Seas, rivers and lochs form the plains
The level of the sea and its twice daily tides may seem one of life’s unchanging constants – not so. Within the not too distant past, sea levels have been quite different and indeed are likely to change in the future, as a result of global warming and the rise of the land as it recovers its equilibrium after the enormous weight of the ice has been lifted.
The coast of East Lothian and Berwickshire has been affected by fluctuating sea levels since the ice melted some 14,000 years ago. The record of this is clearly imprinted all round the coast. Some 5,000 years ago sea level was about 8 metres higher than at present and formed a raised beach. This is either a wide plain or a narrow terrace backed by an ancient cliff. Just like the present beach the raised beach is made of shelly sand, shingle or mud. Higher beaches relate to sea levels as they were 8,000 years ago or even earlier.
Along the coast, the sands and silts of the beaches are light enough to be readily carried along in the wind, particularly where exposed and dry in the intertidal zone. Blown sand form dunes covered in rough grasses on the raised beach terraces. Notable dunes occur in the Gullane – Muirfield area, site of several golf courses, where the sand was blown off the large intertidal estuary of Aberlady Bay. Dunes on the Belhaven Sands have reclaimed naturally the intertidal area and formed a new island in the last 100 years.
Rivers and streams carve out valleys. They carry stones, sand and mud downstream in a meandering channel. In times of flood the river overflows its banks, the flow slackens and its load of sediment is laid down in the valley bottom as a deposit called alluvium. This is why rivers have a flat strip along the bottom of their valleys (known as a haugh), commonly with natural embankments or levees next to the river where most sediment was dropped. Similarly many lochs have silted up to form flat hollows.
All the large rivers have associated alluvial plains, commonly giving the best agricultural land. They have also been chosen for settlements and as sites for large towns such as Haddington and most of the Border towns.
Unfortunately perhaps not exactly the best choice – nature still tries to deposit alluvium on the ‘flood-plain’ from time to time – as plaques on walls of many towns and villages attest.