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Fieldwork in Wales day 2 1/2

Posted by Lindy on October 27, 2009


Water quality:


What was needed: Thermometers strips,  0.5 m of down pipe as explained below, watch with second hand.

The 2 thermometers (one low and one high temperature) were both on sticky backed strips. These were stuck to the bottom edge of a piece of down pipe. The thermometers needed to be kept 10 cm below the surface of the water for 1 minute. So a tape was fixed 10cm from the end of the pipe with the thermometers on, that gave the level and keep the hands dry (and warm). The down pipe was lowered into the water until it reached the level of the tape and timed for I minute. The temperature was recorded.  The thermometer strips showed temperatures rising in gaps of 2. If 3 strips were highlighted, the middle one was recorded. If 2 adjacent number bars were highlighted equally, the average of the pair was recorded.

Dissolved oxygen

What was needed: chemical test tablet, the small tube from the kit, a watch with a second hand, the conversion chart for ppm (parts per million) against temperature.

The small bottle was filled up to the top with water. 2 tablets were added. The bottle was left for 5 minutes. The colour was tested against the colour chart and recorded. Using the conversion chart, the ppm was also recorded.


What was needed: chemical test tablets,  a tube with lid provided in the kit, colour chart.

A sample of water enough to fill tube to the 10ml marker was collected from the river. 1 testing tablet was added and the top was placed on the bottle. It was shaken until the tablet had dissolved and then the colour was checked against the colour chart and the pH was recorded.


What was needed: turbidity disc, container from the kit, comparison chart.

The disc was fixed to the bottom of the container. The water was taken from the river to fill the container and the visibility of the disc was assessed by comparison with the chart. The result was recorded.

The velocity of the river:

What was needed: a supply of aging oranges free from the veg shop, a 30m tape, a stop watch, a fishing net to catch the oranges.

A 10 metre distance was measured along the river bank. The start and the finish was marked. 3 oranges were dropped in the river in different spots across it. This was because it was obvious that the water passing through in different parts of the river varied in velocity and so to get a full range gave a better estimate of the average surface velocity.

The time taken to go from start to finish was recorded. The oranges were hopefully caught after they had passed the finish. Using velocity = distance/ time, the velocity was estimated and recorded. Then the average surface velocity could be found by adding the 3 results and dividing by 3.

The width, depth and cross-section of a river, discharge:

What was needed: the down pipe (to measure depth), the tape (to measure width), velocity measurements

The width was measure using the tape. By exploration, the maximum depth, along the line where the width was measured was also recorded. These 2, given the narrow width of the river, was seen as sufficient to estimate the cross section

cross section

Triangle A = ½ small base x depth

Triangle B = ½ long base x height

Total cross-section area estimate = ½ small base x depth + ½ long base x height

= ½ height ( short base + long base) = ½ height x width

Discharge = velocity (average) x total cross-section estimate

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