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Geo FactsheetJanuary 1997 Number 8

Coastal ManagementSince they are often extensive areas of flat, fertile, picturesque land, coastal areas are very attractive for a wide range of human activities.However, approximately 25% of the English coastline has been heavily developed for housing, industry, agriculture and leisure and isalways under attack from both the local weather and the action of the sea, resulting in coastal erosion. This Factsheet will discuss theproblems caused by coastal erosion and the techniques used to reduce them.

GroynesBreakwater (timber, rock orother materials) at 90° to thecoastline to slow erosion andsediment drifting by deflectingstrong currents, and to build upbeach level.

PoldersTimber or concrete enclosures toencourage sedimentation, causing build upof the coastline.

What is Coastal Erosion?

Coastal erosion can be defined as the loss ofland and the encroachment of the sea. It is acomplex process involving considerableinteractions between the followingcomponents:

• Wind• Wave action• Tides• Types of sediment and sediment

transport patterns• Storms

Coastal erosion is a significant problem to landuse. It results in cliff face slumping, loss of coastalland which may have been developed for humanactivities, erosion of beaches and flooding. Forexample, studies of the Kent coastline haveindicated retreat of cliff areas by 27m between1872 and 1970. It is therefore essential to devisecoastal management plans to minimise any threatto life and to protect natural and man-madefeatures.

Coastal Management

Coastal management plans have two fundamentalaims:

• To provide defence against water inundation(flooding)

• To provide protection against coastal erosion.

The main component of these plans is thepresence of coastal defences. These can bebroadly divided into two categories:

Soft coastal defencesThis is the use of natural systems in coastaldefence, for example, salt marshes and beaches,which can absorb and adjust to wave and tideenergy. Soft coastal defence involves manipulatingand maintaining these systems, without changingtheir fundamental structure.

Hard coastal defences - These are rigid‘engineering’ solutions, made principally ofconcrete. Examples include sea walls,breakwaters, groynes and jetties (See Fig 1).

The principle objective of hard engineering is toresist the energy of waves and tides by a fixedstructure. At present, such structures protectapproximately 10% of the British coastline.

The widespread use of hard coastal defences incoastal protection has both advantages anddisadvantages (Table 1).

Fig 1. Examples of hard coastal defences

Stabilise cliff face.

Exam hint - Students should showunderstanding that coastal erosion and theresultant coastal land forms, such asbeaches and cliffs, are a result of theinteraction between all of these factors andthe shoreline.

BouldersReduce wave energy reachingcoastline and stabilise sediments.

DrainageConcrete WallAbsorb wave energy, preventingerosion and flooding.

Iron Bar

High tide

Storm

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Coastal Management Geo Factsheet

Modern Coastal Management

The problems identified with local scale hardcoastal defences and an increased understandingof the erosional and depositional processeswhich operate over many miles of coastline haveresulted in the Ministry of Agriculture, Fisheriesand Food (MAFF) developing ShorelineManagement Plans (SMPs). These use anholistic approach, which means looking at thelarge scale effect of any management technique.All SMPs have the same fundamental aims:

• Produce site specific management planscovering coastal cells (see Fig 2).

These are sections of coast where the system oferosion and deposition is to a large extent self-contained.

• Take account of natural coastal processesand current and future land use.

• Provide sustainable coastal defences.These are defences which are economical andnot environmentally damaging at the presenttime, or in the future.

• Encourage co-operation between DistrictCouncils and the Environment Agency, theagencies jointly responsible for coast andflood protection.

• Account for rising sea level and increasedstorm frequency.

Table 1. Advantages anddisadvantages of hard coastalprotection

Advantages

• Effective on a local scale through bothabsorbing and reducing wave energy andretaining local structures.

• Protection and reassurance for peopleand property in the coastal environment.

• Increase in land available for human use.Hard sea defences such as sea wallsmake coastal land available foragricultural development such as theDutch Polders. Groynes and breakwatersmaintain beaches which have a highrecreational value.

Disadvantages

• Localised or isolated coastal protectioncan be counter-productive on a largerscale. Defence work in one area hasconsequences for neighbouring regions,e.g. groynes may prevent sedimentreaching a spit formation in an areafurther down the coastline, or offshorebreakwaters may interefere with naturalcurrents and sediment transport, causingerosion.

• Hard coastal defences such as sea wallsrequire continual, expensive maintenance.To upgrade a concrete armoured sea wallcosts around £3000 to £5000 per metre.

• Hard defences cannot respond to predictedsea level changes due to global warming,e.g. Southern Britain is predicted a 15m to80m sea level rise by 2050, combined withincreased storm frequency, causing severeproblems for existing defences.

• Sea defence walls directly behind naturalecosystems, such as saltmarshes, preventthe ecosystem responding to sea levelchange and increased erosion.

SMPs can only achieve these aims through acombination of both ‘hard’ and ‘soft’ approaches.One of the major components of soft coastaldefences are salt marshes.

The Value of Salt marshes

Salt marshes are found in the tidal zonebordering the sea or estuaries. They arecomposed of grasses and other low growingvegetation colonising sediment deposits(See Fig 2).

