Sea level rise and the resultant effects on human life developed into a widely discussed and hotly debated issue, during the late 20th and throughout the 21st century.
The need for such debates to reach a consensus of action is clear, with events such as hurricane Katrina creating 28 foot high storm surges [1] and causing 3,560 miles of Levee failure, along the Mississippi River and canal systems of New Orleans [2]. Katrina death toll estimates range between 1,600 and 2,000 and the area suffered huge biodiversity loss and industrial decline as a result of the flood. Such impacts have all been identified as avoidable, if flood protection had been built correctly and areas of land were allowed to return to their natural salt marsh environments [3].
As sea level rise and flooding have the potential to accelerate to the highest levels of prediction made to date [4], decisions concerning flood defence must be held sooner rather than later. This post will document some of the main choices available to policy makers and hopefully shed some light on the options of future flood defence.
The Options
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| Figure 1: 5 Policy Options for Dealing with Sea Level Rise [5] |
As figure 1 shows, there are five generic options for sea defences, all of which will be explained henceforth.
Option 1: Do Nothing
As the name suggests, this technique allows the sea to engulf the land as it rises, with no resistance from man made constructions. This option is taken when the economic value of the land does not justify spending money to save it [6]. This option is considered environmental friendly, but does involve the handing over of national land to the elements, which could prove to be a very hard pill for some governments to swallow.
Option 2: Managed Realignment
As figure one shows, this form of management allows a certain area of the land to become an intertidal mudflat or salt-marsh, through the removal of a sea wall. The extent of the land loss is controlled by a new, spatially depressed wall.
An example managed realignment at work can be seen on Wallasea island, in the Thames Estuary, where six breaches in the current sea wall allowed the creation of 115 hectares of wetland, at a cost of £8 million [7]. As well as providing a habitat for a vast selection of fauna and flora, the land can act as a natural flood defence, if a storm surge was to occur along the Thames Estuary again, making the realignment economically, socially and environmentally viable. Please see the following video for more information on the benefits of the move [7].
Of course, there are issues of land ownership, which will inevitably get in the way and increase the cost of any realignment that is proposed. The simple solution is to pay the land owners an equal amount to what they would expect to get from the land within a determined time frame, however such issues require delicate negotiation and should not be approached in a brash manner.
Option 3: Hold the Line
Such an approach is adopted when the consequences of letting the sea inundate the land are too economically damaging, socially unpopular, or environmentally harmful. The defences, such as sea walls and groynes, are maintained and improved, in an effort to keep the sea at bay and protect the land behind from flooding. This option is the traditional choice for European flood defence [8]; as it has been mentioned before, the option of handing over land to the sea has never been overly popular with politicians and landowners alike.
The process of maintaining flood defences does however have one major draw back; the loss of intertidal mudflats, salt-marshes, beaches and other shoreline habitats. Landward migration of such ecosystems is prevented by the coastal defence (figure 2), removing natural habitats and raising issues of ethics and environmental sustainability.
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| Figure 2: What a Conundrum - Coastal Squeeze [9] |
This potentially ecologically catastrophic process is the subject of much debate. The final line falls between the economic drive to maintain anthropogenically populated land and the ecological desire to maintain natural habitats, a debate that seems to run throughout modern development policies.
Option 4: Move Seaward
The choice to tackle erosion through the deposition of sediment in the sea and the artificial creation of land is a largely anthropocentric practice. The decision to move seaward is usually is driven by the want to provide nice beaches for tourism or protect economically valuable land with an extended, humanly constructed area.
Two examples of such an approach can be seen in Koge Bay, Denmark and the Slovenian Coast, Slovenia (figures 3 and 4 respectively)
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| Figure 3: Koge Bay, Denmark. Red line indicates areas of reclaimed land. [10] |
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| Figure 4: Slovenian Coast, Slovenia Reclaimed land around edge of headland [11] |
Such an approach to sea level rise seems counter intuitive and stands a high change of resulting in failure, high economic cost and rapid land loss, is sea levels were to rise above the vertical height of the humanly created land.
