Thames Barrier

[matt_london]

(Inspired by Spooks!) Where does all the water go when the barrier is closed? I guess that is is used to stop water from the sea getting into the city right? So, when the barrier is closed it must build up on the East side of it. Where does this water go? ALSO.. what happens to the water that would normally be flowing out from the country down the Thames. If the barrier is closed it must build up on the West side of the barrier. I'm confused!!!

[Loosehead]

The water goiing out still goes out, through a series of non return valves the water out side just adds a micron to the sea level.

[matt_london]

Yeah but the barrier is not by the sea, its near Canary Wharf so it would be building up there, and would be bigger than a 'micron' (sorry I dont even know how big that is!!!)

[Loosehead]

It would just be spread out back from the barrier.

[matt_london]

If there is sufficient water to need a barrier system then surely there would be sufficient water to break the banks on the East side of the barrier? After all the width of the river is not going to differ by much of a margin from one side of the barrier to the other?

[buildersmate]

The barrier is lifted a couple of hours after low tide. You will know that at low tide the Thames shows huge mud flats on both sides of the river for several miles upstream. Also when the tide surge comes in, the river appears to flow upstream as water floods in from the seaward side. So the answer is that there is enough capacity in the river on the west side of the barrier to store the water coming downstream for the period of about six hours - three hours each side of the high-tide point. Loosehead may be right about one-way return valves - that cease to function of course once the water on the seaward side gets the same height as the other side - these would maximise the opportunity to allow water out before the rising tide closes them off.
I imagine some bright spark calculated the river flow rate, even in the winter after heavy rainfall in S England, could be stored in the basin for six or so hours.

[curlyfilm]

the most technically amazing thing about the barrier, is not the barrier itself, the thames shoreline was raised by three foot for 12 miles (not 100% of distance) west of the thames, which took a amazing amount of work, can't remember the exact details as i only remember this from a school visit about 25 years ago

[curlyfilm]

sorry this don't help the question about the east side, i think that the east side thames river banks are high enough to cope, i think the barrier needs to be shut for 40 minutes to an hour

[buildersmate]

No its longer than that at around 6 hours - see my reply above. If one shut it just before high tide, most of the spare 'capacity' of the Thames to cope with river water coming downstream (whilst the barrier is shut) would have been used up by sea-water already past the barrier and in the upper basin.