<Table> <Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (June 2011) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (June 2011) (Learn how and when to remove this template message) </Td> </Tr> <P> The port of Rotterdam and its surrounding area is susceptible to a storm surge from the North Sea . In the Delta Works flood protection plan various options have been considered for protecting Rotterdam . Finally a unique design was built, the Maeslantkering . This flood barrier consists of two huge doors that normally rest in a dry dock besides the Nieuwe Waterweg . When a flood of 3 metres (9.8 ft) above NAP (mean sea level) is predicted the gates are floated into position, like caissons, and sunk in place . When the water level recedes enough to open the gates, they are floated back into their docks . Another barrier, the Hartelkering, is situated in the Hartelkanaal . </P>

Why is rotterdam the busiest port in europe