Detailed Island Risk Assessment in Maldives

Volume III: Detailed Island Reports

Dh. Kudahuvadhoo – Part 1

DIRAM team

Disaster Risk Management Programme UNDP Maldives

December 2007

Table of contents

1. Geographic background

1.1 Location

1.2 Physical Environment

2. Natural hazards

2.1 Historic events

2.2 Major hazards

2.3 Event Scenarios

2.4 Hazard zones

2.5 Recommendation for future study

3. Environment Vulnerabilities and Impacts

3.1 General environmental conditions

3.2 Environmental mitigation against historical hazard events

3.3 Environmental vulnerabilities to natural hazards

3.4 Environmental assets to hazard mitigation

3.5 Predicted environmental impacts from natural hazards

3.6 Findings and recommendations for safe island development

3.7 Recommendations for further study

4. Structural vulnerability and impacts

4.1 House vulnerability

4.2 Houses at risk

4.3 Critical facilities at risk

4.4 Functioning impacts

4.5 Recommendations for risk reduction

1. Geographic background

1.1 Location

Kudahuvadhoo is located on the southern end of South Nilandhe Atoll (Dhaalu Atoll),

next to the Kudahuvadhoo Kanduolhi (reef pass) at approximately 73° 39' 3"E and 4° 22'

28" N (Figure 1.1). It is located at about 181 km from the nation’s capital Male’ and about

113 km from the nearest Airport Laamu Atoll, Kadhoo. Kudahuvadhoo is the Atoll Capital

of Dhaalu Atoll, amongst a group of 7 inhabited islands. It’s nearest inhabited islands are

Maaenboodhoo (8 km), and Vaanee (13 km). Dhaalu atoll is located along the western

line of atolls.

10

Location Map

of Kudahuvadhoo

kilometers

N

50

Kudahuvadhoo

Maaen'boodhoo

Rin'budhoo

Ban'didhoo

Hulhudheli

Meedhoo

Vaanee

South Nilandhe Atoll(Dhaalu Atoll)

73

° 0

0'

E

2° 45' N

3° 00' N

Figure 1.1 Location map of Kudahuvadhoo.

1.2 Physical Environment

Kudahuvadhoo is a fairly large island with a length of 1040m and a width of 880 m at its

widest point. The total surface area of the island is 69.7 Ha (0.69 km2). The reef of

Kudahuvadhoo is one of largest in Maldives with a surface area of 5601 Ha (56.01 km2).

The reef also hosts 3 other uninhabited islands.

Kudahuvadhoo is located at the southern tip of the reef system, approximately 450m

from the southern wave break zone and 320m from the eastern reef edge. The depth of

the reef flat is quite shallow averaging less than -1m MSL. The island has an elevation

ranging from +0.45 to +1.5m MSL along the island topographic profile survey line. The

island could be describes as located on an east west orientation and appears to be

growing towards west.

Kudahuvadhoo has a natural harbour due the extensive lagoon on the western side of

the island. The lagoon extends to about 12km within the reef. The growth of the island

towards west has meant that sand is constantly deposited within the deep lagoon

creating a steep underwater slope on its western end and allowing vessels to approach

close to the shoreline.

The island had large areas of undeveloped land allowing the presence of strong

vegetation cover on its southern side. Much of this new land is now being developed for

Tsunami related resettlement schemes, agriculture, recreation and is predicted to be

depleted in the near future.

The existing natural environment of the island has been modified, especially in the

northern side, although the extent of coastal modifications is small compared to most

other inhabited islands. Major modifications include development of a harbour, land

reclamation from the excess dredge material during harbour development and clearing

of vegetation.

2. Natural hazards

This section provides the assessment of natural hazard exposure in Feydhoo Island. A

severe event history is reconstructed and the main natural hazards are discussed in

detail. The final two sections provide the hazard scenarios and hazard zone maps which

are used by the other components of this study as a major input.

2.1 Historic events The island of Kudahuvadhoo has been exposed to multiple hazards in the past although

its exposure has been limited. A natural hazard event history was reconstructed for the

island based on known historical events. As highlighted in methodology section, this was

achieved using field interviews and historical records review. Table 2.1 below lists the

known events and a summary of their impacts on the island.

Table 2.1 Known historic hazard events of Kudahuvadhoo. Metrological hazard

Dates of the recorded events

Impacts

Flooding caused by Heavy rainfall

• Frequent events commonly occurring during SW monsoon.

Flooding limited to a few topographic low areas on the island. The magnitudes and impacts of these floods are small with water levels barely exceeding 0.3m. However, disruptions to socio-economic activities have occurred in the past with schools and shops being closed for over 24 hours.

Flooding caused by swells or surges

No records of major incidents

-

Flooding caused by monsoonal wind waves or Udha

Annually

Impact limited to 10 m from shoreline. In intensity is very low and rarely effects property or human well-being

Windstorms • 24 June 19871

• 18-20 Dec 19922

Windstorms are common on the island. These events affect housing structures,

1 All dates in italics are adopted from MANIKU, H. A. (1990) Changes in the Topography of Maldives,

Male', Forum of Writers on Environment of Maldives. and news paper reports.

2 Unnamed tropical depression passing over Dhaalu atoll between 18-20 December 1992. Source: UNISYS

& JTWC (2004) Tropical Cyclone Best Track Data (1945-2004).

http://www.pdc.org/geodata/world/stormtracks.zip, Accessed 15 April 2005, Unisys Corporation and Joint

Typhoon Warning Center.

• 5 other major events since 1980’s (dates unknown).

vegetation and crops. The island is generally protected from thick coastal vegetation but even before the settlements expanded, there were reports of windstorm related damages. The effect of wind storm is spread across the entire island.

