
A sharp change in the currents occurs where the ocean colour and salinity change rapidly, signifying the edge of the plume. As the plume waters move away from the river mouth, it appears that the wind ultimately determines its fate. During northwesterly winds, the plume is driven to the south, while during southeasterly winds, it is driven to the northwest (Fig. 3). However, the relative importance of the wind might change when the river flow is much higher. Ultimately, researchers hope that a better understanding of the surface currents in this area will be useful to emergency response operations by providing a way to anticipate the trajectory of, for example, spilled oil or other contaminants.
After three years of planning, design and construction, the Buoy Profiling System (BPS) is now ready to be installed. On Aug 1, the Saanich Inlet-destined 7-m wide buoy structure was successfully launched in Patricia Bay. The next step is to secure the buoy in place 4 km south of the Node using a triple mooring, and the connection of the system to the VENUS Node in Saanich Inlet via a specialized power and communications cable. The buoy is presently tied to the wharf at the Institute of Ocean Sciences (IOS) undergoing final inspections and testing, and will be relocated to the centre of Saanich Inlet at the end of August, where it will routinely profile the seasonally anoxic waters in Saanich Inlet using standard and customized instrumentation.
In the image: Buoy Profiling System is being towed to the IOS dock for final testing; Paul Macoun aboard the buoy.
“Integration of ocean gliders into the ONC observatories is progressing”, advised Paul Macoun – Project Manager of the VENUS Phase II developments. Presently, the engineering team is working up the first of two gliders for deployment off-shore this summer.
“The science community is eagerly waiting for the new system to be available to conduct research in the water column”, confirmed ONC Associate Director of Science Dr. Richard Dewey. After initial testing in Saanich Inlet in July, the glider will have a full field trial in August off the west coast of Vancouver island linking water properties between Barkley Canyon and Barkley Sound”.
In the image: Rowan Fox, a technician working for Dr. Jody Klymak, UVic SEOS, assists VENUS engineers to conduct buoyancy testing at the Marine Technology Centre.
|G2 Slocum Electric glider specifications:|
|Hull Diameter||21.3 cm|
|Vehicle Length||1.5 meters|
|Speed||0.4 m/sec horizontal average|
|Endurance||Typically 30 days, depending on measurements and communication|
|Navigation||GPS, magnetic compass, altimeter, subsurface dead reckoning|
|Sensor Package||CTD and oxygen|
|Communications||RF modem, Iridium satellite, ARGOS, Telesonar modem|
For more details visit Teledyne Webb Research.
In April 2013, the AUV (“Bluefin”) successfully ran a test science mission in Saanich Inlet. Operated by engineers from the UVic's Ocean Technology Lab, led by Dr. Colin Bradley, the AUV enhances capabilities of VENUS – the coastal ocean observatory of Ocean Networks Canada.
For test deployment in Saanich Inlet the AUV was equipped with key oceanographic sensors, oxygen and temperature, and a multibeam sonar to scan the seafloor. The test mission focused on mapping the Inlet structure to assess both the early spring conditions and whether any mid or deep water intrusions have occurred.
According to Dr. Jody Klymak, an oceanographer from the UVic's School of Earth and Ocean Science, who helped to organize the science mission, the main objective of the mission was to fully assess capabilities of the mini-sub. “It is an advanced multipurpose tool, and we would like to see it support ongoing research programs at SEOS”. The AUV is capable of powered flight in waters down to 200m depth and can run for up to 8 hours gathering valuable data from the geographically dispersed areas.
Preliminary assessment of the test-mission data from several weeks ago clearly shows that the deep water renewal event in Saanich Inlet has not occurred yet. The event, a long studied natural phenomena, is a harbinger of the spring-coming in Saanich Inlet, when oxygen-rich waters and nutrients finally reach the seasonally hypoxic fjord.
UBC oceanographer Dr. Mark Halverson has been making use of VENUS Coastal Ocean Dynamics Applications Radar (“CODAR”) data from the Strait of Georgia in his research. His analysis revealed an abrupt cutoff in data availability to the south of the coverage area, rather than the gradual fall-off with distance from the two antennae one would expect from purely physical considerations.