Many of the characteristic physical features ofsaltmarshes enable them to provide a naturalsea defence:

• The binding effect of the saltmarshvegetation, with its extensive root system,causes continual accumulation of sediment.Consequently, tidal inundation becomes lessfrequent and a protective barrier is producedbetween the coast and the sea which reducestidal energy, even during storms. Theshallower the slope of the region, the moreenergy is lost from the waves before theybreak.

• The friction of the rough marsh vegetationreduces tidal energy.

• The creek system covering saltmarshesdivides progressively moving landward.These resultant smaller branches providean increasing surface area to incoming water,increasing friction, so again reducing tidalenergy.

• Saltmarshes are dynamic, being able to adaptto changing tidal range and sea level. This isobviously important with the predictedchanges over the next 100 years.

Exam hint - Students are very often required toexplain how and why the movement of beachmaterial can be controlled. In addition, theyshould understand how hard coastal defencescause sediment supply to coastal features to bothincrease and decrease. For example, beachnourishment, groynes and breakwaterconstruction, dredging and dumping can allincrease levels of sediment in one area, butreduce supply in others.

Pan

CreekSaltmarsh cliff

HWMST

LWMST

Figure 2. Generalised saltmarsh showing main vegetation zones

TidalFlat

Algae

Pioneer ZoneSparse

Vegetation

Low-Mid Marsh ZoneSpecies-poor Puccinella-dominated communities

Mid-Upper Marsh ZoneSpecies-rich communitieswith increasing Festuca

UpperMarsh

SwampsBrackish

communities

TransistionZone

DriftZone

Coastal Management Geo Factsheet

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Acknowledgements;This Geo Factsheet was researched andwritten by James Sharpe..

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Case studyThe Hythe Coastal Protection Strategy for the Shepway Coast

The Shepway coastline is on the south coast of England, extending for over 40km from westof Dungeness to east of Folkestone. The existing coastal defences include:

• Natural coastal defences - sand dunes and sand and shingle beaches.

• Man-made coastal defences - concrete sea walls, timber and iron work groynes andextensive boulders for cliff protection.

Despite these measures, large areas of the coast are periodically flooded, with significantdisturbance to the infrastructure, closure of roads and damage to property. One of the majorreasons for this is that many of the hard coastal defences are nearing the end of their usefullife, highlighting the problem with such structures. The Hythe Coastal Protection Strategy isto reduce the problems which lead to flooding and damage along the coast.

The strategy has 2 main points:

• The construction of two rock groynes and a beach nourishment programme throughdeposition of shingle. This will increase shingle and beach level so as to absorbs morewave energy, reducing attack on the land.

• On-going monitoring and maintenance including monitoring of sediment transport,beach management plans and beach surveys.

This scheme aims to build upon and maximise the use of natural coastal features such asbeaches, reducing the need to construct hard coastal defences and the use of non-sustainablematerials.

Biotic:Nurseries for fish &wildfowlMigratory stopoverGene bankAquaculture potential.

Biochemical:Recycle nutrientsStore organic matter andCO sink.

It is also important that students appreciate thatthe use of natural ecosystems has other widereaching benefits. These are summarised in Table2.

Table 2. Value of coastal saltmarshes and sanddunes

Human:Location for recreationand relaxationAesthetic value.

Water:Store flood waterConserve water duringdroughts.

Managed retreat and managedadvance

There are two main approaches in which naturalecosystems, such as salt marshes and sand dunes,are used in soft coastal defences:

• Managed retreat - This involvesabandoning the current line of sea defencesand then developing the exposed land toreduce wave power, perhaps through saltmarsh development. In this way the scale ofsea walls and other hard coastal defences canbe reduced. This ‘do-nothing approach’ canonly occur where land use permits, i.e. wherethe abandoned land is of low value.

• Managed advance - This attempts to movethe shoreline zone seaward, by increasingthe amount of sedimentation along the coast.There are a wide variety of techniquesavailable for this, including using groynes,polder systems and breakwaters. This isquite a widely used technique, particularlyin Holland and Britain.

Despite the obvious advantages, there are variousproblems associated with using naturalecosystems such as salt marshes in coastalmanagement:

• To successfully establish a saltmarsh athorough understanding of the localenvironment is required, which is both timeconsuming and expensive to obtain. Forexample, information is needed on sedimentavailability and wave action.

• Natural ecosystems such as saltmarshes areprone to disease or pollution events whichcould kill much of the vegetation, resultingin the unbound sediment being washedaway and the loss of the coastal defence.

• Creation of a saltmarsh may also influencethe surrounding coast in ways which arepoorly understood. Sediment load andlevels of algal growth in water courses havenot been thoroughly studied..

GLOSSARY

Accretion - build up of beach material at theshorelineBeach nourishment - artificially increasingbeach level with imported beach materialBreakwater - natural or man-made barrierfor reducing wave energyCoastal Processes - Physical factors suchas waves, tides and sea level rise whichinteract with the shorelineDeposition - Accumulation of beach materialErosion - Wearing away of the shoreline bycoastal processesManaged retreat - Creation of extensivenatural defences, such as salt marshes

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