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Spec mapping (AQA 7037): Paper 1 (Physical), §3.1.3 Coastal systems and landscapes — landforms of coastal deposition (and the transport that supplies them), coastal flooding and management, including the Shoreline Management Plan framework and the four policy options, evaluated against sustainability. This depth lesson treats deposition as the output/store side of the sediment budget developed in lesson 1 and welds it to a critical, evaluative treatment of management as deliberate manipulation of that budget. It draws on the systems and budget framing of §3.1.1, the wave/longshore physics of lesson 2, and links to §3.1.6 Hazards (coastal flood risk). Assessment objectives: AO1 (depositional landform genesis, management techniques), AO2 (applying budget reasoning and management to located coasts), AO3 (cost–benefit and sediment-volume manipulation and evaluation).
At depth, the two halves of this lesson are the same idea seen twice. Depositional landforms are where the sediment budget runs into surplus and material is stored; coastal management is the engineering of that budget — every technique either adds sediment, retains it, removes energy from it, or relocates the line the system is allowed to reach. Framing management as budget manipulation, rather than as a list of structures, is what lifts an evaluation into the top band, because it forces you to ask the systems question: which term does this intervention change, and what happens downdrift as a result?
Longshore drift is the net alongshore movement of sediment driven by waves breaking obliquely; it is the conveyor that links the eroding source to the depositional store.
flowchart LR
WIND[Dominant waves<br/>approach obliquely] --> SWASH[Swash carries sediment<br/>up beach at the wave angle]
SWASH --> BACK[Backwash returns it<br/>straight down under gravity]
BACK --> NET[Net zig-zag transport<br/>ALONG the coast]
NET --> STORE[Deposition where energy falls:<br/>spit / bar / tombolo / marsh]
The process: waves driven by the dominant wind break at an angle, swash pushes sediment obliquely up the beach, backwash drains it straight down the steepest gradient under gravity, and the net result is a zig-zag transport along the coast. As established in lesson 2, the volume transported scales with breaker height to a high power and with sin(2αb) (maximised near a 45° approach), so both energy and angle of approach control the flux.
Quantification and evidence. UK rates are typically 10⁵–5×10⁵ m³ yr⁻¹; Holderness drives ~500,000 m³ yr⁻¹ southward. Direction is inferred from sediment piled on the updrift side of groynes, downdrift pebble fining (attrition), the growth direction of spits, and from direct tracer studies (fluorescent or even radioactive-tagged pebbles tracked over weeks). The key budget insight is that longshore drift is the dominant transfer term between sub-cells: anything that interrupts it (a groyne, a breakwater, a harbour arm) converts an updrift surplus into a downdrift deficit.
Before sediment reaches a spit or bar, it resides in the beach — the system's primary active store and its energy buffer. Beach morphology records the prevailing wave regime: a swash-aligned beach (oriented parallel to the dominant wave crests, so swash and backwash run straight up and down) reaches equilibrium with little net drift, while a drift-aligned beach (oblique to the waves) is a conveyor along which sediment is continually transported. The beach profile is itself dynamic — a berm (a ridge built at the high-tide swash limit by constructive waves), a storm beach (coarse material thrown above normal high water by storm waves), and one or more breakpoint bars offshore (built by destructive backwash) appear and disappear seasonally. Smaller-scale features — beach cusps (regularly-spaced crescentic embayments cut into the upper beach, whose spacing reflects swash circulation) and ripples — record the most recent conditions. Reading these features lets you reconstruct the recent wave climate, and protecting or enhancing the beach (the cheapest, most natural defence) is the implicit goal of much soft engineering.
