Beach nourishment is an adaptation technology primarily used in response to shoreline erosion, although flood reduction benefits may also occur. It is a soft engineering approach to coastal protection which involves the artificial addition of sediment of suitable quality to a beach area that has a sediment deficit. Nourishment can also be referred to as beach recharge, beach fill, replenishment, re-nourishment and beach feeding.
The description of this technology originates from Linham and Nicholls (2010).
Addition of beach material rebuilds and maintains the beach at a width which helps provide storm protection. This approach is mainly used on sandy beaches but the term can also refer to nourishment with shingle or even cobbles. The aim, however, should be to ensure that nourishment material is compatible with the existing natural (or native) beach material (Reeve et al., 2004). Nourishment is often used in conjunction with artificial dune creation.
The benefit of beach nourishment comes from wave energy dissipation; when waves run up a beach and break, they lose energy. Different beach profile shapes and gradients interact with waves to differing extent. The cross-sectional shape of a beach therefore affects its ability to attenuate wave energy. A ‘dissipative’ beach – one that dissipates considerable wave energy – is wide and shallow while a ‘reflective’ beach – one that reflects incoming wave energy seawards – is steep and narrow and achieves little wave energy attenuation. The logic behind beach nourishment is to turn an eroding, reflective beach into a wider, dissipative beach, which increases wave energy attenuation (French, 2001).
As well as helping to dissipate incoming wave energy, beach nourishment addresses a sediment deficit: the underlying cause of erosion. This is achieved by introducing large quantities of beach material to the coastal sediment budget from an external sediment source, also referred to as a borrow site. The term ‘sediment budget’ is used to describe the careful balance which exists between incoming and outgoing sediment. Much like a bank account, when more material is added than removed, a build-up occurs and the shore builds seaward; conversely, when more material is removed than deposited, erosion occurs (Morton, 2004). Nourishment addresses a sediment deficit – the cause of erosion – by introducing large quantities of beach material to the nearshore system. In turn, this can cause the shore to build seaward.
It is important to note that beach nourishment does not halt erosion, but simply provides sediment from an external source, upon which erosional forces will continue to act. In this sense, beach nourishment provides a sacrificial, rather than a fixed barrier against coastal erosion.
Continuing erosional forces will likely return the beach to a state where re-nourishment is required. Figure 1 shows the beach volume at a nourished beach in the UK, over time. It can be seen that over time the volume of the beach declines as a result of natural erosion. When the beach reduces to a critical volume, re-nourishment should be undertaken to avoid damage to coastal infrastructure.
Several methods of nourishment can be utilised, including placement by dredge, trucks or conveyor belts. Sand can be placed to create an extension of the beach width or as an underwater deposit which will be gradually moved onshore under the normal action of waves – this follows current practice in the Netherlands (VanKoningsveld et al., 2008). Placement as an underwater deposit also serves to encourage the dissipation of wave energy, therefore reducing its impact at the shore (Dean, 2002).
Supply of nourishment material by offshore dredging is often favoured because it allows for large quantities of material to be obtained from an area where its removal and onshore transport is reasonably non-disruptive to shoreline communities (Dean, 2002). During dredging, sediment is removed from the seabed along with significant quantities of water. The mixture is referred to as a ‘slurry’ and its liquid characteristics allow for it to be transferred ashore by floating or submerged pipelines or by the ‘rainbow method’ (see Figure 2).
An alternative to offshore dredging is the removal of beach-grade sediment from land-based sources. Sediment is then transported to the target site by truck haul. Only a small percentage of nourishments are carried out in this way and the approach is more suited to smaller-scale operations because of the more labour-intensive way of transportation (Dean, 2002).
Once sediment has been transported to the target beach, it must be deposited appropriately. If utilising offshore dredge sites, sediment can be dumped as an underwater deposit. However, nourishment more commonly brings sediment ashore. Once ashore, sediment may be reworked to form a flat beach. If desired, artificial dunes may also be created on the landward portion of the beach, through the use of bulldozers or other means.
