Coastal defences in Norfolk
Abstract
Coastal erosion is a continuing problem along the North Norfolk coast. A
variety of approaches have been adopted to manage the issues in different
parts of the county.
Introduction
In 1949 the Coast Protection Act provided legislation that gave a Coastal
Protection Authority the power to carry out whatever work they deemed
necessary for the protection of any land in their area. In North Norfolk,
responsibility for coast protection was with the Urban and Rural District
Councils of Wells, Walsingham, Sheringham, Erpingham, Cromer and
Smallburgh. In 1974, North Norfolk District Council was formed and assumed
the coast protection responsibilities of the former Urban and Rural Councils.
In 1993 the Ministry of Agriculture, Fisheries and Food published their
'Strategy for Flood and Coastal Defence' in which they recognised that
coastal processes ignored the administrative boundaries. They identified
sediment cells and sub-cells – separate lengths of coastline for the purposes
of sediment transport. These were chosen as appropriate units for the
development of Shoreline Management Plans.
Shoreline management plans (SMPs)
SMPs in the UK aim to develop sustainable coastal defence schemes.
Sections of the coast are divided up into littoral cells and plans are drawn up
for the use and protection of those zones.
There are four possible policies
1.
2.
3.
4.
maintain existing levels of coastal defence (‘hold the existing line’)
improve the coastal defence (‘advance the existing line’)
allow retreat of the coast in selected areas i.e. managed retreat
(‘retreat the existing line’)
‘Do nothing’ i.e. carry out no coastal defence activity except for
safety measures
Before the introduction of SMPs, coast and flood protection was generally
carried out on a piecemeal basis, which often led to problems being
transferred from one location to another. SMPs are intended to avoid this
problem by bringing together information on coastal erosion and flooding,
sediment transport and tides, human uses and wildlife interest, and
attempting to balance all of these interests.
SMPs include data on:



coastal processes – waves, tides and sediment
coastal defences – where they are and how effective they are in
protecting people, land and property
land use – the type of use, such as residential, agricultural, industrial
and recreational, and its economic value

natural environment – the kinds of environment, landscape and
habitat, and their relative importance.
The SMP document is intended to be reviewed every 5 years.
Sediment or littoral cells
SMPs are based on sediment transport sub-cells (littoral cells). Within these,
the movement of sediment, sand and/or shingle by longshore drift is relatively
independent of adjacent areas. England and Wales has been divided into 11
sediment cells. These are independent lengths of coastline within which there
is movement between a source and a sink. Each cell is then split into
smaller, more manageable units, called sub-cells with boundaries at which
there is only limited exchange of sediment.
Figure 1 – Sediment cells around England and Wales
The East Anglian coastline has been designated as cell 3 and the North
Norfolk coast falls within sub-cells 3A and 3B. The boundary between these
cells is located roughly at Sheringham. Figure 1 shows the direction of the net
longshore movement around Sheringham. The dominant direction of littoral
drift is southeasterly.
In North Norfolk the cliffs are the only significant source of material. The finer
clay and silt particles are deposited all over the North Sea, whereas the larger
material helps to maintain the beaches, the sand dunes at Horsey and the
spit at Blakeney Point. Other larger material is transported offshore where it is
deposited as sandbanks.
The natural environment
The North Norfolk cliffs, which reach a maximum height of 75m, have two
main characteristics that influence coastal erosion;
1.
they are made of soft heterogeneous (varied) materials with a low
resistance, which means that they are very vulnerable to wave
erosion and mass movements caused by undercutting
and
2.
the sand and gravel components of the glacial deposits are
permeable, while the clays are impermeable. The impermeable clay
can trap water percolating through cliffs, causing it to pond and
discharge from the cliff face. This leads to an increase in pore water
pressure in the cliff, reduced strength of the cliff, which may cause
landsliding.
Wave action can undercut these cliffs making them prone to failure,
especially on low cliffs (10 metres or so), such as at Happisburgh. On slightly
higher cliffs (about 20 metres), from West Runton to Cromer for example,
rotational slides occur because the cliff material is not strong enough to
maintain the cliff face at steep angles.
Figure 2 – North Norfolk Coastline
Coastal Erosion rates in North Norfolk
Figure 3 – Mean erosion rate
Source: North Norfolk District Council An introduction to the North Norfolk Coastal Environment
Rates of erosion are highly variable both spatially and temporarily. Highest
rates are found where there is a combination of easily erodable material and
coastlines exposed to strong winds and high wave energy. The lowest rates,
those at Sherringham, Cromer and Bacton, reflect the effectiveness of the
coastal protection schemes there. By contrast, the high rates of erosion
between Overstrand and Trimmingham are the result of the lack of coastal
defences there. Rates vary over time since after a cliff has failed, much of the
debris remains on the shoreline, protecting the cliff for a number of years until
it is removed
In addition, there are regular and irregular changes to the physical
environment that make the Norfolk coastline vulnerable to erosion and
flooding


