Environmental impacts of sea-level rise and associated adaptive strategies Katie Jewitt

1. Environmental impacts of sea-level rise and associated adaptive strategiesKatie Jewitt

2. 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

3. 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

4. Erosion bigger wave base, as well as stronger storm intensity

5. Inundation http://seagrant.gso.uri.edu/newsletter/mar_apr08/coastalcommunities.html

6. 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/

7. 1 meter of sea level riseputs South Louisiana under water. http://healthygulf.org/blog/labels/Global%20Warming.html

8. 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. 

9. Salinity intrusion - threatens freshwater supply - threatens estuarine fisheries and certain seafood species (e.g. oyster) en.wikipedia.org/wiki/North_Sea

10. Ecosystem services: Beach and dunes http://www.longboat-key-florida.info/images/birds-beach-348x278.jpg Habitat http://forums.miamibeach411.com/index.php?ACT=35&fid=39&aid=395_873D9dRDRfRT8H5mQEqH http://www.hedweb.com/animimag/turtles.jpg

11. 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

12. 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

13. 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 measured at site 1 (Massel et al.,1999)

14. 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

15. Adaptation strategies

16. 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

17. Seawalls Waves pounding the sea wall at Walcott, UK, November 9 2007. Photo: John Giles / AP http://safecoast.org/actueelarchief/?actie=weergeven&weergeef=alles

18. Impacts of Seawalls Impacts on beaches: 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.

19. Impacts of Seawalls Impacts on beaches: 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 3) The wave action causes the underlying sand to erode quickly, undermining the wall. 2) As water moves in, it eventually meets the wall, flooding the beach. 1) Sea walls destroy eroding beaches first by reducing the size of the beach.

20. Impacts of Seawalls Impacts on beaches: 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

21. 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

22. 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

23. Groins Groin field

24. 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 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

25. 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

26. This borrow area is graded to drain and is planted in trees restoring bottomland hardwoods and terrestrial wildlife habitat This borrow area is irregularly shaped with smooth side  slopes, varying depths and islands with trees left undisturbed in the middle.  This type design promotes fisheries and waterfowl benefits.  Source: Mississippi Levee Board

27. exclude naturally wide brackish water transition zones with various habitats • Impacts very site-specific • Cases where built in estuaries and rivers:  • channelization of rivers and tidal channels • wetlands may not be able to keep up with sea level rise • loss of wetlands • Reduction of intertidal     habitat

28. Revetments and bulkheads http://www.snh.org.uk/publications/online/heritagemanagement/erosion

29. Revetments and Bulkheads Reflects wave energy, eroding coastline elsewhere Loss of intertidal habitat 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

30. Breakwaters • sediment buildup in lee •  reduction in erosion rates and impacts on sediment budget -> erosion elsewhere • decreased wave activity and impacts on supratidal vegetation • reduction of salt spray • invasion of non-salt tolerant species -> loss of rare habitats • isolation of foreshore from active coastal environment • may reduce oxygen levels, exacerbated by pollution buildup • may reduce circulation of water -> reduce water mixing, decrease flushing times -> pollutant buildup

31. 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

32. Breakwater -- Port at rivermouth • blocks coastal sediment transport • coast attacked hard by wave refracting around breakwater -- increased erosion • stability issue Source: Coastal Wiki

33. 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

34. 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

35. Beach Nourishment Sand transport losses and beach profiles associated with a beach nourishment project. Qualitative relationship between upland economic base and long-term erosion rate. (From Dean and Dalrymple, 2002) Source: http://www.csc.noaa.gov/beachnourishment/html/geo/scitech.htm

36. 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

37. 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 Marked turtle nest and unusual single exposed egg (right foreground) on an eroding Florida beach. Source: NBII Sea Beach Amaranth (Newsday File photo)

38. Marsh building Beneficial in terms of habitat increased wildlife potential for estuaries useful way of using unwanted dredgings for     increased coastal     defense

39. Design consideration for environmental impact assessment • Geographical characteristics • location: whether port is at mouth of estuary, river outlet, or in an isolated environment • Physical characteristics • wave and tide characteristics • sediment budget and transport • Biological characteristics • 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

40. Guidelines to choosing adaptation strategy options • Overview of justification of requirements of coastal defense • Data gathering • Collection of data on physical processes and characteristics • Geology and geotechnics • Nearshore seabed 1.     Bathymetry2.     Seabed sediments • Waves, winds and tides • Coastal defenses (the standard of defense and residual life of existing coastal structures • Data on benefits and costs • Data on environmental constraints and opportunities • Biological, Physical, Socio-economic, Aesthetic, Chemical

41. 3. Assessing the effect of not intervening • 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 • Assessing existing defenses • Predicting future changes in the coastline and standards of defense • Preliminary economic evaluation • Preliminary environmental appraisal

42. Public consultation • Assessing coastal defense options

43. 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