2.4 Classification of Scottish dunes

Classification systems can provide a short hand to facilitate discussions, but they are normally either too simple, ignoring subtle differences of type, or too complex and unwieldy. For the purposes of this guide a simple approach is adopted based on processes and regions rather than form.

Dunes on the Western Isles and north west mainland are subject to wet weather, strong westerly winds and very high energy wave conditions. The dunes are fed by calcium rich sands derived from shells and offshore deposits. The resultant dune systems are low, and are often backed by machair (Plate 15). Many of the systems are within small embayments where they are protected from wave induced longshore transport. Dune systems that are in remote or largely undisturbed areas, and systems where public access is effectively managed often enjoy long term stability, with short term erosion balanced by recovery.

Plate 15

Plate 15 Hebridean beach-machair system, Traigh-na-Berie, Lewis

East coast shorelines that are exposed to the North Sea are influenced by westerly winds blowing offshore as well as onshore winds and waves from the north and east. Post-glacial deposits off the present shoreline originally provided a substantial source of sand which was transported onshore by waves as sea levels rose. Opposing onshore and offshore winds result in high foredunes rather than the lower machair systems of the west coast (Plate 16). When sand supplies were plentiful the dunes grew seaward in a series of ridges, but under present conditions the supplies are generally not balancing the losses. The result, in most areas, is long term recession, with this trend underlying short term cycles of erosion and accretion.

Plate 16

Plate 16 Typical east coast beach-dune system with high and extensive foredune ridge, Belhaven.

The third major Scottish dune type is found within estuaries (Plate 17). Estuaries are influenced by tidal currents as much as by winds and waves. Dune systems along their shores may be extensive, often fed from intertidal sand banks. However, they can be rapidly destroyed as a result of an unpredictable change in flow patterns and a shift in the distribution of intertidal banks and channels.

Plate 17

Plate 17 Estuarine dune system, St Andrews links, Eden Estuary. Shifting tidal channels can cause dramatic changes on the coast.

Finally, there are a few areas, typically in the outer regions of the Scottish Firths, where dunes are still enjoying a long term trend of accretion as the supply of sand exceeds losses (Plate 18). By definition these frontages are of less interest to this Guide.

As noted earlier, simple classifications do not cover the range of variations. Along the Scottish coast there are numerous dune systems, each with its own specific character. The above classification covers most of them, and can be summarised as:

Plate 18

Plate 18 Not all dune systems are eroding. At Tentsmuir, lines of anti-tank blocks from the 2nd World War are now situated over 100m from the shore due to ongoing sand accumulation.