2B.1 - The littoral zone and coastal landscapes

A coast has moving zones

The coastal landscape extends across the shoreline because waves, tides, sediment and organisms connect land with shallow sea.

The backshore lies landward of the normal high-water shoreline. It includes upper beach ridges and dunes; ordinary tides rarely reach it, but storm waves and surge can. The foreshore is the intertidal strip between normal high and low water. It is useful to distinguish this strip even when describing the specification's broader three-zone division. The nearshore extends seaward into shallow water where waves shoal, break and move sediment. Its outer limit is a process boundary rather than a permanently fixed line. The offshore lies farther seaward, beyond the main nearshore breaking zone; waves and currents can still move sediment, especially during storms.

A beach is therefore not just the sand exposed at low tide. Sand stored in an offshore bar may return to the visible beach. A storm can remove a berm, carry sediment seaward and reach the backshore within hours. Tides move the waterline several times a day, whereas dunes and cliffs may change over years. Record the tide, wave conditions and date when comparing coastlines: two images of the same beach can show different waterlines without proving erosion.

Classifying coasts at different timescales

A classification groups coastlines by a stated criterion, so the same coast can belong to several categories.

Long-term controls include bedrock type, geological structure and relative sea-level change. A coast can be rocky or sedimentary, high or low relief, and emergent where former shoreline features stand above present sea level, or submergent where rising relative sea level has drowned landforms. Relative sea level compares sea height with land height: either can move. Drowned valleys retain an inherited shape even while contemporary waves modify their margins.

Shorter-term process classifications describe what currently dominates. A wave-dominated coast is strongly shaped by wave energy; a tide-dominated coast has strong tidal exchange and often channels and tidal flats. River-dominated settings receive important freshwater and sediment inputs. These are relative categories, not claims that other processes disappear. A sheltered estuary may accumulate river-borne mud, while its exposed mouth is reworked by waves.

Classification is most useful when it explains something. “Low-relief, sediment-rich, tide-influenced estuarine coast” predicts tidal channels and muddy intertidal storage more clearly than “a flat coast”. State the spatial scale too: a bay sheltered behind a headland may be low energy within a generally exposed rocky region. An exceptional storm does not by itself overturn a classification based on typical conditions over decades.

Why rocky coasts and coastal plains differ

Coastal form depends on the material available and whether incoming energy removes it faster than new sediment can accumulate.

Rocky coasts contain exposed bedrock that resists marine, rain and wind erosion sufficiently to persist. High-relief rocky coasts have substantial cliffs; low-relief rocky coasts can have low rock platforms and reefs. Resistant geology does not guarantee high cliffs: inherited relief and the orientation of rock layers also matter. In an exposed, high-energy setting, repeated wave attack removes loose material and exploits weaknesses, leaving rock landforms. Wind and rain weather the rock above wave reach, supplying fragments to the shore.

Coastal plains have low relief and substantial sediment cover. Sandy coasts receive material from eroding cliffs, rivers, reworked older deposits and offshore stores. In sheltered estuaries, lower velocities allow fine sediment to settle; tidal currents also redistribute it. A beach can persist even with considerable wave energy if sediment supply and return transport replace losses. Thus the specification's contrast between often high-energy rocky coasts and often low-energy coastal plains is a tendency, not a rule that every sandy shore is sheltered.

Think of a hypothetical exposed rock headland beside a sheltered muddy inlet. The headland's resistant rock and concentrated wave attack favour cliffs and bare platforms. The inlet's low relief, weaker currents at slack water and continuing sediment input favour tidal flats. They are different landscapes within the same regional climate because local materials, exposure and sediment pathways differ. Neither “energy alone” nor “geology alone” explains the contrast.

Using maps and satellite images together

A satellite image reveals coastal patterns, while a GIS helps test which controls are associated with those patterns.

Begin with an image of a UK reach and a reach beyond the UK at comparable scales. Look for cliff shadows and rocky outcrops, pale beach ridges, elongated barriers, branching tidal channels and broad intertidal flats. Digitise contrasting coastal reaches rather than assigning an entire region one label. Overlay bedrock geology, elevation, rivers and exposure information. BGS geology is useful for UK comparisons; a suitable national geological survey layer provides comparable geological evidence elsewhere. Check each layer's date, resolution, projection and licence before combining it.

For an original illustrative comparison, Reach A has a narrow shore beneath a high rock slope and few visible sediment stores; Reach B has a broad low plain, an inlet and branching channels. First classify the visible morphology: rocky/high-relief versus sedimentary/estuarine/low-relief. Then propose controls: stronger geology and exposure at A; sediment input and shelter at B. A geology overlay can test the first inference. Repeat images and wave/tidal records can test the others. The image alone does not measure rock strength, sediment thickness or a long-term erosion rate.

Use a consistent legend and record uncertain reaches rather than forcing every pixel into a category. A turbid plume can suggest sediment in water, but one image cannot establish annual river supply. A wide exposed intertidal area may reflect a low tide rather than permanently wider sediment storage. Classification is an evidence-based interpretation with limitations, not simply recognising a colour.