storm surges – which can raise water levels by as much as 2m
rising sea levels – Norfolk is sinking at about 1mm each year
Figure 4 - Allowances for sea level rise used for the design of coastal
defences
Environment Agency Region
Annual Allowance
Anglian, Thames, Southern
6mm/year
North West, Northumbria
4mm/year
Remainder
5mm/year
Source MAFF 1993 Strategy for Flood and Coastal Defence in England and Wales


high tides – parts of Norfolk have a tidal range of up to 5m
increasing storm frequency and intensity as a possible result of global
warming

The 100-year returning wave height (the size of the most extreme
wave that you would expect to hit a coastline, on average, once in
every 100 years)
Figure 5 – Wave Heights
Kelling Hard to West Runton
West Runton to Walcott
Walcott to Cart Gap
6 to 8 metres
greater than 8 metres
6 to 8 metres
Mean Wave Height
Kelling Hard to West Runton
West Runton to Cart Gap
0.3 to 0.4 metres
greater than 0.4 metres
Human pressures on the Norfolk coast
The North Norfolk coastline is 34.2 km long, and contains nearly 22 km of
coastal defences. This includes:

8.4km of seawall
Figure 6 A traditional type of seawall and wooden groyne similar to that found
at Cromer
Figure 7 – Gabion sea wall, Overstrand
Figure 8 Rock armour and sea wall, Sherringham

13.5km of revetment and
Figure 9 - A sloping timber revetment, used widely on the North Norfolk coast

over 150 groynes
Figure 10 - A semi permeable timber groyne in Mundesley
Figure 11 – A timber groyne, Cromer
In 2001 the total value of these defences was estimated to be around £80
million, although approximately £14 million worth of these are due to be
abandoned under current SMP policies.
Human pressures are very varied. Cromer and Sheringham are the principle
coastal towns in North Norfolk, and there are many small villages along the
coast. Tourism is the principle economy of the coastline, while most of the
clifftop land is used for arable farming. The only major industrial complex on
the North Norfolk coast is the Bacton Natural Gas Terminal, which handles a
significant percentage of Britain's gas supply via pipelines from the North Sea
gas fields.
Figure 12 - Relationships between human activities and coastal zone
problems
Human activity
Agents/consequences
Coastal zone problems
Urbanisation and
Land-use changes (e.g.
Loss of habitats and
transport
for ports, airports); road,
species diversity; visual
rail, and air congestion;
intrusion; lowering of
dredging and disposal of
groundwater table; salt
harbour sediments; water
water intrusion; water
abstraction; waste water
pollution; human health
and waste disposal
Agriculture
Tourism,
recreation and
hunting
Land reclamation; fertiliser
and pesticide use;
livestock densities; water
abstraction
Development and landuse
changes (e.g. golf
courses); road, rail and air
congestion; ports and
marinas; water
abstraction; wastewater
and waste disposal
Fisheries and
aquaculture
Port construction; fish
processing facilities;
fishing gear; fish farm
effluents
Industry (including
energy production)
Landuse changes; power
stations; extraction of
natural resources; process
effluents; cooling water;
windmills; river
impoundment; tidal
barrages
risks; eutrophication;
introduction of alien
species
Loss of habitats and
species; diversity; water
pollution; eutrophication;
river channelization
Loss habitats and species
diversity; disturbance;
visual intrusion; lowering
of groundwater table; salt
water intrusion in
aquifers; water pollution;
eutrophication; human
health risks
Overfishing; impacts on
non-target species; litter
and oil on beaches; water
pollution; eutrophication;
introduction of alien
species; habitat damage
and change in marine
communities
Loss of habitats and
species diversity; water
pollution; eutrophication;
thermal pollution; visual
intrusion; decreased input
of freshwater and
sediment to coastal
zones; coastal erosion
Human pressures on coastal environments create the need for a variety of
coastal management strategies. These may be long-term or short-term,
sustainable or non-sustainable. Successful management strategies require a
detailed knowledge of coastal processes. Rising sea levels, more frequent
storm activity, and continuing coastal development are likely to increase the
need for coastal management.
Coastal management involves a wide range of issues, such as:

