Yr12 Coasts: Hard engineering coastal management – Costs and

Yr12 Coasts: Hard engineering coastal management – Costs and Benefits
(Case Study)
Definition: Hard engineering: the building of structures to resist the power of waves and tides e.g. sea walls. These structures include;
revetments, groynes, gabions, sea walls, rip-rap, offshore breakwaters, cliff pinning, cliff drainage and cliff modification. The benefits
of these schemes is that it offers visible, reassuring protection for communities threatened by coastal erosion. The costs are that the
structures can be expensive to build and maintain; Defence in one place can have serious consequences for another; Defence structures
may need to be continually enhanced as rising sea level renders existing structures inadequate; Structures are sometimes visually
unappealing, spoiling the landscape, which is a significant economic issue in coastal towns that depend on tourism; Result in a narrower
shoreline; and impedes sediment movement between the land the sea.
Hard engineering schemes include:
Sea walls (sometimes recurved): aim to absorb wave energy. Benefits – deflect waves back out into the sea. Costs – maintenance; any
slight gap will be exploited by hydraulic action. They also need drain outlets so that water does not accumulate behind them.
Rock armour (rip rap): Large boulders (usually granite) placed in front of a cliff or sea wall. Benefits - Absorbs wave energy without
causing reflection scour; Long lasting; Cheaper than sea walls. Costs - Reduces recreational value of the beach; Unsightly
Revetments: concrete or wooden structures placed across the beach to take the full force of wave energy. Benefits - Long shore drift
is not hindered; Cheap; Reduce the power of the waves without causing reflection scour. Costs - Limited lifespan so need regular
replacement; Limited effectiveness in storm conditions; Unsightly
Groynes: wooden or stone breakwaters built at nearly right angles to waves. Benefits - Cheaper than sea walls; Reduce long shore drift
and they build up the beach locally; They can be repaired relatively cheaply and easily. Costs - Shorter lifespan than sea walls;
Reduction of long shore drift causes higher erosion rates further up the coastline. This is referred to as Terminal Groyne Syndrome.
Yr12 Coasts: Hard engineering coastal management – Costs and Benefits
(Case Study)
Case study: Holderness Coastline, North-East England, UK
Where: Holderness coastal sediment cell, stretches 50kms from Flamborough Head in the north to
Spurn Head at the Humber estuary.
When: Constantly eroding, 29 villages have fallen into the sea since Roman times.
Specific Physical Causes:
Weather: deep low-pressure systems in the North Sea, particularly in the winter months drive northeasterly dominant winds, higher sea levels (surges) and heavier precipitation which increases subaerial processes and mass movement (slumping).
Waves – destructive north-east dominant waves with a relatively long fetch of up to 800kms provide a
strong backwash, eroding and transporting silts out to sea.
Rip currents - excavate ‘ords’ or deep hollows generates steep high energy waves, which intensifies
coastal erosion e.g. Great Cowden and Easington with recorded rates of 10 metres per year.
Geology – Weak boulder clay cliffs left by the last ice age (12000 years ago), retreating at 1.8 metres
per year. Precipitation saturates the clay, creating a slip plane and rotational slumping. Long-shore
drift carries an estimated half a million tonnes of sediment by suspension southwards per year, with
little deposition leaving narrow, low angle beach profiles susceptible to cliff-foot erosion
Specific Human Causes:
Development: Increasing population density and urban development such as leisure and holiday
facilities at Bridlington and Hornsea increase surface run-off, which need drains; increasing the saturation of the clay geology and
increasing rotational slumping by up to 5 metres per year.
Interfering with natural coastal processes – Groynes at Hornsea, Mappleton and Withernsea have meant that settlements down drift
such as Great Cowden have seen rapid rates of erosion of up to 10 metres per year which may be attributed to sediment starvation
caused by this hard management strategy.
Eustatic changes in sea level – human processes contributing to climate change may increase the incidence of storms in the North Sea
and rates of coastal erosion.
Yr12 Coasts: Hard engineering coastal management – Costs and Benefits
(Case Study)
What are the management strategies and objectives of hard engineering?
