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Coastal setbacks

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Coastal setbacks are ‘a prescribed distance to a coastal feature such as the line of permanent vegetation, within which all or certain types of development are prohibited (Cambers, 1998).  A setback may dictate a minimum distance from the shoreline for new buildings or infrastructure facilities, or may state a minimum elevation above sea level for development.  Elevation setbacks are used to adapt to coastal flooding, while lateral setbacks deal with coastal erosion.

The description of this technology originates from Linham and Nicholls (2010).

Description: 

The ‘setback’ area provides a buffer between a hazard area and coastal development (Fenster, 2005).  The idea is to allow room for the average high water mark to naturally move inland by SLR throughout the economic lifetime of the property.  Setbacks provide protection to properties against coastal flooding and erosion by ensuring that buildings are not located in an area susceptible to these hazards.  Two types of setback can be distinguished; elevation setbacks to deal with flooding and lateral setbacks to deal with erosion (see Figure 1).

illustration © climatetechwiki.org

Figure 1: Types of coastal setback (Source: Linham and Nicholls 2010)

The approach allows erosion to continue along strategic sections of coast while further development is restricted.  This allows eroded sediment to be transported to areas alongshore, thus enhancing the level of protection afforded by helping to maintain wide, natural beaches.  By managing the coast in this natural state, adjustments by the coastline to changing conditions such as SLR can be made without property loss (Kay, 1990).

Setback distances are determined either as: (1) a fixed setback which prohibits development for a fixed distance landward of a reference feature; or (2) a floating setback which uses dynamic, natural phenomenon to determine setback lines and can change according to an area’s topography or measurements of shoreline movement (Fenster, 2005).

Control of development is achieved either by defining a linear exclusion zone along the whole of an administrative unit, or by specifying distinct coastal exclusion zones (Kay, 1990).  Ideally, setbacks should be established based on historic erosion rates or extreme water levels rather than adopting arbitrary distances which do not truly represent the threat from erosion or coastal flooding.

Setback policies are widely used across the world; schemes have been implemented in many countries including Canada, Barbados, Aruba, Antigua, Sri Lanka, USA, Australia (McLean et al., 2001), Denmark, Germany, Norway, Finland, Poland, Spain, Sweden and Turkey (Fenster, 2005).

Advantages of the technology top

Setbacks provide a highly effective method of minimising property damage due to coastal flooding and erosion, by removing structures from the hazard zone.  They provide a low-cost alternative to shoreline erosion or flood protection works such as seawalls or dikes which have their own disadvantages (see Sections 4.1.2 and 4.1.4 respectively).

Unlike hard structures, setbacks help to maintain the natural appearance of the coastline and preserve natural shoreline dynamics (NOAA, 2010).  This allows natural erosion/accretion cycles to occur (Fenster, 2005) and helps to maintain the local sediment budget.  Enhanced downdrift erosion as observed when using hard defences is also less likely to occur.  As such, setbacks can contribute significantly to sustainable management of coastal systems (Fenster, 2005).

Setbacks also help to maintain shoreline access by preventing development immediately on the seafront (NOAA, 2010) as well as providing open space for the enjoyment of the natural shoreline.  Coastal setback zones are commonly promoted as open public recreational space and they can also provide recreational and beach access.

Minimum elevation setbacks also provide higher levels of protection when compared to hard defences.  For example, if a water level in excess of the design standard occurs, an elevation setback will result in shallower and less extensive flooding of developed areas than would occur if hard defences were employed instead; this is shown in Figure 2.

illustration © climatetechwiki.org

Figure 2: Differing flood impacts after failure of structural defences and setbacks (Source: Linham et al., 2010)

Disadvantages of the technology top

Over time, SLR will reduce the size of the buffer zone between structures and the sea.  As a result, setbacks will need to be periodically reviewed to ensure that buffer zones continue to provide sufficient protection; in the US states of South Carolina and Florida, setback distances are reassessed every 10 years (Healy & Dean, 2000).

It is important to emphasise that the establishment of setback does not guarantee that the coast in question will be shielded from strong storms and the associated coastal flooding and erosion (Healy & Dean, 2000).  As with all coastal adaptation measures, residual risk will remain, meaning that the protected areas are still subject to some risk in the case of an event larger than the measure can cope with.  More cautious measures can be taken to reduce residual risk.

Problems may arise as a result of setback review.  For example, reviews may reclassify coastal areas as no-build zones.  This could create conflict if these areas have already been purchased with development in mind.  Secondly, revision of the setbacks may mean existing structures are now within the buffer zone.  Typically, these structures would be allowed to remain, but if significantly damaged or destroyed by a storm, they would usually be required to be reconstructed in line with the new setback line.  In both these instances, compensation may be required for land owners who have lost development potential or have experienced physical loss of property (NOAA, 2010).

