GROUP
Plymouth Field Course 2019
4
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ADCP Transects
ADCP Description:
ESTUARY
Overall, the ADCP data provided us with a detailed view of the water column from station 1 which was situated relatively high up the river next to the River Tavy confluence and finishing at the break water; which was situated roughly in the middle of Plymouth Sound. For the duration of profiling using the ADCP, the bottom tracker feature of the ADCP on board RV Falcon Spirit was switched off. This caused the instrument to not recognise the strong acoustic signal of the ground producing incorrectly calibrated ADCP profiles. In addition, there were large gaps in the data resulting in black spots on the ADCP profiles, potentially caused by interference of the CTD or the malfunctioned bottom tracker. For this reason, the Richardson number could not be calculated. This was due to having incorrect data so the bouyancy could not be analysed.
At Station 1 a clear, fast water stream at the surface was visible between minutes 0 and 1. A possible reason for this could have been due to the influx of fresh water from the Tavy confluence. ADCP 3 showed a stratified surface layer of lower salinity, clearly separated from a well-mixed bottom layer of higher salinity and therefore denser which began at roughly 10m. This separation of layers also occurred in ADCP 5, which had a thick layer of fast flowing water separated by slower moving water from 20m and bellow. At ADCP 6 a high velocity flow was present in the middle of the water column which could have been a water body with less friction due to no surface or bottom friction, thus faster moving. ADCP 10 was a super mixed area with little to no separation. This station is in the middle of the estuary so is quite deep and is evidently very turbulent. There was a minor separation of a very fast flow at 0min in the top left corner which was a potential input into the surface.
ADCP 13 is from station 6 (St. John’s Lake) where a visible front was observed. This
could explain the section of slow flowing water to the far left. ADCP 16 from Station
8 (Breakwater) showed a well-mixed water column. In the transect that started at
the breakwater (ADCP 17), there was an area of faster flow just below the surface.
This could be explainsed by the breakwater causing the water column to become more
shallow and therefore faster flowing. ADCP 18 and 19 were from either side of the
breakwater. On the west of the breakwater (ADCP 18), the water column was deeper
which could explain why the water column was more mixed, compared to the more stratified
water column at the east of the breakwater (ADCP 19) which was shallower. There was
a subsurface layer of faster flowing water on top of slow flowing water, which was
likely to be of a higher salinity (and therefore denser, explaining why this was
at the bottom of the water column).
ADCP Data: