Setback area

Definition of Setback area: A strip along the coastal zone, where certain development activities are prohibited or significantly restricted, as buffer zone for storm tides, coastal erosion and adaptation to sea level rise. This is the common definition for Setback area, other definitions can be discussed in the article

Table 1. Setback lines in different countries. .

The setback area is delimited by setback lines, the distance from the shoreline where private hard constructions are prohibited. The shoreline is generally defined as the high-water line, but in some cases it is defined as the dunefoot or first vegetation line. Setback lines are used as coastal zone planning instrument in many countries, see Table 1. Although these setback lines are laid down in coastal regulations, they are often poorly enforced in practice. An illustration is shown in Fig. 1. Moreover, they are rarely based on a statistical analysis of extreme conditions and in that case they do not offer any guarantee of flood protection. The absence of setback lines can lead to dramatic situations, as illustrated in Fig. 2. See also the article Coastal cities and sea level rise.

Regulations equivalent to coastal setback lines exist in some other countries. In the Netherlands, for example, private building is forbidden in the coastal defense zone (including beach, seadike, first dune row), with further building restrictions in the entire coastal dune area resulting from the European NATURA directives.

In the US, there is no federal directive for coastal setback. Several states impose a setback aera that is related to estimates of local long-term coastline erosion. The width of the setback area varies from 30 to 60 times the mean annual rate of shoreline retreat, taken from a baseline which is the high water mark, the first vegetation line or the crest of the first dune row. See for example South Carolina Beachfront Permitting. Easements (governmental restrictions on land use, including acquisition rights) 'roll' inland when risk zones migrate in response to sea level rise. Transfer of Development Rights (TDR) can be used by municipalities to allow landowners with holdings in a hazard area to trade their development rights to a less sensitive area.

In France, the width [math]L[/math] of the coastal risk zone is defined as [math]L = 100 R + L_{max}[/math], where [math]R[/math] is the average annual retreat rate and [math]L_{max}[/math] the value of the maximum retreat following an extreme event.

In the UK, local planning authorities are encouraged to embed local shoreline management in their spatial plans by identifying coastal change management areas (CCMAs) where rates of shoreline change are significant over the next 100 years, taking account of climate change. Coastal change management areas should make provision for any vulnerable properties and infrastructure that may need to be relocated at a future point.

Due to coastal erosion and sea level rise, fixed setback areas only offer safety for a certain period. This period should not be shorter than the average lifespan of coastal development. Setback lines can then be determined on the basis of forecasts for coastal safety, taking into account trends in shoreline position and sea level rise.

Figure 1. Urbanization of setback area in Kerala (India).

Figure 2. Destruction of fishermen's houses on the beach of Saint-Louis (Senegal) by swell waves at high springtide (March 2015).

References

The main author of this article is Job Dronkers Please note that others may also have edited the contents of this article. Citation: Job Dronkers (2022): Setback area. Available from http://www.coastalwiki.org/wiki/Setback_area [accessed on 22-11-2024] For other articles by this author see Category:Articles by Job Dronkers For an overview of contributions by this author see Special:Contributions/Dronkers J