For more information on both of the projects mentioned, please head to the websites below:
Slovenian Coast: http://www.eurosion.org/shoreline/46sloveniancoast.html
Option 5: Limited Intervention
Again adopted in areas of low economic importance, this option solves the problem of sea level rise, to an extent that prevents the loss of more important land further inland. The near coast is usually allowed to develop into salt marshes and intertidal mud flats, in the hope that these will provide protection for more affluent areas, inland.
Finding Direction in a World of Possibilities
Whilst it is undeniable that some areas of coast line, such as the aforementioned Netherlands, need hard, hold the line defences, to protect areas from rapid and devastating inundation, other areas of the world are currently in a more flexible position. Acknowledgement of such a fact could allow management to find an equilibrium between careful release of land to the seas, and the protection of large human conurbations from flooding.
The options of management should be decided after the specific study of varying lengths of differently affected coastline. This point is supported when the various isostatic sea level changes of the United States of America and the United Kingdom are considered:
The USA
New York: ~ 3mm/year rise, caused by eustatic sea level rise and small scale isostatic subsidence
Texas: ~6mm/ year rise, caused by substantial isostatic sinking, due to oil and groundwater extraction
North Oregon: near constant , up lift and sea level rise are nearly equal
Alaska: Sea level fall, caused by rapid isostatic, glacial rebound
The UK
North, e.g. Aberdeen: <0.5 mm/year rise, cause by isostatic, glacial rebound
South, e.g. Thames Estuary: 1.9 mm/ year subsidence
Such differences make the use of various approaches applicable along a single coastline; a nation-wide Shoreline Management Plan is a blindingly obvious, unsustainable option. Fortunately this has been realised in modern defence planning for example, England's current Shoreline Management Plan is divided along the countries littoral (sediment) cells. These cells are known to have little cell-to-cell interaction, allowing unique management to occur in each, with little worry of any knock-on effects (figure 5).
As the predictions of future sea level rise are full of uncertainties, due to various methods of measurement, misunderstanding of cause and effects and the unknowns of future anthropogenic influences on the earth, decisions made today must be flexible and spatially variable, allowing adaptation to any future changes. Management schemes should reach a balance between the all out defence of some areas, say of high economic value, and the unpopular, but seemingly necessary option of managed realignment and limited intervention. If such a balance is not made and humans decide to go to war with the sea, the chances of success against such a relentless opponent are slim to none.
Whilst the options available to Shoreline Management Plan policy makers are varied, one option we seem not to have available is whether or not to take action. The effect of storm surges, rising sea levels causing erosion and tsunamis are evident across the globe, with the economic, social and environmental cost of restoration after an event far exceeding that of pre-event defence construction and managed land loss.
It seems therefore, logical to prepare for the worst predictions made; those created from the observations of the Ocean Surface Topography Mission, conducted by NASA and CNES , which were publicised in the 2009 Copenhagen Diagnosis. As has been seen before, in events such as Hurricane Katrina, failure to prepare for the maximum level event leaves human populations open to wide scale disruption and destruction. However whilst Hurricane Katrina's effects were confined to New Orleans and the Louisiana state, the effects of maximum sea level rise could stand cause global scale destruction, a point that should encourage a well planned, integrated response to the risk of future sea level rise.
References
Whilst it is undeniable that some areas of coast line, such as the aforementioned Netherlands, need hard, hold the line defences, to protect areas from rapid and devastating inundation, other areas of the world are currently in a more flexible position. Acknowledgement of such a fact could allow management to find an equilibrium between careful release of land to the seas, and the protection of large human conurbations from flooding.
The options of management should be decided after the specific study of varying lengths of differently affected coastline. This point is supported when the various isostatic sea level changes of the United States of America and the United Kingdom are considered:
The USA
New York: ~ 3mm/year rise, caused by eustatic sea level rise and small scale isostatic subsidence
Texas: ~6mm/ year rise, caused by substantial isostatic sinking, due to oil and groundwater extraction
North Oregon: near constant , up lift and sea level rise are nearly equal
Alaska: Sea level fall, caused by rapid isostatic, glacial rebound
The UK
North, e.g. Aberdeen: <0.5 mm/year rise, cause by isostatic, glacial rebound
South, e.g. Thames Estuary: 1.9 mm/ year subsidence
Such differences make the use of various approaches applicable along a single coastline; a nation-wide Shoreline Management Plan is a blindingly obvious, unsustainable option. Fortunately this has been realised in modern defence planning for example, England's current Shoreline Management Plan is divided along the countries littoral (sediment) cells. These cells are known to have little cell-to-cell interaction, allowing unique management to occur in each, with little worry of any knock-on effects (figure 5).
