Source: \Dropbox\web\raspberry_pi\temperature_analysis\

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Water Temperature Measurements - River Torridge 2021-05-07

Sample Measurements

An up-and-back kayak trip, in two kayaks, was made along the River Torridge starting from Appledore and turning around at Halfpenny Bridge. Both kayaks made water temperature measurements.

The trip was undertaken close to Neap Tides. We left Appledore at mid-tide and paddled with the tide up-stream. We waited near Halfpenny Bridge for High Water then followed the out-going tide back to Appledore.

For most of the trip the river is estuarine with large mud banks and sandbanks.

  Appledore Tide Times: 2021-05-07
StateTimeHeight
  Low     09:32 UTC     0.94 m  
  High     15:14 UTC     5.79 m  
  Low     21:47 UTC     0.94 m  




Temperature Time Series

The graph below shows a time series of temperature measurements (vertical axis) covering the period of the trip (horizontal axis). The measurements include times when the kayak was out of the water [points D-E].

Measurements from the blue kayak are shown in blue and from the orange kayak in red. The raw measurements from the orange temperature sensor were 0.32°C warmer than those from the blue sensor, this amount has been subtracted from the values displayed. This discrepency is within the accuracy expected from DS18B20 sensors (±0.5°C).


    Click image below for full size graph




      Features in Graph
LabelTimeHeight
  A     13:21 UTC     leave Appledore  
  B     14:6 UTC     warm water temperatures  
  -     15:14 UTC     High Water Appledore  
  C     15:20 UTC     turn around at Halfpenny Bridge  
  D-E     15:41 - 16:06 UTC     stop for coffee  
  F     16:30 UTC     warm water temperatures  
  G     17:34 UTC     arrive Appledore  




Mapping


      Non-interactive Summary Map


By combining these temperature-time measurements with position-time information from a GPS the location of each temperature measurement can be determined. These values can then be plotted on an interactive map.

In the maps below measurements from both kayaks/sensors are presented as colour coded circles with whites and greens being cold, and reds and purples being warm. By clicking on a circle the actual measurements can be examined. One set of maps shows the measurements made travelling upstream, and the other set downstream.


Discussion

Both the graph and the coloured maps show that the water temperature was about 11.5°C on setting off [A], increased to about 13.0°C in the meander opposite Landcross [B] and then decreased to around 11.5°C at Tadpole Bridge [C]. There was a small temperature spike soon after setting off, and a much larger spike (to 14.0°C) in the meander. In addition there was a negative temperature spike near Tadpole Bridge.

This pattern was repeated on the returen trip. The section [D]-[E] was a break for coffee.

In the meander there was a noticeable amount of flotsam - twigs, sticks, and weed. This appeared to be the highest point the tide reached - and corresponded to the broad temperature peak.

Dry Dock

Adjacent to the old Richmond dry dock in Appledore there was a temperature spike of about 1°C. At this point the kayaks were close to a mud bank which was being encroached by the tide. This might have caused higher temperatures near the shore.






Landcross Meander

As well as a broad rise in temperature in the meander there was a spike of about 1.5°C. On the inner bend (western side) of the meander was a marshy flood plain with a number of channels draining into the river. It is possible that water lying in the mash had been heated during the day and this warmer water was draining into the river.






Tadpole Bridge

Close to Tadpole Bridge there was a negative temperature spike of 0.5°C. There was no obvious cause of such a spike - but if the temperature sensors are removed from the water they are known to suffer from evaporative cooling.