Hold the line – this involves maintaining the existing flood defences and control structures in their present positions and increasing the
standard of protection against flooding in some areas.
Advance the line – this policy involves the construction of a new flood management scheme in front of existing flood defences.
How are coastal management decisions made?
Cost-benefit analysis: considers the social and economic aspects of a strategy. The benefits of a scheme (new businesses or jobs and
savings in lives and property) are divided by the costs of building and maintaining it.
Environmental impact assessments try to assess the effects any strategy will have upon an area. It is especially important along
coastlines as attractive scenery and ecosystems are valuable tourist assets.
Feasibility studies look at the technical merits of a particular scheme and site. Is the engineering planned suited to the local geology
or coastal processes?
Risk assessment involves taking decisions in the light of the likely recurrence interval and what is at risk. Insurance and legal claims
will make this an important consideration in the future.
Shoreline management plans try to decide upon the most appropriate scheme for each part of a littoral cell, in
discussion with all parties (planners, land owners, residents)
Where: Hornsea
Why?: A holiday resort with a promenade and hotel frontage. Here the beach is of great importance both as a tourist feature and a
means of protecting the seawall from wave erosion and winter flooding. Groynes have been repaired and new ones built. In addition
steel ‘doors’ guard the entrance to the beach and the old seawall has been raised slightly. Sand dunes in the south beach are being
planted with trees.
Benefits – groynes seem locally effective, they are relatively low cost compared to sea walls, they are acceptable visually and
development of low-lying land has now been possible
Costs – at a cost of over £5.2 million, is still a significant investment; Trapping of sand may have caused scour at Mappleton; Groynes
rarely work on their own, maintenance is continual and groynes do not hold mud.
Yr12 Coasts: Hard engineering coastal management – Costs and Benefits
(Case Study)
Where: Withernsea
Why: Another resort further south from Hornsea. Here there are also groynes and a sea wall, though the emphasis has been on a more
comprehensive approach. To prevent wave erosion a new wave return wall has been built. The wall is further protected by rip-rap or
rock armour and some beach nourishment. The natural beach has all but disappeared leaving a wave-cut platform in the clay beneath.
Benefits – this will hold the line, calm concerns of local residents and hoteliers and save seasonal jobs in the resort.
At £ 6.3 million this appears good value if it can halt the fall in local property prices.
Costs – costs have limited the length of the sea wall; the rocks have reduced access to the beach and views are restricted. There is a
problem of wave noise.
Where: Easington
Why: This is the latest location to receive help. A revetment of rock armour has been placed at the foot of the cliffs to protect this
natural gas terminal which handles 25% of North Sea production.
Benefits: Secures transfer of North Sea natural gas to the mainland.
Costs: This recent £4.5 million scheme remains untested. Though the site qualified for protection as ‘being in the national interest’, the
scheme fails to protect the actual village despite a public enquiry. There are important SSSI sites to the south and there is
considerable conflict with environmental groups.
Assessment: How successful are these schemes? To what extent are they sustainable?
Mappleton provides a useful case study of the costs and benefits of coastal defence. Whilst this scheme was not traditional hard
engineering it nevertheless raises a number of issues regarding the wisdom of interrupting the natural processes along a coastline.
Erosion rates at Mappleton have long been recorded, and in 1786 the village was 3.5 kms from the sea. By 1988 the sea was on its
doorstep, access to the beach was impossible and houses in Cliff Road were quite literally falling into the sea. There was tremendous
pressure from local residents to save the village, though in the end it was the threat to the coast road (B1242 connecting Hornsea with
Withernsea) that won the day. In 1991 a scheme was implemented at a cost of £2.1 million supported by EU funding. Features of the
scheme included two rock groynes designed to trap beach sediment, a rock revetment to prevent erosion of the cliffs. The cliffs
themselves were re-graded to reduce slumping and there was some nourishment of the beach to encourage deposition. In addition a
new access road was built and a car park and toilets for visitors. The main cost of this scheme was felt down-drift from this scheme at
Great Cowden where sediment starvation due to the rock groynes at Mappleton meant cliff retreat accelerated to 10 metres per year;
illustrating the costs of not understanding how the coastal system works.