A spit is an elongated sand/shingle ridge extending from the coast into open water, built where longshore drift carries sediment past a break in the coastline (an estuary mouth or a sharp change in trend) into deeper, lower-energy water. The drift continues in the old direction, depositing a ridge that grows seaward; wave refraction around the tip curls the distal end landward into a recurved hook, and successive storm directions build multiple recurves that fossilise former tip positions. Behind the spit, sheltered low-energy water lets fines settle and salt marsh colonise.
flowchart TD
DRIFT[Longshore drift along<br/>main coast] --> BREAK[Coast trends away<br/>e.g. estuary mouth]
BREAK --> DEPO[Drift continues; sediment<br/>deposited into deeper water]
DEPO --> GROW[Ridge grows seaward = spit]
GROW --> REFRACT[Refraction round tip<br/>curls distal end landward]
REFRACT --> RECURVE[Recurved hook; repeated by<br/>varying storm directions = multiple recurves]
GROW --> SHELTER[Low-energy water behind spit]
SHELTER --> MARSH[Fines settle; salt marsh colonises]
Spurn Head (East Yorkshire) is the canonical UK spit: a 5.5 km recurved ridge across the Humber mouth, built entirely of Holderness sediment delivered by southward drift. Critically, it is a sediment-flux integrator — it exists only because Holderness keeps feeding it, so it is a store/sink of the same budget whose source is the eroding till cliffs (lesson 1). It has been breached and reformed roughly cyclically over recorded history, and after the December 2013 surge the access road was abandoned so the spit can behave dynamically — a deliberate decision to let the landform roll rather than pin it. A spit also requires a river-mouth or open-water terminus where drift outpaces the river's ability to flush sediment seaward; where a vigorous ebb-tidal jet keeps the mouth scoured, a spit cannot bridge it, which is why some estuaries have spits and others do not. The presence, length and recurve geometry of a spit therefore encode the balance between longshore supply and the flushing energy of the river/tide — a budget reading, not just a shape.
A bar is a ridge that extends across a bay, sealing a lagoon behind it. Where it is built by drift welding a spit across a bay with no major river to keep a gap open, the enclosed water slowly infills. Slapton Ley (Devon) is a freshwater lagoon impounded behind a shingle barrier beach. Barrier islands (the Outer Banks, North Carolina; the Frisian Islands) are detached shore-parallel ridges separated from the coast by a lagoon, typical of low-gradient, sediment-rich, micro-/mesotidal coasts. All of these are mobile under rising sea level, tending to roll over landward if sediment supply allows — which is why pinning them with defences risks drowning them in place.
The roll-over mechanism is worth understanding precisely, because it is central to barrier-coast management under climate change. As sea level rises, storm waves overwash the barrier crest, carrying sediment from the seaward face over the ridge and depositing it on the landward (lagoon) side as washover fans. Repeated overwash thus translates the whole barrier landward and upward, keeping its crest above the rising sea — a natural, self-preserving adjustment, provided the barrier has sediment and space to migrate into. Where a sea wall, road or development fixes the landward edge, overwash sediment is lost and the barrier cannot retreat: it narrows, steepens and ultimately drowns in place (coastal squeeze again). This is why the most sustainable management of barrier and dune coasts often allows overwash and roll-over rather than resisting it — a counter-intuitive policy that only makes sense once the barrier is understood as a mobile sediment store rather than a fixed wall, and a direct application of the systems thinking that frames the whole topic.
A tombolo ties an island to the mainland. Wave refraction and diffraction around the island create a low-energy shadow in its lee where drift-supplied sediment accumulates until the deposit bridges the gap. Chesil Beach links the Isle of Portland to the Dorset mainland (and is also a classic barrier/storm beach), famously showing longshore grading — pea-sized clasts at West Bay coarsening eastward to fist-sized at Portland, a sorting pattern still debated between wave-energy gradient, drift and storm processes.
| Landform | Budget role | Key control | UK example |
|---|---|---|---|
| Spit | Store/sink at a coastline break | Drift + refraction at tip | Spurn Head |
| Bar / barrier | Store sealing a lagoon | Drift across a bay; sea level | Slapton Ley; Chesil |
| Tombolo | Store in a wave shadow | Refraction/diffraction round island | Chesil–Portland |
| Salt marsh | Fine-sediment store; blue carbon | Low energy + suspended supply | Humber, north Norfolk |
| Dune | Aeolian store; sea defence | Onshore wind + dry sand + vegetation | Braunton Burrows |
Two depositional systems are biologically stabilised — vegetation traps and binds the sediment, so the landform and the ecosystem co-evolve through succession.
