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When we sample downstream on a rocky section by the old quarry the children net five or six Bullheads. It is some years since I've seen them and I'm glad that the colony appears to be thriving. The fish range in size from the length of a matchstick to as long and as broad as my thumb.They spread their reddish pectoral fins like a butterfly's wings to clasp the stream bed.
The Satsuma MethodWe calculate the mid-stream surface flow by timing how long it takes a satsuma to progress along a ten metre length of the stream. Two trials 33-38 seconds, so the satsuma would take 55-63 minutes to travel a kilometre, so the speed of flow is roughly 1 kilometre per hour (0.62 mph).The satsuma is ideal for this experiment as it is bright, it floats, it doesn't easily get snagged and, if you loose it, it is bio-degradable.
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