Transcript Document

Environmental impacts of
sea-level rise and
associated adaptive
strategies
Katie Jewitt
Outline
•
•
•
•
Environmental impacts of sea-level rise
Coastal ecosystems and their services
Environmental impacts of coastal protection strategies
Criteria for environmental vulnerability and design
considerations for environmental impact assessment
• guidelines on choosing the preferred strategy
Environmental impacts of sea-level
rise
•
•
•
•
increases erosion of coastline
inundation of low-lying lands
loss of wetlands due to increased erosion and flooding
increased flooding and storm-damage to low-lying
coastal lands
• salinity intrusion
Erosion
bigger wave base, as well as stronger storm intensity
Inundation
http://seagrant.gso.uri.edu/newsletter/mar_apr08/coastalcomm
unities.html
Loss of saltmarsh area (% loss from 2000
baseline), under the IPCC low sea-level
rise scenario, 2080
Loss of saltmarsh area (% loss from
2000 baseline), under the
IPCC high sea-level rise scenario,
http://www.branchproject.org/achieve/wildlifemapping/coastalvulnerability/
1 meter of sea level
riseputs South
Louisiana under
water.
http://healthygulf.org/blog/labels/Global%20Warming.html
Wetland loss
Most coastal wetlands in the mid-Atlantic would be
lost if sea level rises one meter in the next century.
Even a 50-cm rise would threaten most wetlands
along the Eastern Shore of Chesapeake Bay.
Salinity intrusion
- threatens freshwater supply
- threatens estuarine fisheries and certain seafood species (e.g.
oyster)
en.wikipedia.org/wiki/North_Sea
Ecosystem services: Beach and dunes
Habitat
http://www.longboat-key-florida.info/images/birdsbeach-348x278.jpg
p://www.hedweb.com/animimag/turtles.jpg
http://forums.miamibeach411.com/index.php?ACT=35&fid=39&aid=
395_873D9dRDRfRT8H5mQEqH
Ecosystem services: Beach and dunes
•
•
•
•
•
Habitat
Nutrient uptake
food production
wave attenuation
sediment stabilization: dependent on the presence
of vegetation
• raw materials:
sand and gravel
http://www.fao.org/docrep/010/ag127e/AG127E09.htm
Ecosystem services of
marshes, mudflats and other
vegetated communities
• Habitat: support large local fisheries
• Nutrient uptake
• Food production: macroalgae, detritus, migratory birds
• Wave attenuation
• Sediment
stabilization
• Maintenance
of biodiversity
• Production
of raw materials
Wave attenuation by mangrove forest (Rhizophora sp., Aegiceras sp., Ceriops sp.) at
Cocoa Creek, Australia is obvious; measurements at sites 2–5 show the decline in
wave energy transmission through the mangrove forest. The incoming wave was
Coastal erosion sites reported in Asian and Indian Ocean countries; the inset
indicates how clearing of coastal forest such as mangroves has increased the
vulnerability of coasts to erosion (base map source from ITDB, 2004)
www.fao.org/docrep/ 010/ag127e/AG127E86.jpg
Adaptation strategies
Adaptation strategies
• Hard structures:
• Wetland loss
• Influence banks, channels, beach profiles,
sediment transport and morphology
• Soft structures: retain natural coastlines, but
dredging may cause disruption
• Some potential benefits: artificial reefs may
create new habitats, dams may mitigate
salinity intrusion
Seawalls
Waves pounding the sea wall at Walcott, UK, November
9 2007. Photo: John Giles / AP
http://safecoast.org/actueelarchief/?actie=weergeven&weergeef=alles
Impacts of Seawalls
• Impacts on beaches:
o
o
o
o
o
o
Formation of a scour trough
Formation of a deflated profile : the uniform general
lowering of the fronting beach
Formation of beach cusps : semi-circular, seawards opening
embayments
Formation of a rip current trough : a linear shore normal
depression
Terminal scour : accelerated active erosion on beaches and
coasts immediately down-drift
Up-drift sand accretion due to impounding at the up-drift end
of the wall
This is what happens to the beaches if
seawalls are erected. To protect against
toe scour and seawall failure, more and
more armament must be added as you
can see with the multiple layers installed
to protect the Galveston seawall.
