In theoretical terminology the risk of a
hazard is the likelihood of an event or incident occurring multiplied by the seriousness of the event or incident if it occurred. The seriousness is controlled by how vulnerable the adversely affected party was to the hazard. Hazard likelihood and vulnerability interact to create this risk
[1].
As coasts become more developed, the vulnerability component of the equation increases as there is more value at risk to the hazard. The likelihood component of the equation also increases in terms of there being more value on the coast so a higher chance of hazardous situation occurring
[2]. Fundamentally humans create hazards with their presence. In a coastal example,
erosion is a process that happens naturally on the
Canterbury Bight as a part of the coastal
geomorphology of the area and strong long shore currents
[3]
[4]. This process becomes a hazard when humans interact with that coastal environment by developing it and creating value in that area.
In Burton 1978 ‘The Environment as Hazard’ a natural hazard is defined as the release of
energy or
materials that threaten humans or what they value
[5]. In a coastal context these hazards vary temporally and spatially from a rare, sudden, massive release of energy and materials such as a major
storm event or
tsunami, to the continual chronic release of energy and materials such long-term
coastal erosion or
sea-level rise
[6]
[7]. It is this type coastal hazard, specifically around erosion and attributes surrounding erosion that this article will focus on.
Globally the number of people living on the
coast is increasing. It has been stated that there has been over a 35% increase in the
population of
people living on the coasts since 1995
[8]. The average
density of people in coastal regions is 3 times higher than the global average density
[2]. Historically
city development especially large cities were based on coasts due to the
economic benefits of the
ports. In 1950 there were only 2
megacities (cities with greater than 8 million people) in the
coastal zone,
London and
New York. By the mid-nineties there were 13
[9]. Although coastal areas globally have shown population growth and increases in density, very few in-depth quantitative global studies of population have been carried out, especially in terms of distribution across specific environs, like coasts
[2]
[10]. The spatial distribution and accuracy of global data must be significantly improved before realistic quantitative assessments of the global impacts of coastal hazards can be made. As currently much of the data is collected and analysed in the aftermath of
disasters
[11].
Historic studies have put estimates of the number of deaths due to
cyclones over the last 200 years around the
Bay of Bengal exceeding 1.3 million
[9]. However in
developed countries, as can be expected, the death toll is significantly lower but the economic losses due to coastal hazards are increasing. The United States of America (
USA) for example had major losses in
Hurricane Andrew, which hit
Florida and
Louisiana in 1992
[10].
This rushing to the coast is exhibited in
property value. A study by Bourassa et al. (2004) found in
Auckland
New Zealand, wide sea views contributed on average an additional 59% to the value of a waterfront property. This effect diminished rapidly the further from the property was from the coast. In another study it was found that moving 150m away from the
Gulf of Mexico lowered property values by 36%
[12]
[13].
Insurance premiums in coastal hazard areas are an inconsequential determinant of property values, given the significant amenity values provided by the coast in terms of views and local
recreation. Sea-level rise, coastal erosion, and the exacerbating interaction between these two
natural
phenomena are likely to pose a significant threat for the loss of
capital assets in coastal areas in the future
[14]. It is hard to say if the vulnerability to coastal hazards by those residing there is perceived yet dominated by the amenity value of coasts or simply ignored.
Coastal erosion is one of the most significant hazards associated with the coast. Not in terms of a rare massive release of energy or material resulting in loss of life, as is associated with tsunami and cyclones, but in terms of a continual chronic release that forms a threat to infrastructure, capital assets and property
[15]
[6].
Storm induced large erosion events are a part of the natural
evolutionary process of fine
sediment, gently sloping
beaches. Increased
wave energy in storms leads to the removal of
foreshore,
berm and
dune sediments. These displaced sediments are then deposited as near
shore
bars and act to dampen the wave energy lessoning the amount of sediment that is being eroded from the coast. When wave energies decrease post storm events, the sediments from these newly deposited near shore bars are returned to the upper beach, rebuilding the berm. This self-correcting
cycle is an active balance between wave energies and fine sediment
deposition
[4]. This store of sediment being available for erosion in storms and re-depositing when the event has subsided is an important natural
buffer
mechanism against protecting the
mainland from erosion and minimising coastal retreat
[16]
[17].
Sand dunes are very
dynamic
fragile structures that act as stores of sediment used to carry out the coastal processes mentioned above. This removal of the upper beach sediments is important from a hazard perspective as this is the area of the coast that is often utilised for property development due to the high prices sea front properties with a view can achieve
[12]. In
Pegasus Bay, New Zealand, storm events in 1978 and 2001 caused significant erosion of the
New Brighton and Waimairi sand beaches. In the 1978 storm event houses on the seaward side of the New Brighton Spit suffered from undercutting as the dune sediment in which they were built on was eroded by high wave energy
[4]. This same storm event caused similar erosion damage to houses built on the upper dunes in
Raumati Beach, on the
west coast of the
North Island, New Zealand
[18]
[19]. Bulldozing and bulk removal of sand from protective coastal dunes is therefore an extremely hazardous activity, and one that has been widely carried out in New Zealand in order to form a surface on which to build on to obtain sea views
[18].
In Kirk (2001) coastal erosion on the Canterbury bight, South Canterbury was said to have reached up to 8 m per year. This coastal process could be measured in more ways than one, the afore mentioned distance of coastal retreat or the decreased
dollar value of developed assets, land and
infrastructure that are at risk
[18]. To date, erosion on the Canterbury Bight has led to the loss of
agricultural land, threatened valuable infrastructure including
holiday
settlements, and reduced coastal lagoons and wetlands
[20].
Historically, erosion on the Canterbury Bight was a natural process, but has now been exacerbated by human intervention. The
Waitaki River was the dominant source of sediments for the beaches between
Oamaru and
Timaru. Since the damming of the Waitaki River in 1935 erosion of the coastal cliffs has become the primary source of sediment in the north flowing current moving up the coast of
South
Canterbury
[18].
This
destruction of
sand dunes is often then
mitigated with
construction of
seawalls,
revetments and
groynes in often futile attempts to prevent storm erosion hazards to unsuitably located assets and infrastructure on coasts. These
engineered methods are commonly ineffective and frequently actually
magnify the hazard or just move the hazard down coast. In
Porthcawl,
South Wales, a seawall constructed to stop erosion in 1887 was replaced in 1906, 1934 and finally in 1984 when the beach was paved as each prior structure was undermined by further erosion. The loss of
aesthetics due to the lack of a sand beach resulted in
tourists utilising alternative beaches. Therefore incurring an even greater economic loss on top of the cost of the engineering
[21].
The alternative to hard engineering measures is sand dune
conservation. This involves
protecting the sand dunes and allowing the natural buffering processes to occur. Dune protection and conservation can be facilitated in a number of ways, actively with
dune
planting and
sand
fencing, or with better
planning by developing away from or well behind the dune structures not on them
[22]
[23]. On the New Brighton
Spit the spread of
marram grass (Ammophila arenaria) has resulted in effective dune
stabilisation in areas. However this
invasive
exotic
species has mostly replaced
indigenous species like
pingao (Desmoschoenus spiralis) meaning that although the
stability of the coastal area has gained, the
historic,
native
cultural
values of the area have suffered
[22]
[18].
A further soft-engineering method for protecting the
shoreline is
beach nourishment, due to cost this is a solution that has been used primarily for the
benefit of the tourism
industry
[21]. As a result of erosion
Miami Beach had almost no stored sediment left by the mid 1970’s, consequently, visitor numbers declined and development of the area decreased. A beach nourishment program was setup resulting in an
influx of development and infrastructure in the late 1970s. Miami Beach was rejuvenated to such an extent that annual
revenue from
foreign tourists alone is $2.4 billion, compared to the $52 million cost of the 20-year nourishment project.
Tax revenue from tourists who visit Miami Beach alone more than covers the cost of beach nourishment projects across the
nation. Using the capitalised annual cost of the project, for every $1 that has been invested annually on the nourishment, Miami Beach has received almost $500 annually in foreign exchange
[21]
[24].
In theoretical terminology the risk of a
hazard is the likelihood of an event or incident occurring multiplied by the seriousness of the event or incident if it occurred. The seriousness is controlled by how vulnerable the adversely affected party was to the hazard. Hazard likelihood and vulnerability interact to create this risk
[1].
As coasts become more developed, the vulnerability component of the equation increases as there is more value at risk to the hazard. The likelihood component of the equation also increases in terms of there being more value on the coast so a higher chance of hazardous situation occurring
[2]. Fundamentally humans create hazards with their presence. In a coastal example,
erosion is a process that happens naturally on the
Canterbury Bight as a part of the coastal
geomorphology of the area and strong long shore currents
[3]
[4]. This process becomes a hazard when humans interact with that coastal environment by developing it and creating value in that area.
In Burton 1978 ‘The Environment as Hazard’ a natural hazard is defined as the release of
energy or
materials that threaten humans or what they value
[5]. In a coastal context these hazards vary temporally and spatially from a rare, sudden, massive release of energy and materials such as a major
storm event or
tsunami, to the continual chronic release of energy and materials such long-term
coastal erosion or
sea-level rise
[6]
[7]. It is this type coastal hazard, specifically around erosion and attributes surrounding erosion that this article will focus on.
Globally the number of people living on the
coast is increasing. It has been stated that there has been over a 35% increase in the
population of
people living on the coasts since 1995
[8]. The average
density of people in coastal regions is 3 times higher than the global average density
[2]. Historically
city development especially large cities were based on coasts due to the
economic benefits of the
ports. In 1950 there were only 2
megacities (cities with greater than 8 million people) in the
coastal zone,
London and
New York. By the mid-nineties there were 13
[9]. Although coastal areas globally have shown population growth and increases in density, very few in-depth quantitative global studies of population have been carried out, especially in terms of distribution across specific environs, like coasts
[2]
[10]. The spatial distribution and accuracy of global data must be significantly improved before realistic quantitative assessments of the global impacts of coastal hazards can be made. As currently much of the data is collected and analysed in the aftermath of
disasters
[11].
Historic studies have put estimates of the number of deaths due to
cyclones over the last 200 years around the
Bay of Bengal exceeding 1.3 million
[9]. However in
developed countries, as can be expected, the death toll is significantly lower but the economic losses due to coastal hazards are increasing. The United States of America (
USA) for example had major losses in
Hurricane Andrew, which hit
Florida and
Louisiana in 1992
[10].
This rushing to the coast is exhibited in
property value. A study by Bourassa et al. (2004) found in
Auckland
New Zealand, wide sea views contributed on average an additional 59% to the value of a waterfront property. This effect diminished rapidly the further from the property was from the coast. In another study it was found that moving 150m away from the
Gulf of Mexico lowered property values by 36%
[12]
[13].
Insurance premiums in coastal hazard areas are an inconsequential determinant of property values, given the significant amenity values provided by the coast in terms of views and local
recreation. Sea-level rise, coastal erosion, and the exacerbating interaction between these two
natural
phenomena are likely to pose a significant threat for the loss of
capital assets in coastal areas in the future
[14]. It is hard to say if the vulnerability to coastal hazards by those residing there is perceived yet dominated by the amenity value of coasts or simply ignored.
Coastal erosion is one of the most significant hazards associated with the coast. Not in terms of a rare massive release of energy or material resulting in loss of life, as is associated with tsunami and cyclones, but in terms of a continual chronic release that forms a threat to infrastructure, capital assets and property
[15]
[6].
Storm induced large erosion events are a part of the natural
evolutionary process of fine
sediment, gently sloping
beaches. Increased
wave energy in storms leads to the removal of
foreshore,
berm and
dune sediments. These displaced sediments are then deposited as near
shore
bars and act to dampen the wave energy lessoning the amount of sediment that is being eroded from the coast. When wave energies decrease post storm events, the sediments from these newly deposited near shore bars are returned to the upper beach, rebuilding the berm. This self-correcting
cycle is an active balance between wave energies and fine sediment
deposition
[4]. This store of sediment being available for erosion in storms and re-depositing when the event has subsided is an important natural
buffer
mechanism against protecting the
mainland from erosion and minimising coastal retreat
[16]
[17].
Sand dunes are very
dynamic
fragile structures that act as stores of sediment used to carry out the coastal processes mentioned above. This removal of the upper beach sediments is important from a hazard perspective as this is the area of the coast that is often utilised for property development due to the high prices sea front properties with a view can achieve
[12]. In
Pegasus Bay, New Zealand, storm events in 1978 and 2001 caused significant erosion of the
New Brighton and Waimairi sand beaches. In the 1978 storm event houses on the seaward side of the New Brighton Spit suffered from undercutting as the dune sediment in which they were built on was eroded by high wave energy
[4]. This same storm event caused similar erosion damage to houses built on the upper dunes in
Raumati Beach, on the
west coast of the
North Island, New Zealand
[18]
[19]. Bulldozing and bulk removal of sand from protective coastal dunes is therefore an extremely hazardous activity, and one that has been widely carried out in New Zealand in order to form a surface on which to build on to obtain sea views
[18].
In Kirk (2001) coastal erosion on the Canterbury bight, South Canterbury was said to have reached up to 8 m per year. This coastal process could be measured in more ways than one, the afore mentioned distance of coastal retreat or the decreased
dollar value of developed assets, land and
infrastructure that are at risk
[18]. To date, erosion on the Canterbury Bight has led to the loss of
agricultural land, threatened valuable infrastructure including
holiday
settlements, and reduced coastal lagoons and wetlands
[20].
Historically, erosion on the Canterbury Bight was a natural process, but has now been exacerbated by human intervention. The
Waitaki River was the dominant source of sediments for the beaches between
Oamaru and
Timaru. Since the damming of the Waitaki River in 1935 erosion of the coastal cliffs has become the primary source of sediment in the north flowing current moving up the coast of
South
Canterbury
[18].
This
destruction of
sand dunes is often then
mitigated with
construction of
seawalls,
revetments and
groynes in often futile attempts to prevent storm erosion hazards to unsuitably located assets and infrastructure on coasts. These
engineered methods are commonly ineffective and frequently actually
magnify the hazard or just move the hazard down coast. In
Porthcawl,
South Wales, a seawall constructed to stop erosion in 1887 was replaced in 1906, 1934 and finally in 1984 when the beach was paved as each prior structure was undermined by further erosion. The loss of
aesthetics due to the lack of a sand beach resulted in
tourists utilising alternative beaches. Therefore incurring an even greater economic loss on top of the cost of the engineering
[21].
The alternative to hard engineering measures is sand dune
conservation. This involves
protecting the sand dunes and allowing the natural buffering processes to occur. Dune protection and conservation can be facilitated in a number of ways, actively with
dune
planting and
sand
fencing, or with better
planning by developing away from or well behind the dune structures not on them
[22]
[23]. On the New Brighton
Spit the spread of
marram grass (Ammophila arenaria) has resulted in effective dune
stabilisation in areas. However this
invasive
exotic
species has mostly replaced
indigenous species like
pingao (Desmoschoenus spiralis) meaning that although the
stability of the coastal area has gained, the
historic,
native
cultural
values of the area have suffered
[22]
[18].
A further soft-engineering method for protecting the
shoreline is
beach nourishment, due to cost this is a solution that has been used primarily for the
benefit of the tourism
industry
[21]. As a result of erosion
Miami Beach had almost no stored sediment left by the mid 1970’s, consequently, visitor numbers declined and development of the area decreased. A beach nourishment program was setup resulting in an
influx of development and infrastructure in the late 1970s. Miami Beach was rejuvenated to such an extent that annual
revenue from
foreign tourists alone is $2.4 billion, compared to the $52 million cost of the 20-year nourishment project.
Tax revenue from tourists who visit Miami Beach alone more than covers the cost of beach nourishment projects across the
nation. Using the capitalised annual cost of the project, for every $1 that has been invested annually on the nourishment, Miami Beach has received almost $500 annually in foreign exchange
[21]
[24].