If performed well, the benefits of nourishment are many and varied. Most importantly, beach nourishment reduces the detrimental impacts of coastal erosion by providing additional sediment which satisfies erosional forces. Shoreline erosion will continue to occur, but the widened and deepened beach will provide a buffer to protect coastal infrastructure and other assets from the effects of coastal erosion and storm damage.
Beach nourishment is a flexible coastal management solution, in that it is reversible. This is highly beneficial as it allows the widest range of coastal management options to be passed to the next generation.
Alongshore redistribution of the added material will occur through a process known as longshore drift, under the action of waves, tides and wind. Longshore drift is caused by waves approaching the shore obliquely, carrying beach sediments with them. When waves return to the sea however, the movement is always perpendicular to the shore. This initiates a gradual alongshore movement of sediment as shown in Figure 3. As a result of sediment redistribution by longshore drift, beach nourishment is likely to positively impact adjacent areas which were not directly nourished. This may provide wider benefits including reduced beach and cliff erosion for the entire coastal cell (a coastal cell is a stretch of coastline within which sediment movement is self-contained. Sediment within one coastal cell is not transported or shared with adjacent cells).
Addition of sediment which closely resembles the native beach material will help retain the natural landscape of the beach, while providing an increased capacity for coping with coastal erosion and flooding. The natural appearance of nourishment projects also means these schemes are aesthetically pleasing.
Coastal tourism heavily depends on ‘sun, sea and sand’. As a result, beach nourishment has the potential to promote recreation and tourism through beach widening (Nicholls et al., 2007b). This may serve to enhance pre-existing tourism or may serve to attract tourists to the area, thus encouraging development.
It is also possible to provide ecological benefits through beach nourishment. Schemes have been shown to provide enhanced nesting sites for sea turtles when designed with the requirements of these creatures in mind (Dean, 2002). This in turn, may serve to promote ‘eco-tourism’, with consequent development benefits.
Today, nourishment is very popular in developed countries but has also found application in developing nations, such as Brazil (Vera-Cruz, 1972; Elfrink et al., 2008), Nigeria (Sunday & John, 2006), Korea (Kim et al., 2008), Ghana (Nairn et al., 1998) and Malaysia (Brøgger & Jakobsen, 2008). The technology and methods involved are well established and many contractors experienced in beach nourishment are available worldwide to undertake such projects.
As already stated, nourishment is not a permanent solution to shoreline erosion. Periodic re-nourishments, or ‘top-ups’, will be needed to maintain a scheme’s effectiveness. This will require regular re-investment but can be viewed as a maintenance cost, such as those associated with hard engineered structures.
As with any type of shore protection works, reducing the risk of coastal flooding and erosion will result in an increased sense of security. To some extent, this is desirable. However, even in the presence of protective measures, the coastal zone remains susceptible to extreme coastal flooding and erosion events, and will remain exposed to natural disasters with long return periods. If not carefully regulated, protective measures may promote unwise development in these risky areas as a result of the increased sense of security.
Depositing sediments onto beaches can generate a number of negative environmental effects, including direct burial of animals and organisms residing on the beach, lethal or damaging doses of water turbidity – cloudiness caused by agitation of sediments – and altered sediment compositions which may affect the types of animals which inhabit the area (Dean, 2002). As a result, projects must be designed with an understanding of, and concern for, the potential adverse consequences for the environment. Special consideration should be given to the impacts upon important or rare species resident in the coastal zone.
Placement of fill material on the beach can disrupt beach and ocean habitats, such as bird and sea turtle nesting, if schemes are not designed appropriately. This is especially the case if sand grain size/composition does not match the native beach materials (IOC, 2009).
The application of beach nourishment is expected to grow in the future and as a result, there may be higher demand for high quality sediment. Limited availability of large contractors, coupled with an increase in demand for nourishment projects have already caused cost increases for nourishment projects in the Netherlands where it is widely applied (Hillen et al., 2010). This upward trend is likely to be observed elsewhere in future.
