What if the chunnel collapse in such a way that if filled with water. Would water continue to flow out of each end of the chunnel? Or has if been designed so that flooding would not extend beyond itself?
You do realise the entrances are above sea level? So, if the tunnel would collapse in the middle, it would just flood up to sea level. If the hole were huge you could get water entering so fast some of it might rise above sea leve and escape, but then the level would settle back to sea level which is below ground level.
More on the Chunnel here
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Its length is 31 miles, of which 23 miles are underwater.
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Its average depth is 150 feet under the seabed.**
31-23=8; assuming symmetry, 4 miles on either end are above sea level. As sailor
said, some momentum of in-rushing water might create wave action rushing towards the ends, but this wave would have to travel 4 miles laterally and climb 150 feet vertically to reach the tunnel end.
The stations in both London and Paris are such unique places, that it is almost worth the cost of a ticket to visit them. 
[sup]almost[/sup]
Is the connection to St. Pancras open yet, or does Eurostar still come into Waterloo? Where will the connection to St. Pancras be routed - through the city, or around it on new track?
I’m sure that this has been studied. I mean, you know that there’s some kind of self-destruct device built into those tunnels in case a war breaks out and they become a liability.
It won’t be completely open until 2007.
The first phase will run from the Chunnel terminal through Ashford and the North Downs tunnel and over the Medway to “Pepper Hill, between Gravesend and Southfleet, where a junction will enable section 1 of the new railway to turn south along the alignment of the disused Gravesend West Branch railway,to join the existing Railtrack network at Fawkham Junction, approximately 8km (5 miles) east of Swanley. From Fawkham Junction Eurostar trains will use existing tracks to reach the international terminal at Waterloo until the opening of Section 2.” This phase is almost complete.
For the second phase they’re tunneling northward under the Thames, then west to St Pancras.
See http://www.ctrl.co.uk/, and especially http://www.ctrl.co.uk/planning/description.asp?L=3&SL=11 for the route description.
I think we need to clarify:
The majority of it is under the ocean itself – in the clay / mud / rock below the seabed: So, 23 miles of it are a 150 feet below the seabed and not 150 feet below sea level.
Also, it seems it takes about four miles at each end to rise from 150 feet below the seabed to around sea level (perhaps just a little above) – where it breaks ground in France and England and somewhere just behind the coasts.
So my guess is the most likely place for an uncontrollable breach by water would be not on the stretch under the seabed itself but on the part where it begins to rise from under the seabed to reach sea level – but I’m no engineer.
Fwiw, I don’t think anything would pour out the ends if it were breached, the ends being at or just above sea level.
Don’t be silly; why would England invade France? Again?