Cells, budgets and the littoral zone

Treat the coast as an open system. Energy enters as waves, wind, tides and currents; sediment enters from cliffs, rivers, offshore and — increasingly — from lorries. Sediment leaves alongshore, offshore and inland as blown sand. The store is the beach, the dune and the nearshore bar.

• The littoral zone is the belt from the landward limit of the highest storm waves out to the point where waves cease to move sediment on the sea bed. Divide it into the backshore (affected only by storm waves), foreshore (the intertidal zone, where most wave action occurs), nearshore (breaker zone, where waves shoal and break) and offshore.
• Sediment cells (littoral cells) are lengths of coastline, usually bounded by prominent headlands, within which the movement of sediment is largely self-contained. England and Wales are divided into 11 major cells for management purposes. They are best thought of as closed for practical management, open in reality — some sediment always leaks past a headland or offshore.
• The sediment budget is the balance of inputs and outputs within a cell over time. It is the single most useful idea in the whole option, because it converts every landform and every management decision into an accounting problem.

Dynamic equilibrium: a beach in balance still changes constantly — steepening under summer constructive waves, flattening and losing sand offshore under winter storms, then rebuilding. The negative feedback is elegant: a storm strips the beach, but the flattened profile dissipates wave energy over a wider surf zone, reducing further erosion.

Thinking in budgets

Your turn — a sediment budget

A deficit of 13 000 m³ per year means this beach is shrinking. Note what the nourishment achieved: 3 000 m³ against a 13 000 m³ hole. In an exam, that is your evaluation — the scheme slows the loss, it does not close it.

Waves, tides, currents and surges

Waves are generated by wind transferring energy to the water surface by friction. Wave energy depends on wind speed, duration and fetch — the uninterrupted distance of open water over which the wind blows. A long fetch is why the western coasts of the British Isles are high-energy and the Kent coast is not.

In deep water, water particles move in circular orbits and the wave form travels, not the water. As the wave enters shallow water (roughly where depth is less than half the wavelength) it shoals: friction with the bed slows the base, the orbit becomes elliptical, the wave steepens, shortens and finally topples forward — it breaks.

• Tides — the gravitational pull of the Moon (and, less strongly, the Sun) generates two bulges of water that the rotating Earth passes through. Alignment gives large spring tides; opposition gives smaller neap tides. The tidal range determines where wave energy is applied: a macro-tidal coast spreads erosion over a wide vertical band; a micro-tidal coast concentrates it, which is why the Mediterranean has sharp, well-developed notches.
• Currents — longshore currents move water and sediment parallel to the shore; rip currents return water seaward through gaps in a bar; ocean currents redistribute heat and, over long distances, fine sediment.
• Storm surges — a deep low-pressure system raises the sea surface (roughly 1 cm per millibar of pressure drop) and strong onshore winds pile water against the coast. Add a spring high tide and the water level can exceed defences designed for normal conditions. Surge, not rainfall, is what drowned the Netherlands and eastern England in 1953.

Which waves, which beach?

Marine erosion, transport, or sub-aerial?

Tap a process, then tap the column it belongs to. Cliff retreat is almost always a partnership — the sea undercuts, the slope collapses — and examiners want to see you separate the two.

How the sea does its work

Erosion — four processes, and you must name the one that fits the rock:

• Hydraulic action — the sheer force of water hitting the cliff. Its powerful cousin is wave quarrying (cavitation): air is compressed in a joint or bedding plane as the wave hits, then explosively decompresses as the wave withdraws, prising the rock apart. Most effective on well-jointed rock.
• Abrasion (corrasion) — waves hurl shingle and sand at the cliff face; the sediment, not the water, does the cutting. The dominant process where a beach of hard clasts exists.
• Attrition — clasts collide and wear each other down, becoming smaller and rounder. This does not erode the cliff; it changes the sediment, and it explains why beach material is finer and rounder downdrift.
• Solution (corrosion) — chemical dissolution, significant on limestone and chalk coasts.

Transport — the four modes are the same as in a river: traction (rolling), saltation (bouncing), suspension (fines carried in the water column) and solution (dissolved load).

Longshore drift is the engine of the whole coastal sediment system. Waves approach at an angle to the shore (set by the prevailing wind); swash carries sediment obliquely up the beach; gravity pulls the backwash straight back down the steepest gradient, at right angles to the shore. Repeat a few thousand times and sediment zig-zags along the coast.

Deposition occurs simply where energy falls below the threshold needed to keep a given grain size moving — in the lee of a headland or a spit, in a bay, in a sheltered estuary, or when a wave loses energy on a wide, gently sloping foreshore. Large clasts drop first; the finest material travels furthest.