Subsequent investigation revealed an overly-restrictive software setting that has since been modified. All ocean-current data going back to the commissioning of the VENUS CODAR array in August 2012 has been reprocessed, extending the coverage of the array southward by about 3 km.
This animated figure shows the coverage area before and after the reprocessing. Thanks go to Dr. Halverson for pointing out this anomaly, allowing us to improve our product. Our users are not mere customers, but active collaborators in the VENUS mission to provide data to the oceanographic community.
The VENUS BPS winch system test on the OTTB Buoy is progressing. Soon after installation in December 2012, the system underwent a site acceptance test with the manufacturer. Following on from this, the Data Management group has now developed a real time linkage between the system and the database. The next stage is to develop the software infrastructure to command and control the system.
The picture shows the instrument cage (centre) being lowered into position under the winch (centre left). An engineer from MacArtney A/S (next to winch in blue) was on site at this time to conduct the site acceptance test. VENUS engineer Paul Macoun (in red) is spooling in winch cable to take up slack as the OTTB crane is lowered.
We anticipate that the software development will be complete by the end of February 2013, at which time the system will come off the OTTB buoy. The next step will be integration with the custom-built buoy at the Marine Technology Centre.
See Buoy Profiling System (BPS) on the map of the VENUS Saanich Inlet array.
Stacked in the image are 48 plots generated from 16 sensors of the VENUS Ferry System installed on a BC Ferries M/V Queen of Alberni. The comprehensive system monitors oceanographic and atmospheric conditions while the ferry transits between Nanaimo (Duke Point) and Vancouver (Tsawwassen).
Oceanographic parameters collected by the system include seawater temperature, salinity, density, dissolved oxygen, turbidity, and the relative concentration of chlorophyll.
Meteorological measurements focus on marine atmospheric boundary layer conditions and include air temperature, humidity, pressure, wind speed and direction, incoming solar radiation, and out-going irradiance.
The image shows a day of data collected on Jan 5th, 2013. For each parameter, data are plotted in a number of distinct ways to show alternate characteristics of the geospatial and temporal nature of the variations.
The data collected by the ferry system are retrieved daily through a series of communications over the cellular network between the ferry and VENUS shore station. Check out the latest ferry data plots at the BC Ferry plots page.
View full-resolution image (right-click link to download) to see the full-sized plots.
The Ocean Technology Lab's (UVic) Bluefin AUV has been retrofitted with a suite of instruments to support science experiments in Saanich Inlet (and beyond).
In the image, the vehicle is in a test tank at the UVic’s Marine Technology Centre (MTC), undergoing a ballasting exercise and general readiness testing on Dec. 14, 2012. AUV missions in Saanich will begin early in 2013.
A joint team of VENUS and UVic/Ocean Technology Lab engineers tested a winch system on the Ocean Technology Test Bed (OTTB) Buoy in Saanich Inlet. The winch is part of the VENUS Buoy Profiling System (BPS) – a water column instrument platform – destined to become a part of the Saanich Inlet array of VENUS. The core structural component of the BPS, 8-meter wide buoy, has been refurbished and currently is at the Marine Technology Center. The testing of the winch conducted in the last week is a planned step on the way to get the BPS ready for its deployment, preliminary scheduled for late springs/summer 2013.
The VENUS data team adds another animated data product to its data plots gallery.
This animated image depicts measurements of the surface ocean currents in the Strait of Georgia over a recent 24-hour period.
The currents are measured using a “CODAR” (Coastal Ocean Dynamics Applications Radar) system. The VENUS CODAR system consists of two antennae, one at the Iona Wastewater Treatment plant, near Vancouver Airport, the other at the Westshore Coal Terminal, near the BC Ferries port at Tsawwassen. These are labelled in the image as “VION” and “VCOL”, respectively.
Each image in the sequence shows the current averaged over an hour. The size of the arrows is proportional to the current magnitude. The location of each measurement is at the midpoint of the corresponding arrow.
The depicted measurements span an entire tidal cycle, but the flood and ebb tides seen in the animation are not symmetric: the southward-trending ebb tide is considerably stronger than the northward-trending flood tide. This is most likely due to the prevailing winds over the last few days which have been from the NW, pushing surface currents to the south. The ebb tide reinforces this flow and thus appears very strong, while the flood tide works against the wind driven flow and thus appears weaker.