Research Document 2019/008

Analysis of the variability of the ocean currents in the Coast of Bays area

By Ratsimandresy, A.W., Donnet, S., Snook, S., and P. Goulet

Abstract

While of importance for processes such as transport of particles to and from aquaculture sites, little has been done to study the ocean current regime to support the aquaculture activities in the Coast of Bays, an area of the south coast of Newfoundland. To complete this gap and to understand the nearshore water circulation, Acoustic Doppler Current Profilers (ADCPs) were used to measure ocean currents in the Coast of Bays between 2009 and 2014. This work describes statistics of measured water currents and results of tidal analyses (sea level and ocean currents). The analyses were performed on two layers within the water column, namely the upper 0-20 m depth and the layer below 20 m.

Significant spatial and temporal variability of the currents was observed. Low median speeds were found in sheltered coves and higher median speed in constricted areas such as those around sills and those within narrow channels. The maximum recorded current speed at each station was generally five to ten times larger than its median speed. In the vertical, the current speed near the surface was generally higher than that at depth with median speed in the upper 20 m being more than 1.3 times that at depths below 20 m. Median current speed tended to be slightly higher in the fall compared to other seasons. The analysis of the monthly variability of the current speed shows the highest maximum current speeds happening in summer or fall months. Tidal contribution to the variance of the sea level was high (~84%) while that of the vertically averaged currents was very low (~10%) except in the upper Bay d’Espoir where it was around 25%. This suggests that in addition to the tides, other and more important forcing drive the coastal circulation in the Coast of Bays region.

This information serves as a baseline for ocean current conditions and for understanding the role of tides in driving the water circulation in the area. It also helps in assessing the potential connection among aquaculture sites and helps in the development of regulatory measures (e.g. Bay Management Areas) to ensure the sustainability of aquaculture activities in Newfoundland and Labrador.

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