Move seaward

Land claim

nst — Tue, 07 Feb 2017 13:09:59 +0000

Land claim nst Tue, 02/07/2017 - 14:09

The main objective of land claim is neither erosion nor storm reduction. The aim of land claim is to create new land from areas that were previously below high tide. These 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 sea level rise

Based on information from ClimateTechWiki.

General Description

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. Typically this measure is undertaken to gain land (French, 1997), today especially around coastal cities (like Singapore and Hong Kong), where very high land values are justifying the costs.

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). 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. 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.

Advantages and disadvantages of the technology

The key advantage of land claim is the gain of additional coastal land for uses such as agriculture or development. Apart from the valuable land, this additional coastal land can function as a buffer and reducing the risks of flooding.

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). 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).

Any type of land claim will cause the displacement of water during a natural tidal cycle. 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).

Financial requirements and costs

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.

Institutional and organisational aspects

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.

Key lessons learnt

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. 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.

Environmental concerns may provide another barrier to implementation. 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

Relevant case studies and examples

EXAMPLE: Artificial Island - Amager Beach, Copenhagen (DK)

Bird, E. (2005) Appendix 5: Glossary of Coastal Geomorphology in Schwartz, M.L. (ed.). Encyclopedia of Coastal Science. The Netherlands: Springer, 1155-1192.

Burgess, K., Jay, H. and Nicholls, R.J. (2007) Drivers of coastal erosion in Thorne, C.R., Evans, E.P. and Penning-Rowsell, E.C. (eds.). Future Flooding and Coastal Erosion Risks. London: Thomas Telford, 267-279.

French, P.W. (1997) Coastal and Estuarine Management. London: Routledge.

Measure category

Prevention

EXAMPLE: Artificial Island - Amager Beach, Copenhagen (DK)

nst — Wed, 07 Dec 2016 08:37:02 +0000

EXAMPLE: Artificial Island - Amager Beach, Copenhagen (DK) nst Wed, 12/07/2016 - 09:37

Coastal floods or storm surges

Erosion

Channel, Coastal and Floodplain Works

Move seaward

Combined approach (grey + green)

Amager Beach is a constructed island in the southern part of Copenhagen. It was built between 2004 and 2005. It not only serves recreational purposes for the local population, but is also a coastal defense structure to protect the main coastline. This artificial approach is a very good example of combining ecosystem based approaches with coastal defense aspects.

Amager Beach is an artificial island in the southern part of Copenhagen. It was built from 1.5 million cubic meters of raw material, mainly because the old beach had “required almost annual additions of sand to keep it from disappearing into the shallow waters of the Baltic channel” (Cohen 2010: 124). Now, it is a recreational area, which can be used all year round. The island is 2 km. long and the lagoon is 400 m. at its widest point. In the northern part of the island, a more natural landscape with sand dunes can be encountered. In the south more park-like elements are installed. There are facilities for playing beach volley, surfing, flying kites or swimming. It is very clear that the simple concept of the Beach Park and its unique features provide a great setting for continued development of activities and architecture in the area (HOGK 2013). “In its new locale, Amager Beach is self-preserving because the waves are large enough to pull the sand both onto and away from the beach” (Cohen 2010: 124).

Between 2004 and 2005 the island was built and the city of Copenhagen invested 25 million euros to develop a piece of ‘engineered nature’. The project was based on an open dialogue with various stakeholders: focus groups, interest organisations and local users were involved in a continuing effort to develop the project’s qualities (HOGK 2013). This is an example of how water attracts resourceful residents and businesses, making this area an attractive address in Copenhagen (State of Green). It shows that ecosystem based approaches can be very cost-effective.

Relevant case studies and examples

Land claim

Literature sources

Cohen, Nevin (2010): Green Cities. An A-to-Z Guide. SAGE Publications, 576 p.

