The storm surge barrierThe storm surge barrier was built in the Hollandse IJssel on the municipal boundary of Capelle aan den IJssel and Krimpen aan den IJssel , east of Rotterdam . Because the Hollandse IJssel is an important shipping route, it could not be closed with a dam.On the other hand, a closure could make the drinking water supply in a large part of South Holland more secure due to less influx of salt water into the polders. That is why it was decided to use a storm surge barrier with two movable slides that hang between concrete towers. Normally the ships pass under the gates. Only at very high tide, the gates are lowered, so that the river is completely closed off. Ships can then still pass through the Algera lock, a lock located immediately north-west of the barrier and which has a width of 24 meters.The two gates of the barrier are more than eighty meters wide and 11.5 meters high and are each suspended from steel cables between two towers with a height of 45 meters.When the sliders are up, the four towers between which the sliders are attached are lit up in blue. When the sliders are down, the towers are lit red. In this way you can also see in the dark when the barrier is closed, which is safe for ships.The total costs of the Storm Surge Barrier Hollandse IJssel amounted to approximately forty million guilders .Source: (wikipedia)There are a number of useful websites available but the following document in particular is recommended but not aprticulalrly suitable for a smartPhone.https://staticresources.rijkswaterstaat.nl/binaries/Factsheet%20Hollandsche%20Ijssel_tcm21-65741.pdfhttp://www.deltawerken.com/Hollandse-IJsselkering/56.htmlhttps://www.rijkswaterstaat.nl/water/waterbeheer/bescherming-tegen-het-water/waterkeringen/deltawerken/hollandsche-ijsselkering.aspx
