Holkham National Nature Reserve - Threats

Threats

The underlying geology of the North Norfolk coast is Cretaceous chalk, exposed at Hunstanton cliffs just to the west of the SSSI, but buried by soft Quaternary glacial debris for the entire length of the SSSI coast. Unlike the soft, rapidly eroding cliffs further east, the coast of the SSSI has shown a less consistent pattern, with a net accretion of beach material between 1880 and 1950. However, this coastline is threatened by climate change, with sea level rising an estimated 1–2 mm per year for the last 100 years, increasing the risk of flooding and coastal erosion.

Half the area of the salt marshes that formed in the lee of Scolt Head Island has been reclaimed in the last 300 years, creating ecologically important, but very fragile, grazing marshes. Although Holkham is low-lying and can flood in severe weather conditions, it is protected by the spit that developed at the Holkham Gap in the 1990s and the dunes along the coast, which are increasingly being stabilised by vegetation. The Environment Agency's management plan until 2105 is to rely on the natural protection of the dunes, intervening only if work is necessary to maintain their effectiveness in the face of a potential sea level rise of 1.1 m (3 ft) by that date. The shingle that makes up Scolt Head Island is moving westwards and southwards at up to 3.5 m (10 ft) per year. This may affect the movement of sediment, and lead to some erosion of the dunes and beaches at Holkham, but should not destroy their effectiveness as a sea defence unless the island reattaches to the mainland at some date in the distant future.