24 Aug 2011

Denmark’s largest molehill: DHI primps the coast around the future Fehmarnbelt link

A tunnel connecting Denmark and Germany, tens of thousands of vehicles each day – and a unique recreational area that combines the need for deposition of surplus soil from the tunnel excavation with the need for coastal and nature rehabilitation, whi

A tunnel connecting Denmark and Germany, tens of thousands of vehicles each day – and a unique recreational area that combines the need for deposition of surplus soil from the tunnel excavation with the need for coastal and nature rehabilitation, while enhancing recreational and tourist assets. DHI makes sure this artificial landscape develops into a piece of new nature.

What would you do with 16 million m3 of soil? You could build a gigantic molehill, as big as six of the great pyramids of Giza. Or you could just use it to create the perfect landscape, in an area that has previously made some bad experiences with man-made landscape changes.

One of Europe’s largest infrastructure projects is a fixed link over the Fehmarnbelt connecting Denmark and Germany. An immersed tunnel for both cars and railway is the preferred solution, planned to significantly cut travelling times and create opportunities for increased growth and prosperity for more than 10 million residents in the Fehmarnbelt Region.

 Tunnel Portal Danemark

Possible layout of the Danish tunnel gateway, including a pocket beach and a coastal lagoon (Source: Femern A/S)

With an excavation depth of about 12 m and a length of about 18 km, digging that tunnel will bring 16 million m3 of soil to the surface. It will serve a very enjoyable purpose: with the surplus soil and a helping hand, what is today a highly engineered landscape will be turned into a nature-like recreational oasis. This new landscape will connect the tunnel portals to the adjacent coastal stretches in a soft way, thereby minimising the visual impact of the portal buildings and adding new landscape features to the area. DHI, as sub-consultant to the Ramboll-Arup-TEC JV, together with Schønherr A/S is taking care of their layout.

“For 20 years I’ve been pushing the idea of an environmentally worthwhile use of excavated soil. Finally, in this project a major infrastructure development is enriched with a working-with-nature approach”, says Karsten Mangor from DHI. “Besides adding new nature, environmental and recreational values to the area, these artificial ’natural’ landscape elements will partially rehabilitate an area which has suffered severely from engineering projects of the past. It will re-establish some of the environmental values, which were lost in connection with the construction of a major dike along the coast in the area following a major flooding event in 1872.”

The new landscape will contain all the features that constitute a beautiful and recreational Danish coastline: ample sandy beaches, a pocket beach, a coastal lagoon with wetlands and even an active cliff. Typical local landscape elements have inspired its setup, further including grazing areas, dunes, islands and tidal meadows. Covering a coastline stretch of approximately 6 km, the area shall be bedded out with local plant and bush species, which will secure sustainability.

Usually, molehills are regarded a frontyard nuisance. With the help of DHI, however, Denmark’s largest molehill will be a pleasure to everyone – from the tunnel diggers in need to dispose their soil to the local population and tourists gaining areas for recreation and revival, and also to the coastal environment.