COASTAL MANAGEMENTG3.4

KEY TERMS

Hold the line: Maintaining the current coastline

Advance the line: Constructing and expanding a coastline

Retreat the line: Deciding the stages of retreat

We protect areas of:

high economic value like: urban areas, industrial areas and tourist areas.

High Environmental value: NNR, SSSI, ecosystems, biomes and habitats

COST BENEFIT ANALYSIS

Revetments Wooden or rock barriers placed at the foot of the cliff or the top of the beach. This breaks up the energy of the waves.

£4500 a metre

Fairly inexpensive.Does work at absorbing energy.

Looks very unnatural.

Gabions Wire cages filled with rocks that can be used to build up concrete walls.

These can be use to support weak cliffs.

£5000-£50 000 for 100 metres depending on height.

Inexpensive and flexible. Encourages upper beach stability. May blend into the landscape as soil collects in-between the rocks and vegetation starts to grow.

Can look unsightly to begin with. The metal cage can rust and if broken could become very dangerous.

Barrages Large scale engineering products involving the construction of a partly submerged wall in a bay. Controls water flow in and out of the bay. Could be used to generate tidal power.

£200 million Multipurpose use of the bay.

VERY expensive and potentially damaging to natural habitats because shoreline processes and environments are disturbed.

Offshore Breakwater

A partly submerged barrier designed to break up waves before they hit the coast.

£100 000-£300 000 depending on the materials used.

Effective barrier

Visually unappealing and potential navigation hazard.

Type Description Annotated Diagram Cost Benefits Disadvantages

Sea Wall A concrete wall that is generally found at the top of the beach. It has a curved face in order to reflect the waves back towards the sea.Can be found at Highcliffe beach.

£6000 per metre

It is effective at stopping the sea from flooding the land and damaging cliff faces.Creates a promenade for people to walk on.

Is expensive and an eyesore. It can take a long time to build.

Groynes Timber or rock structures built at right angles. They trap sediment and prevent it being taken along the shore by longshore drift which stops sediment being build up on the beach.

£5000-£10,000 each at 200 metre intervals

Builds beaches which increases tourists in that areas which further increase the economy of that area.Greater protection to the land behind it. Works alongside natural processes to build up the beach.

Interrupts longshore drifts that starves beaches further down of sediment. It also leads to erosion elsewhere which means the problem is shifted and not solved. Rock Groynes can look unattractive.

Rock Armour (rip rap)

Large rocks placed on the foot of the cliff or top of the beach to form a permeable barrier to the sea only allowing some water to pass through.

£100 000-£3000 000 for 100 metres

Easy to construct.Often used in fishing and sunbathing in tourism.

The rocks are normally taken from other parts of the coast or even from abroad so don’t fit into the local geology and can look out of place. Can be dangerous when people climb over them.

Type Description Cost Benefits DisadvantagesBeach nourishment

This is the addition of sand and pebbles to an existing beach- to make it higher or wider. The sediment is usually dredged from nearby seabed, this means that it blends in well with the existing beach material.

£300 000/ 100 metres

This is a relatively cheap and easy to maintain technique. It looks natural and blends in with the existing beach. Increases tourist potential by creating a bigger beach.  

Unfortunately this type of management technique needs constant replenishment and maintenance. This is due to the natural process of erosion and long shore drift which takes away the material that has been put in place by the nourishment scheme.

Dune regeneration

Marram grass can be planted to stabilise sand dunes and help them become re-established. Areas can be fenced off to keep people away from newly planted dunes this means that they won’t get erode by people walking on them.

£200-£2000/ 100 metres

This technique as well as again being relatively cheap provides a natural coastal environment. It provides important habitats for wildlife. It is sustainable.

It can be time consuming to plant Marram grass and to fence off areas of coast. This is a long term project. People may not respond positively to being banned from certain areas.

Marsh Creation

This is a form of managed retreat, by allowing low-lying coastal areas to become flooded by the sea. The land becomes a salt marsh.

Varies depending on the size of the area and the need to compensate landowners.

Relatively cheap and often involves land reverting to the way it was before being managed for agriculture. Provides a buffer to powerful waves- creating a natural defence. Creates an important wildlife habitat.

Agricultural land is lost. Farmers or landowners need to be compensated for loss of land.  

Land use management

Even if some areas of the coast will eventually be eroded or flooded, land –use management can minimise the impact. For example, caravan parks on cliff tops are appropriate, because the caravans can easily be moved and re-sited.

  This is an appropriate behavioural approach to coastal management that is essentially sustainable.

Some people might not want to have land uses restricted at the coast. Difficult to implement retrospectively. People may not want to move some areas cannot move the sea may still erode even further back so that settlements inland become on the coast.

Managed retreat

Managed or planned retreat allows the sea to erode inward unimpeded by management techniques. As the shore erodes, buildings and other infrastructure are either demolished or relocated inland. The natural course of erosion is allowed to take place, this may happen in places not considered to be of value.

Compensation may need to be paid for.

Usually less expensive then costly hard engineering techniques, that may only be a temporary solution, especially in highly erosive areas. Allows the coast line to maintain a natural shoreline, this means that areas of wetland may just move further back and not be destroyed. Enables shoreline inhabitants to migrate inland as the shoreline erodes.

Can be politically difficult to implement, especially where significant development has already occurred. May cause depreciation of shorefront property values.People may not want to move.

HARD ENGINEERING Christchurch Bay

OVERVIEW TO CHRISTCHURCH BAY Christchurch bay is located on the South Coast of England. It is formed between the headland- Hengistbury Head near Christchurch, Dorset

and a spit at Hurst, Keyhaven close to the town of Lymington in Hampshire.

Christchurch bay is located within cell 5 of the England and wales sediment cells however this stretch of coast acts as a sub cell on its own with little

sediment leaving this area and coming into the area.

