Information and Advsiory Note Number 73, February 1997

Coastal erosion and defence
III. Coastal defences and the natural heritage

1. Introduction

1.1 This Information And Advisory Note is one of three covering different aspects of coastal erosion and defence. It provides information on the various styles of coastal defence most commonly employed in Scotland to manage coastal erosion, focusing upon the potential environmental impacts and benefits associated with each, and offering guidance for SNH staff on responding to proposals for such defences. Related Information and Advisory Notes include No. 36 Coastal erosion and defence. I. Scottish Natural Heritage and the Coast Protection Act, which examines the legislation governing coast protection and recent changes of relevance to SNH, and No. 72 Coastal erosion and defence. II. Coastal erosion and coastal cells, which examines the causes and consequences of coastal erosion from a conservation perspective and the potential application of coastal cells and shoreline management plans to management of erosion in Scotland.

2. Background

2.1 Coastal defence covers two related but distinct issues: coast protection, which is concerned with works designed to manage or prevent erosion of the coastline, and sea defence, which relates to schemes intended to manage or prevent flooding or inundation of the coastline. Of the two, coast protection works are the more common type of coastal defence in Scotland, though in some instances they may also fulfil a sea defence role. Moreover, new coast protection works are proposed much more regularly than new sea defences and, also as a result of recent changes in coast protection legislation, SNH is consulted much more frequently regarding these. This Information and Advisory Note focuses, therefore, upon coastal erosion and coast protection, though the environmental impacts and benefits of the different forms of coastal defence works are broadly similar, whether intended to manage erosion or flooding.

2.2 Coastal erosion is, in general, a natural process affecting most coastlines in Scotland at rates ranging from <1mm per year on hard igneous cliffs to 4m per year or more on certain dune coastlines. Although much of the Scottish coastline is composed of relatively hard rock formations, these are often overlain by softer, unconsolidated sediments, deposited during or since the last Ice Age as glacial tills, dunes, machair/links plains and shingle ridges. Where such deposits are built upon or developed in some other manner, coast protection is often sought to help prevent or reduce land loss. Typical forms of development in such settings in Scotland include golf courses, MoD establishments, roads and, locally, industry, housing and built leisure and recreation facilities such as promenades, slipways and footpaths. Historical and archaeological monuments are especially common in many dune and links or machair areas of the Western and Northern Isles. All these interests may lead to proposals for coast protection. Many coastal areas are also farmed or forested, though it is rare for coast protection to be cost effective in such situations.

2.3 Most major coast protection schemes in Scotland are promoted by Coast Protection Authorities (CPAs), under the Coast Protection Act 1949. In April 1996 each unitary council with a coastline became the CPA for that area. The right of the CPAs to construct coastal defences is a permissive one; none are under any obligation to protect land or property. Schemes promoted by CPAs are subject to approval by the Scottish Office who may attach specific conditions to any consents granted. Under the Coast Protection Act, new schemes proposed by CPAs must also be advertised and, except for emergency works, consultation conducted with certain organisations, including SNH. This applies even if the site concerned has no designated natural heritage interest.

2.4 Various other bodies with coastal responsibilities, such as road, rail and harbour authorities also have the right to protect their own interests from erosion. Such authorities have special powers under the Coast Protection Act and need only give the relevant CPA 28 days notice of their intentions. They need not consult SNH under the Coast Protection Act, though this does not obviate them from the need to obtain other consents or licences as appropriate. These may include, for instance, a FEPA licence from SOAEFD, under the Food and Environment Protection Act 1985, should the works entail construction below MHWS (See para. 5.6), and consent from SNH for work carried out on SSSIs.

2.5 Apart from these, the primary responsibility for protection of land from coastal erosion lies with individual landowners, subject to the consent of the CPA. In such instances Scottish Office approval is not necessarily required and SNH need not be consulted under the Coast Protection Act; again this does not remove the requirement for the landowner to obtain other consents, licences and planning permission as appropriate, including consent from SNH for work carried out on SSSIs. Further details of this legislation are contained within Information and Advisory Note No. 36.

2.6 Sea defences are governed by separate legislation, principally the Flood Prevention (Scotland) Act 1961. This Act confers permissive powers upon the unitary authorities to “take measures for the prevention or mitigation of flooding of nonagricultural land in their areas …”. These powers are broadly analogous to those relating to coast protection.

