world, as reported by Vanderburgh et al. (2010) for
Columbia River littoral zone.
Sea-level rise (SLR) today has been largely attributed to
global warming. Global warming has added water to the
oceans by melting ice in the polar regions, but the greater
contributor is thought to be thermal expansion of the
oceans, a rise in sea level due to increasing water temperature. It has vulnerable and direct impact on coastal communities ($10 % of population lives within an elevation
of 10 m above mean sea level) (McGranahan et al.,
2007). Although sea level has been rising since the end
of the last glaciation (nearly 11,000 years), the rate of
sea-level rise has increased over the past 200 years as average temperatures have increased. Sea level has risen
10–25 cm in the past 100 years, and it is predicted to rise
another 50 cm over the next century. Tide gauge data indicate that the global sea level has risen, on average, by
1.5–2.0 mm/year in the last century (Miller and Douglas,
2004), and since 1993, the rate has increased to 3 mm/year
(Church and White, 2006). There are large regional variations of sea level (Cazenave and Llovel, 2010). Since
2003, the mean rate of global sea-level rise has declined
to 2.5 Æ 0.4 mm/year (Ablain et al., 2009).
The absolute rate of sea-level rise in a region is mainly
due to two factors: (1) the increase in volume of water in
the ocean basins as a result of increasing glacial ice melting and (2) the thermal expansion of near-surface seawater
(Milne et al., 2009; Stammer et al., 2013). Several studies
indicate that eustatic sea level will continue to rise because
of global warming caused by increasing concentrations of
greenhouse gases in the atmosphere. More locally other
processes must be considered including vertical land
motions such as subsidence or uplift due to tectonic and
volcanic activity, subsidence due to sediment loading,
ground water pumping, and oil and gas extraction
(Woppelmann et al., 2007).
The IPCC Report suggests that the global sea level will
be $600 mm by 2100 AD. This means the annual rate of
increase would be 6.45 mm. Furthermore, if the ice caps
continue to melt, there could be a 1 m rise of eustatic sea
level by the end of the twenty-first century (Pfeffer et al.,
2008). Sea-level rise has a direct impact on shoreline
changes due to a higher shift in the zone of wave action
on the beach. This would lead to shoreline recession,
which will be larger on gentler slopes. Bruun (1962) developed a model which estimates shoreline recession with
respect to rise in sea level. The effect of sea-level rise will
be manifested by greater erosion of beaches and bluffs,
increased flooding, inundation of low-lying areas, intrusion of salt water into aquifers, and higher water tables
(Gornitz, 1991; Nicholls and Leatherman, 1995).
Sea-level rise will strongly impact most coastal landforms
(e.g., beaches, lagoons, estuaries, deltas, coral reefs, mangroves, etc.), but the impacts would be spatially variable
depending on local factors. Low-lying areas of developing
countries are likely to be the most greatly impacted
(Nicholls et al., 2007).
Shoreline changes due to anthropogenic activities
Anthropogenic activities such as construction of coastal
structures (harbors, breakwaters, seawalls, and vented
dams across rivers), mining of sand and shells, and urbanization and industrialization mainly affect the shoreline
configuration and coastal morphology. Bulkhead- and
revetment-type seawalls have been built along the eroding
shores. Sandbags and gabions have also been used in these
erosion-prone areas (Figure 7). However, they can induce
severe erosion in several locations along the coast and
increase the beach slope in front of the seawall as well as
on adjacent beaches. Seawalls often produce rubble along
the coast and degrade recreational beaches with episodic
damages. Groin trap littoral drift resulting in the accumulation of sediment on the updrift side and erosion on the
downdrift side. A large quantity of sediment is arrested
by these structures, causing a deficit in sediment supply
along the coast.
Extensive mining of sand and lime shells in the estuaries and river mouths also leads to accelerated erosion
along the coastline. Reduction or loss in supply of sediment affects the dynamic equilibrium of beaches and hastens erosion. In the last few decades, rapid urbanization
and industrialization such as construction of houses,
fish-processing units, major oil refineries, etc., have accelerated changes in the coastal region. Tourism and recreation are other human activities that often damage natural
vegetation, which can enhance coastal erosion and change
shoreline configuration.
Shoreline-change analysis and predictions
methods
Research on coastal changes provides important environmental indicators for coastal management (Welch et al.,
1992; Stokkom et al., 1993). Coastal mapping methods
are valuable tools to understand shoreline changes. Shoreline mapping provides critical shoreline data for models
used to represent shorelines in the geographic database.
Shoreline-change analysis methods can be applied. By
knowing the data acquisition method, the inherent errors
that normally exist in the underlying measurement processes can be identified and modeled. Also, by knowing
the models used to represent shorelines in the geographic
database, the level of abstraction of the real world inherent
in these models can be recognized. This directly influences shoreline-change analysis results.
The most effective and economic instruments used in
shoreline mapping and shoreline-change monitoring are
satellite sensors, Global Positioning Systems (GPS), and
all-weather sensors (Li et al., 2001). Shorelines can be
extracted from the stereo-matched and geo-referenced
aerial photographs both manually and automatically. The
manual extraction of shoreline features is a process that
involves digitizing the water and land interface, which is
known as the instantaneous shoreline at the time of aerial
photography. The automatic shoreline extraction process
SHORELINE CHANGES
597
Columbia River littoral zone.
