Maeslantkering, Storm surge barrier in South Holland, Netherlands

Maeslantkering is a storm surge barrier on the Nieuwe Waterweg at Hoek van Holland, South Holland. It has two hollow steel gates, each 210 metres long and 22 metres high, held by 237-metre steel trusses weighing 6,800 tonnes. The gates normally rest in dry docks on land, leaving a 360-metre gap for shipping; when closed, they float out and are filled with water to sink onto a stone sill.

The Maeslantkering was built from 1991 to 1997 as the final stage of the Delta Works, after the original plan to raise dikes 50 kilometres inland proved too costly and would have required demolishing historic town centres. Queen Beatrix opened it on 10 May 1997, and it closed for the first time that same day at 16:30. The first storm-surge closure came on the evening of 8 November 2007.

The barrier's name comes from the Maeslant, a former shoal in the Nieuwe Waterweg. Since 1997 the site has hosted an annual test closure, usually in late September or early October, when the public watches the gates move. The visitor centre, designed by Wim Quist, explains the Delta Works and the BOS computer system.

The barrier stands where Het Scheur becomes the Nieuwe Waterweg at Hoek van Holland. A visitor centre at the site explains water management and the barrier's technology. The gates are tested annually, usually at the end of September or the beginning of October, with public activities; outside those moments they rest open in their dry docks.

The barrier is designed to close only about once every ten years, and in its first decade of operation no storm ever triggered it; the first storm closure came on the evening of 8 November 2007. Each year, usually in late September or early October before the storm season, the gates are tested in public.