Good quality scientific or historic data are required to establish setbacks according to coastal flood or erosion threats.  Such data is not always readily available, especially in developing countries where monitoring programmes are less well established.  In the absence of such data, it is possible that setbacks established either provide too little protection or are too restrictive of shoreline development (Fenster, 2005).

Setbacks do not serve to protect existing structures in the hazard zone.  If these are to be protected, other adaptation approaches are required.  Additionally, setback policies only serve to prolong the lifetime of structures built on the shoreline.  With continued shoreline erosion or SLR, another shoreline policy will eventually be needed if these structures are to be preserved (NOAA, 2010).

Financial requirements and costs top

Again, the costs of implementing a coastal setback approach will be variable, depending on local conditions.  A number of costs will be incurred when implementing setback in any situation.  They are discussed below.

Firstly, a decision must be taken as to how far to set back.  Costs involved in taking this decision include the collection and analysis of historic erosion rates or water levels, the cost of modelling likely shoreline evolution, and the associated cost of buying in modelling services and expert consultation.  The cost at this stage will vary depending on the method used to determine setback distance.  Less technical solutions are likely to be cheaper.

Secondly, the setback policy must be communicated to relevant bodies in order that the policy is taken into account in the planning process.  Costs involved at this stage may also involve the additional costs of incorporating coastal setback into local planning policies.

Finally, enforcement is essential.  The cost of enforcement may however be low as it is possible to enforce setback via pre-existing local planning bodies.

Additional costs may be incurred if private landowners are required to be compensated for loss of development potential and also when the setback distance undergoes periodic review.

Coastal setbacks are generally accepted to be an inexpensive solution.  In a study by Shows (1978), engineering costs of installing a coastal setback line in Florida, USA, were estimated to be US$11,700/km with mandatory five-year reviews expected to cost US$23,000/km.  Annual administrative costs were estimated at approximately US$4,800/km (costs converted to 2009 prices) (Shows, 1978).

Implementation of a setback policy is likely to have the lowest costs when implemented proactively, before significant, inappropriate development occurs.  In this way it should be possible to minimise compensatory payments to private landowners.

Institutional and organisational requirements top

In order to implement setbacks as an adaptive response to climate change, it is necessary to implement the measure proactively.  Because of the largely predictable nature of coastal erosion and the long lead times involved in SLR, planning policies can be put in place now to restrict inappropriate development which would be susceptible to coastal flooding or erosion in future (Kay, 1990).

In the past, hard defences have been employed, sometimes for political reasons such as wanting to be ‘seen to be doing something’.  A proactive setback policy must bear this political factor in mind by stressing the acceptability of a setback policy via a full coastal research and monitoring programme, together with public education and participation schemes (Kay, 1990).

It should be relatively straight forward to implement setbacks at a local level.  The approach can be incorporated into pre-existing land-use planning regulations and building codes, where these exist.  If a meaningful rather than arbitrary setback is to be employed however, factors such as the coast type, presence of physical defences and the influence of coastal processes must be accounted for (Sanò et al., 2010).

In addition to the differences in the type of setback which may be used, variations exist with respect to how setbacks are administered and who administers them.  The technical standards for establishing setbacks vary widely in practice (Fenster, 2005).

Although setbacks distances may be best informed when based on the findings of scientific models (The SCAPE model (Walkden & Hall, 2005) predicts shoreline erosion based on the type of material the coast is composed of, wave conditions and other forcing factors.  CLIFFPLAN (Meadowcroft et al., 1999) is another process-based simulation model for cliff erosion), defining a setback need not be a highly scientific endeavour.  Arbitrary setbacks require less advanced technology and therefore, may be more usable on a local scale.  Even using high technology, the degree of uncertainty in assigning a setback is significant.  Therefore, investing heavily in high-tech modelling solutions which provide more accurate setbacks may still be misguided.  Ultimately, it is preferable to be conservative (Healy & Dean, 2000) although this can lead to implementation of sub-optimal setback distances.

Barriers to implementation top

One of the most significant barriers to the implementation of setbacks, is public opposition.  This is especially likely to be the case if the public believe setbacks are too large or, in the case of individual landowners, if their land packets fall within the new restricted development zone.  In this case it is important to communicate the need for large setbacks to the public.  Compensating private landowners for lost development potential is also likely to make implementation smoother.