Droughts No major event have been reported

Earthquake No major event have been reported

Tsunami 26th Dec 2004 The effect of tsunami 2004 was limited on this island. Flooding occurred on the southern and parts of eastern side. There were no major structures in this area and as a result lost was very little. The flood itself came only about 150m on the southern side and up to a 300m on the eastern side. All these areas were uninhabited. Tsunami floods destroyed a number of agricultural fields, however. One farmer reported a loss of MRF 30,000 worth of crops. The repercussions for the damage were far reaching. He supplied vegetables to a number of islands within the atoll and employs 12 staff seasonally. The staff and the farmer therefore endured loss of income. Apart from the agricultural fields; the only notable damage to the island was to its Harbour. The outer harbour walls collapsed and part of the quay wall was damaged beyond repair. It is still in use but appears unstable.

The historic hazardous events for Kudahuvadhoo showed that the island faced the

following hazards: 1) windstorms, 2) flooding caused by heavy rainfall, and 3) tsunami.

Impacts and frequency of these events vary significantly. Windstorms are the most

commonly occurring events followed by flooding due to heavy rainfall. The occurrence of

windstorms is usually limited to SW monsoon although occasional localised ‘freak

storms’ due to low pressure systems forming above Maldives effects the island during

NE monsoon. It is noteworthy that in spite of the exposure to southern Indian Ocean

swell waves, flooding from swell waves or storm surges are almost non-existent in the

historical records. The absence of historical records on swell related flood events in

nearby islands with similar geographic settings such as Nilandhoo and Magoodhoo,

further enhances this finding. The tsunami of 2004 is by far the most significant hazard

event in Kudahuvadhoo with substantial economic damage. However, despite its

location in a high tsunami hazard zone, the scale of impacts in Kudahuvadhoo is small

compared to the other nearby islands such as Vilufushi, Kolhufushi, and Vaanee. The

reasons behind the lack of impacts will be explored in latter sections.

2.2 Major hazards

Based on the historical records, meteorological records, field assessment and Risk

Assessment Report of Maldives (UNDP, 2006) the following meteorological, oceanic and

geological hazards have been identified for Kudahuvadhoo.

• Windstorms

• Heavy rainfall (flooding)

• Tsunami

• Long distance swell waves and local wind waves

• Earthquakes

• Climate Change

2.2.1 Swell Waves and Wind Waves

Long distance swell waves

Kudahuvadhoo Island is exposed to effects of swell waves approaching from the

Southern Indian Ocean. No site specific wave studies have been undertaken for

Kudahuvadhoo but studies undertaken around the country reports a

predominantly southwest to a southerly direction for swell waves (Kench et. al

(2006), Young (1999), DHI(1999) and Binnie Black & Veatch (2000)). As a result

the island is directly in the path of these long distance waves which occasionally

reaches abnormal levels capable of flooding (see Figure 2.1).

0

Laamu Atoll

SW Sw

ell Waves

SW Sw

ell Waves

SW Sw

ell Waves

SW Sw

ell Waves

SW Sw

ell Waves

SW Sw

ell Waves

SW Sw

ell Waves

SW Sw

ell Waves

SW Sw

ell Waves

SW monsoon Wind waves

Kudahuvadhoo

Thaa Atoll

Dhaalu Atoll

25

kilometers

Meemu Atoll

Estimated wave propogationpatterns around Kudahuvadhoo

NE MonsoonWind waves

Abonormal S

E swell w

aves

Abonormal S

E swell w

aves

Abonormal S

E swell w

aves

Abonormal S

E swell w

aves

Abonormal S

E swell w

aves

Abonormal S

E swell w

aves

Abonormal S

E swell w

aves

Abonormal S

E swell w

aves

Abonormal S

E swell w

aves

50

Figure 2.1 Estimated (predominant) wave propagation patterns around

Kudahuvadhoo.

The shape of the reef and island, and location of the island within the reef system

appears to control the flow of wave energy reaching its shoreline (Figure 2.2).

Hence, unlike islands located on the western rim of the island (for example G.Dh.

Thinadhoo), Kudahuvadhoo enjoys more protection due to its location on the

southern rim. Based on an estimation of wave behaviour around Kudahuvadhoo,

it is highly likely that waves approach the reef system at an angle and refract

along the reef slopes before they dissipate their energy on the reef edge and reef

flat. The wider reef flat is also likely to play a major role in energy dissipation

before they reach the shoreline. Kench and Brander (2006) reported a relationship

between wave energy propagation across a reef flat and, reef width and depth. Using

their proposed Reef Energy Window Index, the percentage of occurrence of gravity

wave energy on Kudahuvadhoo reef flat is approximately 30%.

Wave defractionon reef system edge

meters

500 1,000

Directio

n of Swell

Waves

Kudahvadhoo

Wave Refraction andbreaking on reef slopes and edge

0

Reef Flat

Reduced wave rayson reef flat

Wave Crests

May 2007 Flood Extent

Figure 2.2 Estimated behaviour of swell waves around Kudahuvadhoo.

Udha

Flooding is also known to be caused in Kudahuvadhoo by a gravity wave phenomenon

known as Udha. These events are common throughout Maldives and especially the

southern atolls of Maldives during the SW monsoon.

The intensity and impacts of udha waves are usually very low with flooding occurring

within 10m of coastline at less than 0.3m height above the ground. It is not expected to

be a major hazard in the short-term.

The origins of the udha waves as yet remain scientifically untested. No specific research

has been published on the phenomenon and has locally been accepted as resulting from

local wind waves generated during the onset of southwest monsoon season. The

relationship has probably been derived due to the annual occurrence of the events

during the months of May or June. It is highly probable that waves originate as swell

waves from the Southern Indian Ocean and is further fuelled by the onset of southwest

monsoon during May. The timing of these events coincides as May marks the beginning

of southern winter and the onset of southwest monsoon. The concurrent existence of

these two forms of gravity waves during the southwest monsoon is confirmed by Kench

et. al (2006) and DHI(1999). It is also questionable whether the southwest monsoon

winds waves alone could cause flooding in islands since the peak tide levels on average

are low during May, June and July. Furthermore the strongest mean wind speeds in

Male’ has been observed for November and is more consistent during October to

November than during May and June period (Naseer, 2003). This issue needs to be

further explored based on long term wave and climatological data of the Indian Ocean

before any specific conclusions can be made. However if the relationship does exists,

this phenomena could prove to be a major hazard in the face of climate change since

the intensity of southern Indian Ocean winter storms is expected to increase.

