­
River tides, why the flood is faster than the ebb in The AnswerBank: Science
Donate SIGN UP

River tides, why the flood is faster than the ebb

Avatar Image
belP | 15:43 Sat 01st Nov 2008 | Science
2 Answers
On the coast the time between high tide and the next low tide is about the same as the time between low tide and the next high tide (approx 6 1/4 hours).

But in a tidal river it's different: the tide comes in faster than it goes out (fast flood, slow ebb), and the further upstream you are the bigger the difference. So high tide at Hammersmith Bridge is about 40 mins later than at London Bridge, but low tide at Hammersmith is about 2 hours later than LBridge. For example here are the tide times for today (from easytide.ukho.gov.uk):

High at L Bridge 03.10
High at H'smith 03.49 + 39 mins
High at R'mond 04.14 + 1 1/4 hrs

Low at L Bridge 09.52
Low at H'smith 11.48 + 2hrs
Low at R'mond 13.00 + 3 hrs

Can anyone explain why this is?
Gravatar
Rich Text Editor, the_answer

Answers

1 to 2 of 2rss feed

Best Answer

No best answer has yet been selected by belP. Once a best answer has been selected, it will be shown here.

For more on marking an answer as the "Best Answer", please visit our FAQ.
I presume the explanation lies in the flow of the fresh river water..

The incoming tide acts as a dam so as well as the incoming tide itself, there is a build-up of water that has flowed down the river. That adds to the rising tide and makes the water rise even faster making the high tide advance quicker.

When the tide eventually goes out, there is all that extra water that has been dammed up by the tide that then has to flow out whilst still being added to by more fresh water arriving down the river. This larger volume therefore takes longer to drain away making the low tide delayed.
Question Author
Thanks for that answer, I think that's probably it.!

1 to 2 of 2rss feed

Do you know the answer?

River tides, why the flood is faster than the ebb

Answer Question >>

Related Questions

Sorry, we can't find any related questions. Try using the search bar at the top of the page to search for some keywords, or choose a topic and submit your own question.

Complete your gift to make an impact