A revetment is a protective facing laid on a sloping bank or embankment to absorb wave and flow energy and prevent erosion of the surface beneath. The distinction from a retaining wall matters: a retaining wall resists the lateral earth pressure of a soil mass, while a revetment armours the face of a slope that is already stable in its own right. Revetments are used on river banks, coastal frontages, reservoir slopes, spillways and highway embankments.
Rigid and flexible revetments
Rigid revetments — mass concrete, concrete slabbing, grouted stone — present a continuous impermeable face. They perform well against direct wave attack but tolerate no differential settlement, and once undermined at the toe they fail progressively along the length of the failure. Flexible revetments — rock armour, gabion mattresses, articulated concrete block systems, open stone asphalt — deform with the bank, drain freely and can be repaired locally. Most UK inland and estuarine work now favours the flexible types, both for durability and for the ecological and visual advantages of a permeable, vegetable-colonising surface.
Rock armour, riprap and gabion mattress compared
Rock armour, also called riprap, is graded quarried stone placed in a layer thick enough that individual stones are not displaced by the design wave or flow. It needs large stone and adequate layer thickness, and it needs a filter beneath it. A gabion mattress — a shallow wire mesh basket, typically 150 to 300 mm thick, filled with smaller stone — achieves comparable hydraulic performance with much smaller rock, because the mesh binds the stones into a single mass. Where good armour stone is expensive or the section depth is constrained, the mattress is usually the more economical solution; where the design event is severe or the exposure is marine, graded rock in a thicker layer is more robust.
The filter layer and the toe
Two details decide whether a revetment lasts. The filter beneath the armour prevents fines being washed out of the bank through the voids in the facing, and is provided either as a graded granular layer or as a geotextile selected for the particle size distribution of the subsoil. Omitting or wrongly specifying the filter causes the bank to hollow out behind an apparently intact facing. The toe fixes the bottom of the revetment below the anticipated scour depth, usually with a buried toe trench, a rock toe or a mattress apron. A revetment that terminates above scour level will be undermined and rolled down the slope. The CIRIA and CUR Rock Manual (C683) sets out the UK design approach for both.
Selecting a revetment type
The decision is driven by the hydraulic loading (wave height or flow velocity), the availability and cost of stone, the acceptable section thickness, the settlement expected in the underlying ground, and the ecological objectives for the frontage. Live and hybrid solutions — a mattress with soil-filled cells planted through the mesh, or a rock toe with a bioengineered upper bank — are increasingly specified where a hard face at the waterline can be combined with a vegetated slope above.
Related ViaCon solutions
ViaCon supplies gabion and mattress systems for bank protection and erosion control. See our geotechnical solutions range. Related glossary entries: rock armour, reno mattress, gabion and erosion control.
Frequently asked questions about revetment
What is a revetment?
A revetment is a protective facing placed on a sloping bank or embankment to absorb wave and flow energy and prevent erosion. It armours the surface of a slope rather than retaining the soil mass behind it.
What is the difference between a revetment and a retaining wall?
A retaining wall resists the lateral earth pressure of a soil mass and allows a change in level. A revetment sits on an existing stable slope and protects its surface from erosion — it carries no significant earth pressure.
Is rock armour a revetment?
Yes. Rock armour, also called riprap, is one of the most common flexible revetment types. Gabion mattresses, articulated concrete blocks and open stone asphalt are the other principal flexible forms.
Why does a revetment need a filter layer?
Without a filter, water moving through the armour washes fine material out of the bank behind it, and the slope hollows out while the facing still looks intact. The filter is provided either as a graded granular layer or as a geotextile matched to the subsoil particle size.