Storm Surges

The Disaster Risk Assessment report of 2006 (UNDP, 2006), reported that

Kudahuvadhoo was located in a moderate storm surge hazard zone with

probable maximum event reaching 0.6m above MSL or 1.53m with a storm tide.

The combined historical records of nearby islands in Meemu, Thaa and Laamu

Atoll does not show any flooding caused by a storm surge. The occurrence of

any abnormal swell waves or surge on Kudahuvadhoo reef flat is dependent on a

number of factors such as the wave height, location of the original storm event

within the Indian Ocean, tide levels and reef geometry.

Future swell event prediction

Due to its location, swell related flooding should be considered a serious hazard for

Kudahuvadhoo. The island is expected to be exposed to storm waves mainly from south

and west south west as shown in the map (Figure 2.3). Events beyond this arch may not

influence the island due to the protection offered by Laamu and Thaa Atoll.

Historic storm events 1945 - 2007

Possible range ofswell wave directionin Dh.Kudahuvadhoo:SE to S

Figure 2.3 Historical storm tracks (1945-2007) and possible direction of swell waves for Kudahuvadhoo Island.

At present, it is very difficult to forecast the exact probability of swell hazard event and

their intensities due to the unpredictability of swell events and lack of research into their

impacts on Maldives. Assessment in Kudahuvadhoo is further limited by the lack of

historical events. However, since the hazard exposure scenario is critical for this study a

tentative exposure scenario has been estimated for the island.

There is a probability of major swell events occurring every 20 years with probable water

heights above 0.5 m and every 5 years with probable water heights of 0.2-0.5 m. Events

with water heights less than 0.2 m are likely to occur annually especially as Udha.

The timing of swell events is expected to be predominantly between November and

June, based on historic events and storm event patterns (see Table 2.2).

Table 2.2 Variation of Severe storm events in South Indian Ocean between 1999 & 2003 (source: (Buckley and Leslie (2004)).

Severe wind event variation

Longitude band Winter Summer

30 °E to 39 °E 12.5 17

40 °E to 49 °E 7.5 10

50 °E to 59 °E 7.5 26

60 °E to 69 °E 6 14

70 °E to 79 °E 6 6

80 °E to 89 °E 12 6

90 °E to 99 °E 12 8

100 °E to 109 °E 8 3

110 °E to 119 °E 15 7

120 °E to 130 °E 13.5 2

The reclamation plans for Kudahuvadhoo were incomplete at the time of this study. The

existing drafts show land reclamation for an airstrip on the southern half of the island.

After this development the reef flat width will be reduced to approximately 250m. This

reduction in the reef flat width will increase the percentage of occurrence of gravity wave

energy on this reef flat to approximately 40% and therefore increasing the probability of

flooding caused by surges by 20%. Similarly the impact of flooding will increase relative

to encroachment of settlement to coastal areas, even if the probability of flood events

remains constant. Potential increase in frequency and intensity of flood events are also

probable with climate change and is addressed in a latter section.

2.2.2 Heavy Rainfall

The rainfall pattern in the Maldives is largely controlled by the Indian Ocean monsoons.

Generally the NE monsoon is dryer than the SW monsoon. Rainfall data from the three

main meteorological stations, HDh Hanimaadhoo, K. Hulhule and S Gan shows an

increasing average rainfall from the northern regions to the southern regions of the

country (Figure 2.4). The average rainfall at S Gan is approximately 481mm more than

that at HDh Hanimadhoo.

0

500

1000

1500

2000

2500

3000

3500

1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003

Year

Me

an

an

nu

al ra

infa

ll (

mm

)

Gan Hulhule Hanimadhoo

Figure 2.4 Map showing the mean annual rainfall across the Maldives archipelago.

The closest meteorological station to Kudahuvadhoo is Kadhoo airport which became

operational in 1986. Unfortunately this study does not have access to Kadhoo data.

Moreover, Kadhoo data may be limited for long term trend observation due smaller

number of detailed observation years. Hence, to resolve the issue, data from Hulhule’

has been used. It is recommended that further assessment be made once Kadhoo data

becomes available.

The mean annual rainfall of Hulhule’ is 1991.5mm with a Standard Deviation of 316.4mm

and the mean monthly rainfall is 191.6mm. Rainfall varies throughout the year with mean

highest rainfall during October, December and May and lowest between February and

April (See Figure 2.5).

Figure 2.5 Mean Monthly Rainfall in Hulhule’(1975-2004).

Historic records of rainfall related flooding on the island of Kudahuvadhoo indicates that

this island is often flooded and its intensity is high in certain areas. Records for all

incidents have not been kept but interviews with locals and research into newspaper

reports show that localised levels of flooding within sections of the island. These areas

usually correspond to topographic lows within the island. Moreover, substantial

topographic variations exist within the island, as is common on larger islands of

Maldives. Settlement expansion into and along the edges of these low lying areas have

exposed them to flood impact. Heavy rainfall related flooding has been reported to reach

up to 0.3 m above the ground level in central areas of the island.

The impacts of flooding so far reported has not been disastrous, but has had continued

impacts on the community such as disruptions to socio-economic functions such as

temporary school and business closures, occasional damage to personal property and

crops.

It would be possible to identify threshold levels for heavy rainfall for a single day that

could cause flooding in Kudahuvadhoo, through observation of historic daily rainfall data.