Wave refraction: as waves approach an irregular coast they slow first in the shallow water off a headland. The wave crest bends, so the orthogonals (energy lines) converge on the headland and diverge into the bay. Result: erosion is concentrated on the headland and deposition occurs in the bay. That single mechanism explains the entire headland-and-bay landscape, and it is a negative feedback — over time it tends to straighten the coast.

The land attacking itself

Cliff retreat is rarely the sea alone. The sea removes the debris and undercuts the base; sub-aerial processes acting on the cliff face deliver the collapse.

• Weathering — freeze-thaw in jointed rock; salt crystallisation in pores; hydration and oxidation; biological weathering by roots and by boring organisms; carbonation on limestone. All of it weakens the rock before the wave arrives.
• Rockfall — blocks detach from a steep, well-jointed face, usually after undercutting has removed the support. Fast, brittle, and typical of hard rock.
• Slumping (rotational slip) — the classic failure of saturated clay or till cliffs. Water infiltrates, pore-water pressure rises, the shear strength of the material falls below the shear stress acting on it, and a mass rotates downward along a curved (concave) failure plane, leaving a stepped, hummocky, back-tilted cliff.
• Landslide — movement along a planar surface, often a bedding plane dipping seaward.
• Runoff and soil creep — surface water gullies the cliff face; slow creep moves regolith downslope year on year.

The examinable link: heavy rainfall raises pore-water pressure and therefore reduces shear strength, while a storm at the cliff foot increases shear stress by removing the toe support. A wet winter followed by a storm surge is the classic recipe for a major cliff failure — and it is why "erosion rates" jump in a single event rather than proceeding smoothly.

Diagnosing a cliff failure

Cliffs, platforms and the headland sequence

• Wave-cut notch and platform. Erosion (quarrying and abrasion) concentrates between high and low water, cutting a notch. The overhang eventually collapses; the cliff retreats parallel to itself, leaving behind a gently seaward-sloping wave-cut (shore) platform. Crucially, the platform is self-limiting: as it widens, waves break further out and lose more energy crossing it, so the rate of retreat slows. A negative feedback.
• Headlands and bays — form on a discordant coast, where alternating bands of resistant and less resistant rock meet the sea at right angles. Wave refraction then does the rest. (On a concordant coast, with rock bands parallel to the sea, you get a straight coast, coves such as Lulworth, or a Dalmatian coastline.)
• Cave, arch, stack, stump — waves exploit a line of weakness (a joint, fault or bedding plane) in a headland: quarrying widens it into a cave; caves cut from both sides meet to form an arch; the roof, unsupported and weathered from above, collapses into a stack; the stack is undercut and reduced to a stump, visible only at low tide.
• Geos and blowholes — a geo is a narrow, steep-sided inlet cut along a fault or joint. A blowhole forms where a vertical joint above a cave is enlarged, so wave compression forces spray up through the cliff top.

Name that landform

Tap a description on the left, then the landform it defines. The description contains the mechanism — that is the part worth marks.

Beaches, spits, bars and dunes

• Beach. Sand beaches are wide and gently sloping (fine sand has a low percolation rate, so backwash stays strong and drags material back down). Shingle beaches are steep (high percolation, so backwash is weak). Look for berms (ridges at successive swash limits), storm beaches (a coarse ridge at the top, thrown up by exceptional waves), and ridges and runnels (bar-and-trough on the low-angle foreshore of macro-tidal sand beaches, cut by drainage channels at low tide).
• Spit. Longshore drift carries sediment along the coast; where the coastline abruptly changes direction (at an estuary or bay), the drift continues into open water and deposits, building a ridge attached to the land at one end. A recurved (hooked) end forms where a secondary wind or wave direction curls the tip landward. Behind the spit, in the sheltered water, silt and clay settle out, colonised by halophytes: a salt marsh develops.
• Bar. A spit that grows right across a bay, sealing off a lagoon behind it. (Offshore bars form differently — from destructive waves dragging sediment seaward.)
• Tombolo. A ridge of sediment joining an island to the mainland, built where the island causes wave refraction on both sides, creating a low-energy zone in its lee where sediment accumulates. Chesil Beach links the Isle of Portland to the Dorset mainland.
• Salt marsh and mudflats. In estuaries, fine sediment is trapped where fresh and saline water meet — the salt causes clay particles to flocculate (clump and settle). Pioneer halophytes such as Salicornia and Spartina trap more sediment, raise the surface, reduce the period of tidal inundation and allow less salt-tolerant species in: a textbook halosere succession, complete with creeks and salt pans.

