Geographical trends Lagoon depth Continuity of The Indian Ocean atoll rim Proportion of tsunami and the rim with : islands A reef island perspective

Mohamed Ali SAARC Coastal Zone Management Centre Effects of storms Occurrence of faros Lagoonal islands

Atolls Reefs 1. Reef-top, ‘table’ Patch Thoddoo, Faros Kashidhoo Knolls

2. Closed

Rasdhoo, Islands , Single multiple 3. open Lagoonal Peripheral Ari, Baa, Raa

1 The major ecosystems: 1. Coastal vegetation (heylhi) 1. Coastal vegetation (heylhi) 2. Evergreen moist forests 3. Mangroves 4. ‘pond’ ecosystems

5. coral reefs Coastal Vegetation 6. Seagrass beds „ Special vegetation types „ Important function „ Special habitat „ Threatened species „ Useful species

2. Evergreen moist forests 3. Mangroves Mangroves found on 150 islands (12%)

Mostly small in size „ 496 species noted „ Endemic, rare, Associated with enclosed or semi-enclosed threatened, brackish water bodies locally known as endangered kulhi, or with chasbin (marsh) species Not estuarine based (no rivers) „ Special/different 13 species habitats Most diverse of the Indian Ocean islands Very rare species locally, globally Some very threatened Special habitat

2 Distribution of mangroves 1. Pond-based mangrove

70 NothernAtollsCentral Atolls SouthernAtolls C 60 Adduatholhu A B Ethtthigili 50

40 Thiladhunmathi

30 Ihavandhippolhu percentage ofislands with mangroves

20 Nilandheatholhudhekunuburi Maalhosmadulu dhekunuburi Faadhippolhu Huvadhooatholhu

10 Felidheatholhu Nilandheatholhu uthuruburi Nilandheatholhu Fasdhooethere Mulakatholhu

Kolhumadulu 2. Marsh-based mangrove Maalhosmadulu uthuruburi Ariatholhu Hadhdhunmathi Male’atholhu uthuruburi Maamakunudhoo Goidhoo Rasdhooatholhu 0 Maleatholhu dhekunuburi

3. Fringing mangrove Island surface forms

4. Embayment mangrove

3 size and damage

33.3 impacts 35 30 26.1 25 20 14.5 % 13 13 15 10 5 0 >10 10-20 20-40 40-80 80+

size Orientation and damage

50 44.9

40 34.8

30 % 20 11.6 5.8 Location and damage 10 2.9 0 80 66.7 E-W N-S NW-SE NE-SW other 70 60 orientation 50

% 40 30 21.7 20 11.6 10 0 w est east other location

7°N Thiladhunmathee Atoll Observed direction of wave / flood water 6 Observed profile

Vashafaru

5

Filladhoo

4

3

2

Hanimaadhoo

1

Nolhivaranfaru 0

Nolhivaramu 73°E

4 Filladhoo Kelaa m Run-up Height 1.9m W E （above MSL） 2 m W E 2 1 Highest Tide Level 1 Highest Tide Leve Inhabited Area Coconut Forest 0 MSL 0 MSL Coastal Coconut Forest Coconut Forest Coastal Vegetation Coastal -1 Vegetation Lowest Tide Leve Inhabited Area Coconut Forest / Arable Land / Arable Land / Arable Land Shrub / Park 100m -1 Lowest Tide Level

100m

Kelaa

Vashafaru Distribution of houses completely destroyed

Filladhoo

Lagoon Play ground Baarah

Court

Hanimaadhoo Office 1 5 1 1 School

Friday Nolhivaramu mosque 100m

Nolhivaranfaru Nolhivaram

m W E 2 Run-up Height 1.4m W E (. ) （above MSL） m Highest 2 1 Tide Level Highest 1 Tide Level Coastal MSL Coastal Coconut Forest Inhabited Area Coconut Forest MSL Inhabited Area Coconut Forest Coastal 0 Vegetation 0 / Cemetry Vegetationvegetation Vegetation -1 Lowest Tide Leve -1 Wall collapsed Lowest 100m at school Tide Level 100m Kelaa

Vashafaru

Filladhoo

Baarah

Hanimaadhoo

Nolhivaranfaru

Nolhivaramu

5 7°N m W Baarah E North Malé 3 Run-up Height 1.8m 2 （above MSL） 6 Atoll

1 Highest Tide Level Inhabited Area Coconut Forest Coconut Forest Coastal Vegetation School / Mosque / Cemetery 5 0 MSL

-1 Lowest Tide Level 100m 4 m The first Flood water 3

S N 3 2 Kelaa Vashafaru Highest Tide Level 1 e fil o p r 2 Filladhoo MSL 0 The second Lowest Tide Level Baarah Flood water -1 1

-2 Hanimaadhoo 100m

Nolhivaranfaru 0 Nolhivaramu 100m Malé 73°E

Dhiffushi, North Malé Atoll 7°N

The Second Flood Water South Malé Atoll 30 min. after the first flood water The first Run-up Height 1.8m The First Flood Water e m rofil flood water 6 above MSL p 2 （ ） Run-up Height 1.5m The second

r

（above MSL） flood water e

c

l

a WEm

e 1 d 5 Highest Tide Level a r

e Inhabited Area a 0 MSL Part of this ridge was 4 washed away by Lowest Tide Level scouring -1 100m 100m 1998 Aerial Photograph 3

2

Guraidhoo 1

0

73°E

6 Maafushi, South Malé , South Malé Atoll Atoll The First Flood Water The First Flood Water m Run-up Height 2.5m Run-up Height 2.4m m The Second Flood Water above MSL 3 The Secoind Flood Water （above MSL） （ ） 15 min. after the first flood water The second 15 min. after the first flood water Run-up Height 1.4m flood water 2 Run-up Height 1.6m （above MSL） 2 pro file （above MSL） Partially Scoured WE 1 WE 1 Highest Tide Level The first Highest Tide Level flood water Inhabited Area Coconut Inhabited Area Trees MSL MSL 0 0 Lowest Tide Level Lowest Tide Level -1 100m N 100m -1

DigitalGlobe 2 Jan. 2005 100m

The second Flood water Pr of ile

The first flood wa ter Guraidhoo N

200m DigitalGlobe 2 Jan. 2005

Simulation study is needed to determine the effect Why less damage in northern if the northern atoll rim was continuous Maldives? Factors Atoll Which Acts? Height of island Rim Beach Ridge Particular reef topography Monsoon Intensity Discontinuous7°N High Proportion of passages in Maldives (open/Closed) Developed Reducing tsunami run-up Strong at the eastern side of atolls 6 Development of higher islands and beach ridge Orientation (E-W, N-S, ..) Extending the influence to lagoon and the western 5 at the northern Maldives side of atolls where stronger monsoon intensity

Reef type (faro, patch) 4 Safer coral islands are Reducing the influence to 3 developed under Island form, (ridge, bowl-shaped..) lagoon and the western stronger energy environments side of atolls Island shape (circular, elongated) 2 Reinforcement tsunami Critical Factors size (small, medium, large) run-up at the eastern side of atolls 1 1. Shape of coral reef Modifications (harbour, reclamation) 2. Height of island Weak Continuous Low 3. Development of 0 Undeveloped beach ridge

73°E

7