3. Coastal defence options

3.1 Traditional forms of coastal defence, and the ones still most commonly applied, consist of structures designed to resist natural processes such as wave action and sediment movement. These are generally known as “hard engineering” options and include:

3.2 Particularly in more rural settings, or those with a high conservation value, “soft engineering” options are often considered. These are designed to emulate, harness or manipulate natural processes. Examples applied in Scotland include:

3.3 Soft engineering options applied elsewhere, but which may, conceivably, be proposed in Scotland include:

3.4 Certain other coastal defences combine elements of hard and soft engineering. These include:

strongpoints (mounds of rock armour placed strategically along an eroding cliffline; these halt erosion where placed but allow temporary retreat of the intervening land until a series of stable bays is formed).

4. General environmental impacts of coastal defences

4.1 Few forms of coastal defence have a benign effect upon the environment, as all are designed to counter the natural evolution of the coastline. Any form of defence which reduces or prevents sediment loss from a previously eroding coastline reduces sediment supply to the beach and in so doing may contribute to increased erosion elsewhere.

4.2 Because they resist natural processes, hard defences will, in general, have a more damaging effect upon the environment than soft defences, although the scale of the works concerned is clearly significant in this respect. By interfering with waves, currents or sediment movement the effects of such defences are not restricted just to the protected site but may include changed patterns of erosion and deposition on neighbouring beaches. Effects commonly associated with the forms of hard defence listed above, apart from groynes, include:

4.3 If well designed, sea walls and revetments may offer a greater level of security in the short term than most forms of soft defence but they require regular maintenance and, in the long term, may be subject to failure as soft sediment around or below them is washed out.

4.4 Because they interrupt the drift of sediment alongshore, groynes are particularly likely to cause or increase erosion downdrift of the defended shoreline unless they are combined with a programme of beach renourishment or until beach levels have increased to a sufficient height that sediments can bypass them.

4.5 From a landscape and amenity perspective, most hard defences appear stark and out of keeping with the landscape. Obtrusive engineered structures can often adversely affect those qualities of the coast which people most enjoy - the naturalness, openness and sense of freedom from the man-made world.

4.6 Most soft defences involve moving beach sediment or creating the conditions necessary for sediment deposition. Where sediment is moved or added to a beach (e.g. beach renourishment) the new beach profile will be out of equilibrium with the processes acting upon it and so erosion of the added material may be expected over time. Thus, such measures generally need to be repeated periodically, albeit over a number of years in some instances.

4.7 With all soft defence initiatives there is an element of uncertainty about how the beach will respond after implementation of the scheme or defences concerned. Mathematical modelling of beach behaviour may be valuable in this respect and, indeed, should be a fundamental component of any major scheme, such as the renourishment of a town beach. However, it is often only by trial and error that the optimum conditions or practices for retaining a ‘healthy’ beach or promoting sand deposition can be identified. Monitoring of such schemes and modification of the techniques employed as necessary are, therefore, crucial to their success.

4.8 Because of the diversity of soft defences available, a list of environmental impacts common to all is difficult to produce, but typical impacts may include:

4.9 Although coastal defences are rarely of benefit per se to the natural heritage, their effects can often be reduced or mitigated and, in certain circumstances, they may add to the habitat diversity of a site. Table 1 lists potential environmental impacts and opportunities for mitigation for all the defences listed above.

Table 1. Potential Environmental Impacts And Benefits Or Opportunities For Mitigation Associated With Different Forms Of Coastal Defence

5. Responding to coastal defence proposals - background

5.1 Unless caused by anthropogenic activities (such as sand extraction, trampling or overgrazing) or in the rare circumstances of a unique habitat or feature being permanently lost coastal erosion is not in itself undesirable from a conservation perspective. It is, for the most part, a natural process, fundamental to the natural functioning and evolution of the coastline and is essential for the maintenance of many coastal habitats as well as contributing greatly to the landscape character of Scotland's coastline. Moreover it may, in places, be vital for the generation and supply of beach sediment. Consequently, except where erosion has been introduced artificially to a system, the aim of conservation management should be not to combat it but to maintain the natural process.

5.2 From a conservation perspective, therefore, the general objectives in assessing proposals for coastal defence should be to:

5.3 Many, if not most, coastal defence schemes in Scotland are proposed for sandy shorelines. Such beaches often undergo cycles of erosion and advance, including seasonal fluctuations relating to changes in wave activity over the course of a year. Because beach erosion occurs so rapidly relative to beach advance, there is often a perception that erosion is the prevalent process, even though there may be little evidence of long-term coastal retreat. In such cases, it may be appropriate to encourage monitoring of the position of the coastal edge over the course of a few years and/or assessment of coastal changes from the analysis of past aerial photographs and OS maps. This will help to demonstrate whether or not concerns of coastal retreat are valid and, if not, may help prevent the implementation of potentially costly and environmentally damaging defences.

