Bank Holiday Weekend

River here at Days (Dorchester) has continued to rise overnight and still going up this morning, it will almost certainly burst its banks today and all that water will carryon down. Weekend is a right off:(
 
Do not be fooled by the apparent calm on the surface, there was definitely more water passing through yesterday than there had been the day before. Rest assured, below the surface the water is very ferocious. A lot of the weirs look more tame, due to the tail water (lower level) climbing, making the fall (height difference above/below the lock/weir) considerably less than normal. There is therefore significantly less turbulence as the water flows past the weirs, as the water is not tumbling as far. I hope that was not too technical!
 
A good point. Still interested to know how long, in the absence of more rain, it would typically take to get back to normal levels and flows? A week or less?
 
shades said:
Do not be fooled by the apparent calm on the surface, there was definitely more water passing through yesterday than there had been the day before. Rest assured, below the surface the water is very ferocious. A lot of the weirs look more tame, due to the tail water (lower level) climbing, making the fall (height difference above/below the lock/weir) considerably less than normal. There is therefore significantly less turbulence as the water flows past the weirs, as the water is not tumbling as far. I hope that was not too technical!
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PhWooaar I didn't think the picture of Hambledon Lock's weir (on another thread) looked tame at all...
Quite the reverse. Nasty.

I can't get my head around - given that the downstream level is high, when I look at the EA levels pages for Hurley, it shows the level as being within range??

here

So where's all the water gone?
 
Surely this depends on how much water there is to shift through and the tides at the other end. As much as I'd love to know too (was hoping to be out on the boat for most of the next 10 days originally) I think that there isn't really an answer to this.

Happy to be proved wrong though :-)
 
PaulTG said:
Surely this depends on how much water there is to shift through and the tides at the other end. As much as I'd love to know too (was hoping to be out on the boat for most of the next 10 days originally) I think that there isn't really an answer to this.
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Of course there is no exact answer but I really have no feel for how quickly a body of water moves down the river.
 
shades said:
Do not be fooled by the apparent calm on the surface, there was definitely more water passing through yesterday than there had been the day before. Rest assured, below the surface the water is very ferocious. A lot of the weirs look more tame, due to the tail water (lower level) climbing, making the fall (height difference above/below the lock/weir) considerably less than normal. There is therefore significantly less turbulence as the water flows past the weirs, as the water is not tumbling as far. I hope that was not too technical!
Click to expand...

Not too technical; I can understand the difference between laminar and turbulent flow, and I know what a submerged hydraulic jump is, but the flow is still definitely slower here in the reach above Penton Hook today and the level is no more than 6" above normal; not saying that that won't change like, just how it is right now.
 
jecuk said:
Of course there is no exact answer but I really have no feel for how quickly a body of water moves down the river.
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based on a highly scientific "pooh-sticks" method of flow calculation (how long it takes a bit of flotsam to flow past my boat) the river here is flowing at about 4-4.5 kmh, so a "piece" of water should be able to travel (say) the 77 km from Henley Bridge to Teddington Lock in less than 24 hours
 
I can't get my head around - given that the downstream level is high, when I look at the EA levels pages for Hurley, it shows the level as being within range??


So where's all the water gone?[/QUOTE]

Each weir is exremely efficient. As you mentioned Hambleden let us use that as the example. I am told that the level above Hambleden is only up about 5 inches above normal, but the level below the lock is about 4 feet above normal. Hambleden Weir is able to throw vast amounts of water into the area below it. This water then "queues up" to try and get downstream to the next weir at Hurley which is over 4 miles away. So although water does its very best to run level, in reality there is quite a gradient to it, which is exaggerated as the flow increases. therefore the water will stack up at the top end of each reach, more so on the longer reaches, whereas the level above the lock tends not to vary as much. The lockkeeper alters the weir (until he is unable to open any more) and adjusts the flow to maintain the normal level.
 
Very high and fast at Onsey yesterday, was hoping to launch at the weekend but will probably leave it till next week.
 
Going on since the ice age !

And the good thing thing apart from the rather boaty centric views on here:),is the entire river is getting a blooming good spring-clean with all that man made sh*te being dislodged ,plastic bags,bottles and even worse stuff.
More importantly silt and dead vegetation is being washed away helping everything in the food chain and ensuring a healthy river.
 
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oldgit said:
And the good thing thing apart from the rather boaty centric views on here:),is the entire river is getting a blooming good spring-clean with all that man made sh*te being dislodged ,plastic bags,bottles and even worse stuff.
More importantly silt and dead vegetation is being washed away helping everything in the food chain and ensuring a healthy river.
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Great thats really cheered me up knowing that... :p
 
So although water does its very best to run level, in reality there is quite a gradient to it, which is exaggerated as the flow increases. therefore the water will stack up at the top end of each reach, more so on the longer reaches, whereas the level above the lock tends not to vary as much.
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I didnt think water could do that . :confused:
 
Cuchilo said:
I didnt think water could do that . :confused:
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Amazing isn't it. I find it hard to fathom myself.
It was best described to me as a funnelling effect - The weirs are designed to transfer large quantities of water quickly, the reaches between the weirs are not.
 
shades said:
Amazing isn't it. I find it hard to fathom myself.
It was best described to me as a funnelling effect - The weirs are designed to transfer large quantities of water quickly, the reaches between the weirs are not.
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Fascinating all to do with Mr. Bernoulli.

I was expecting somebody to say the water was all over the meadows at Medmenham..

Still your answer's a lot better!

Only on this Thames forum can you get decent information on how the River "works".
 
shades said:
Amazing isn't it. I find it hard to fathom myself.
It was best described to me as a funnelling effect - The weirs are designed to transfer large quantities of water quickly, the reaches between the weirs are not.
Click to expand...

Thank you - that explains why the water at the Gavi residence is so much higher than that at RR_123 (who is something of a "downriver" beast)
 
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