River Lyn

Site of Special Scientific Interest · 51.1818, -3.8582

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Also within

Devon County EXMOOR National Park

Condition (Natural England)

Favourable (2)
UnitFeatureConditionArea (ha)Assessed
SS701440 — Favourable 15.83 2009-02-02
SS722491 — Favourable 1.28 2008-10-02

Habitats

Fast flowing river and stream

Geology & landscape

Geological Feature: Gorge / Ravine

Landscape processes: Fluvial

Description

River Lyn SSSI Description This is a new Geological Conservation Review site within Exmoor National Park. The River Lyn occupies a catchment of 95 kilometres2 of gently sloping moorland on the west of Exmoor. The river was the scene of a unique rainfall sequence and associated flood event in August 1952, following a period of prolonged and heavy rainfall. The large volumes of water and sediment moved during these floods created a suite of geomorphological landforms which are still visible today. In the upper reaches of the catchment, at Cannon Hill, both erosional and depositional landforms are found. These include erosional slope scars and depositional boulder deposits. In the lower reaches of the catchment of the river flows through a gorge at Lynmouth, where a suite of large boulders now occupies the river bed. These boulders were-deposited during the 1952 flood when the competency of the river was much greater and are testimony to the power and magnitude of the flood event. This site is therefore important in demonstrating the effects of high magnitude – low frequency flood events and their influence on the development of geomorphological systems and landforms.

Plant communities

A9 — Fast flowing river and stream, Marginal and inundation, Pond ditch and canal, Sluggish river and stream

Potamogeton natans community

Schoenoplectus lacustris, Juncus bulbosus, Sparganium angustifolium, Sparganium erectum, Sparganium minimum, Alisma plantago-aquatica, Lobelia dortmanna, Equisetum fluviatile, Myriophyllum alterniflorum, Elodea canadensis, Lemna minor, Lemna trisulca, Nymphaea alba, Callitriche platycarpa, Callitriche stagnalis, Littorella uniflora, Potamogeton natans, Ranunculus trichophyllus, Glyceria fluitans, Chara subspinosa

A14 — Fast flowing river and stream

Myriophyllum alterniflorum community

Isolepis fluitans, Juncus bulbosus, Fontinalis antipyretica, Lobelia dortmanna, Equisetum fluviatile, Myriophyllum alterniflorum, Lemna minor, Callitriche stagnalis, Littorella uniflora, Potamogeton filiformis, Potamogeton gramineus, Potamogeton natans, Ranunculus peltatus, Chara spp., Nitella hyalina

A17 — Chalk river and stream, Fast flowing river and stream

Ranunculus penicillatus ssp. pseudofluitans community

Berula erecta, Nasturtium officinale, Elodea canadensis, Lemna minor, Callitriche stagnalis, Veronica beccabunga, Polygonum amphibium, Polygonum hydropiper, Potamogeton crispus, Potamogeton pectinatus, Ranunculus penicillatus ssp. pseudofluitans

A18 — Fast flowing river and stream

Ranunculus fluitans community

Fontinalis antipyretica, Fontinalis squamosa var. curnowii, Myriophyllum alterniflorum, Myriophyllum spicatum, Elodea canadensis, Mentha aquatica, Lemna gibba, Lemna minor, Potamogeton perfoliatus, Ranunculus fluitans, Glyceria fluitans, Phalaris arundinacea