Unfortunately, the nearest weather station, Kadhoo, is 113 km south of the island

reducing its applicability to local level analysis. Moreover, we were unable to acquire

daily historical data of Kadhoo itself. Available limited severe weather reports shows that

Kadhoo received a maximum precipitation of 110.8mm for a 24 hour period on 21th

November 2004 and the island of Meemu Atoll Muli, 82 km NE of Kudahuvadhoo,

received a maximum of 193mm on 15 November 2003 (DoM, 2005). Based on

interviews with locals, the 2004 event did not have an impact on the island but the 2003

event caused moderate levels of flooding for 2 days. The interviewees were unable to

recall a single event with significant impact, suggesting a low intensity of flood events.

The probable maximum precipitations predicted for Hulhule’ and S.Gan by UNDP (2006) are as follows as shown in Table 2.3:

Table 2.3 Probable Maximum Precipitation for various Return periods in Hulhule’ and Gan. Station Return Period

50 year 100 year 200 year 500 year

Hulhule’ 187.4 203.6 219.8 241.1 Gan 218.1 238.1 258.1 284.4

Given the high variations in rainfall in Kadhoo, these figures may vary. Based on the field

observations and correlations with severe weather reports from Department of

Meteorology ((DoM, 2005) the following threshold levels were identified for flooding

(Table 2.4). These figures must be revised once historical daily rainfall data becomes

available.

Table 2.4 Threshold levels for rainfall related flooding in Kudahuvadhoo. Threshold level (daily rainfall)

Impact

50mm Puddles on road, flooding in low houses, occasional minor damage to household goods in most vulnerable locations, disruption to businesses and primary school in low areas.

100mm Moderate flooding in low houses; all low lying roads flooded; minor damage to household items, temporary (minor to Moderate) disruptions to socio-economic functions for less than 24 hours

150mm Widespread flooding on roads and low lying areas. Moderate damage to household goods, disruptions to socio-economic functions for more than 24 hours.

200mm Widespread flooding on roads, low areas and houses. Moderate damage to household goods, sewerage network, backyard crops, disruption to socio economic functions for more than 24 hours, gullies created along shoreline, possible damage to road infrastructure.

230+mm Widespread flooding around the island. Major damages to household goods and housing structure, socio economic functions disrupted for more than 48 hours, businesses closed, damage to crops, damage to road infrastructure, sewerage network and quay wall.

Quite often heavy rainfall is associated with multiple hazards especially strong winds and

possible swell waves. It is therefore likely that a major rainfall event could inflict far more

damages those identified in the table.

2.2.3 Wind storms and cyclones

Maldives being located within the equatorial region of the Indian Ocean is generally free

from cyclonic activity. There have only been a few cyclonic strength depressions that

have tracked through the Maldives, all which occurred in the northern and north central

regions. According to the hazard risk assessment report (UNDP, 2006), Kudahuvadhoo

falls within the second least hazardous zone for cyclone related hazards and has a

maximum predicted cyclonic wind speeds of 56 Kts (see Figure 2.6). There are no such

records for the southern region, although a number of gale force winds have been

recorded due to low depressions in the region. Winds exceeding 35 knots (gale to strong

gale winds) were reported as individual events in Kadhoo weather station annually

between 2002 and 2006, all caused by known low pressure systems near Maldives

rather than the monsoon (DoM, 2005). The maximum wind speed in Kadhoo during this

period was approximately 46 kts.

Hazard Zones

1 0.0

2 55.9

3 69.6

4 84.2

5 96.8

Kulhudhufushi

Fonadhoo

Thulusdhoo

Vilufushi

Gan

Villingili

Hithadhoo

Thinadhoo

Kudahuvadhoo

Feydhoo

probable maximumcyclone wind speed (kts)

Figure 2.6 Cyclone hazard zones of the Maldives as defined by UNDP (2006).

Interviews with the locals have indicated that the island has been affected by numerous

wind storms. Unfortunately records have not been kept for these events, especially their

dates or its impacts. However two events have been identified that had moderate impact

on the island: June 1987 and December 1992 events. The event of June 1987 affected a

number of islands across of Maldives causing damage to crops, vegetation and housing

structures. The December 1992 event reached wind speeds over 25 knots and caused

moderate damage to crops and vegetation. Damage to properties was mostly caused by

falling trees, especially breadfruit trees (Artocarpus altilis).

Hence, wind speeds close to near gale winds (see Table 2.5) have caused moderate

damage to property and trees on the island. Kudahuvadhoo does have lush vegetation

on the southern side dominated by larger trees species, which acts to minimise the

direct exposure of properties when winds approach from a south to south westerly

direction. Much of this vegetation is now being cleared for development activities,

especially for the new stadium and tsunami resettlement housing.

In order to perform a probability analysis of strong wind and threshold levels for damage,

daily wind data is crucial. However, such data was unavailable for this study.

Table 2.5 Beaufort scale and the categorisation of wind speeds.

Beau- fort No DescriptionCyclone

category

Average wind

speed (Knots)

Average wind

speed

(kilometres per

hour)

Specifications for estimating speed over land

0 Calm Less than 1 less than 1 Calm, smoke rises vertically.

1 Light Air 1 -3 1 - 5

Direction of wind shown by smoke drift, but not by wind

vanes.

2 Light breeze 4 - 6 6 - 11

Wind felt on face; leaves rustle; ordinary wind vane moved

by wind.

3 Gentle breeze 7 - 10 12 - 19

Leaves and small twigs in constant motion; wind extends

light flag.

4

Moderate

breeze 11 - 16 20 - 28 Raises dust and loose paper; small branches moved.

5 Fresh breeze 17 -21 29 - 38

Small trees in leaf begin to sway; crested wavelets form on

inland waters.

6 Strong breeze 22 - 27 39 - 49

Large branches in motion; whistling heard in telegraph

wires; umbrellas used with difficulty.

