German Water bridge?

Question

The following question was asked of me on my Physics final. Can someone give me a good, detailed explaination? I figured Archimedes' or Bernoulli's principle..

http://farm1.static.flickr.com/182/442622526_1dbbcadb0c_o.jpg
Have you ever seen a WATER bridge over a river? Even after you see it, it is still hard to believe! This is the Water Bridge in Germany … What a feat! Six years, 500 million euros, 918 meters long… now this is engineering! This is a channel-bridge over the River Elbe and joins the former East and West Germany , as part of the unification project. It is located in the city of Magdeburg, near Berlin . The photo was taken on the day of inauguration.

To those who appreciate engineering projects, here’s a puzzle for you armchair engineers and physicists. Did that bridge have to be designed to withstand the additional weight of ship and barge traffic, or just the weight of the water?

Answer 1

Just the weight of the water. The weight of the barge is matched by the weight of water displaced by the hull. That displacement results in a miniscule rise in the height of the water, but that change is spread over the length of the river, not just the section above the bridge.
So if the bridge is designed to hold water that is as deep as the walls of the bridge, then adding barges will never add to the load. At worst the water will overflow.

Answer 2

It has to support the water weight - which is based on the depth of water in the bridge. So as the water level in the bridging canal rises, the load on the water bridge will also rise.

I saw something like this in Holland - but this photo looks a bit odd. I would be very surprised to see 3-4 such large ships this close together.

Answer 3

Archimede's principle. A ship passing is just the same as the displaced amount of water passing. I don't imagine that requires any special engineering consideration.