Over the years, landowners on the 2.5 kilometre stretch of beachfront property west of Liseleje tried to protect the coast themselves with homemade concrete walls, wooden structures, car tyres and various stone structures. In most cases, however, their efforts fell short, and the beach continued to wash away.
The aesthetic quality of the coast was considerably reduced. Frederiksborg County, the local government body responsible at the time, decided to take action and recruited COWI to oversee the development of a collective shore protection scheme for the entire coastline.
Following an in-depth assessment of the natural conditions at the site, COWI drew up a project design and supervised the coastal protectionscheme's implementation, which was completed in 1999.
Combination of methodsCOWI's assessment of the conditions along the coast showed that the best solution was a combination of shore protection measures, including the creation of shore parallel breakwaters made from quarry stones. The other methods were beach nourishment and the construction of revetments to protect the foot of the high slope from erosion due to waves and storm surge.
Nine breakwaters, each about 70 metres long, were combined with initial beach nourishment using 70,000 cubic metres of sand. Initialnourishment involves a large volume of sand by comparison with the subsequent maintenance nourishment, which to date has been avoided at Liseleje as the breakwaters have been efficient in retaining the sandy beaches. Helpful breakwaters
"Breakwaters are helpful in reducing the loss of sand along the foreshore. The structures also provide shelter from the waves and thereby collect sand behind them in what is known as a ‘tombolo’. This allows people to walk along the beach, as opposed to groynes, which are positioned at right angles to the beach," says Christian Helledie, a coastal morphologist at COWI.
By Gitte Roe Eriksen, cht@cowi.com Published: 12.08.2008
Christian Helledie Coastal morphologist, cel@cowi.com