Linham et al. (2010) extensively researched the unit costs of beach nourishment. Costs were shown to typically vary from US$3-15/m3 (at 2009 price levels) where dredge sites are available locally (Linham et al., 2010). The most important determinant of nourishment costs appears to be the transport distance for the beach material.
Most of this data was collected in developed countries because this is where the vast bulk of nourishment occurs today. In developing countries, costs would, in general, be expected to be similar or possibly higher, due to their less developed coastal engineering industry.
Wide variation in costs is apparent between and within countries. This is a result of the numerous factors detailed below (CIRIA, 1996; Linham et al., 2010):
- Project size and resulting economies of scale
- Distance between dredge and target sites
- Number of journeys required between dredge site and nourishment area
- Seabed shape at the borrow site – determinant of the dredger size which can be used and therefore affects the number of journeys that must be made
- Recharge material – coarser material causes greater equipment wear and tear which is likely to be passed on to customers by contractors
- Estimated material losses
- Availability (and size) of dredgers
- Degree of site exposure – determines type of dredger to be used and may also shorten working hours when a site is subjected to energetic winds and waves
- Tidal range – large tidal ranges provide time constraints on when dredgers are able approach close enough to shore to deposit material. This is turn can affect the time required to complete a project
- Third party requirements
Payment to contractors is usually based on the delivered volume of sediment. This normally requires surveys of the visible and underwater sections of the beach to be completed both pre- and post-nourishment.
The ongoing cost of monitoring should be accounted for when considering the overall cost of nourishment. Monitoring costs are likely to vary with local labour costs and, as such, could vary significantly between countries (Mason, pers. comm.).
Large-scale beach nourishments will typically require extensive engineering studies and specialised knowledge and equipment. This may include dredgers and pipelines that need to be hired from a specialised contractor. However, it is also possible to conduct nourishment on a smaller scale. Beach-grade sediment can be transferred from land-based sources or from depositional to erosional areas by truck haul. Because of the smaller-scale nature of this approach and because readily available equipment could be used, nourishment by truck haul may be more practicable at a local level.
Once nourishment has been carried out, ongoing beach monitoring is needed in order to evaluate nourishment success and to determine when re-nourishment will be required. Given appropriate training and technology, monitoring should be possible at a local/community level. Nourishment schemes should be evaluated as a whole, however, which may require the participation of multiple communities if nourishment is undertaken on a large scale.
Beach nourishment requires a suitable source of sediment to be identified in close enough proximity to the nourishment site. This ensures that costs are kept at a reasonable level. Sediment availability is highly variable around the globe and suitable sources may not be easily found. The increasing popularity of beach nourishment worldwide may therefore cause sediment availability problems as demand increases. This problem is already being experienced in small island settings where sand is frequently carried large distances for nourishment projects.
Beach nourishment requires highly specialised equipment and knowledge including dredgers and pipelines that will need to be hired from a specialised contractor. Hillen et al. (2010) have noted the limited number of large contractors available and also highlighted the associated cost increase due to high demand. Local site characteristics will also influence the type and size of dredger which can be used – this can further limit the availability of dredgers.
Public awareness of how beach nourishment schemes work can also present a barrier. This is especially the case when using shoreface nourishment or underwater sediment deposition. Using these techniques, the advantages of nourishment may not be immediately noticeable and unless the public are educated on how the scheme works, they may doubt the benefits of nourishment and oppose such projects. The public should also be made aware that nourishment is not a permanent solution and that re-nourishments will be required. If this is not communicated, the public may again believe the scheme has failed and resent further spending on re-nourishment. This will be especially the case if public funding is used to cover nourishment costs.
Beach nourishment can act as a cost-effective disposal option for maintenance dredging of harbours and channels. The use of dredge material also combats the potential lack of suitable sediments offshore. Care must be taken when utilising dredge material however, as harbour dredges can contain high levels of pollutants which must be carefully monitored.
Beach nourishment can also be employed in conjunction with other adaptation technologies and can help to address the drawbacks of these hard technologies, which include beach lowering and downdrift sediment starvation.
If nourishment provides ecological benefits, it can also serve to encourage ecotourism and will provide an income stream for the local economy.
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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