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Coastal Geography - Part 2
7.0 IMPACT OF COASTS ON HUMAN LIFE
In the recent years, a large number of regional, national and sub-national scale studies have been conducted on coastal impacts. The studies have been focused on exposure to sea level rise, extreme water levels and the physical impacts of flooding, submergence and erosion.
Increased exposure to coastal flood risks: Population growth, economic growth and urbanization have led increased exposure to flood risks in densely populated areas. The population exposed to the 1 in 100 year coastal flood is projected to increase from about 270 million in 2010 to 350 million in 2050 due to socio-economic development only. For 136 port cities above one million inhabitants the number of people exposed to a 1-in-100 year extreme sea level is expected to increase from 39 million in 2005 to 59 million by 2070 through 0.5 m GMSL rise alone and to 148 million if socio-economic development. Due to socio-economic development Asia is expected to continue to have the largest exposed population and Sub-Saharan Africa the largest increases in exposure.
Industry, Infrastructure, Transport, and Network Industries: Industries which thrive on coasts and their supporting infrastructure like transport (ports, roads, rail, airports), power and water supply, storm water and sewerage are highly sensitive to a range of extreme weather and climate events including temporary and permanent flooding.
The need to relocate these industries will increase due to human coastal development. Climate variability and climate change drivers need to be given proper importance in life cycle assessment of industry, infrastructure, transport and network industries. Climate impacts on coastal industries and infrastructures vary considerably depending on geographical location, associated weather and climate and specific composition of industries within particular coastal regions (high confidence).
Hurricanes like Katrina (2005), causing US$100 Million of damage to Mississippi's ports Irene (2011) and Sandy (2012), which led to a week-long shut-down of the Port of New York. This resulted in economic damages reaching US$ 50 billion.
Due to rising sea levels vulnerability to flooding of railroads, tunnels, ports, roads and industrial facilities at low-lying areas will be exacerbated. Sea level rise will reduce the extreme flood return periods and will lower the design critical elevations of infrastructure such as airports, tunnels, coastal protections and ship terminals. A hypothetical 1 m rise in relative sea level projected for the Gulf Coast region between Alabama and Houston over the next 50-100 years would permanently flood a third of the region's roads as well as putting more than 70% of the region's ports at risk. Coastal infrastructural instability may result from natural hazards triggered by groundwater-level (GWL) variations resulting from rising sea level.
Fisheries, Aquaculture, and Agriculture: Fisheries and aquaculture and the associated post-harvest activities globally create millions of jobs and contribute significantly to the dietary animal protein of millions of people and to the world merchandise trade. In addition to small-scale fisheries and aquaculture, which are important for the food security and economy of coastal communities coastal zones also support significant agricultural activities, e.g., rice production in the low-lying deltaic regions of Asia.
Climate variability and change impact fish production which is the major source of income for the fisherfolk. At times it leads to icrease distribution ranges of fishes and a change in the species of fish available. In Australia in 2011 it was found that there was an increasing abundance of some fish species of warm temperate origin and a decline in abundance for fewer other species. In Bangladesh and in other low lying island nations, seawater inundation has become a major problem for traditional agriculture.
Depending upon the latitude, location and climatic factors, fisheries may be impacted either negatively or positively. Climate change can impact the pattern of marine biodiversity through changes in species' distributions, and may lead to large-scale redistribution of global catch potential depending on regions. It is estimated that the global economic costs of production loss of mollusks due to ocean acidification by the year 2100 could be over 100 billion US$. As a result of increased sea temperatures, the reduction in coral cover and its associated fisheries production is expected to lead in the Caribbean basin to a net revenue loss by 2015.
Negative impacts of rising ocean temperatures will be felt in the temperate regions whereas positive impacts will be felt in the tropical and subtropical regions. Changes to the atmosphere-ocean in the Pacific Island countries are likely to affect coral reef fisheries by a decrease of 20% by 2050 and coastal aquaculture may be less efficient.
Coastal Tourism and Recreation: Coastal tourism is the largest component of the global tourism industry. More than 60% of Europeans opt for beach holidays and beach tourism provides more than 80% of US tourism receipts. More than 100 countries benefit from the recreational value provided by their coral reefs, which contributed US$11.5 billion to global tourism.
