Thames Flood Barrier

The Thames Barrier was destroyed by the Tenth Doctor in order to drown the children of the Racnoss, who were emerging from a hole drilled to the center of the earth by Torchwood using H.C. Clements, using the Thames to stop people from stumbling upon the secret research taking place. (DW: The Runaway Bride)

In an alternate timeline, the encounter between the Doctor and the Empress ended differently. Although she was still killed, the Doctor also died, leading to a chain of events that drastically altered Earth history. The Thames remained closed for over a year, resulting in a great number of financial problems for Britain as a whole as well as the locals who had to cross the Thames on a regular basis. (DW: Turn Left)