Tides/currents Etc

kpnut · February 14, 2023

Following on from a discussion a few days ago, (which I now can’t find), during which we were musing on why the aweigh app was giving odd readings, I decided to start reading a very large book I’ve had for years. The Land Use, Ecology and Conservation of Broadland by Martin George, published in 1992.
It’s a book I won in the raffle at an open day at Barton Broad Nature Reserve in about 1997 and has been in the possession of my daughter for the last 15 years while she went off to uni to study freshwater ecology. She recently found it in her muddle and returned it to me.

A passage on page 60 (just in case anyone else has this book and wants to look it up) caught my eye. I’ll have to quote it word for word I’m afraid.

“At Yarmouth yacht station the river continues to ebb for about an hour and a quarter after the tide has started to flow up the river Yare (thus carrying water from the Bure up into Breydon Water). But the water in the Bure is rising rather than falling during this period.
Conversely, water levels in the lower Bure start to fall long before the the flood tide has ceased to run. At Stokesby for example, the upstream flow continues for almost 2 hours after the water level has started to drop. Similarly, the ebb commences in Fleet Dyke and Ranworth Dam while the sections of the river Bure with which these waterways are connected are still on the flood”.

Now, for those very familiar with the Broads and their tides etc, that’ll be no surprise, but it poses lots of questions and certainly should encourage us all to look out of the window and ‘watch the bubbles’ rather than relying too much on the tide tables.
If water coming of the Ranworth Dam on the ebb meets water still going up the Bure on the flood, that must mean that the ebbing water is actually carried upstream rather than down.

kpnut · February 14, 2023

Also an earlier paragraph on the same page got me pondering too.

“A further complication is that the direction of the tide-induced currents does not change at the same time as the water attains it’s highest and lowest levels. At Reedham for example the gradients set up on the river Yare during a tidal cycle cause the ebb to continue to run until the water downstream has attained the same level as that upstream. During this period, the water level will be rising at Reedham even though the tide is on the ebb. After a brief period of slack water, the gradient in the river will be reversed, and the tide will flow upstream on the flood until the water levels in the lower reaches of the river have fallen sufficiently to cause another gradient reversal, and a consequent change in the direction of the tidal current”.

So the bottom line is the water runs in two directions at once. I’m totally confused and will just rely on my what I see!!!

Hope someone finds this of interest and no-one loses any sleep over it!

grendel · February 14, 2023

it certainly reflects what I have seen at Polkeys mill, with the flow going out, yet the river level rising, and vice versa later on with the flow coming in, yet the river level is dropping.

though it doesnt so much explain it as just describe what we see happening.

me I just go with the flow (or should that be against the flow?)

ie stop the boat, see which way she moves, moor accordingly