We supply rocks with all appropriate size and weight for coastal and shore protection and standard weights include
300kg, 500kg, 1000kg, 1500kg, 2000kg, 2500kg and 3000kg.
Rock revetments may be used to control erosion by armoring the dune face. They dissipate the energy of storm
waves and prevent further recession of the backshore if well designed and maintained. Revetments may be carefully
engineered structures protecting long lengths of shoreline, or roughly placed rip-rap protecting short sections of
severely eroded dunes.
Rock revetments are widely used in areas with important backshore assets subject to severe and ongoing erosion
where it is not cost effective or environmentally acceptable to provide full protection using seawalls. The function
of permeable revetments is to reduce the erosive power of the waves by means of wave energy dissipation in the
interstices of the revetment.
Permeable revetments can also be built from gabions, timber or concrete armour units. Concrete units are normally
too costly for use as dune protection, but may be appropriate where high value back shore assets must be protected
and armour rock is difficult to obtain. They are often considered to be more unattractive than rock.
Revetments may not prevent on going shoreline recession unless they
are maintained, and, if necessary, extended. If the foreshore continues
to erode, the rock revetment may slump down, becoming less
effective as a defense structure, but will not fail completely. Repairs
and extensions may be necessary to provide continued backshore
protection at the design standard.
Rock revetment schemes can have a
significant impact on the shoreline
and should not be implemented
without specialist assistance from a
competent coastal consultant and
contractors. Information on the
design of rock structures is available
from the CIRIA/CUR “Manual on the
use of rock in coastal and shoreline
engineering”. The accompanying
figures provide initial guidance but
this should be confirmed for each
As with all rock structures on the
shoreline the rock size, face slopes,
crest elevation and crest width must
be designed with care. Rock size is dependent on incident wave height,
period and direction, structure slope,
acceptance of risk, cross-sectional
design, and the availability/cost of
armour rock from quarries. In general
1-3 tons rock will suffice, provided
that it is placed as at least a double
layer, with a 1:1.5 to 1:3 face slope,
and there is an acceptance of some
risk of failure.
Structure face slopes are a
compromise between flatter faces
that absorb more wave energy, and
therefore suffer less toe scour and
allow use of smaller rock, and steeper
faces that give the structure a smaller
footprint and require less rock
volume. A slope of 1:2 is a reasonable
compromise and is in keeping with
natural dune slopes.
The structure should be constructed
within a shallow trench and a
geotextile filter should be laid under
the rocks to prevent the migration
of sand upwards and the settlement
of the rocks into the beach. The
geotextile should be wrapped around the base layer of rocks, and the rock toe should be set below the lowest
expected beach level.
The length of the structure must be sufficient to protect the backshore
assets at risk. To avoid localized scour the structure ends must return into
the eroding dune face over the final 20m-40m and should be buried by as
much as 5m-10m, depending on the expected rate of future erosion. The
face slope over this final section can be flattened to 1:3 or 1:4 to increase
wave absorption. The revetment length may need extending from time to
time as erosion of the adjacent dune frontages may continue.
The structure crest elevation must be above the wave run-up limit during
storms to prevent further dune erosion. During very extreme storms
some overtopping damage will be inevitable, and the designers must
determine the acceptable risk depending on potential damage and the
probability of extreme events.
If the beach-revetment interface is well above normal spring tide levels
there may be opportunities to use beach recycling, fencing and vegetation
transplanting to encourage dune growth. However, as revetments are only
likely to be used where erosion problems are severe, then it is unlikely that this opportunity will arise.
In the latter case fencing and
transplanting should be used
along the structure crest to
soften the landscape impact
and encourage dune recovery.
Large rock revetments in areas
open to the public will be a safety
hazard. To increase hydraulic
efficiency the rocks should be placed randomly to form
a rough surface with large voids. The rocks may move
when walked on and the voids may be large enough to
fall or climb into, and may result in children becoming
trapped or injured. Where structures extend down the
shoreline below the normal spring tide levels the lower
rocks will be covered by algae and other marine growth,
and may be extremely slippery.
Safe access routes, usually concrete steps with hand rails, should be built at intervals
across large revetments and
should lead to controlled paths
through the dunes. The crest of
large rock revetments should
be blinded, with the interstitial
voids infilled with smaller rock
to form a reasonable surface
for safe walking. During
severe storms this surface may be damaged and need
maintenance to replace dislodged rocks and refill voids.
In all cases the structures should be well signed to warn
the public of hazards and discourage access except at
The above discussions relate to large, engineered
revetments. Less substantial defenses may be formed as
rip-rap slopes, but only in low energy situations. Widely
graded rock from small boulders up to armour rock
can be placed along estuary shores or well protected coastal sites. This approach may well be subject to regular storm damage, requiring maintenance to reform the
slopes. Necessary maintenance work may well be harmful to the environment as heavy equipment will be active on
the beach and may need to gain access through the dunes. Burial of the rip-rap slopes will reduce the visual impact,
while fencing, thatching and transplanting may encourage covering dune growth.
Construction costs for revetments are mainly dependent on structure dimensions, but can be heavily influenced by
the availability of suitable rock and transport methods. Rock structures can be assumed to have an unlimited life with
respect to economic assessments, while smaller rip-rap slopes will require regular maintenance costs to be included
in the budget.
The construction of any substantial defense along a dune face
will have a significant impact on the landscape and on the natural
interchange of sand between beach and dune. The natural succession
of dune habitats from foredunes back to grey dunes or machair
will be disrupted. Sand can be blown from the beach and over the
structure to reach the dunes, but cannot be returned to counter
erosion of the upper beach during storms. The consequences
can be increasing shoreline recession, with the need to extend
the revetment to cope with increasing wave attack. Where the
revetment is built high on the beach face the erosion pressures are
Rock revetments provide robust, long term protection for important
backshore assets. The revetment crest can form a public walkway,
reducing trampling of the dunes. Inclusion of safe access routes
down to the beach will improve amenity value.