On my prime meridian walk across England I visited the Thames Barrier near Greenwich. Here is a photo (that's the Millennium Dome in the background) of a few of the eleven futuristic pods strung across the river. In the face of a storm surge from the North Sea, huge gates rise up from the river floor between the pods to hold back the tide. Like the Dutch, the English made a decision to protect a great city from storm surges and followed through, in what turned out to be a great feat of civil engineering.
There is a mini-museum at Thames Barrier Park that shows how the mechanism works. It is interesting to compare these models to the display of lifting machinery at the late Victorian Tower Bridge.