Why is the beach steep?

Eustatic, isostatic, emergent, submergent

Two different things can change the relative position of land and sea, and you must keep them apart:

• Eustatic change is a change in the volume of water in the ocean — global. Causes: ice sheets growing (locking water up, sea level falls) or melting (sea level rises), and thermal expansion of a warming ocean. A eustatic change affects every coast at once.
• Isostatic change is a change in the height of the land — local or regional. The weight of an ice sheet depresses the crust into the mantle; when the ice melts, the crust slowly rebounds (isostatic recovery), a process still running in northern Britain and Scandinavia thousands of years after deglaciation. Tectonic uplift and the compaction/subsidence of sediment do the same job.

Britain is the perfect demonstration: Scotland is still rising (isostatic rebound after the loss of its ice) while south-east England is sinking (partly the far-field forebulge collapsing, partly sediment compaction) — so the same global eustatic rise produces a much greater relative rise in Essex than in Argyll.

Emergent landforms — where the land rises relative to the sea:

• Raised beach — a former beach, with its sand and rounded pebbles, stranded above the present high-tide line.
• Relict (fossil) cliff — a degraded cliff line, now inland and vegetated, often with a fossil wave-cut notch and caves at its base, far from the reach of any wave.

Submergent landforms — where the sea rises relative to the land, drowning the pre-existing landscape:

• Ria — a drowned river valley: a winding, branching inlet, deepest at its mouth, with a V-shaped cross-section. Common in south-west England.
• Fjord — a drowned glacial trough: straight, steep-sided, U-shaped in cross-section, very deep inland but with a shallow rock threshold at its mouth where the glacier thinned and eroded less.
• Dalmatian coast — a drowned concordant coastline in which rock ridges lie parallel to the sea, so drowning leaves long, thin islands parallel to the shore (named after the Croatian coast).

The high-level point: most of the world's coastlines are not in equilibrium with present sea level. They are still adjusting to the roughly 120 m of eustatic rise that followed the last glacial maximum. Every ria, fjord and raised beach is evidence that the coast you are looking at was shaped under conditions that no longer exist.

Ria or fjord?

Your turn — rate of cliff retreat

Retreat rates are calculated from repeat survey: fix a marker inland, measure its distance to the cliff edge, and come back years later.

Now evaluate the number. A mean of 1.8 m per year conceals the truth: soft-cliff retreat is episodic. Several quiet years may be followed by a single storm that takes ten metres in a night. A planner who assumes a smooth 1.8 m a year will site a road correctly on average and lose it in a decade.

Holderness — the anatomy of a retreating coast

The Holderness coast runs roughly 60 km from the chalk headland of Flamborough Head south to the sand and shingle spit of Spurn Head, at the mouth of the Humber. It is widely described as among the fastest-eroding coastlines in Europe. Understand why, in four linked steps:

• 1. Geology. South of Flamborough, the cliffs are glacial till — unconsolidated clay, sand and boulders dumped by the last ice sheet. Till has almost no cohesion when wet; it is not "rock" in any meaningful sense. (Flamborough itself, being chalk, retreats far more slowly — which is exactly the discordant-geology contrast an examiner wants.)
• 2. Process. The cliffs are attacked by destructive waves with a long fetch across the North Sea, amplified by storm surges funnelling south into the narrowing basin. Meanwhile rainfall saturates the till, raising pore-water pressure, and the cliffs fail by rotational slumping. Marine erosion at the toe and sub-aerial mass movement above work as a pair.
• 3. Sediment. Till erodes into a large volume of fine material — mostly clay and silt, which is carried away in suspension and lost offshore rather than remaining as a protective beach. Only a small fraction is sand and shingle. So the coast erodes fast, but builds almost no beach with which to defend itself: a structurally negative sediment budget at the cliff.
• 4. Transfer. What sand and shingle there is moves south by longshore drift, and it is this southward drift that feeds and sustains Spurn Head. The spit is the cliffs' sediment, relocated. Erosion here is deposition there.

The terminal groyne effect — the evaluation everyone gets marks for. Settlements such as Mappleton and Withernsea are protected by groynes and rock armour. Groynes work by trapping longshore drift, so the beach in front of the town grows and dissipates wave energy. But the drift did not stop existing; it simply arrives downdrift with no sediment in it. The first unprotected cliff south of the final ("terminal") groyne is therefore attacked by waves with full erosive capacity and no beach to absorb them, and it retreats faster than it would have done had nothing been built at all. Protecting one settlement has externalised the cost onto its neighbour. This is the sediment budget with a human face — and it is why AQA asks about sediment cells and ICZM.

