01A store, not a wall. Storms borrow sand from the dune and move it onto the beach or offshore.
A dune protects by being expendable. Its bulk offers sand to an eroding beach; roots and stems help rebuild the ridge between storms. An apparently untidy, shifting profile can be a sign of a coast doing its work.
Material
Sand + vegetation
Footprint
Broad
Behaviour
Mobile reserve
Read the field notes
Look for: a steep, freshly cut seaward face after a storm, followed by small sand hummocks around pioneer grasses. These are different moments in the same sediment cycle.
The catch: a dune needs a supply of dry beach sand and room to migrate. Trampling breaks vegetation cover; buildings behind the ridge can prevent its landward retreat. A planted ridge on a sediment-starved beach is not a self-renewing defence.
Soften / Living surface
Salt marsh
02Friction across a width. Stems slow water; roots bind the fine sediment beneath them.
A marsh spreads the work over thousands of small stems. Its shallow platform and vegetation can reduce wave energy before it reaches the land. Each flood also brings a chance to trap sediment and build the surface upward.
Material
Silt + vegetation
Footprint
Very broad
Behaviour
Living buffer
Read the field notes
Look for: branching creeks, different plant bands at different elevations, and a ragged seaward edge. The creeks are the marsh’s circulation system, not defects to be filled.
The catch: wave reduction depends on marsh width, water depth and plant condition. A marsh may drown if its surface cannot keep pace with rising relative sea level. Where an embankment blocks inland migration, the habitat can be squeezed out entirely.
Hold / Rough armour
Rock revetment
03Strength with gaps. A rough, porous slope dissipates energy through turbulence.
A revetment makes a durable face for an erodible shore. Large interlocking rocks take the first impact; the voids between them interrupt the flow. Hidden beneath, smaller layers keep the ground from washing out through the armour.
Material
Graded rock
Footprint
Sloping apron
Behaviour
Armoured edge
Read the field notes
Look for: displaced stones, hollows behind the crest and exposed filter fabric. A tidy-looking upper slope can conceal an undermined toe.
The catch: armour fixes the land’s position but does not feed the beach. As the beach lowers, the rocks become more exposed and less passable. Quarrying, transport and the loss of intertidal space are part of the structure’s footprint too.
Hold / Sediment trap
Groyne field
04A brake on drift. The beach builds on one side of each barrier, not equally on both.
Groynes reach across a beach to slow sediment travelling along it. The retained beach, rather than the groyne itself, absorbs much of the wave energy. Read the difference in sand level on either side to see transport made visible.
Material
Timber or rock
Footprint
Cross-shore rows
Behaviour
Redistributes sand
Read the field notes
Look for: a sawtooth shoreline and exposed lower planks on the sand-poor side. The pattern may reverse when seasonal wave directions change.
The catch: trapping sand can leave a neighbour short of it. Groynes do not manufacture sediment, and may need an initial beach nourishment scheme to avoid mining the adjacent coast. The end of a groyne field deserves as much attention as its centre.
Hold / Fixed boundary
Sea wall
05A line with a foundation. The visible face is only one part of the defence.
A sea wall puts a firm boundary around a place we have decided to keep. Its crest limits flooding; its face resists direct attack. A recurved top can turn some uprushing water seaward, but cannot promise a dry promenade in every storm.
Material
Concrete or masonry
Footprint
Narrow face
Behaviour
Reflects energy
Read the field notes
Look for: joints, drains, repaired cracks and changes in beach level at the base. Water behind the wall must be able to escape without carrying the ground with it.
The catch: reflection and local scour can deepen water at the toe. A fixed wall on a retreating shore may eventually leave little beach in front of it. Overtopping, foundation failure and flooding around the ends remain possible even when the face is intact.
Make room / Changed boundary
Set-back embankment
06Move the decision inland. A breached outer bank gives the tide a larger space to occupy.
Managed realignment changes which land is defended. A new bank is built farther inland and the old boundary is opened deliberately. Between them, tidal habitat may develop: not an untouched wilderness, but a carefully negotiated new shore.
Material
Earth + tidal space
Footprint
Landscape-scale
Behaviour
Accommodates tide
Read the field notes
Look for: old ditches becoming tidal creeks, remnants of the former bank and a new embankment tracing higher ground. Elevation helps determine whether the new habitat becomes mudflat or marsh.