Sea-level rise (SLR) today has been largely attributed to
global warming. Global warming has added water to the
oceans by melting ice in the polar regions, but the greater
contributor is thought to be thermal expansion of the
oceans, a rise in sea level due to increasing water temperature. It has vulnerable and direct impact on coastal communities ($10 % of population lives within an elevation
of 10 m above mean sea level) (McGranahan et al.,
2007). Although sea level has been rising since the end
of the last glaciation (nearly 11,000 years), the rate of
sea-level rise has increased over the past 200 years as average temperatures have increased. Sea level has risen
10–25 cm in the past 100 years, and it is predicted to rise
another 50 cm over the next century. Tide gauge data indicate that the global sea level has risen, on average, by
1.5–2.0 mm/year in the last century (Miller and Douglas,
2004), and since 1993, the rate has increased to 3 mm/year
(Church and White, 2006). There are large regional variations of sea level (Cazenave and Llovel, 2010). Since
2003, the mean rate of global sea-level rise has declined
to 2.5 Æ 0.4 mm/year (Ablain et al., 2009).
The absolute rate of sea-level rise in a region is mainly
due to two factors: (1) the increase in volume of water in
the ocean basins as a result of increasing glacial ice melting and (2) the thermal expansion of near-surface seawater
(Milne et al., 2009; Stammer et al., 2013). Several studies
indicate that eustatic sea level will continue to rise because
of global warming caused by increasing concentrations of
greenhouse gases in the atmosphere. More locally other
processes must be considered including vertical land
motions such as subsidence or uplift due to tectonic and
volcanic activity, subsidence due to sediment loading,
ground water pumping, and oil and gas extraction
(Woppelmann et al., 2007).
The IPCC Report suggests that the global sea level will
be $600 mm by 2100 AD. This means the annual rate of
increase would be 6.45 mm. Furthermore, if the ice caps
continue to melt, there could be a 1 m rise of eustatic sea
level by the end of the twenty-first century (Pfeffer et al.,
2008). Sea-level rise has a direct impact on shoreline
changes due to a higher shift in the zone of wave action
on the beach. This would lead to shoreline recession,
which will be larger on gentler slopes. Bruun (1962) developed a model which estimates shoreline recession with
respect to rise in sea level. The effect of sea-level rise will
be manifested by greater erosion of beaches and bluffs,
increased flooding, inundation of low-lying areas, intrusion of salt water into aquifers, and higher water tables
(Gornitz, 1991; Nicholls and Leatherman, 1995).
Sea-level rise will strongly impact most coastal landforms
(e.g., beaches, lagoons, estuaries, deltas, coral reefs, mangroves, etc.), but the impacts would be spatially variable
depending on local factors. Low-lying areas of developing
countries are likely to be the most greatly impacted
(Nicholls et al., 2007).
Shoreline changes due to anthropogenic activities
Anthropogenic activities such as construction of coastal
structures (harbors, breakwaters, seawalls, and vented
dams across rivers), mining of sand and shells, and urbanization and industrialization mainly affect the shoreline
configuration and coastal morphology. Bulkhead- and
revetment-type seawalls have been built along the eroding
shores. Sandbags and gabions have also been used in these
erosion-prone areas (Figure 7). However, they can induce
severe erosion in several locations along the coast and
increase the beach slope in front of the seawall as well as
on adjacent beaches. Seawalls often produce rubble along
the coast and degrade recreational beaches with episodic
damages. Groin trap littoral drift resulting in the accumulation of sediment on the updrift side and erosion on the
downdrift side. A large quantity of sediment is arrested
by these structures, causing a deficit in sediment supply
along the coast.
Extensive mining of sand and lime shells in the estuaries and river mouths also leads to accelerated erosion
along the coastline. Reduction or loss in supply of sediment affects the dynamic equilibrium of beaches and hastens erosion. In the last few decades, rapid urbanization
and industrialization such as construction of houses,
fish-processing units, major oil refineries, etc., have accelerated changes in the coastal region. Tourism and recreation are other human activities that often damage natural
vegetation, which can enhance coastal erosion and change
shoreline configuration.
Shoreline-change analysis and predictions
methods
Research on coastal changes provides important environmental indicators for coastal management (Welch et al.,
1992; Stokkom et al., 1993). Coastal mapping methods
are valuable tools to understand shoreline changes. Shoreline mapping provides critical shoreline data for models
used to represent shorelines in the geographic database.
Shoreline-change analysis methods can be applied. By
knowing the data acquisition method, the inherent errors
that normally exist in the underlying measurement processes can be identified and modeled. Also, by knowing
the models used to represent shorelines in the geographic
database, the level of abstraction of the real world inherent
in these models can be recognized. This directly influences shoreline-change analysis results.
The most effective and economic instruments used in
shoreline mapping and shoreline-change monitoring are
satellite sensors, Global Positioning Systems (GPS), and
all-weather sensors (Li et al., 2001). Shorelines can be
extracted from the stereo-matched and geo-referenced
aerial photographs both manually and automatically. The
manual extraction of shoreline features is a process that
involves digitizing the water and land interface, which is
known as the instantaneous shoreline at the time of aerial
photography. The automatic shoreline extraction process
SHORELINE CHANGES
597