Setbacks may also be opposed by residents who are now deemed to live within the new building exclusion zone.  Although in most cases, structures will be allowed to persist within the no build zone, restrictions may be placed upon rebuilding in the event of damage or destruction during storms.  In most cases, it is accepted practice that reconstruction or significant modifications to structures within the exclusion zone are not permitted.

Retroactive application of coastal setbacks is unlikely in a number of cases: (1) coastal cities and urbanisations, (2) industrial areas and uses associated with maritime activities and, (3) traditional developments integrated with the coastal landscape (Sanò et al., 2010).  This may prove a barrier to the effectiveness of coastal setbacks because coastal vulnerability remains for those who are allowed to persist in the hazard zone.

In order to implement effective and meaningful setbacks, information on historic erosion rates or extreme water levels is required.  Without this information, creation of effective setbacks is problematic.  It is also recommended that coastal process-based models be used to help predict long-term shoreline evolution.  In order to operate these models, a degree of expertise is required.  Although setback may be more effective when these approaches are used, it is nevertheless possible to implement setbacks in their absence, using conservative but more arbitrary setback distances.

In many coastal areas, there is pressure to develop the coastal zone, especially when attempting to encourage tourism.  As a result, coastal regulations are often ineffective and developments within the exclusion zone proceed regardless (Sanò et al., 2010).

Opportunities for implementation top

A significant opportunity for the implementation of setbacks lies in the potential to tie the policy in with existing land use and building regulations.  There is potential for the same bodies that regulate building standards and planning permissions to ensure that new developments do not occur within the setback zone.

Setbacks can also be implemented in combination with complementary schemes such as sand dune reconstruction or wetland restoration.  Setbacks would ensure that these environments are given sufficient space to develop and adapt to climate change.  This provides the double benefit of maintaining natural protective features, as well as providing a buffer zone against coastal flooding and erosion.

References top

Cambers, G. (1998) Planning for Coastline Change: Coastal Development Setback Guidelines in Antigua and Barbuda.  Paris: UNESCO.  Available from: http://tiny.cc/j5va7 [Accessed: 19/08/10].

Fenster, M.S. (2005) Setbacks in Schwartz, M.L. (ed.).  Encyclopedia of Coastal Science.  The Netherlands: Springer, 863-866.

Healy, T.R. and Dean, R.G. (2000) Methodology for delineation of coastal hazard zones and development setback for open duned coasts in Herbich, J.B. (ed.).  Handbook of Coastal Engineering.  New York: McGraw-Hill, Chapter 19.

Kay, R. (1990) Development controls on eroding coastlines: Reducing the future impact of greenhouse-induced sea level rise.  Land Use Policy, 7 (4), 169-172.

Linham, M. and Nicholls, R.J. (2010) Technologies for Climate Change Adaptation: Coastal erosion and flooding. TNA Guidebook Series. UNEP/GEF. Available from: http://tech-action.org/Guidebooks/TNAhandbook_CoastalErosionFlooding.pdf

McLean, R.F., Tsyban, A., Burkett, V., Codignotto, J.O., Forbes, D.L., Mimura, N., Beamish, R.J. and Ittekkot, V. (2001) Coastal zones and marine ecosystems in Bijlsma, L. and Sanchez-Arevalo, I. (eds.).  Climate Change 2001 – Impacts Adaptation and Vulnerability.  Contribution of Working Group II to the Third Assessment Report of the Intergovernmental Panel on Climate Change.  Cambridge: Cambridge University Press.

Meadowcroft, I.C., Hall, J.W., Lee, E.M. and Milheiro-Oliveira, P. (1999) Coastal Cliff Recession: Development and Application of Prediction Methods.  HR Wallingford Report SR549.

NOAA (National Ocean and Atmospheric Administration) (2010) Construction Setbacks.  Charleston, SC: NOAA.  Available from: http://tiny.cc/ibrme [Accessed: 22/07/10].

Sanò, M., Marchand, M. and Medina, R. (2010) Coastal setbacks for the Mediterranean: a challenge for ICZM.  Journal of Coastal Conservation, 14, 33-39.

Shows, E.W. (1978) Florida's coastal setback line – an effort to regulate beachfront development.  Coastal Management, 4 (1), 151-164.

Walkden, M.J.A. and Hall, J.W. (2005) A predictive Mesoscale model of the erosion and profile development of soft rock shores.  Coastal Engineering, 52 (6), 535-563.

 

Author affiliations: 

Matthew M. Linham, School of Civil Engineering and the Environment, University of Southampton, UK 

Robert J. Nicholls, School of Civil Engineering and the Environment and Tyndall Centre for Climate Change Research, University of Southampton, U