Michael de Laine

By Michael de Laine, The Copenhagen Voice 1 June 2009

Højer flood gate was constructed in 1861, when the polder Ny Frederikskog was diked in. This flood gate has an open gate, so masted vessels could pass through and dock at Højer’s harbour, inside the the diked in area. A kilometre to the west of Højer flood gate is Vidå flood gate in the advanced dike protecting the marshlands from the Wadden Sea.

Here, there is a two-metre difference between high tide and low tide – and there are two high tides and two low tides a day, with a time difference of about 6 hours and 12 minutes between a high tide and a low tide.

But the area is renowned for storm floods, as the storm flood indicator at Højer flood gate shows: the highest here is from 1825, when the water reached 5.33 m over Danish Normal Zero sea water level. More recently and elsewhere along the Wadden Sea coast, 5.50 m over Danish Vertical Reference (a revised sea water level indicator) was reached in 1999, when winds reached a speed of 180 km/h (110 miles/h) – hurricane-force winds on the Beaufort scale, classified as force 12. According to reports, the water reached within 30 cm of the top of the dike at Ribe – and the storm hit land at the lowest point of low tide.

What would have happened at high tide is unimaginable.

What will happen if global warming does increase the sea level by 2 m (half the height of the lowest band on the storm flood indicator) and the storms floods are as bad is also unimaginable if the advanced and inner dikes are not raised and strengthened.

History is not promising with examples. ‘The Great Drowner’ reputedly killed between 15,000 and 30,000 people when it hit the coast of Schleswig-Holstein in 1362, destroying 30 churches.