 |
| Figure 5: UK Littoral Cells [12] |
Whilst the options available to Shoreline Management Plan policy makers are varied, one option we seem not to have available is whether or not to take action. The effect of storm surges, rising sea levels causing erosion and tsunamis are evident across the globe, with the economic, social and environmental cost of restoration after an event far exceeding that of pre-event defence construction and managed land loss.
It seems therefore, logical to prepare for the worst predictions made; those created from the observations of the Ocean Surface Topography Mission, conducted by NASA and CNES , which were publicised in the 2009 Copenhagen Diagnosis. As has been seen before, in events such as Hurricane Katrina, failure to prepare for the maximum level event leaves human populations open to wide scale disruption and destruction. However whilst Hurricane Katrina's effects were confined to New Orleans and the Louisiana state, the effects of maximum sea level rise could stand cause global scale destruction, a point that should encourage a well planned, integrated response to the risk of future sea level rise.
References
[1] D, Willie, 2005. Hurricane Katrina Pulls Its Punches in New Orleans [online]. Available at: http://news.nationalgeographic.com/news/2005/08/0829_050829_hurricane.html [01.05.2011]
[2] I.L. van Heerden, 2007. The failure of the New Orleans levee system following Hurricane Katrina and the pathway forward. Public Administration Review 67, 24-35
[3] Sweet, W. (2007) Protecting the big easy from the next big one. IEEE Spectrum 44(3), 10-12
[4] Allison, I. , N.L. Bindoff, R.A. Bindschadler, P.M. Cox, N. de Noblet, M.H. England, J.E. Francis, N. Gruber, A.M. Haywood, D.J. Karoly, G. Kaser, C. Le Quéré, T.M. Lenton, M.E. Mann, B.I. McNeil, A.J. Pitman, S. Rahmstorf, E. Rignot, H.J. Schellnhuber, S.H. Schneider, S.C. Sherwood, R.C.J. Somerville, K. Steffen, E.J. Steig, M. Visbeck, A.J. Weaver, (2009) The Copenhagen Diagnosis, Updating the World on the Latest Climate Science. The University of New South Wales Climate Change Research Centre (CCRC), Sydney, Australia.
[5] Blogger.com, 2008. Coastal Zone Management [online]. Available at: http://www.jamo-czm.blogspot.com/ [01.05.2011]
[6] West Dorset District Council, n/d. Consideration of the Risk and Coastal Defence Options [online]. Available: http://www.dorsetforyou.com/2072 [01.05.2011]
[7] Geographical Association, 2009. Wallasea Island Case Study: How did the Wallasea Island Project Develop? [online]. Available at: http://www.geography.org.uk/resources /flooding/wallaseaisland/development [01.05.2011]
[8] Parliament Office of Science and Technology, 2009. Coastal Management, [online]. Available at: http://www.parliament.uk/documents/post/postpn342.pdf [01.05.2011]
[9] L. Carl, 2010. The New Ecology of Risk: Balancing Flood Risk Mitigation with Economic Development in the Humber Region [online]. Available at: http://www2.hull.ac.uk/science/ geography/prospective_students/phd/research_students/lewis.aspx [01.05.2011]
[10] P. Sistermans & Nieuwenhuis, O (n/d). Koge Bay, Denmak, [online]. Available at: http://www .eurosion.org/shoreline/6kogebay.html [01.05.2011]
[11] M. Vahtar, n/d. Slovenian Coast, Slovenia [online]. Available at: http://www.eurosion. org/shoreline/46sloveniancoast.html [01.05.2011]
[12] Coasts and Country Projects Limited, n/d. What is a Shoreline Management Plan? [online]. Available at: http://www.coastandcountryprojects.co.uk/whatsmp.html [02.05.2011]
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