Christchurch Bay comprises a 16km section of open coastline exposed to dominant waves from the south-west.

This area of coast erodes at between 1-3m/ year

HENGISTBURY HEAD Hengistbury Head is a sandstone headland located in

Dorset on the south coast close to Christchurch between Southampton and Bournemouth.

HH is a SSSI

The headland on the west side of the bay. The groyne that sticks out into the sea makes sure that sediment from Bournemouth bay doesn’t spread into that of Christchurch bay.

HENGISTBURY HEAD

Hengistbury Head was provided with a natural defence in the form of heavy Ironstone Doggers that fell from crumbling cliffs to the beach below and built protective barriers, both on the beach and off shore. Consequently erosion at Hengistbury Head was a slow if not stationary process. The area had been stable for around 2000 years.

Beach Replenishment with shingle. Shingle is less prone to long shore drift and reduces the overall loss of sand, however it does not completely solve the problem and has to be repeated approximately every ten years. It is also unpopular with those who enjoy the sandy nature of the Hengistbury beaches. Major beach replenishment last took place at Hengistbury Head in 2005/6.

Gabion Revetment – Which have to be replaced once destroyed by the sea

Groynes – cost £80000 each

Rock armour which can cost up to £5000 per rock

Without HH it is likely that low lying Christchurch would be flooded.

NAME THE EROSIONAL FEATURES IN THIS PHOTO

Destructive waves

Rock Armour

Slumping Cliff

Mass Movemen

t

Groyne

SOFT ENGINEERING The Black Water Estuary

KEY TERMS 1. What is ‘coastal squeeze’? Coastal squeeze occurs when beaches and salt marshes are trapped

between rising sea level and hard defences such as seawalls and flood embankments. On natural coastlines, beaches and salt marshes would simply migrate inland, but the presence of hard defences (e.g. sea walls) make this impossible. Thus instead the sea rises over the salt marshes, gets pinned against the sea wall, leading to deeper water which subsequently causes erosion.

2. Define what is meant by ‘Managed Realignment’? Managed retreat or managed realignment is a sustainable coastal

management solution. It involves setting back the shoreline and allowing the sea to flood areas that were previously protected by embankments and seawalls.

BACKGROUND

Location: Essex Rate of erosion: 0.3-1m per year In some areas the erosion is up to 2m per year

(Cobmarsh Island) Hard engineering schemes in the estuary have

become to hard to maintain This has lead to soft engineering approaches

being implemented. The area is at risk of coastal flooding due to

rising sea level and the Isostatic movement of theSouth Coast (sinking)

Northey Island

Orplands

Bradwell on sea

Cobmarsh Island

Mersea Island

Ray Creek

Tollesbury Fleet

Abbots Hall Farm

TECHNIQUES IN PLACE Coastal realignment (retreat) was implemented at Tollesbury Fleet in 1995.

After an existing sea wall was breached and 21 hectares of farmland breached. This flooded area has led to the creation of a saltmarsh. (A new sea wall has been built on higher land)

Beach nourishment: Mersea Island Marsh Stabilisation: encourages sediment build –up at Ray Creek Coastal realignment (retreat) was implemented at Bradwell – on – sea

when the sea wall was breached 1995- sea wall breach at Orplands. 40 hectares of farmland flooded! -

coastal realignment 1991 Northey Island – sea wall breach – land flooded as part of a coastal

realignment.

ABBOTS HALL FARM When was the sea wall at Abbotts Hall Farm breached? 

The sea wall at Abbotts Hall Farm was deliberately breached in October 2002.

What is the purpose of allowing the sea wall at Abbotts Hall Farm be breached

The scheme works by allowing salt water back onto the land originally reclaimed by the construction of the sea wall over 3000 years ago. 

Why was the breaching of the sea wall timed to precede spring tides?

The breaching of the sea wall was timed to precede spring tides, allowing each tide to float in seeds from the existing marsh outside the breached wall. By midsummer, thousands of new salt marsh seedlings were covering the fields. The development of 81 ha of mudflat, pioneer salt marsh and coastal grassland had begun.

What positive changes has this sea wall breaching at Abbott Farm Hall bought about? 

Salt marsh is rare in Europe so this is a positive ecosystem development

Reduced the pressure on sea walls elsewhere along the Blackwater Estuary

Saved £500, 000 in sea defences ((reduced the cost of maintaining non-sustainable or expensive sea defences)

Created a natural defences against flooding and erosion

Created new wildlife habitats, i.e. inter-tidal mudflats and salt marshes

Restored valuable sediment sinks

JUDGEMENT - IS IT SUSTAINABLE? Which schemes are more sustainable?

Is it better to repair a sea wall or to flood an area of the same value and create a salt marsh?

When the sea wall at Orplands was breached it would have cost £600000 to repair which is the same as the cost of losing 40 hectares of land to saltmarsh which is self repairing and sustaining and will defend the coast for longer.

Salt marshes create a better environment and habitat

Grazing land has been lost

Sometimes the mud doesn’t turn to marsh. The mud is easily erodible as the sediment is not bound together by the roots of the plants.

A certain amount of land will be lost in this process while beaches are being built up resulting in settlements, farmland and other property being destroyed. Because of this, managed retreat is often not a socially acceptable plan and may invoke the need for compensation to land-owners. Furthermore managed realignment may interrupt communications and thus there may be the need for new roads and pipelines to be laid.

Hard engineering is usually more expensive and a short term measure. Which is likely to be breached or eroded as well. The hard engineering schemes will need replacing – gabions at HH

Soft engineering whiles sometimes costing the same amount in land lost can be a long term solution to the erosional coastline. By letting salt marshes form the beach and land will be protected by this natural self repairing barrier.