Summary 1: ADAPTIVE MANAGEMENT

Appropriate locations Locations with low value, life expired or moveable backshore assets
Costs Depends on backshore assets
Effectiveness Short term loss of assets, but highly sustainable over medium to long term
Benefits Allows natural processes to continue with possible strategic benefits spread over adjacent areas. No ongoing management costs.
Problems Backshore assets are lost or moved, often causing conflict due to differing perceptions of values

General description

Many cases of dune erosion may be best managed by not interfering with the natural processes, but instead accepting that erosion will occur and adapting backshore management accordingly. This approach will involve relocation and monitoring costs, but these may be much lower than the cost of protection.

Adaptive management should be considered at all sites before considering any of the other options set out in this guide.

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Defend or adapt?

Function

Dune erosion is often cyclical with periods of loss balanced by periods of gain. Erosion may also not be constant alongshore, with areas of loss balanced by adjacent areas of gain. Works undertaken to arrest the rate of erosion at a specific site may be detrimental to subsequent natural recovery at that site, and may increase erosion along adjacent frontages. The nett result may well be accelerated long term shoreline recession. Alternatively defensive works, such as groynes or revetments, may become redundant if natural recovery causes the defences to be completely buried by sand. In either case the efforts to influence dune erosion would be either wasted or damaging.

Adapting to erosion, or the potential for erosion, by moving, replacing or demolishing structures or other assets that are at risk will avoid the need for interference with coastal processes. Better still is the initial control of any form of development along the shoreline dunes, though in many instances it will be too late to adopt this preventative approach.

Common assets at risk around Scottish dune systems are golf course tees and greens, amenity areas and footpaths, caravan sites and grazing land. Although these features may be viewed as essential to the character of the coast, the costs involved in re-siting or replacement could well be much lower, and more sustainable into the future, than the costs of constructing defences to protect them.

Methods

The decision to abandon or move backshore assets should be based on the actual or perceived value of the assets at risk, the costs of effective erosion management alternatives (including future maintenance costs) and the environmental acceptability of those defences. It must also be based on a clear understanding of the physical and biological processes affecting the beach/dune system and predictions of the likely future evolution of the shoreline. This understanding will require investment in studies of past shoreline evolution and existing conditions, combined with a monitoring programme to allow ongoing reassessment of the evolution predictions.

If management of marine erosion is being considered it is assumed that assets of value are being threatened. These assets may be natural, such as a rare habitat or a particularly interesting geomorphological feature. In general erosion of such features would be considered part of their natural evolution and therefore preferable to management interference. More often the assets will have socio-economic importance, ranging from amenity access to a beach up to an industrial complex or power station. The shoreline manager must start by considering the value of the assets that may be at risk, then try to establish an understanding of the likely future evolution of the beach/dune system. Finally the manager must determine whether it is better to lose/move the assets or attempt to prevent or reduce the erosion.

The value of the backshore may be assessed in economic terms, based on the present replacement cost of buildings, infrastructure or land. The assessment should also consider the wider values such as potential loss of jobs, transport routes, rare habitats, recreation or cultural heritage (i.e. archaeological sites). Within Scotland there is no formal procedure for undertaking the benefit analysis, allowing each case to be treated on its own merits. If a formal approach is required for high value sites the methods used by the Ministry of Agriculture, Fisheries and Food in England provide a useful model (MAFF, 1993b).

In some cases, such as remote Highland beaches, the value assessment may be relatively straightforward and may lead to the rapid conclusion that any works would need to be very low cost and directed more at short term recreation and habitat management rather than attempts to prevent marine erosion. In other cases, including areas on the east and south west coasts that are heavily developed for industry or housing, the decision may also be straightforward, leading to substantial investment in major permanent defence works. More commonly the users of this guide will be concerned with the complicated issues arising from situations lying between these two extremes.

Having formed an initial view on the value of the backshore the manager must consider the likely evolution of the shoreline, and the potential for any backshore flooding as a result of erosion. This is a difficult task as there is often a lack of data, and what there is will often be skewed towards the very recent past. It must be remembered that dune development can be measured over timescales of decades or centuries, whereas substantial erosion can occur in a single storm. The services of a specialist consultant are likely to be required for important or complicated sites.

