These measurements were made on an out and back trip from Dittisham to Warfleet Cove (Dartmouth). The outbound trip followed a falling tide and the return trip a rising tide. The wind was southerly to start, rising to a south westerly Force 4 on the return.
| Label | Time | Height |
|---|---|---|
| - | 06:25 UTC | High Tide at Dartmouth |
| A | 10:03 UTC | leave Dittisham |
| B | 11:12 UTC | arrive Warfleet Cove |
| - | 12:18 UTC | Low Tide at Dartmouth |
| C | 12:17 UTC | leave Warfleet Cove |
| D | 13:32 UTC | arrive Dittisham |
| - | 18:35 UTC | High Tide at Dartmouth |
The following graphs show the measurements made as a function of time. The points marked A and B show the start and end of the outbound section; and C and D the start and end of the return trip.
... click on an image for a full size graph ...
By combining observations made from the kayak the with position-time information from a GPS the location of each measurement can be determined. These values can then be plotted on an interactive map.
In the maps below measurements from the kayak are presented as colour coded circles. By clicking on a circle the actual measurements can be examined.
On the maps the left hand track (Dartmouth side) is the outbound trip; and the right hand track(Kingswear side) is the return trip.
... click on maps for full size image ...
Fresh water flows down the River Dart. The section of the Dart from the sea up to Totnes is tidal so sea water and fresh water mix.
With an incoming tide, salt water pushes up the estuary and mixes with the fresh water from the river. The concentration of salt reduces as you approach Totnes.
Sea water typically has a salt concentration of 3.1 to 3.3%.
Leaving Dittisham the salt concentration was 2.7% and increased to 3.1% at Warfleet Cove.
On the return trip the concentration decreased from 3.1% to 2.4%.
Dissolved oxygen values ranged from around 100% near Dittisham down to 89% at Warfleet Cove.
In this section of the Dart the high salinity values compromise the nitrate measurements. Although the 'nitrate' sensor is around 1000 times more sensitive to nitrate ions than cloride ones. Salinity values above 20 ppt completely mask nitrate levels of up to 20 ppm.
The graphs at the top show that the measured 'nitrate' values follow the observed salinity ones - so the nitrate graph is shown as a red line to indicate that these measurements are erroneous.
The pH values observed ranged only from 8.19 to 8.28 (i.e. slightly alkaline).
Turbidity (or cloudiness) is measured using an instrument which measures the amount of light scattered at right angles to a light beam. Clear water will scatter very little light but as cloudiness increases more light is scattered.
In the present instrument the intensity of light scattered is repored as a frequency; with higher frequencies corresponding to greater turbidity.
Higher values of turbidity were measured when passing Dartmouth, and on the approach to Dittisham.
A spike was noticed in all the measurements at 13:17:30 (13:18:40 in the case of the Turbidity probe whose clock was incorrectly set).
This was at a point just before the Greenway Boat House (Greenway being the holiday home of Agatha Christie)
At this point where the water was very shallow.