Why does the tide of Thames river go backwards sometimes?
In: Physics
Rivers don’t have tides, they have a flow (from higher to lower ground, towards the sea.)
Some rivers, like the Thames, are flat enough and wide enough for the tide of the sea they enter to push the river water back during high tide. When low tide comes, the river can start flowing in its natural direction again.
That’s my best attempt.
It helps that the Thames has a half-tide lock and weir at Richmond. This stops the river level falling between Richmond and Teddington so the boats up there don’t beach. Holding back the fresh water flow makes it easier for the tide to flow upriver.
Going the other end, the Thames Barrier is an incredible structure (500 metres long and 20 metres high), designed to hold back the highest tides so they don’t flood the city. It has four gates that weigh 3,700 tons each.
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