7 Near gale 28 - 33 50 - 61

Whole trees in motion; inconvenience felt when walking

against the wind.

8 Gale Category 1 34 - 40 62 - 74 Breaks twigs off trees; generally impedes progress.

9 Strong gale Category 1 41 - 47 75 - 88

Slight structural damage occurs (chimney pots and slates

removed).

10 Storm Category 2 48 - 55 89 - 102

Seldom experienced inland; trees uprooted; considerable

structural damage occurs.

11 Violent storm Category 2 56 - 63 103 - 117

Very rarely experienced; accompanied by widespread

damage.

12 Hurricane Category 3,4,5 64 and over 118 and over Severe and extensive damage. The threshold levels for damage are predicted based on interviews with locals and

housing structural assessments provided by risk assessment report (UNDP, 2006), as

shown in Table 2.6.

Table 2.6 Threshold levels for wind damage based on interviews with locals and available meteorological data. Wind speeds Impact

1-10 knots No Damage 11 – 16 knots No Damage 17 – 21 knots Light damage to trees and crops 22 – 28 knots Breaking branches and minor damage to

open crops, some weak roofs damaged 28 – 33 knots Minor damage to open crops, minor to

moderate damage to vegetation, probability of damage to property due to falling trees.

34 - 40 knots Minor to Moderate to major damage to houses, crops and trees

40+ Knots Moderate to Major damage to houses, trees falling, crops damaged

2.2.4 Tsunami

UNDP (2006) reported the region where Kudahuvadhoo is geographically located to be

a very high tsunami hazard zone. Kudahuvadhoo Island was considered ‘lucky’ to

escape without substantial damage to properties or infrastructure. This is perhaps due to

the fact that other nearby islands such as Kohufushi and Vilufushi were almost

completely devastated. Island within Dhaalu Atoll itself, especially the neighbouring

Vaanee also experienced extensive damage.

According to official reports 20% of the island was flooded. Field surveys and aerial

photographs immediately after the event revealed that approximately 30% of the island

was flooded. Flooding occurred on the southern and parts of eastern coastline. There

were no major structures in this area and as a result impact was minimal. The flood itself

came only about 150-200 m on the southern side and up to a 300 m on the eastern side.

All these areas were uninhabited. The main damage occurred to the agricultural fields,

however. One farmer reported a loss of MRF 30,000 worth of crops. Apart from the

agricultural fields; the only notable damage to the island was to its Harbour. The outer

harbour walls collapsed and part of the quay wall was damaged beyond repair.

The tsunami run-up height at the eastern shoreline of the island was reported to be

approximately 0.8m above MSL reducing to 0.1 m, 300 m inland. Run-up height on the

southern shoreline was estimated at 0.9m. It is difficult to identify the local tsunami

induced tide level due to the absence of a nearby tide station. Tsunami induced tide

level within the lagoon predicted using the tide data from the nearest tide station at

Hulhule’ shows that the island experienced water heights higher than 0.2 above the

average northern coastline (Figure 2.7). The small levels of flooding from the northern

side, most likely reflects this rise.

Figure 2.7 Water level recordings from the tide gauge at Hulhule’ indicating the wave height of tsunami 2004 (source: University of Hawai’i SeaLevel Centre, http://ilikai.soest.hawaii.edu/uhslc/iot1d/male1.html)

Comparatively higher exposure of the southern half of Dhaalu Atoll may be partially due

to the refraction of the wave caused by the Indian Ocean bathymetry as it travelled

westwards Maldives (Ali, 2005). The Indian Ocean bathymetry (Figure 2.8) shows

shallower water depths extended far offshore at around the central region of the

Maldives (at around the atolls of Laamu – Meemu). This shallower area caused the

wave to bend away from the southern atolls and became focused towards the central

region of the country. It is likely that a similar pattern may persist in any future event if

the waves originate from the northern Sundra trench.

Fig 2.8 Submarine topography around Maldives archipelago and modelled wave refraction for the December 2004 tsunami (source: Ali (2005)). The predicted probable maximum tsunami wave height for the area where

Kudahuvadhoo is located is 2.5 – 3.2 m (UNDP, 2006). Examination of the flooding that

will be caused by a wave run-up of 4.5m for the island of Kudahuvadhoo indicates that

such a magnitude wave will flood much of the island. The first 150-200m from the

shoreline will be a severely destructive zone (Figure 2.9). The theoretical tsunami flood

decay curve was plotted for a wave that is applied only for the direct wave from the

south eastern oceanward side of the island. It’s also is well understood that the tsunami

wave will also travel into the atoll lagoon which will cause the water level in the atoll

lagoon to rise. This could cause flooding of the island from the lagoonward side of the

island, if the water level rises above the height of the island. The maximum tsunami

wave induced water level height predicted for the atoll lagoon near Kudahuvadhoo is

1.8m. This could flood the island from the lagoonward side.

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

0 100 200 300 400 500 600 700 800 900 1000

Distance from oceanward shoreline (m)

Height rel MSL (m)

Extent of most

destructive zone

Threshold level of flooding for severe structural damage

Figure 2.9 Tsunami related flooding predicted for Kudahuvadhoo based upon theoretical flood decay curve and the maximum probable tsunami wave height at Kudahuvadhoo. Despite the prediction of a 2.5-3.2 m tsunami in Kudahuvadhoo (UNDP, 2006), it is

important to note the geophysical settings of Kudahuvadhoo which could make it

comparatively less exposed to severe intensity of such events. Characteristics such as

island orientation, reef orientation, vegetation cover and presence of multiple coastal

ridges could help controlling the intensity and even height of water run-up on the island.

Furthermore, the lack of intensity may have been attributed to the lack of development

on the south eastern and eastern half of the island. Unlike most islands devastated in

the region, Kudahuvadhoo had a 380 m vegetated buffer zone, between the settlement

and the coastline. In effect, only a handful of people witnessed flood waters on the

southern side while majority of the population witnessed rising waters near the harbour.