State of Green (2015): Rethinking urban water for new value in cities. https://stateofgreen.com/files/download/7899

HOGK (2013): Amager Beach. In: Landezine (http://www.landezine.com/index.php/2013/01/amager-beach-by-haslov-and-kjaersgaard/)

Scale

Local

Measure category

Protection

Artificial reefs

nst — Fri, 10 Jun 2016 12:04:39 +0000

Artificial reefs nst Fri, 06/10/2016 - 14:04

Estuarine floods

Coastal floods or storm surges

Erosion

Move seaward

Combined approach (grey + green)

Grey infrastructure

Artificial reefs are shore parallel rock mound structures set part way down the beach face. They may be long single structures or form a series of reefs extending for some distance alongshore. They are submerged for at least part of the tidal cycle, and are therefore less intrusive on the coastal landscape, have less impact on upper beach longshore processes and add a new intertidal habitat to sandy foreshores.

Based on kindly provided information by the Scottish Natural Heritage

Technical feasibility

Reefs dissipate part of the incident wave energy before it reaches the dune face, protecting the upper beach from erosion and encouraging deposition. Long structures (sills) reduce wave energy over an extended frontage, resulting in a more stable upper beach and dune face. Shorter, segmented reefs protect short lengths of the shore, allowing erosion to continue elsewhere. The result is an embayed shoreline with upper beach deposits (salients) forming behind the reefs.

As with all rock structures on the shoreline the rock size, face slopes, crest elevation and crest width must be designed with care. Randomly dumped rock with a high void to solid ratio is hydraulically more efficient than placed and packed rock.

Reefs may actually increase shoreline problems if they are used in areas subject to strong nearshore tidal currents. Scour along the seaward face and around the ends of reefs should be monitored, and structure maintenance undertaken prior to failure where beach levels drop.

Reef construction may need to be accompanied by an ongoing programme of beach recycling or nourishment to ensure that sediment redistribution is not unduly damaging to unprotected frontages. Regular monitoring and management are required to establish a successful scheme. Monitoring must include adjacent shorelines as well as those immediately within the reef scheme.

Reefs are of little use within estuaries where currents, rather than waves, are the main erosive force.

Political & social feasibility

Rock structures on recreational beaches should be built with a view to minimising the potential for accidents involving beach users slipping between rocks. As the structures are separated from the shore as the tide rises, and then become submerged, they are potentially hazardous to anyone using them as a perch. Rocks below the level of Spring tides will tend to be covered with marine growth including slippery algae, again forming a public hazard. The submerged reefs will form a hazard for water sports and navigation, and must be clearly marked with appropriate beacons. Wave induced currents around the ends of reefs can be locally strong and a danger to swimmers.

But the reefs will also form a new intertidal habitat, bringing rocky shore communities to a sandy beach. The structures may well prove to be popular with beach users for example for snorkeling or diving activities.

Positive Feedback from Bulgaria: No Pollution Process

Cost of implementation & maintenance

Costs for reef schemes depend on structure dimensions and spacings, but are genereally considered to be moderate to high and additionally need some shoreline maintenance. They can be heavily influenced by the availability of suitable rock (or other material), transport and the costs of any recycling or nourishment. Work windows are limited to low tide periods and may be influenced by stormy seas. Rock structures can be assumed to have an unlimited life with respect to economic assessments.

Ecological feasibility

Even though this form of defence is intended to give only partial protection to the shoreline the impacts on shoreline processes, intertidal habitats and landscape will still be high, and may be unacceptable in environmentally sensitive areas. Erosion in the lee of the gaps may well continue for several years after construction while a new beach planshape develops. Long, sill type, reefs with no gaps may suffer from a build up of fine sediment, seaweed or other debris along the inshore side - gaps provide a flushing mechanism.

Comment from Italy: Environment can be considered important

Key lessons learnt

Artificial reefs can reduce wave energy and therefore slow down coastal erosion. The planning and construction of these must be undertaken with much care, because they can impact negatively the coastal system. But the rocks can also from new intertidal habitats. These would not only beneficial for flora and fauna but could also be beneficial for the tourism sector.

Measure category

Mitigation