planning

coastal protection

cliff stabilization and ground movement studies

coastal infrastructure including seawalls, esplanades, car parks, paths

control of beaches and public safety

recreational activities and sport

beach cleaning

pollution and oil spills

offshore dredging

management of coastal land and property.
Types of defences and their functions
The best defence against erosion, encroachment or inundation by the sea is
a natural wide flat beach topped off at the inshore end with either sand dunes
or a shingle bank. These natural structures absorb the wave energy and offer
protection to the hinterland, be it flood plain or erodable cliff.
However, if the coastline is being eroded and there are valuable properties to
protect, some form of coastal protection is usually used. A wide variety of
measures have been used in North Norfolk, ranging from natural shingle
beaches to concrete sea walls and revetments. However, erosion of the cliffs
provided the material on the beaches. By limiting erosion, the creation of new
beach material is prevented.
Figure 13 – Coastal protection methods used along the North Norfolk coast
Kelling Hard to Weybourne
no coastal defences
Weybourne



Shingle bank, 250m long
Timber and steel palisade (breastwork) buried within the bank to
provide stability during storm conditions
A shingle bank will provide the best defence if it is able to evolve
naturally and gradually retreat inland - this will be allowed to happen
at Weybourne - the car park may occasionally flood, and to prevent
this flooding affecting the 6 properties behind the car park, the Council
intends to construct a small flood bank
Weybourne to Sheringham

no defences
Sheringham
Sheringham town frontage is protected by a seawall/promenade with a
groynage system in front. Rock armour has been placed along the base of
the seawall to provide protection against wave attack. The groynes at
Sheringham include both wooden and rock structures. Numerous cliff drains
are also present at Sheringham.
Sheringham East to West Runton


timber revetment and groyne system
'Managed Retreat' – the revetment is no-longer being maintained - it
is in a poor state of repair and has failed at many locations. Eventually
the revetment will fail completely
West Runton to Cromer West

two small seawalls at East and West Runton otherwise no defences
Cromer




wide, black topped, promenade running for the majority of the town
frontage, backed by graded vegetated cliffs or solid brick/stone walls
approximately 15-30m high
cliff drainage is still present
the seawalls are generally in reasonable condition
the groynes are generally of a solid design and many are showing
signs of wear especially the larger groynes to the east of the town.The
main defences at Cromer were built between 1859 and 1900 and
have been extensively repaired and extended since then.
Cromer to Overstrand
'Do Nothing' – the timber groynes are not being maintained and will be
allowed to fail
Overstrand