This tends to suggest the ‘remoteness’ of the southern areas. With increasing

development in the area, especially the tsunami resettlement, an event of similar

magnitude will cause more significant damage today.

2.2.5 Earthquakes

There hasn’t been any major earthquake related incident recorded in the history of

Kudahuvadhoo or even Maldives. However, there have been a number of anecdotally

reported tremors around the country.

The Disaster Risk Assessment Report (UNDP 2006) highlighted that Thaa Atoll is

geographically located in the lowest seismic hazard zone of the entire country.

According to the report the rate of decay of peak ground acceleration (PGA) for the zone

1 in which Kudahuvadhoo is located has a value less than 0.04 for a 475 years return

period (see Table 2.7). PGA values provided in the report have been converted to

Modified Mercalli Intensity (MMI) scale (see column ‘MMI’ in Table 2.7). The MMI is a

measure of the local damage potential of the earthquake. See Table 2.8 for the range of

damages for specific MMI values. Limited studies have been performed to determine the

correlation between structural damage and ground motion in the region. The conversion

used here is based on United States Geological Survey findings. No attempt has been

made to individually model the exposure of Kudahuvadhoo Island as time was limited for

such a detailed assessment. Instead, the findings of UNDP (2006) were used.

Table 2.7 Probable maximum PGA values in each seismic hazard zone of Maldives (modified from UNDP, 2006). Seismic hazard zone

PGA values for 475yrs return period

MMI3

1 < 0.04 I 2 0.04 – 0.05 I 3 0.05 – 0.07 I 4 0.07 – 0.18 I-II 5 0.18 – 0.32 II-III

Table 2.8 Modified Mercalli Intensity description (Richter, 1958).

MMI Value

Shaking Severity

Description of Damage

I Low Not felt. Marginal and long period effects of large earthquakes.

II Low Felt by persons at rest, on upper floors, or favourably placed.

III Low Felt indoors. Hanging objects swing. Vibration like passing of light trucks. Duration estimated. May not be recognized as an earthquake.

IV Low Hanging objects swing. Vibration like passing of heavy trucks; or sensation of a jolt like a heavy ball striking the walls. Standing motor cars rock. Windows, dishes, doors rattle. Glasses clink. Crockery clashes. In the

3 Based on KATZFEY, J. J. & MCINNES, K. L. (1996) GCM simulation of eastern Australian cutoff lows.

Journal of Climate, 2337-2355.

upper range of IV, wooden walls and frame creak. V Low Felt outdoors; direction estimated. Sleepers wakened.

Liquids disturbed, some spilled. Small unstable objects displaced or upset. Doors swing, close, open. Shutters, pictures move. Pendulum clocks stop, start, change rate.

VI-XII Light - Catastrophe

Light to total destruction

According to these findings it is unlikely that Kudahuvadhoo will receive an earthquake

capable of causing destruction. It should however be noted that the actual damage may

be different in Maldives since the masonry and structural stability factors have not been

considered at local level for the MMI values presented here. Usually such adjustments

can only be accurately made using historical events, which is almost nonexistent in

Maldives.

2.2.6 Climate Change

The debate on climate change, especially Sea Level Rise (SLR) is far from complete.

Questions have been raised about SLR itself (Morner et al., 2004, Morner, 2004) and

the potential for coral island environments to naturally adapt (Kench et al., 2005,

Woodroffe, 1993). However the majority view of the scientific community is that climate

is changing and that these changes are more likely to have far reaching consequences

for Maldives. For a country like Maldives, who are most at risk from any climate change

impacts, it is important to consider a cautious approach in planning by considering worst

case scenarios. The findings presented in this section are based on existing literature.

No attempt has been made to undertake detailed modelling of climate change impacts

specifically on the island due to time limitations. Hence, the projection could change with

new findings and should be constantly reviewed.

The most critical driver for future hazard exposure in Maldives is the predicted sea level

rise and Sea Surface Temperature (SST) rise. Khan et al. (2002, Woodroffe, 1993)

analysis of tidal data for Gan, Addu Atoll shows the overall trend of Mean Tidal Level

(MTL) is increasing in the southern atolls of Maldives. Their analysis shows an

increasing annual MTL at Gan of 3.9 mm/year. These findings have also been backed

by a slightly higher increase reported for Diego Garcia south of Addu Atoll (Sheppard,

2002). These calculations are higher than the average annual rate of 5.0 mm forecasted

by IPCC (2001), but IPCC does predict a likely acceleration as time passes. Hence, this

indicates that the MTL at Gan by 2100 will be nearly 0.4m above the present day MTL.

Similarly, Khan et al. (2002) reported air temperature at Addu Atoll is expected to rise at

a rate of 0.4C per year, while the rate of rise in SST is 0.3C. Although no specific studies

have been done for Thaa Atoll, the findings from Addu Atoll could be used as a guide to

predicted changes.

Predicted changes in extreme wind gusts related to climate change assumes that

maximum wind gusts will increase by 2.5, 5 and 10 per cent per degree of global

warming (Hay, 2006). Application of the rate of rise of SST to the best case assumption

indicates a 15% increase in the maximum wind gusts by the year 2010 in southern

Atolls.

The global circulation models predict an enhanced hydrological cycle and an increase in

the mean rainfall over most of the Asia. It is therefore evident that the probability of

occurrence and intensity of rainfall related flood hazards for the island of Gan will be

increased in the future. It has also been reported that a warmer future climate as

predicted by the climate change scenarios will cause a greater variability in the Indian

monsoon, thus increasing the chances of extreme dry and wet monsoon seasons (Giorgi

and Francisco, 2000). Global circulation models have predicted average precipitation in

tropical south Asia, where the Maldives archipelago lies, to increase at a rate of 0.14%

per year (Figure 2.10).

