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Water Temperature Measurements - Torbay South - 2020-09-15


These measurements were taken on a kayak trip from Broadsands east to Brixham, then north to Roundham Head and then south back to Broadsands.

Low tide was at 10:05 UTC and high tide at 16:36. The wind was a light northerly weakening throughout the day, the sky was clear and the sea was glassy smooth.

Time Series

The graph below shows a time series of temperature measurements (vertical axis) covering a three-and-a-half hour period (horizontal axis). The gap shows times when the kayak was out of the water.

    Time Table
  11:12     11:52     Broadsands to Brixham  
  13:06     13:57     Brixham to Roundham Head (Goodrington)  
  13:57     14:35     Roundham Head to Broadsands  

Paddling from Broadsands to Brixham the temperature was almost constant at about 17.6°C. The only exception was at the start within Broadsands Bay (before 11:15 UTC) where the temperature was warmer (in the range 17.6 to 18.7°C). Low tide had been at 10:05 UTC so at this time the sea was advancing up the beach.

In contrast after leaving Brixham and heading directly across the Bay to Roundham Head the temperature increased from about 17.7 to 20.0°C.

Returning south along the coast the sea temperature mostly remained high except just south of Shell Cove where we played in some rock canyons.

Off Dartmouth 3 hours before high water the tidal stream is 0.5 knots from 235° during Springs and 0.3 knots from 235° during Neaps. This trip was undertaken a few days after a Neap tide and the streams within Torbay are likely to be considerably less than those off Dartmouth.

Measurements Overlaid on Maps

The following link shows measurements of temperature overlaid on an interactive map. The colour of the circles are indicative of the temperature and the detailed values can be read by clicking on these circles.

      Overview of temperatures - see above link for interactive version.

The graph below shows schematically the vertical temperature profile of the sea

In light wind daytime conditions solar heating warms the top few centimetres of the water.

In strong winds, or breaking waves, the water column near the surface is mixed so that the temperature is relatively uniform.

On the first leg (Broadsands to Brixham) small waves, driven by the light northerly wind, were breaking on the rocks. It seems likely that this resulted in mixing surface and lower layers to give little or no vertical temperature gradient. During this passage the sea temperature was about 17.5°C.

On the leg from Brixham to Roundham Head the sea was glassy smooth (see photo above) this appears to have allowed allowed the surface layers to warm. In this section the temperature reached 20°C.

The temperature mostly remained relatively high between Roundham Head and Broadsands. In this section the northerly wind was parallel to the coast and any waves produced travelled along the coast without breaking. Thus it would appear that the surface warming was not destryed by turbulence.

There were some 'dips' in temperature. At least one such dip can be related to playing in rock canyons. In these regions small changes in sea level caused the water to 'slop around' - presumably resulting in mixing.

      Low temperatures in the rock canyons.

      Torbay Chart