Restoration of a boulder reef in Kattegat - a numerical study of the design parameters and impact on sediment transport
Type:
Presented during:
CEDA Dredging Days 2007 - The Day After we Stop Dredging, Rotterdam
Authors:
Niemann S L, Bundgaard K E, Deigaard R, Hansen I S, Skourup J, Larsen J J, Johnsson M, Hammer P, DHI Water & Environment and Dalgas A H, The Danish Forest and Nature Agency, Denmark
Abstract: Offshore stone reefs have been destroyed to a large extent in Danish waters due to the exploitation of stones for construction purposes causing deterioration of important natural habitats with a high biodiversity. The Danish Forest and Nature Agency is undertaking the LIFE-Nature project 'BLUEREEF' to restore the conservation status of the offshore stone reef habitat on the shallow area Læsø¸ Trindel in Kattegat, which is under increasing deterioration due to the past excavation of the natural stabilising boulders and present erosion due to the harsh environmental hydrodynamic conditions in the area. The restoration of the stone reef is expected to involve the placing of approx. 60,000 m3 of boulders to cover an area of 6.5 ha and to construct a number of conical and oblong artificial reef structures. A comprehensive numerical modelling study of the hydraulic conditions and the sediment transport at the site is carried out along with the design phase of the reefs. The purpose of the modelling is to provide the data for the design parameters (currents, sea level and wave heights) and to investigate the impact on the conditions for sediment transport, erosion and deposition in the project area and the possible impact on sensitive features in the surroundings, notably another natural habitat, an area of submarine structures formed by leaking gases from the sea bed approx. 1-1.5 km east of the project area.
Keywords: restoration, numerical modelling, design parameters, sediment transport