Rate of increase = 0.135% per year

0

2

4

6

8

10

12

2010 2020 2030 2040 2050 2060 2070 2080 2090

Year

Incre

ase

of

pre

cip

ita

tio

n (

%)

Figure 2.10 Graph showing the rate of increase of averaged annual mean

precipitation in tropical south Asia (Adger et al., 2004).

There are no conclusive agreements over the increase in frequency and intensity of

Southern Indian Ocean Storms. However, some researchers have reported a possible

increase in intensity and even a northward migration of the southern hemisphere storm

belt (Kitoh et al., 1997) due rise in Sea Surface Temperatures (SST) and Sea Level

Rise. If this is to happen in the Southern Indian Ocean, the frequency of and intensity of

storms reaching Kudahuvadhoo Island coastline will increase and thereby exposing the

island more frequent damages from swell waves. The increase in sea level rise will also

cause the storms to be more intense with higher flood heights.

The above discussed predicted climate changes for Kudahuvadhoo and surrounding

region is summarised in Table 2.9. It should be cautioned that the values are estimates

based on most recent available literature on Maldives which themselves have a number

of uncertainties and possible errors. Hence, the values should only be taken as guide as

it existed in 2006 and should be constantly reviewed. The first three elements are based

climate change drivers while the bottom three is climatological consequences.

Table 2.9 Summary of climate change related parameters for various hazards. Element Predicted

rate of

change

Predicted change (overall rise) Possible impacts on

Hazards in Gan Best Case Worst Case

SLR 3.9-5.0mm /yr

Yr 2050: +0.2m

Yr 2100: +0.4m

Yr 2050: +0.4m

Yr 2100: +0.88m

Tidal flooding, increase in swell wave flooding, reef drowning

Air Temp 0.4°C / decade

Yr 2050: +1.72°

Yr 2100: +3.72°

SST 0.3°C / decade

Yr 2050: +1.29°

Yr 2100: +2.79°

Increase in storm surges and swell wave related flooding, Coral bleaching & reduction in coral defences

Rainfall +0.14% / yr (or +32mm/yr)

Yr 2050: +1384mm

Yr 2100:

Increased flooding, Could effect coral reef growth

+2993mm

Wind gusts 5% and 10% / degree of warming

Yr 2050: +3.8 Knots

Yr 2100: +8.3 Knots

Yr 2050: +7.7Knots

Yr 2100: +16.7 Knots

Increased windstorms, Increase in swell wave related flooding.

Swell Waves

Frequency expected to change.

Wave height in reef expected to be high

Increase in swell wave related flooding.

3.3 Event Scenarios

Based on the discussion provided in section 2.2 above, the following event scenarios

have been estimated for Kudahuvadhoo Island (Tables 2.10, 2.11, and 2.12).

Table 2.10 Rapid onset flooding hazards Hazard Max

Prediction

Impact thresholds Probability of Occurrence

Low Moderate

Severe

Low

Impact

Moderate

Impact

Severe

Impact

Swell Waves

(wave heights on reef flat – Average Island ridge height +1.9m above reef flat)

NA < 2.3m

> 2.3m > 3.0m High Moderate Low

Tsunami

(wave heights on reef flat)

3.7m < 2.3m

> 2.3m > 3.0m Moderate

Low Very low

SW monsoon high seas

1.5m < 2.3m

1.0.1.

> 2.3m > 3.0m High Very low Unlikely

Heavy Rainfall

(For a 24 hour period)

241mm <60mm

> 60mm >175mm

High Moderate Low

Table 2.11 Slow onset flooding hazards (medium term scenario – year 2050). Hazard Impact thresholds Probability of Occurrence

Low Moderate Severe Low Moderate Severe

SLR: Tidal Flooding

< 2.3m

> 2.3m > 3.0m Moderate Very Low Very Low

SLR: Swell Waves

< 2.3m

> 2.3m > 3.0m Very high Moderate Low

SLR: Heavy Rainfall

<60mm >60mm >175mm Very High

Moderate Low

Table 2.12 Other rapid onset events. Hazard Max

Prediction

Impact thresholds Probability of Occurrence

Low Moderate Severe Low Moderate Severe

Wind storm NA <30 knts

> 30 knts > 45Knts

Very High

High Moderate

Earthquake

(MMI value4)

I < IV

> IV > VI Very Low

Unlikely none

2.4 Hazard zones Hazard zones have been developed using a hazard intensity index. The index is based

on a number of variables, namely historical records, topography, reef geomorphology,

vegetation characteristics, existing mitigation measures (such as breakwaters) and

hazard impact threshold levels. The index ranges from 0 to 5 where 0 is considered as

no impact and 5 is considered as very severe. In order to standardise the hazard zone

for use in other components of this study only events above the severe threshold were

considered. Hence, the hazard zones should be interpreted with reference to the hazard

scenarios identified above.

2.4.1 Swell waves and SW monsoon high Waves

The intensity of swell waves and SW monsoon udha is predicted to be highest 50m from

the coastline on the ocean ward side (see Figure 2.11) and 30 m from the lagoonward

side. Swell waves higher than 3.0 m on reef flat are predicted to penetrate inner island

4 Refer to earthquake section above

up to or beyond 200m from the coastline. The longest run-up would be from the

oceanward coastline where it could penetrate 250 m inland. The run-up on the island is

controlled by topography as the flood waters decay below 0.4 m. The presence of

multiple ridges on the oceanward side helps prevent flood run-up beyond 250 m.

The lagoonward side is relatively safe form swell related flooding due to the protection

provided by the atoll rim. However, waves could refract around the reef system and the

island causing flooding close to the shoreline. Such impacts are predicted to be limited

to 10-30 m from the lagoonward coastline and their intensity is expected to remain low.