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Clear felling of forestry along an eroding coastline. Mature trees can pull up large areas of soil when toppling; felling them in advance of coastal erosion minimises this damage and may reduce the rate of retreat.

Ideally, investigations will combine site monitoring over several years with a desk study of available data. Historic maps, charts, surveys and aerial photographs give an indication of long term rates of shoreline change, while engineering records may indicate whether changes are related to human interference or are indicative of natural trends. Wind, wave and water level records will provide evidence to assess the likely frequency of events leading to erosion or accretion, and will allow any recent storm related damage to be set into a long term context. Backshore topographic surveying of any lowlying areas will establish the potential for flooding in the event of dune breaching.

Often these investigations will lead to the conclusion that shoreline change is cyclical over periods ranging from seasons to decades, but that there is also an underlying trend of recession. Rapid erosion over a period of, say, five years will cause great concern to those interested in the backshore, but this may be preceded or followed by decades of accretion or stability. A panic response to the erosion may well lead to the construction of inappropriate and unnecessarily costly defences. A more reasoned response may be to recognise that the rapid erosion is an unusual fluctuation within a long term, gradual trend of recession. Continued rapid erosion may well be unlikely, but any management decision would have to recognise that the backshore assets will ultimately be at risk.

Having established a reasonable understanding of the coastal processes, a plan should be formulated for both short and long term management. In the short term it may be appropriate to initiate delaying tactics such as vegetation transplanting, dune fencing or beach recycling (Summaries 2 to 5). These activities can reduce the impacts of short term storm events, but are unlikely to reverse a long term trend of shoreline recession. Plans for the longer term may need to recognise likely recession rates and the importance of moving assets out of the risk areas.

Costs associated with adaptive management are site specific and can not be generalised. Accepting the gradual loss of a site valued as an undeveloped public recreation area may incur no actual cost at all apart from monitoring and minor works to delay erosion or encourage recovery (Summaries 2 to 5). At the other end of the scale the demolition and replacement of threatened shoreline buildings or recreational facilities may cost many thousands of pounds.

The alternative long term management approaches are to design and implement substantial and costly schemes, allowing for the future management of on-going local and regional erosion. These approaches are considered in Summaries 6 to 17.

Impact

Adaptive management will result in the controlled loss of backshore assets and the continued evolution of dune habitat and land form. This approach can be highly emotive, with local interest groups protesting vigorously and demanding that more positive actions be taken. However, it must be accepted that both erosion and accretion are natural elements of dune evolution, and that maintenance of natural evolution is, wherever possible, preferable to costly and environmentally disruptive intervention.

Best practice and environmental opportunities

Adaptive management minimises interference with the natural processes and ecosystem of an evolving dune system. Although a strict do-nothing approach could be taken, it may often be appropriate to implement short term works to manage and repair storm related erosion within a longer term policy of controlled adaptation. These complimentary approaches are discussed within option Summaries 2 to 5.

Monitoring, consultation and education are at the heart of adaptive management. The shoreline should be continuously assessed using data collected from site, combined with any available historic or published data. The monitoring will allow the management policy to be reviewed from time to time. Methods for appropriate beach/dune erosion monitoring are set out in Appendix 2 of this Guide. Impacts of the policy on recreation, land use and habitats should also be monitored.

Consultation is required to assess the values associated with the backshore, and to develop a consensus view on how to deal with the assets. This process is firmly linked with education, requiring the manager to set out the background issues in a language that can be readily appreciated by those who are affected.

Those responsible for the management of eroding dunes should be aware of the potential danger to the public of a collapsing dune face. Dangers exist both from falling down the face and from being buried at the base. Warning signs set up along the crest and at public access points should be the minimum response to these dangers.

Adaptive management should be incorporated into a long term coastal zone management programme that includes land use planning and environmental management over an area that may well extend beyond the immediate dunes. The approach allows for the sustainable, long term management of the shore, with no commitment to costly or environmentally disruptive engineered schemes.