BARCHAN DUNES ON THE DUTCH COAST

Willem Krommenhoek

Barchan dunes are a rare phenomenon on the Dutch coast and can sometimes be observed on the bigger sand planes on the islands north-west of the Dutch coast in the North Sea. In early May of 2011 I visited the island of Ameland and witnessed a unique view when after a period of three days of strong winds from the north-west (6 on the scale of Beaufort) I visited the beach. Over abouta length of two kilometers on the beach which is about 500 meters wide , there where tens and tens of barchan dunes with an averagesize of about ten meters between the "horns" and a height of a few decimeters to a meter and a half.

Barchan dunes are arc-shaped sand ridges possessing two "horns" that face downwind. The downwind slope has an angle of repose of about 35 degrees. This angle is the steepest angle of descent or dip of a slope relative to the horizontal plane when material on the slope face is on the verge of sliding. The upwind slope is packed by the wind and stands at about 15 degrees.

Barchan dunes can stretch to a hundred meters between the "horns". Famous for its spectacular examples of barchan dunes is the Great Sand Dunes National Park in Colorado. However, the small scale North Sea beach barchan dunes are unique and rare and with a short lifespan. When the wind changed to south-west after a couple of days, the beautiful barchan dunes were soon deformed into shapeless piles of sand.