western edge has a length of timber revetment and a short section of
block revetment before the start of the Seawall, promenade and
groyne system that stretches for about 600 metres along the frontage.
The defence then becomes a timber revetment once more
beaches at Overstrand are generally low, exposing the steel sheet
piled foundations both the walls and the revetments. The defences in
general are showing signs of ageing and it is expected that major
repair works will be needed in the near future
ground water percolating through the cliffs is a considerable problem
at Overstrand and a number of cliff drains and boreholes exist to try to
reduce the erosion this causes
cliff failure at Clifton Way in the early 1990s resulted in surface and
sub-surface drains, rock armour to hold the slip's 'toe' in place
Overstrand to Trimingham


timber revetment and groyne system to Sidestrand
Sidestrand on to Trimingham no defences
Trimingham



wooden revetment and groyne system
revetment has a concrete apron to provide better foundations for the
structure.
revetment has been largely destroyed by landslides; beach levels at
Trimingham have also dropped, exposing the apron, which in turn
creates a scouring effect causing further erosion of the beach. The
apron is currently acting as a seawall at Trimingham, but it was not
designed to do this and is consequently being severely damaged
Trimingham to Mundesley

continuous line of revetment along with a permeable groyne system
Mundesley



end of the revetment running from Trimingham defends the western
edge of the village
use of a concrete block revetment for about 400 metres before the
start of a seawall, with promenade
groyne system
Mundesley to Bacton

continuous wooden revetment and groyne system protects the Natural
Gas Terminal at Bacton.
Bacton to Walcott (Ostend)



concrete seawall starts at the end of the revetment
seawall consists of a low-level concrete apron backed by an inclined
concrete face with a wave wall at the top
built in 1952/54 and requires annual maintenance to keep it in a
suitable condition
Ostend to Happisburgh

timber revetment and Groyne system runs through to Happisburgh
Happisburgh


problem area - Beach Road runs out to the cliffs and properties here
are situated right on the cliff edge
in 1990 a storm destroyed around 300 metres of wooden revetment to
the east of Happisburgh

in 1996 another length of revetment was lost - rapid cliff erosion
followed and six cliff top properties were lost
at the base of the cliff there is a combination of gabions/flexible
concrete blocks/3" steel tubes banded together to lie in a breastwork all enclosed by bullhead rail piles and timber bracing - this secondary
defence is thought to offer little actual protection

Cart Gap

a seawall runs east towards Sea Palling and west towards
Happisburgh for 600 metres
Defences
Figure 14 – Coastal management strategies defined
Seawalls
Seawalls include early designs such as the concrete, vertical faced walls at
Sheringham, to the more highly designed modern wave reflecting walls as at Cart
Gap. Seawalls are intended to reflect and/or refract all the wave energy away from
the land behind. However, the reflected wave can result in increased erosion or scour
of the beach immediately in front of the seawall. If the erosion is allowed to continue
unrestrained the seawall will become unstable and eventually collapse.
The effectiveness of seawalls depends upon their cost and their performance. Their
function is to prevent erosion and flooding but much depends on:




sloping or vertical
permeable or impermeable
rough or smooth , and
material from which they are formed (clay, steel, or rock for example).
In general, flatter, permeable, rougher walls perform better than vertical, impermeable
smooth walls.
Rock armour
Rock armour has become increasingly important in coastal defence works over the
last 20 years. Hard igneous rock, such as granite, that is exceedingly resistant to
erosion, is placed on the beach leaving large void spaces. When waves hit the rock
they are only partially reflected, and can flow round the rocks, expending their energy,
which reduces scour. Another advantage of using rock is that if the rocks are moved
during heavy storms it is easy to replace them in the correct position.
Rock armour is also used to protect the base of seawalls.
Timber revetments
Timber revetments were first constructed as a cheaper alternative to a solid seawall.
The revetment is designed so that it will break the force of the wave without reflecting
the energy, which might cause scouring of the beach. Sediment, which can be sand,
shingle or pebbles, is carried through or over the revetment structure by an incoming
wave. However, the sediment cannot easily return seaward once the force of the
wave has been dissipated. This action results in a build-up of material behind the
revetment and the increased depth of material protects the foot of the cliff from being
attacked by the sea.
Block revetments
Block revetments consist of a steel or timber framework that acts as containment for
concrete or rock fill material. Block revetments are fairly cheap to construct because
they are often built from spare or scrap material; however, they can be unsightly.
Groynes
The purpose of a groyne is to create and maintain a healthy beach on its updrift side.
This is achieved through two main processes:
1. groynes acting as a barrier to physically stop sediment transport (sand) in the
direction of littoral drift through the system. This causes a build-up of the
beach on the groyne's updrift side
2. groynes interrupting the tidal flow forcing the tidal current further offshore
beyond the groyne end. This slows the tidal current inshore, causing the
deposition of heavier sediments and encouraging the beach to grow in size
Impermeable and permeable groynes
Impermeable groynes are solid and are designed to intercept all material arriving on
the updrift side. This allows a large beach to develop for example at the east end of
Cromer.
Permeable groynes allow some sediment to pass through. These groynes are
generally known as ‘Erpinghams’ (after the Rural District Council in which they were
initially used).
Beach nourishment
Beach nourishment involves adding large quantities of material to a beach in order to
build it up. The material added needs to be similar to the material naturally found on
the beach. Offshore dredging can provide a good source of suitable material for
beach nourishment schemes or alternatively the sediment can be obtained from landbased quarries.
Offshore Breakwaters
The purpose of the breakwaters is to prevent storm waves from reaching the beach
and to alter the natural processes so that a wider beach is able to develop behind
them. For example, nine offshore breakwaters have been constructed by the
Environment Agency to protect the coast around Sea Palling.
Gabions
Gabions are steel wire baskets filled with rock (often local flint in North Norfolk).
Gabions are normally used on eroding cliff faces where their purpose is to:


provide stability to the cliff face, preventing failure, and
permit water to drain away that might otherwise contribute to landsliding.
Gabions are relatively cheap and easy to construct.
Cliff drains
Cliff drains are often present on the cliff faces behind seawalls where they collect
water from the cliffs and transport it through the seawall. This helps to reduce
instability caused by water in the cliffs.
Boreholes
Boreholes are vertical shafts in the ground. Surface water and groundwater that is
intercepted by the borehole is transported straight into the chalk, which reduces the
amount of water available to cause instability in the cliffs.
Managed natural retreat
The cost of protecting Britain’s coastline was up to £60 million annually until the mid1990s. Since then government cuts have reduced this. Part of the problem is that
southern and eastern England are slowly sinking while sea level is rising. The risk of
flooding and hence the cost of protection are rising. ‘Managed retreat’ allows nature
to take its course — erosion in some areas, deposition in others. Benefits include less
money spent and the creation of natural environments. In parts of East Anglia, hard
engineering structures are being replaced by bush defences and some farmland is
being sacrificed to erosion and being allowed to develop into salt marsh.
Figure 15 - Impacts of coastal management strategies
Type of
Aims/methods
Strengths
Weaknesses
management
Hard engineering methods which are used to control natural
processes
Cliff base
stop cliff or beach
management erosion
Sea walls
large-scale concrete
easily made;
expensive;
curved walls designed to good in areas of
life span
reflect wave energy
high density
about 30-40
years;
foundations
may be
undermined
Revetments porous design to absorb easily made;
limited life
wave energy
cheaper than sea span
walls
Gabions
rocks held in wire cages
cheaper than sea small scale
absorb wave energy
walls and
revetments
Groynes
prevent long shore drift
relatively low
cause
costs; easily
erosion on
repaired
downdrift
side;
interrupts
sediment
flow
Rock armour large rocks at base of
cheap
unattractive;
cliff used to absorb wave
energy
small-scale;
may be
removed in
heavy
storms
Offshore
reduce wave power
cheap to build
disrupts
breakwaters offshore
local
ecology
Rock
reduce longshore drift
relatively low
disrupts long
strongpoints
cost; easily
shore drift;
repaired
erosion
downdrift
Cliff face strategies used to reduce the impacts of subaerial
processes
Cliff
removal of water from
cost effective
drains may
drainage
rocks in the cliff
become new
lines of
weakness;
dry cliffs
may
produce
rockfalls
Cliff
lowering of slope angle
useful on clay
uses large
regarding
to make cliff safer
(most other
amounts of
measures are
land –
not)
impractical
in heavily
populated
areas
Soft engineering - working with nature
Off shore
waste materials e.g. old
low technology
long-term
reefs
tyres weighted down, to
and relatively
impacts
reduce speed of
cost effective
unknown
incoming wave
Beach
sand pumped from
looks natural
expensive;
nourishment seabed to replace
short-term
eroded sand
solution
Managed
coastline allowed to
cost effective;
unpopular;
retreat
retreat in certain places
maintains a
political
natural coastline
implications
‘Do nothing’
accept that nature will
cost effective!
unpopular;
win
political
implications
Red-lining
planning permission
cost-effective
unpopular;
withdrawn; new line of
political
defences set back from
implications
existing coastline
Approximate costs for coastal defences

