The main objective of land claim is neither erosion nor storm reduction. The aim of land claim is instead, to create new land from areas that were previously below high tide. However, if land claim is designed with the potential impacts of climate change in mind, measures can be taken to reduce the exposure of these areas to coastal flooding. For example, in Singapore and Hong Kong, there are enforced minimum reclamation levels to account for future SLR.
Land claim is likely to be accomplished by enclosing or filling shore or nearshore areas (Bird, 2005). Several alternative terms may be used when referring to land claim; these may include land reclamation, reclamation fill and advance the line.
The description of this technology originates from Linham and Nicholls (2010).
This is a more aggressive form of coastal protection which may more accurately be termed ‘attack’ or ‘advance the line’ under the shoreline management typology. Land claim is typically undertaken to gain land, for agricultural or development purposes (French, 1997). It is particularly common around coastal cities, such as Singapore and Hong Kong, where land values are very high, therefore justifying the costs. In recent years, large-scale land claims have also been conducted in Dubai, for residential, leisure and entertainment purposes. These developments include the Isle of Palms and the World.
By shortening the coastal length, land claim can contribute to coastal defence, as has been accomplished on the North Sea coast of Germany (Sterr, 2008). In the future, the main benefit of land claim will remain the additional land, but under a rising sea level, coastal defence benefits will also be considered.
Coastal land claim is most frequently employed in estuaries or deltas due to the shelter afforded to potential industrial developments, such as ports and due to the availability of large areas of cheap, flat land, accessible from both land and sea (French, 1997). In areas such as deltas, with positive sediment budgets, land claim has often been facilitated by steady accretion (e.g. Li et al., 2004), but this is likely to be increasingly less common through the 21st century, as sediment supplies fail (e.g. Syvitski et al., 2009). However, engineered land claim will continue, such as the Isle of Palms, Dubai and the implications of SLR will still need to be considered.
In order to enclose areas for land claim, hard coastal defences must be constructed seaward of the existing shoreline. Dike and seawalls are typically constructed to protect the claimed land from flooding by the sea (Burgess et al., 2007).
Land claim generally takes place on the higher areas of the intertidal zone. This is because the higher elevation means wave energy will be reduced through interaction with lower intertidal habitats, and because less material will be required to build up the claimed land in relation to sea level. Higher elevation areas are also selected because the required defences will not need to be as high in order to prevent overtopping. Finally, if required for agriculture, the upper intertidal zone presents the most mature soil and will be more suited to farming than lower areas (French, 1997).
Lower elevation intertidal areas and sub-tidal areas can also be used for land claim, although these projects will require greater engineering and investment. If low-elevation areas are to be claimed, it is necessary either to heavily protect these areas from inundation or significantly increase their elevation through the deposit of sediments. The latter can be achieved in a similar way to the deposition of sediments during beach nourishment. Ambitious land claim projects have been implemented in both Singapore and Hong Kong where both intertidal and sub-tidal areas have been reclaimed by elevation raising, for development purposes.
As mentioned above, the two main methods of land claim are: (1) enclosing and defending shore or nearshore areas; and (2) filling shore or nearshore areas, often using the same techniques used in beach nourishment. These approaches are illustrated in Figure 4.18. When considering adaptation to climate change, land claim using fill methods is perhaps more appropriate as it does not carry such a great flood risk.
The key advantage of land claim is the gain of additional coastal land for uses such as agriculture or development. In terms of development, coastal land can be very valuable due to accessibility by both land and sea which is essential for port development and due to its highly desirable location for housing and leisure facilities.
Land claim can be traced back approximately 2000 years. Early on, land claim was carried out largely to provide agricultural land, particularly in areas where the hinterland was unsuitable for cultivation. More recently, land has been claimed for port and harbour facilities and for the construction of industrial sites (French, 1997). Although the physical gain of land is beneficial, it is now understood that land claim can also generate a number of negative impacts.
The process of land claim requires either the enclosure of intertidal habitats by hard defences, or the raising of their elevation above that of sea level to prevent inundation. This causes the direct loss of intertidal habitats such as saltmarshes, intertidal flats and sand dunes (French, 1997). This is significant because many bird and plant species have specifically adapted to life in these zones. Furthermore, these areas are largely in decline due to coastal squeeze and human development.
Another disadvantage is dewatering. By draining reclaimed land which has a high water content, land is caused to dry out, compact and shrink (French, 1997), thus reducing its elevation in relation to sea level. This causes a difference between land elevations inside the flood defences, where compaction and shrinkage has occurred and outside, where natural intertidal environments continue to naturally accrete sediments. This difference in elevation is also exacerbated by SLR and results in an ever increasing requirement for flood defences (Burgess et al., 2007). It also requires an ongoing commitment to defend these areas (French, 1997).
The use of hard defences to claim low-lying land, as shown in Figure 1, can be detrimental because these structures cause erosion and scour of the shoreline. Hard defences also prevent habitat adjustment in response to changing factors such as SLR (French, 1997).
Any type of land claim will cause the displacement of water during a natural tidal cycle. This is illustrated by Figure 2. Because of this displacement, incoming tides have a smaller area to inundate. This will cause water depths to increase and will mean intertidal areas are submerged for longer – this has the potential to cause negative biological consequences and can also increase the tidal range upstream (French, 1997).
By displacing large volumes of water, land claim can also alter the basic erosional/accretional characteristics of an estuary. An estuary’s erosional/accretional characteristics are closely linked to the magnitude of incoming and outgoing tides. Estuaries naturally accrete sediment when they are flood-dominant, i.e. when the incoming tide is greater in magnitude than the outgoing tide. However, by displacing water on the incoming tide, land claim can cause estuaries to switch to ebb-dominance, thus enhancing seaward sediment transport, erosion and increases in depth (Friedrichs et al., 1992). This can cause a previously stable estuary to develop erosion problems if the volume of land claim is sufficient.
