2- How did the Porlock pebble ridge alter the morphology of the coast?

As the drift aligned spit gradually enclosed Porlock Bay an area of freshwater and brackish marsh with extensive reed beds began to form behind the pebble ridge fed by three main streams flowing down into the bay from the inland Exmoor plateau.  This had the effect of infilling much of the bay and progressively altering it from a saline to a predominantly freshwater or brackish marshland ecosystem.  Ballance (2001 p i) says this:

“We do not know very much about the marsh before 1700.  In 1420, men were paid for taking cygnets for Lady Harrington from “le lac”, which was presumably then a freshwater pool formed by three main streams behind the shingle bank or “chesil” – see the  map of about 1710-1720 (Resource 11).  This clearly shows an oval-shaped pool behind the shingle, fed by three converging streams, with a narrow outlet to the sea.  It is labelled “Porlock Pill” or Fish Pond.  An outlet through the shingle bank is shown and if there was no controllable sluice at this outlet then the pond would have been subject to fluctuations of sea water at high tides”.

Ballance also describes how a large decoy (Resource 13) was constructed on the south west of the marsh sometime during the 18^th century.  This was a system imported probably from Holland where food attracts wildfowl (mostly wading birds, duck and geese) to a pond from which they are enticed and driven up  curved pipes to a catching area.  The decoy on Porlock Marsh had ten pipes, an exceptionally large number.  Further information about the duck decoy can be found on the Exmoor Historic Environment Record .

Resource 12 shows the building which probably served as the decoy man’s house which fell into disuse by 1820 and was subsequently converted into a linhay – a two storied open fronted building with a hay loft above and livestock housing below. The freshwater marsh ecosystem and particularly a small mere and reed bed fen which developed behind the pebble ridge, comprised a rich and varied mosaic of wetland habitats the importance of which was recognised with the designation of Site of Special Scientific Interest (SSSI) status in 1990.  A report from the National Rivers Authority (1992 p 3) described the environment here as ‘a diverse and regionally important site comprising strandline vegetation, shingle, maritime grassland, saltmarsh, swamp and brackish water habitats’.

Consolidate Your Thinking

• What is the purpose of designating locations as SSSIs in England – information on SSSIs here
• For what specific biological reasons was Porlock Marsh designated an SSSI – see the citation here
• Make brief notes now on the characteristics of freshwater and brackish wetlands such as that which formed at Porlock Marsh behind the ridge using the links below.  Think particularly about their biodiversity and human value:

http://jncc.defra.gov.uk/page-1430

Wildlife Trusts River Info

Go to Question 3  - How did human activity alter the marsh