Rotational currents moving off the
90º angle of the seawall cause
accelerated erosion to adjacent
properties.
Impacts of Seawalls
• Impacts on beaches:
o
o
o
o
o
o
Formation of a scour trough
Formation of a deflated profile : the uniform general
lowering of the fronting beach
Formation of a rip current trough : a linear shore normal
depression
Terminal scour : accelerated active erosion on beaches and
coasts immediately down-drift
Up-drift sand accretion due to impounding at the up-drift
end of the wall
Formation of beach cusps : semi-circular, seawards
opening embayments
1) Sea walls destroy eroding beaches first
by reducing the size of the beach.
2) As water moves in, it eventually meets
the wall, flooding the beach.
3) The wave action causes the underlying sand to erode
quickly, undermining the wall.
Impacts of Seawalls
• Impacts on beaches:
o
o
o
o
o
o
Formation of a scour trough
Formation of a deflated profile : the uniform general
lowering of the fronting beach
Formation of a rip current trough : a linear shore normal
depression
Terminal scour : accelerated active erosion on beaches and
coasts immediately down-drift
Up-drift sand accretion due to impounding at the up-drift
end of the wall
Formation of beach cusps : semi-circular, seawards
opening embayments
Eccles, UK. Photo: Mike Page, Marinet
Coastal protection efforts to protect a valuable tourism base; meanwhile,
the adjacent shore with less economic value has minimal and improper
protection. Even revegetation with waru to replicate planting at the
neighbouring resort failed; the coast was then abandoned and left to
erode
Source: http://www.fao.org/docrep/010/ag127e/AG127E87.jpg
Increasing the success of seawalls
• a wall which cuts off an area's only supply of sediment (e.g.
a cliff) will have a major impact on the beach, while an area
which has many sources of sediment (e.g. from offshore and
longshore drift) will have alternate sources and will not have
to rely on the fronting beach
• wave energy will dissipate naturally over beach profiles, and
so the further inland sea walls can be placed, the fewer
problems with interference with incident waves, and the less
seaward penetration into the surf zone
• walls which dissipates energy, by absorption or by random
deflection on an irregular surface; or focus wave energy on
revetment
• nourish fronting beach
Groins
Groin field
Groins and jetties
• Sediment accretion in the updrift side,
sediment erosion in the downdrift side
• Narrowing of beach on downdrift side
• Interruption of longshore transport
• modification of channel processes
o
interaction of jetty and river mouth dynamics critical
in the functioning of the sediment supply and
transport processes
Mitigation: pumping of sediment to transfer
material mechanically around jetties
Dikes and Levees
• May have similar impacts as emergent
breakwaters on coastal hydrodynamics,
sediment transport and geomorphology
• exclude natural dynamics (regular
flooding) from the diked marshlands
• Borrow area
This borrow area
is irregularly shaped
with smooth side
This borrow area is graded
to drain and is planted in
trees
restoring
hardw
Source:
Mississippi bottomland
Levee Board
• exclude naturally wide brackish water
transition zones with various habitats
• Impacts very site-specific
• Cases where built in estuaries and rivers:
o channelization of rivers and tidal channels
o wetlands may not be able to keep up with
sea level rise
o loss of wetlands
• Reduction of intertidal
habitat
Revetments and bulkheads
http://www.snh.org.uk/publications/online/heritagemanagement/erosion
Revetments and Bulkheads
• Reflects wave energy, eroding coastline
elsewhere
• Loss of intertidal habitat
o
For a 1m rise, 29-66% coastal wetland loss
with retreat, but 50-82% if protected with
bulkheads
• Increase in the rate of lowering of
fronting beach
Breakwaters
• sediment buildup in lee
• reduction in erosion rates and impacts on sediment budget > erosion elsewhere
• decreased wave activity and impacts on supratidal
vegetation
o reduction of salt spray
o invasion of non-salt tolerant species -> loss of rare
habitats
• isolation of foreshore from active coastal environment
o may reduce oxygen levels, exacerbated by pollution
buildup
o may reduce circulation of water -> reduce water mixing,
decrease flushing times -> pollutant buildup
