Jubilee River

boatone

boatone

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Just a few cables from Boulters Lock
www.tmba.org.uk
Someone asked on another thread how the Jubilee River operates for flood relief.
I have managed to find some info which I interpret as best I can.

The JR leaves the river above Boulters Lock and follows fairly closely just south of the M4 ( you can see it from the westbound carriageway as you approach the Windsor junction) before dropping south to rejoin the river just above Black Potts Viaduct at Datchet - see map below.

The diagram shows the relationship between the river level and the operation of the JR in flood conditions.
I believe the figures may have been revised since this data was published in November 2005 but basically the JR relief starts operating when the flow at Maidenhead Bridge reaches 180cumecs and, as flows increase the JR is adjusted via the Taplow sluices to take the excess maintaining the main river at 180cumecs until the JR flow reaches its maximum capacity of 145cumecs (this has, I believe been increased slightly but the aim is to not permit the JR to rise above 300mm below bankside). The JR is then maintained at that maximum level and any further increase in total flow is carried by the main river.
The Taplow Sluices appear to be operated in 8 stages, stage 8 being maximum flow and 0 being fully closed.

jubileeriverflow.jpg


jubileerivermap.jpg
 
Thats interesting stuff, one rumour/myth I keep hearing though, is the limit of the Jubilee river is governed by not wishing to flood the nature reserves that have now been created around it, presumably this is the 300mm below bankside limit?
 
Chris_d said:
Thats interesting stuff, one rumour/myth I keep hearing though, is the limit of the Jubilee river is governed by not wishing to flood the nature reserves that have now been created around it, presumably this is the 300mm below bankside limit?
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I believe there have been occasional representations to allow use of the JR for recreational purposes other than its original usage definitions and consents which are specifically for flood relief. I am aware that there is concern re wildlife issues but I don't think they are permitted to over-ride genuine flood relief requirements. As I understand it the 300mm freeboard is a maximum capacity constraint. IIRC there was some damage in the early days.
 
This is all sounds reasonable, but the conspiracy theorists never listen to the truth:D

I guess as it is not a natural river so allowing it burst its banks may damage its structure and cause it start taking a new route or short cut back to the main stream.
 
The Jubilee River it may now be. It is still the Maidenhead flood alleviation scheme
to everyone below its exit point !!!
 
dash300 said:
The Jubilee River it may now be. It is still the Maidenhead flood alleviation scheme
to everyone below its exit point !!!
Click to expand...

Yes thats its purpose isn't it? I know peeps below think it floods them out and saves Maidenhead but its the same amount of water, it just arrives from two channels instead of one:)
 
Chris_d said:
Yes thats its purpose isn't it? I know peeps below think it floods them out and saves Maidenhead but its the same amount of water, it just arrives from two channels instead of one:)
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Exactly right - it sends more water downstream more quickly. During the enquiry stage of this relief scheme that is exactly what the objectors flood risk engineers said.Floods occur when too much water arrives at the same time. The project was a calculated displacement scheme to reduce the risk of flooding at Maidenhead. The scheme as posted, is put into effect by levels taken at Maidenhead.
 
dash300 said:
Exactly right - it sends more water downstream more quickly. During the enquiry stage of this relief scheme that is exactly what the objectors flood risk engineers said.Floods occur when too much water arrives at the same time. The project was a calculated displacement scheme to reduce the risk of flooding at Maidenhead. The scheme as posted, is put into effect by levels taken at Maidenhead.
Click to expand...
I am not going to get embroiled in a long running aggrowotsit on this but what you say is a somewhat distorted version of the truth :D

Imagine that the JR was not there in recent weeks. The actual water contained within the JR would be flowing down the main river so that would be an increase in main river flow. In a way, the JR is adding water capacity in the same way as a flood plain does.
 
"Exactly right - it sends more water downstream more quickly. During the enquiry stage of this relief scheme that is exactly what the objectors flood risk engineers said.Floods occur when too much water arrives at the same time. The project was a calculated displacement scheme to reduce the risk of flooding at Maidenhead. The scheme as posted, is put into effect by levels taken at Maidenhead. "



Thats wrong though isn't it look at the graphs above, it sends the same amount of water down at the same rate but split between two channels so that it doesn't overflow the banks. Before it was built I watched it being developed at Hydraulics research in Wallingford, they had huge models of the whole area and you could see how it worked in real time. You can't send more water down faster but you can split it over more channels.
 
It shouldn't be forgotten that the problem was the planners at the RBWM continually gave planning permission against EA advice for more housing in the flood plain, whereas South Bucks DC followed the advice and didn't. When it came to building the flood relief channel is was doubly unfair to the have it on the Bucks side to alleviate the problem caused by the Berkshire Council.
 
boatone said:
Also, once all the main river weirs are fully drawn, it is not possible to hold any water back so any increase in flow will all move downriver or, where obstructed. spread out over low lying land i.e. FLOOD.
Click to expand...

Yes again. The river would flood into the Maidenhead flood plain thus reducing the flow to areas further downstream.
 
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