5.4 Simple monitoring may be conducted by measuring, periodically, the distance to the coastal edge from a series of fixed points such as pegs or fence posts located a few metres inland of the coastline. A greater distance may be required for dynamic dune coastlines. Fixed point photography may also be employed but measurements of coastal position using this method are less quantifiable. More detailed guidelines on monitoring of coastal landforms is available, if required, from the Earth sciences branch, Scottish Natural Heritage, Edinburgh.

5.5 Where a designated area is concerned, it may not be possible to agree a form of defence which is environmentally acceptable. Alternatively, the nature or significance of the direct or indirect effects upon the site's natural heritage may be unclear. In such cases the scheme's proponent should be encouraged to prepare an environmental impact assessment. One means of achieving this may be via the local Planning Department. In 1994, coast protection works were added to the list of schedule 2 category developments under the environmental assessment (Scotland) regulations 1988, through which the EC 1985 Directive on environmental impact assessment is implemented. Consequently, where a planning department considers that the defences are likely to cause significant environmental effects to a “sensitive location”, such as a SSSI, NSA, SPA or SAC (including proposed SPAs and SACs), it may require the proponents of the scheme to prepare an environmental assessment of the impact of the works. For obvious reasons, this option may be difficult to pursue where the scheme's proponent is also the planning authority.

5.6 Under the Food and Environment Protection Act 1985 Part II, any operation which entails the deposition of any material, or placement of any construction, below the Mean High Water Mark of Spring Tides (MHWS), requires a licence from SOAEFD. This legislation thus encompasses virtually all coastal defence schemes and may help to support objections to coastal defence proposals which might damage the marine environment, such as dumping on beaches.

5.7 SNH, SOAEFD and Historic Scotland are currently funding research into patterns of sediment movement around Scotland's coastline, including the definition of coastal cells. This information should assist area staff in the prediction of effects of proposed works and, it is hoped, form the basis for strategic planning of coastal defences founded upon a sound understanding of coastal processes. An overview report, outlining the location of coastal cells around the Scottish coastline, should be available to all SNH offices by spring 1997. More detailed, regional reports showing sediment transport directions as well as cell locations, should be available by autumn 1997.

5.8 In England and Wales knowledge of coastal cell location is being applied through the preparation, by the Coast protection authorities and others, of shoreline management plans. These are documents which “set out a strategy for coastal defence of a specified length of coast, taking account of natural coastal processes and human and other environmental influences and needs” (MAFF, 1995). The application of shoreline management planning to the Scottish coastline is currently being investigated by SNH. Further information is contained in Information and Advisory Note No. 72.

6. Responding to coastal defence proposals - checklist

6.1 In formulating a response to coastal defence proposals, it may help to consider the following questions:

6.2 Following this assessment it should be possible to determine whether to object to the proposals or not. Alternatively, further information or clarification of certain points may be sought or suggestions made by which potential environmental impacts may be reduced or benefits realised (see Table 1). Certain other measures may help safeguard the natural environment from the damage which coastal defences may cause; where appropriate:

7. References and further reading

ASH Consulting Group 1994. Coastal erosion and tourism in Scotland. SNH Review No. 12. SNH, Battleby

H R Wallingford, 1995. Coastal cells in Scotland. Report to SNH, Scottish Office Agriculture Environment & Fisheries

Department and Historic Scotland. H R Wallingford Report EX 3176.

MAFF, 1993. Coastal defence and the environment. Ministry of Agriculture, Fisheries and Food. Report 1993 PB 1191.

MAFF, 1995. Shoreline management plans. A guide for coastal defence authorities. Ministry of Agriculture, Fisheries and Food Report 1995 PB 2197.

Soulsby, E.M. and Duck, R.W., 1995. Coastal processes and landforms. 4. Coastal Protection. Unpub. report to Scottish Natural Heritage. 17pp. (Available from Earth Sciences Team.)

8. Authors

George Lees, Scottish Natural Heritage.

Kathy Duncan, Scottish Natural Heritage.

Additional information was supplied by Drs Eve Soulsby and Rob Duck, of St Andrews University, and Rory Summerling of RMS Consultants.

9. Contacts for further advice and information

George Lees, Coastal Geomorphologist
Kathy Duncan, Coastal Ecologist
Sandy Downie, Marine Conservation Officer
All located at:
Scottish Natural Heritage
Advisory Services
2 Anderson Place
EDINBURGH
EH6 5NP.
Tel: 0131-447 4784