County Wildife Site Criteria for Cornwall Appendices

TIDE-SWEPT CHANNELS PHTGeneral DescriptionThe term 'tidal rapids' is defined as 'strong tidal streams resulting from a constriction in the coastlineat the entrance to, or within the length of, an enclosed body of water such as a sea loch. Depth isusually shallower than five metres.'In deeper situations tidal streams may generate favourable conditions for diverse marine habitats (e.g.the entrances to fjordic sea lochs, between islands, or between islands and the mainland, particularlywhere tidal flow is funnelled by the shape of the coastline). Strong tidal streams may be felt down to30 m.National ContextTidal streams occur at many places around Britain. Both the Menai Strait in North Wales and theScilly Isles provide good examples of tide-swept communities considered to be of nationalimportance.The morphology of fjords and fjards is therefore very different to lowland marine inlets and theestuaries of the south and east of the British Isles. However, in south-west England, eustatic changehas created rias by drowning coastal river valleys such as the Dart, Tamar and Fal. At the narrowentrances of these rias, strong tidal currents have generated diverse habitats of biological significance.Maerl beds are also closely identified with the conditions found in tidal narrows and rapids in thesouth-west (the Fal estuary) and the north of the British Isles (Orkney).The extent of this habitat in Cornwall is not currently known.For this habitat we will take all areasAppendix 4 - Information Relating to Priority Habitat TypesCounty Wildlife Sites Criteria