It is actually UB38 which they are going to move. UB33 was a similar submarine also sunk by contact with a mine in the same vicinity. UB indicates that it is a small coastal submarine as opposed to the more familiar U prefix denoting an oceangoing submarine.
They both came to grief on the Dover Barrage which was an immense line of nets and mines stretching from Folkestone to Cap Gris Nez, maintained by a huge fleet of drifters from the Dover Patrol. In the early years of the war, this used British mines which were of a most unsatisfactory design. The German mine was much more effective and this was subsequently copied and used in great numbers in the Dover Barrage so it is more than likely that these submarines were sunk by German designed mines.
All British sunken warships are designated as war graves which must not be disturbed and it looks as though they have accorded the same respect to the German wreck. Curiously, merchant ships are not similarly protected although there has been a recent test case which may change that.
The submarines present location potentially presents a problem to deep draught vessels, meaning very large tankers and bulk carriers. Container ships, passenger vessels, ferries, etc, have a much smaller draught.
http://www.trinityhouse.co.uk/media_centre/press_releases/press_release.html?id=88331
http://www.uboat.net/wwi/boats/index.html?boat=UB+38
http://shipsintheportofdover.fotopic.net/c1532591.html