Breakwater -- Port in isolated
environment
• sea without tide and very little river contribution
 if the coast is rocky, erosion is negligible
 if the coast is sandy, erosion is important but
will be limited in space if there is no coastal
current
Breakwater -- Port at rivermouth
• blocks coastal sediment transport
• coast attacked hard by wave refracting around breakwater -increased erosion
• stability issue
Source: Coastal Wiki
Breakwater -- Port at mouth of large
estuary
• Naturally, mudflats and wetlands may migrate downstream
due to river flow
• breakwater canalise river, preventing sedimentation, and
therefore migration of the mudflat areas toward downstream
-> loss of valuable mudflats
Breakwaters -- potential benefits
• new habitat for kelp, marsh and seagrasses
• (if built of stone) provide hard substrates beneficial to algae,
barnacles and oysters
• creates foraging area for fish
• habitat for fishes, higher fish species richness than natural
reefs(?) (but other study suggested lower observed total
diversity)
• trade-off when a natural habitat is replaced by a man-made
structure
Beach Nourishment
Qualitative relationship between upland economic base and long-term
erosion rate. (From Dean and Dalrymple, 2002)
Sand transport losses and beach
profiles associated with a beach
nourishment project.
Source: http://www.csc.noaa.gov/beachnourishment/html/geo/scitech.htm
Beach Nourishment
• burial of shallow reefs and invertebrates
• reduce food availability for birds, fishes
and crabs
• replacement of habitat from nearshore
benthic community to an intertidal and
supratidal beach and dune
Beach Nourishment: potential
environmental benefits
• Increased habitat for sea turtle nesting,
• nesting and foraging areas for sea birds,
• Habitat for beach flora, e.g. sea beach amaranth
and bitter panica
Sea Beach Amaranth (Newsday File photo)
Marked turtle nest and unusual single exposed egg (right
foreground) on an eroding Florida beach.
Source: NBII
Marsh building
• Beneficial in terms of habitat
• increased wildlife potential for estuaries
• useful way of using unwanted
dredgings for
increased coastal
defense
Design consideration for environmental
impact assessment
• Geographical characteristics
o location: whether port is at mouth of estuary, river outlet,
or in an isolated environment
• Physical characteristics
o wave and tide characteristics
o sediment budget and transport
• Biological characteristics
o need to maintain coastal wetlands?
identify key ecosystems in surrounding areas
- geographical characteristics:
-- - biodiversity
key species
effects of nutrient fluxes
effects on larval dispersal and recruitment
Guidelines to choosing adaptation
strategy options
1. Overview of justification of requirements of coastal defense
2. Data gathering
1.Collection of data on physical processes and characteristics
• Geology and geotechnics
• Nearshore seabed
1. Bathymetry
2. Seabed sediments
• Waves, winds and tides
• Coastal defenses (the standard of defense and residual life of
existing coastal structures
1.Data on benefits and costs
2.Data on environmental constraints and opportunities
 Biological, Physical, Socioeconomic, Aesthetic, Chemical
3. Assessing the effect of not
intervening
1.Assessing hydrodynamics and sediment transport rates
• Wave conditions, at a location just offshore from surf zone
• Tidal levels including the effects of surges
• Information on the joint probability of large waves and high
tidal levels to provide estimates of the conditions that any
defense may encounter
1.Assessing existing defenses
2.Predicting future changes in the coastline and standards of
defense
3.Preliminary economic evaluation
4.Preliminary environmental appraisal
1.Public consultation
2.Assessing coastal defense options
Conclusions
• adaptation methods all have their own environmental pros
and cons, with hard structures typically being detrimental to
the environment
• a combination of different structures (hard and soft) is often
beneficial
• important to evaluate each site case-by-case basis to select
the best environmental procedure
• detailed environmental appraisal and data analysis is
necessary for preparation
• important to look at the coastal system as a whole,
integrative manner, rather than tackle the SLR problem in a
piecemeal fashion