Salt marsh develops where suspended silt/clay settles in sheltered intertidal water and is colonised through a halosere (succession beginning in saline conditions):
The vital depth point is that vertical accretion lets a marsh keep pace with sea-level rise — if it has sediment supply and space to migrate landward. Where a sea wall blocks landward migration as the sea rises, the marsh is compressed and drowned — coastal squeeze — converting a self-maintaining, blue-carbon-storing store into a loss. Marsh management is therefore inseparable from the sediment budget and from the decision about where the defence line sits. The succession is also a textbook of ecological concepts AQA may probe: it is an autogenic primary succession (the colonising plants themselves modify the habitat — raising the surface, adding organic matter, reducing salinity — and so drive their own replacement), it exhibits a clear zonation that doubles as a spatial and temporal sequence (walking landward up a marsh is, in effect, travelling forward through time as the pioneer zone seaward accretes to become middle marsh), and its productivity (cord-grass marshes are among the most productive ecosystems on Earth) underpins both its blue-carbon value and its role as a nursery for estuarine fisheries. These ecosystem-service dimensions are exactly what tip a management evaluation from "protects birds" toward a rigorous, multi-axis sustainability argument.
Dunes form where onshore wind blows dry beach sand against an obstacle, colonised through a psammosere:
| Zone | Name | Keystone species | Conditions |
|---|---|---|---|
| 1 | Embryo dunes | Lyme grass, sea rocket | Saline, mobile, wind-exposed |
| 2 | Fore (yellow) dunes | Marram (Ammophila) | Alkaline (pH ~8), dry, nutrient-poor |
| 3 | Grey dunes | Fescue, mosses, lichens | Stabilised, humus building |
| 4 | Dune slacks | Creeping willow, orchids | Wet hollows at the water table |
| 5 | Mature dunes / climax | Heather, gorse, then woodland | Acidic, humus-rich soil |
Marram is the engineer: deep rhizomes bind the sand and it grows upward through accreting sand, so it builds the very dune it stabilises. Across the succession, soil acidifies and organic content rises (centuries-long), and biodiversity peaks in the grey-dune/slack zones before closing canopy reduces it. Blowouts (wind/trampling erosion of the sward) reset patches to earlier seral stages. Dunes are a natural sea defence — a wide dune dissipates storm-wave energy and stores a sediment reserve — so their stabilisation (marram planting, boardwalks, fencing) is a soft-engineering technique in its own right.
A nuance worth carrying into an evaluation is that dune systems present a conservation paradox: complete stabilisation, while it protects the coast and the dune from blowout, can be bad for biodiversity, because many rare dune specialists (natterjack toads, dune-slack orchids, sand lizards) depend on bare, mobile sand and early-successional habitat. Over-management that fixes every dune and over-vegetates the slacks therefore destroys the very habitats that designation (many UK dunes are SSSIs/SACs, e.g. Braunton Burrows in Devon, a UNESCO Biosphere) is meant to protect. The most sophisticated dune management now deliberately reintroduces dynamism — re-mobilising selected dunes, grazing to suppress scrub — accepting some instability as the price of biodiversity. This is the same "work with the process" philosophy that runs through the whole management section, and recognising that stability and biodiversity can conflict is a discriminating evaluative point.
The Shoreline Management Plan divides the coast into management units and assigns one of four policies; the discipline is to read each as a budget decision:
| Policy | Action | Budget effect | Typical application |
|---|---|---|---|
| Hold the Line | Maintain/upgrade defences | Freezes the line; often cuts downdrift supply | High-value settlements, infrastructure |
| Advance the Line | Build seaward | Adds reclaimed land; rare | Land reclamation, ports |
| Managed Realignment | Move the defence landward | Restores intertidal store + supply | Low-value land; habitat creation |
| No Active Intervention | Let nature operate | Maintains natural source/transfer | Remote, low-value frontages |
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