Seawalls cost approximately £5000 per metre although this depends
on the size and design of the structure.





Rock costs about £40-50 per m3. A rock groyne costs about £125,000
, while using rock as toe Armour or 'Rip Rap' costs between £1000
and £3000 per metre.
Timber revetment costs around £1500 per metre.
Timber groyne cost £1000 per metre. If a typical groyne is 100 metres
long then that is £100,000 per groyne.
Beach nourishment probably costs about £10 per m3 of material and,
of course, involves many thousands of m3 of material.
Offshore breakwaters, such as those at Sea Palling, are very
expensive, costing millions of pounds each.
Cost-Benefit Analysis
Cost/benefit analysis is an economic tool, used to demonstrate that public
money is being spent appropriately. A scheme will not go ahead unless it can
be shown that the benefits (environmental, economic and social) outweigh
the costs of the development.
The table below shows the issues considered during cost-benefit analysis.
Figure 16 Cost-benefit analysis table
Costs
Benefits
 cost of building
 Protected buildings, roads and
infrastructure (gas, water, sewage,

electricity services)
 maintainenance/repair


 increased erosion downdrift due  Land prices rise
beach starvation or reduced LSD
 Peace of mind for residents

 Employment on coastal defence 
 Reduced access to beach during
works
works

 Reduced recreational value

 Reduced accessibility

 Smaller beach due to scour

 Disruption of ecosystems and habitats

 Visually unattractive
 works disrupt natural processes
Conclusion
Rates of erosion on the North Norfolk coast are high. This is the result of
many factors including soft and varied bedrocks, exposure to storm winds,
high tides, rising sea levels, occasional storm surges and a sinking coastline.
The coastline is important for a range of human activities including
residential, tourism, agriculture, some industry and energy-related land uses.
These land uses need a varying degree of protection. In some agricultural
areas the land has been allowed to retreat naturally, whereas residential,
tourist and energy developments have largely been protected. Hence there is
a varied approach to coastal management. To date the strategies appeared
to have worked although repair has been required.
Further references
http://www.defra.gov.uk/environment/marine/iczm/index.htm
This is the portal for DEFRA’s Integrated Coastal Zone Management. This
contains information about a number of coastal protection schemes around
Britain, including sustainability of marine resources. There are a number of
downloadable newsletters that provide contrasting examples of integrated
coastal zone management.
http://www.environment-agency.gov.uk/subjects/flood/?lang=_e
This is the Environment Agency’s portal to flooding including coastal flooding.
This includes aspects of coastal flooding as well as inland flooding. There is a
useful search section.