Figures, honestly. Long-term mean retreat along the till cliffs is widely reported as of the order of one to two metres per year, but the published figures vary considerably with location, with the period measured and with the method used, and retreat is highly episodic. Dozens of villages recorded in medieval documents have been lost to the sea. Quote the mechanism with confidence and the rate with a hedge — that is what a good geographer does.

Hard, soft, and the strategic choice

Hard engineering — build a structure that resists the sea:

• Sea wall — reflects wave energy. Effective and reassuring, but very expensive, visually intrusive, and a reflective wall scours the beach in front of it, undermining its own foundation. It also cuts off cliff sediment input to the cell.
• Groynes — timber or rock fences perpendicular to the shore, trapping longshore drift to build a wider beach. Cheap and effective locally — and the direct cause of the terminal groyne effect downdrift.
• Rip-rap (rock armour) — large boulders at the cliff foot, dissipating energy in the voids between them. Cheap and quick; ugly, can be undermined, and rock is often imported from far away.
• Revetments — sloping, often slatted structures that absorb and dissipate wave energy rather than reflecting it. Offshore breakwaters force waves to break early.

Soft engineering — work with the sediment system:

• Beach nourishment — import sand or shingle to rebuild the beach, restoring the natural energy-dissipating store. Looks natural, maintains amenity and tourism value; but it is a continuous cost (the sea takes it away again), and the dredged source area is itself damaged.
• Dune stabilisation and marsh creation — plant marram, fence and board-walk to prevent trampling, restore saltmarsh. Cheap, ecologically positive, sequesters carbon; but it only protects low-energy coasts.
• Managed realignment (managed retreat) — deliberately breach or set back the defence line and allow the sea to flood low-value land, creating intertidal marsh that absorbs energy naturally. Cheaper in the long run, creates habitat, and is the only strategy that is sustainable under sea-level rise. But it is politically explosive: someone's land, home or farm is being given up, and compensation is contested.
• Do nothing / no active intervention — a legitimate policy choice where the value of the land does not justify the cost of defending it.

The strategic frameworks you must be able to name:

• Shoreline Management Plans (SMPs) — drawn up for whole sediment cells, not individual towns, precisely because of the downdrift problem. Each stretch is assigned one of four policies: hold the line, advance the line, managed realignment, or no active intervention.
• Cost-benefit analysis (CBA) — defences are funded only where the value of the property and infrastructure protected exceeds the cost. This is why a city gets a sea wall and a farm does not — and why CBA is criticised for undervaluing communities, heritage and ecosystems that have no market price.
• Integrated Coastal Zone Management (ICZM) — manage the whole coastal zone (land and sea, all stakeholders, all economic activity) as one interconnected system, over the long term, with local participation. It is the correct answer to the terminal-groyne problem, and it is hard to deliver, because it requires many authorities to accept that one place must lose so that the system as a whole can work.

Judging a scheme

Writing the evaluative essay

Paper 1 essays are marked on AO1 (knowledge), AO2 (application and analysis) and — decisively — a conclusion that answers the question. Two question types dominate this option:

• "Coastal landforms are the product of the sediment budget." To what extent do you agree? Use the budget as your organising frame: erosional landforms occur where the budget is negative and the cliff is exposed; depositional landforms occur where energy falls and the budget is positive. But qualify hard: geology (lithology, jointing, dip, concordant vs discordant) determines where erosion concentrates; sea-level change means many landforms are relict and out of equilibrium with the current budget; and human intervention now rewrites the budget directly. Judgement: the budget explains the rate and direction of change; structure and inherited sea level explain the form.
• "Assess the effectiveness of coastal management strategies." Refuse the "hard bad, soft good" script. Argue by criterion: effective at what — protecting property? preserving the sediment cell? cost over 50 years? equity between communities? ecological value? A sea wall scores highly on the first and terribly on the second and fourth. Managed realignment reverses that. Judgement: effectiveness depends on the spatial scale at which you assess it — schemes that succeed at the settlement scale routinely fail at the sediment-cell scale, which is precisely the argument for ICZM.

Habits that lift a script: (1) always name the process before the landform; (2) use the sediment cell as the unit of analysis — it converts vague description into systems argument; (3) exploit negative feedback (widening platform, flattening storm profile, accreting marsh) as your analytical trump card; (4) hedge numbers you cannot source, and never invent one.

Sharpening the judgement

The big ideas to know

That is the whole of AQA 3.1.3. Press Finish to see your score.