Heron Fraser May 2022

time sequence of salt wedge intrusion

Imaging the Salt Wedge
Sands Head to Steveston, Fraser River Mouth
CSL Heron, May 23, 24, 25^th, 2022

page version
May 30th 2022

surface expression of river plume front
75 m depth, SE of river mouth

John E. Hughes Clarke
Center for Coastal and Ocean Mapping
University of New Hampshire

Mathew Wells
Dept. Physical and Environmental Sciences
University of Toronto

CSL Heron professionally skippered by Jada Cavanaugh.

Research Objectives

This field program was undertaken in order to support two objectives:

The PHD thesis of Indra Prasetyawan (UNH) on imaging estuarine turbulence
The NSERC-supported research of Prof. Mathew Wells (UofT) looking at suspended sediment behaviour across shearing haloclines.

Operational Window:

The original plan was to operate using the spring tide window of June 11th to 16th. Due, however, to other ship commitments of JHC, this earlier window had to be utilized.
Three days were scheduled with a transit into the estuary in the afternoon of the 23rd, the full day of the 24th, and a transit out in the morning of the 25th.

the net result was ....

Oceanographic Variability

Over the course of the 3 days, 220 MVP profiles were obtained (46 on the 23rd, 132 on the 24th and 37 on the 25th). The MVP standardly operated to within 3m of the bottom (typical overshoot of about 0.5m) and with a 1 minute pause after each recovery. Dip density was thus much higher steaming upstream than downstream. Generally ~ 7 knots through the water was used for upstream legs, and ~ 5 knots through the water for downstream legs.

showing all dips on each day - especially the high gain (clipped) and low gain optical backscatter.

MAY 23rd. - ALL MVP Profiles

NOTE the significant thermal intrusion at 5m depth.
Note also the optical noise (?) within the top meter, presumably due to surface light contamination.

MAY 24th. - ALL MVP Profiles

surface optical noise still present

MAY 25th. - ALL MVP Profiles

Note the highest optical backscatter seen on all 3 days.
Note the lack of a thermal intrusion
Note also the lack of any near-surface optical backscatter noise, perhaps due to fish facing consistently down?

All MVP dips collected on the 4 transects are presented as linked tar balls below. Two formats are provides, both native to the Brooke Ocean MVP sensor. They are:

.m1 - containing all the observed and derived hydrographic components as well as the high-gain optical backscatter voltage (which is clipped).
.raw - containing a subset of the data as well as the low-gain optical backscatter (which is the best proxy for the suspended sediment load as it is not clipped).

Specific Longitudinal Profiles

The most pertinent observations tend to come from looking at discrete longitudinal sections. Over the course of the 3 days, four sections from off the delta lip to the Woodward Reach were collected. They are presented here below with preliminary comments.

ADCP data is presented as the along-channel flow component. Colours saturate at +2m/s (red) or -2m/s (blue).

May 23rd (JD 143) 2022 - Section A (steaming upstream)
Comments: - Late ebb tide, lowest water level observed - salt wedge fully arrested. ADCP set to 1m bins (all subsequent surveys utilized 0.5m bins). clear presence of a warm subsurface layer coming in from the open ocean.

Detailed Sections - click for 2.5m alongtrack resolution EM2040 WCD and MVP Temperature, Salinity and Optical Backscatter Overprinted.

all mvp dips in line

May 24th (JD 144) 2022 - Section B (steaming downstream)
Comments: - Weak late flood tide - salt wedge inflowing and past bend extending half way up Steveston Reach.

Detailed Sections - click for 2.5m alongtrack resolution EM2040 WCD and MVP Temperature, Salinity and Optical Backscatter Overprinted.

all mvp dips in line

May 24th (JD 144) 2022 - Section C (steaming upstream)
Comments: - lower high water - maximum observed penetration of salt wedge. Inflowing salt layer of similar speed as outflowing surface waters.

Detailed Sections - click for 2.5m alongtrack resolution EM2040 WCD and MVP Temperature, Salinity and Optical Backscatter Overprinted.

all mvp dips in line

May 25th (JD 145) 2022 - Section A (steaming downstream)
Comments: - Just after a weak low water. Salt wedge is almost all downstream of the bend. Note the remarkably murky conditions close to the seabed upstream of the salt wedge, implying entrainment of river bed sediment once the river shear can interact directly with the bottom.

Detailed Sections - click for 2.5m alongtrack resolution EM2040 WCD and MVP Temperature, Salinity and Optical Backscatter Overprinted.

all mvp dips in line

Suspended Sediment Sampling:

Nine Nisken Bottles were successfully triggered on the upstream section (C_Up) on Mat 24th (JD144). They were collected at three depths at three locations.

For each, the closest pair of MVP dips is indicated (see tar ball linked from the 144 C_Up transect above).

Downstream Samples:

#	lat/lon deg/min/sec	decimal lat/lon	depth (m)	closest MVP dips	comments
1	49 06 40.4899 N -123 -17 -01.9928 W	49.111247 -123.283887	1	250 252
2	49 06 32.2498 N -123 -17 -31.8306 W	49.108958 -123.292175	5	247 248
3	49 06 34.4135 N -123 -17 -10.8881 W	49.109559 -123.286358	8	249 251

Midstream Samples:

#	lat/lon deg/min/sec	decimal lat/lon	depth (m)	closest MVP dips	comments
4	49 07 24.8307 -N -123 -15 -10.7057 W	49.123564 -123.252974	2	263 266
5	49 07 22.4391 N -123 -15 -19.2473 W	49.122900 -123.255346	7	263 265
6	49 07 20.0058 N -123 -15 -29.4972 W	49.122224 -123.258194	11	262 264

Upstream Samples:

#	lat/lon deg/min/sec	decimal lat/lon	depth (m)	closest MVP dips	comments
7	49 07 01.7967 N -123 -11 -17.3246 W	49.117166 -123.188146	2	287 286
8	49 07 03.7465 N -123 -11 -22.3182 W	49.117707 -123.189533	6	286 287
9	49 07 06.9151 N -123 -11 -30.4765 W	49.118588 -123.191799	11	285 286

Other Thoughts.....

Hopefully we'll be able to come back on the stronger spring tides in late June.

page developed by JEHC, May 25th-31st 2022