The catch: land, livelihoods, access and freshwater drainage all change. The size and position of breaches affect tidal flow and erosion. Making room is an engineering decision and a social one; compensation and long-term stewardship belong in the design.
02 / Side by side
Every edge has a trade-off.
02
Compare what a defence asks of its site, not just what it is made of. Use the checkboxes on the entries to narrow this table. Filtered-out entries keep their picks; with no picks, all six are shown.
Showing all six structures.Showing your selected structures.
Site, sediment and stewardship · qualitative comparison
Structure
Needs from its site
Sediment consequence
Continuing work
01 / SoftenDune ridge
A sandy beach, wind supply and room to move.
Stores sand, then releases it during erosion.
Manage access; protect natural rebuilding.
02 / SoftenSalt marsh
Suitable tidal elevation, sediment and sufficient width.
Traps fine material; can build elevation.
Monitor levels, creeks and habitat migration.
03 / HoldRock revetment
A stable foundation and space for a sloping apron.
Stops bank erosion; adds no beach sediment.
Inspect the toe, filters and displaced armour.
04 / HoldGroyne field
Alongshore sediment transport and a managed beach system.
Retains material locally; may reduce supply downdrift.
Repair structures; monitor and replenish the beach.
05 / HoldSea wall
Reliable foundations, drainage and a defensible alignment.
May intensify local scour; fixes the landward beach limit.
Maintain joints, drains, toe protection and crest.
06 / Make roomSet-back embankment
Available inland space, suitable levels and public agreement.
Creates new tidal pathways and deposition areas.
Maintain the new bank; track channels and habitat.
No universal lifespan or protection rating is given: water levels, wave climate, ground conditions and maintenance change the answer.
03 / Reading the whole shore
Ask where the water goes next.
03
The most revealing place to stand is often at the end of a defence. Here the straight certainty of a wall returns to an irregular beach. Sand may gather on one side and disappear on the other. The structure has not stopped a process; it has changed its address.
Start with the sediment. Where does it enter this stretch of coast, how does it travel, and where can it leave? Then look at the space behind the shore. A marsh with room to migrate and a marsh pinned against a road may look similar today, yet have very different futures.
Finally, ask what is being protected, for whom, and for how long. Holding a harbour entrance may be essential. Holding every metre of a low-lying coast indefinitely is a different proposition. Good adaptation keeps those questions open rather than hiding them behind concrete.
A short vocabulary of moving edges
Longshore drift: the net movement of beach sediment along the coast, driven by waves and currents. Its direction can change with the weather.
Overtopping: water passing over a defence crest. This can happen through wave action even when the still-water level is below the top.
Scour: the local removal of bed or beach material by moving water. At a structure’s toe, it can threaten the foundation.
Coastal squeeze: loss of intertidal habitat when a rising sea shifts its suitable elevation landward but a fixed boundary prevents migration.
Sediment cell: a coastal area within which sediment sources, pathways and sinks are strongly connected. It is a useful planning unit, not necessarily a closed box.
How to use this atlas in the field
Visit from a public path in calm conditions, and compare observations at different tides. Look at old photographs and maps before deciding that a present-day beach profile is typical.
Stay off armour stone, groynes and exposed marsh mud. Waves can overtop a wall without warning; do not approach its seaward edge to inspect it. These schematic drawings are a reading aid, not engineering designs or safety guidance.
Editorial method & further reading
This is an original explanatory atlas, not a survey of named sites. The drawings are intentionally simplified and not to scale. “Soften”, “hold” and “make room” describe a primary strategy; real schemes often combine all three.
For more detailed technical and policy context:
US Army Corps of Engineers, Coastal Engineering Manual, EM 1110-2-1100 — coastal processes and structure design.
CIRIA, CUR & CETMEF, The Rock Manual, C683, 2007 — the use of rock in hydraulic engineering.
IPCC, Climate Change 2022: Impacts, Adaptation and Vulnerability, Cross-Chapter Paper 2 — cities and settlements by the sea.
Conceptual scope: temperate sedimentary coasts. Coral reefs, mangroves, ice-affected shores and harbour breakwaters need atlases of their own.
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