The construction of hard defences prevents interactions between the sea and the hinterland. If coastal deposits such as sand dunes, mudflats or saltmarshes are located behind these defences, they are prevented from contributing to the local sediment budget. This can be problematic because these sediment deposits are required during times of erosion. Without them, a future sediment deficit and consequent erosion problems are likely to occur (French, 1997).
Land claim can also introduce contamination to the coastal zone and acidification of coastal waters. This can be problematic if claimed land is to be used for agriculture or when coastal waters are important for fishing. Contaminants may be introduced through the use of dredged sediments for land elevation raising – caused by the input of hazardous chemicals from industries located on the coast, from ships or from upstream river sources. Acidification on the other hand, has been linked to the action of bacteria in estuarine sediments which create sulphuric acid when exposed to air (Anderson, 1991).
Work by Linham et al. (2010) into coastal defence unit costs, found that the cost of land claim by elevation raising in South-East Asia varies from US$3-5 per cubic metre of material used, at 2009 price levels. For land claim in Hong Kong Harbour, Yim (1995) stated the costs of land claim per square metre of claim are US$3.9 when utilising marine fill and US$6.4 when using land-based fill material (prices normalised to 2009 levels).
While these costs may be representative of South-East Asia, global unit costs for land reclamation are not widely available. The financial costs of land reclamation are dependent on a number of factors:
- Chosen method of reclaim (enclosing previously intertidal areas using hard defences or raising the elevation of previously submerged land)
- Availability and proximity of fill material from onshore or offshore sites
- Number, type, size and availability of dredgers
- Requirement for hard protection measures to defend reclaimed land from coastal flooding and erosion
- Project size and resulting economies of scale
- Estimated material losses
If land claim is conducted by enclosing previously intertidal areas, the additional costs of providing hard protective measures, such as seawalls or dikes, to prevent flooding and erosion of these areas is important. Ongoing maintenance costs for these structures must also be considered.
If land claim is achieved by raising the elevation of previously submerged land, the cost of fill material is likely to be the main determinant of project cost. In turn, this cost will be influenced by the availability of appropriate materials, their proximity to the construction site and the characteristics of the reclaim site – this influences the type of dredging equipment which can be used. Changes in the cost of fill material are likely to occur in future due to increased demand and greater restrictions on dredging.
The institutional and organisational requirements of land claim projects are likely to depend on the scale and ambition of the project. Small-scale land claim for agricultural uses is more likely to be achievable at the community level than large-scale island enlargement and creation as seen in Singapore or Dubai. These large-scale projects will require the involvement of large organisations and large amounts of funding.
Land claim on the upper intertidal margins will be the easiest to accomplish at a local level, due to the presence of a lower energy wave climate and reduced fill material requirements. Land claim in greater water depths will require the construction of significant defensive measures and will call for significant quantities of fill material.
Small-scale land claim projects have been undertaken for centuries and as such, the technological requirements of these schemes appear minimal. Historic projects tended to consist of dike construction to exclude the sea, followed by drainage measures. However, historic land claims have led to significant environmental problems which were not foreseen. These problems are discussed under the disadvantages of land claim. Therefore, while land claim may be possible at a local level, the impacts must be borne in mind and weighed carefully against the benefits. If a project goes ahead, involvement of organisations with a good scientific and technology base could serve to reduce negative impacts.
One barrier to the use of land claim is potential long-term costs. Land claim creates land which will require protection from coastal flooding and/or erosion. This requires construction of defences such as seawalls or dikes with associated construction and ongoing maintenance costs.
Environmental concerns may provide another barrier to implementation. Land claim is most frequently undertaken in estuaries, due to the shelter afforded and availability of large areas of cheap, flat land, accessible from both land and sea (French, 1997). However, a number of bird, plant and animal species have specifically adapted to life in these zones. By reclaiming land in these areas, environmentally important intertidal habitats are lost, and knock-on impacts such as alterations to ebb/flood dominance may also occur. As a result, environmental opposition to land claim may mount. In the EU, compensation for lost habitats is required; this is likely to become more widespread in other countries throughout the 21st century.
As outlined in the disadvantages section, the detrimental impacts of land claim are now better understood than in the past. Our knowledge of these impacts is likely to reduce the uptake of land claim projects based on the precautionary principle.
Opportunities for land claim exist where demand for land in the coastal zone is high. Coastal land is required for three main uses; (1) transport – mainly ports and airports; (2) leisure; and (3) residential. Due to these uses, land claim mainly takes place around cities. With projected increases in coastal zone populations, land claim may provide a highly valuable source of land. The creation of high value coastal land may also have beneficial developmental impacts.
Land claim through elevation raising may also be a cost-effective method of disposing of dredged material from ports, harbours and navigation channels. This could reduce the overall cost and eliminate the need to identify offshore disposal sites for dredge material. As with beach nourishment, pollutant levels in the dredge material should be carefully monitored.
Anderson, I. (1991) Land reclamation poisons coastal waters. New Scientist, 1797, p 11.
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Syvitski, J.P.M., Kettner, A.J., Overeem, I., Hutton, E.W.H., Hannon, M.T., Brakenridge, G.R., Day, J., Vörösmarty, C., Saito, Y., Giosan, L. and Nicholls, R. J. (2009) Sinking Deltas. Nature Geoscience, 2, 681-689.
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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, UK