Floating sticks
What is river velocity?
River speed is referred to as river velocity, which changes along the river. It plays a crucial role in shaping landscapes and altering the aquatic ecosystems. River velocity is determined by factors such as gradient, discharge, and channel characteristics. It reflects the river's energy and capacity to transport sediment. River velocity can also affect aquatic ecosystems by impacting organism distribution and abundance. Fast-flowing rivers can erode riverbanks and shape distinct landforms that alter habitats, while slow-flowing rivers facilitate sediment deposition and provide more space for organisms to settle. The velocity of rivers can also affect aquatic animals' migration upstream or downstream in their life cycle. As it carries pollutants along the river, it also facilitates accumulation of pollutants downstream, which can effect water quality. River velocity is essential for scientific research and enriches our appreciation of rivers as dynamic and ever-changing factors in the natural landscape.
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Measuring river velocity is an essential method of understanding the dynamics of water flow in rivers. There are various methods that can be used. One common method is the float method, where an object is released on the water's surface, and the time it takes to travel a known distance is recorded. The velocity can then be calculated based on the formula velocity = distance/time. We can find out how fast the water is flowing by playing poohsticks.
Illustration from 'The Poohsticks Handbook: A Poohstickopedia' by Mark Evans (Egmont Publishing).
Illustrations by Mark Burgess after E H Shephard. Copyright 2015 Disney Enterprises Inc.
Based on the 'Winnie-the-Pooh' works by A.A. Milne and E.H. Shephard.
Poohstick!
Find a stick near a bridge over the Water of Leith near your home. Pick up any little stick you like from the surroundings (remember not to break any branches to get the stick, just grab those that have fallen). Determine which direction the River is flowing and stand on the side of the bridge facing the upstream. On a count of three, drop the sticks into the River simultaneously (no throwing, just gently dropping them). As soon as the stick hits the water and starts floating, start the timer, then walk quickly to the other side. The excitement lies in watching which stick emerges first on the downstream side. Once the stick emerges, stop the timer. If you divide the time it takes the stick to flow through the bridge by the width of the bridge, you will get the river velocity. You can repeat this process a few times to get an average velocity. Is the River flowing faster or slower than you think?
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If there is another bridge nearby, you can extend the distance for the stick to flow, which is from one bridge to another. It is fun to take turns being the timekeeper and the one dropping the stick between parents and children. Compare the result with the previous one. Is there any difference between them? Which one do you think is closest to the accurate flowing speed?
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Or, if you are on a bridge that is right at the river meander, you can test the difference in river velocity between dropping the stick on the inner bank and outer bank separately. Can you observe any difference? Do you know why that was the case?
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Playing Poohstick is a fun way to explore the river and learn about the science behind river flow. Through this game, you can observe river velocity and learn about the effects of river meanders on the speed of the water. It is a great way to bring the family together and have some outdoor fun!