Extreme events have directly impacted coastal tourism and tourist infrastructure. Climate change impacts on the Great Barrier Reef include coral bleaching in the summers of 1997-98, 2001 -02 and 2005-06 and extreme events including floods and cyclones have led to a high level of concern for climate change and various resilience initiatives have been proposed and developed by the Great Barrier Reef Marine Park Authority. According to various studies increased temperature in mid-latitude countries and increased storms in tropical areas could redirect tourist flows from mid-latitude countries to tropical coastal regions.
8.0 COASTAL MANAGEMENT TECHNIQUES
Management of coastlines is also important to help protect natural habitat and businesses. This has prompted governments to engage in coastal management though it is considered to be expensive.
Coastal management uses both hard and soft techniques. Hard techniques are high technology, high cost, human made solutions whereas Soft engineering techniques are low tech, low cost solutions that work with nature to reduce erosion.
8.1 Hard Engineering Techniques
Sea Walls: Sea walls are giant walls that span entire coastlines and attempt to reduce erosion and prevent flooding in the process. They are very expensive and require constant maintenance. They also produce a strong backwash in waves which undercuts the sea wall making their long term sustainability questionable.Traditionally, sea walls are large flat walls however more modern sea walls have a curved structure that reflects waves back into incoming waves, breaking them up and further reducing erosion.
Groynes: Groynes are low lying wooden walls that extend out to sea. The idea of groynes is to capture sand that moves down the beach via longshore drift and help build up a larger section of beach in front of an area that's experiencing coastal erosion. The new beach will increase the distance that waves have to travel to reach the coast and, in the process, they'll lose most of their energy, reducing their impact. Groynes are pretty effective but they remove a lot of the sand that's present down-drift of the beach which will result in a thinner beach at this area. This, in turn, means that sections of the coast will be more exposed to erosion down drift of the groynes which can create new problems relating to coastal management.
Gabions: Gabions are bundles of rocks in a metal mesh. They're placed at the base of a cliff in an attempt to reduce the impact of waves on the cliff and prevent the cliff from being undercut. They are an inexpensive way of coastal management but are not particularly effective.
Revetments: Revetments are concrete (or in some cases wooden) structures that are built along the base of a cliff. They absorb the energy of the waves, preventing the cliffs from being eroded. At times they have rippled surfaces, which further help to dissipate the wave energy. Revetments are normally successful at reducing coastal erosion but they are expensive to build. Once built however, they don't require as much maintenance as a sea wall.
Riprap: Riprap are just rocks and stones that have been put against the base of a cliff. They're similar to gabions in their purpose but they aren't bound together in a mesh. However the rocks are susceptible to being moved by the sea.
Breakwaters: Breakwaters are offshore concrete walls that break incoming waves out at sea so that their erosive power is reduced to next to none when they reach the coast. Breakwaters are effective but they can be easily destroyed during a storm.
8.2 Soft Engineering Techniques
Beach Nourishment: In this technique, sand and shingle are added to a beach in order to make it wider. This increases the distance a wave has to travel to reach the cliffs and so the wave will lose more energy and have less erosive power when it reaches the cliffs. The sand and shingle has to be obtained from elsewhere and is normally obtained from dredging.
Land Management: Land management is often used to help protect and rebuild dunes. Sand dunes act as a good barrier against coastal flooding and erosion and are a natural defence against the sea. However, it is essential that dunes must be left relatively undisturbed so boardwalks are constructed and sections of sand dune systems are marked as out of bounds to the general public in order to reduce the erosion of the dunes by humans.
Marshland Creation: Marshlands can be used to break up the waves and reduce their speed which reduces their erosive power. The marshlands also limit the area which waves can reach preventing flooding. The marshlands can be created by encouraging the growth of marshland vegetation such as glassworts.
Beach Stabilisation: Beach stabilization like beach nourishment aims to widen the beach and dissipate as much wave energy as possible before it reaches the cliffs. Beach stabilisation involves planting dead trees in the sand to stabilise it and lower the profile of the beach while widening the beach too.
POPULATIONS ON COASTS
LEGAL ZONES IN SEAS
COMMENTS