Eco-technological Management of Atoll Islands against Sea Level Rise
Hajime Kayanne (Univ. Tokyo)
Fongafale Is., Funafuti Atoll, Tuvalu Sea level rise?
Coastal erosion
Inland inundation Loss of sandy beach along Fongafale coast (lagoon side), Funafuti, Tuvalu
Funafuti MasterPlan, Blue Banana Films Change in land-use pattern in Fongafale Is.
Over the central depression area, 1896:Swamp and mangrove extended, 1943: An air strip was constructed, 2004: Residential area has been extended since 1980s.
Yamano et al. (2007) How have atoll islands formed?
Coral gravels
Atoll islands are formed by corals and forams Corals and forams have formed the island 1/2 to 3/4 of the island sediment is composed of foram sand (Baculogypsina or Amphistegina), which has formed the island for the Coral debris last 1800 years.
Coral reef
Foraminifera sand
But corals and forams are dying…
Dead corals are overed by macroalgae Baculogypsina in front of the populated area. Density (#/m²)
10 ⁴ 10
Healthy corals in a remote area. Down town (DT) Production Ecosystem deterioration by bad water quality
Loss of coral is crucial for Tuvalu as it forms a foundation and natural breakwater.
Daily utilization by local people
Reduced layer 2-3cm E-coli Tide below the sand surface! 100000 2.5
10000 2.0
1000 1.5 （ｍ）
100 1.0 Tide (m) Tide
During ebb tide, e-coli of 25,000 Sea level level Sea
coli (MPN/100mL)coli 10 0.5
- MPN/100mL, 25 times higher than Japan
E environmental criteria. 1 0.0 7:00 9:00 11:00 13:00 15:00 17:00 transportation運搬 Causeway between islands blocks sand transportation from ocean reef flat to lagoon
erosion
Sand transportation is blocked by jetties, and escaped to the deep lagoon via dredges. sedimentation Vertical seawalls induced erosion at their foot.
Original landscape
Loss of coastal vegetation
Countermeasure plans to Production regenerate sandy beach Ecosystem rehabilitation Increasing sand production and reef foramation. Sand production 運搬 transportation Sand drift Beach Removal of obstacles for nourishment sand transportation (causeway, jetties, dredges)
sedimentation
Beach nourishment Coastal vegetation Monitoring for evaluation Production Improvement of coastal eivironment is required bofore or in parallel with any ecosystem rehabilitation challenges. Then Foram culture
Tuvalu
Coral culture and transplantation
Okinotorishima transportation
72 m3/year
Removal of jetties Backfill dredges Optimum width: 20 m Optimum depth: reef flat sedimentation
beach nourishment
Open-cut the causeway Presentstatus Low Challenge level High Rehabilitation ecosystemof Open Beachnourishment
- cut thecauseway Short
- term Replanting coastalvegetation Coral and
Backfilldredges Removal ofjetties
= foram land Time scale
culture
Environmentimprovement Waste management sandy beach Regenerationof
Ecosytem Sewage treatment
rehabilitation Long
Ultimategoal
- term
Before 2011.3.11
2011.3.11
We have learned that only artificial consruction can never save lives. A hope… Distribution of atolls in the world
barrier Mahe, Maldive atoll fringing others reef reef Majuro, Marshall Islands Funafuti, Tuvalu Sea level is rising and will rise +18 - +59 cm
IPCC (2007)
+1 m
Rahmstorf (2007) by the end of this century.