SW monsoon high waves (udha) are not expected to have an impact beyond 50m of the

coastline and are more likely to influence the coastline right around the island.

0 150 300

metres

Hazrad Zoning MapSwell Waves, Udha

& Storm Surges

High

Intensity Index

Low 1 2 3 4 5

Contour lines represent intensity

index based on a severe event

scenarios

300

Hazrad Zoning MapSwell Waves, Udha

& Storm Surges

Intensity Index

1 2 3 4 5 High

Contour lines represent intensity

index based on a severe event

scenarios

0 150

metres

Low

Figure 2.11 Hazard zoning map for swell wave, storm surges and southwest

monsoon high seas.

2.4.2 Tsunamis

When a severe threshold of tsunami hazard (>3.0 m on reef flat) is considered, 70% of

the island is expected to be directly affected (Figure 2.12). If the waves reach beyond

4.0 m MSL 90% of the island is likely to be flooded due the prevalent tide levels. High

intensity waves will flush through the island from the eastern and southern side while

tide related surges will occur within the atoll, flooding the northern coastline. The

intensity of flood waters will be highest 200-250 m from the shoreline. The water run-up

is expected to be controlled on the southern and south eastern side by the presence of

second relic ridge 250 m from the coastline. Similar high areas exist around the island

which could control the flood waters as the wave decays.

Wave height around the island will vary based on the original tsunami wave height, but

the areas marked as low intensity is predicted to have proportionally lower heights

compared to the coastline.

30030000

HighHigh

Contour lines represent intensity

index based on a severe event

scenario

(wave heights +3.0m MSL)

150

metres

150

metres

Hazrad Zoning MapTsunami

Low

Intensity IndexIntensity Index

1 2 3 4 51 2 3 4 5Low

Figure 2.12 Hazard zoning map for tsunami flooding.

2.4.3 Heavy Rainfall

Heavy rainfall above the severe threshold is expected to flood parts of the settlement

(Figure 2.14). The areas predicted for severe intensity are the topographic lows in the

southern and central parts of the island. These areas act as drainage basins for the

surrounding higher areas and due the large size of the island the ‘catchments area’ is

considerable for surface runoff during heavy rainfall.

The intensity is generally expected to be low in most locations. The hazard zone

presented in the map below is based on the topographic surveys done on the island.

Due to the large size of the island it was impossible to assess the topographic variation

across the entire island during this project. Hence the hazard zones shown below should

be considered as the most prominent zones only. More detailed assessment is required

once high resolution topographic data becomes available.

30030000

HighHighLowLow

Contour lines represent intensity

index based on a severe event

scenario

(+175mm in 24 hours)

Note: White areas

represent areas with

no data

150

metres

150

metres

Intensity IndexIntensity Index

1 2 3 4 51 2 3 4 5

Hazrad Zoning MapHeavy Rainfall

Figure 2.14 Hazard zoning map for heavy rainfall related flooding.

2.4.4 Strong Wind

The intensity of the strong wind across the island is expected to remain fairly constant.

Smaller variations may exist between the west and east side where by the west side

receives higher intensity due to the predominant westerly direction of abnormally strong

winds. The entire island has been assigned an intensity index of 4 for strong winds

during a severe event.

2.4.5 Earthquakes

The entire island is a hazard zone with equal intensity. An intensity index of 1 has been assigned. 2.4.6 Climate Change

Establishing hazard zones specifically for climate change is impractical at this stage due

to the lack of topographic and bathymetric data. However, the predicted impact patterns

and hazard zones described above are expected to be prevalent with climate change as

well, although the intensity is likely to slightly increase.

2.4.6 Composite Hazard Zones

A composite hazard zone map was produced using a GIS based on the above hazard

zoning and intensity index (Figure 2.15). The coastal zone approximately 200m from the

oceanward coastline and the topographically low areas within the island are predicted to

be the most intense regions for multiple hazards. The eastern side is particularly

identified as a hazard zone due to the exposure to swell waves, storm surges, udha and

tsunamis. The overall composite increase in intensity for hazard zones have resulted

from high exposure to intense windstorms across the island.

300300

HighHigh

Contour lines represent intensity

index based on severe event

scenarios

metres

150150

metres

1 2 3 4 51 2 3 4 5LowLow

Intensity IndexIntensity Index

Hazard Zoning MapMultiple Hazards

00

Figure 2.15 Composite hazard zone map.

2.5 Limitations and recommendation for future study The main limitation for this study is the incompleteness of the historic data for different

hazardous events. The island authorities do not collect and record the impacts and

dates of these events in a systematic manner. There is no systematic and consistent

format for keeping the records. In addition to the lack of complete historic records there

is no monitoring of coastal and environmental changes caused by anthropogenic

activities such as road maintenance, beach replenishment, causeway building and

reclamation works. It was noted that the island offices do not have the technical

capacity to carryout such monitoring and record keeping exercises. It is therefore evident

that there is an urgent need to increase the capacity of the island offices to collect and

maintain records of hazardous events in a systematic manner.

The second major limitation was the inaccessibility to long-term meteorological data from

the region. Historical meteorological datasets atleast as daily records are critical in

predicting trends and calculating the return periods of events specific to the site. The

inaccessibility was caused by lack of resources to access them after the Department of

Meteorology levied a substantial charge for acquiring the data. The lack of data has

been compensated by borrowing data from alternate internet based resources such as

University of Hawaii Tidal data. A more comprehensive assessment is thus

recommended especially for wind storms and heavy rainfall once high resolution

meteorological data is available.

The future development plans for the island are not finalised. Furthermore the existing

drafts do not have proper documentations explaining the rationale and design criteria’s

and prevailing environmental factors based on which the plan should have been drawn

up. It was hence, impractical to access the future hazard exposure of the island based

on a draft concept plan. It is recommended that this study be extended to include the

impacts of new developments, especially land reclamations, once the plans are finalised.

The meteorological records in Maldives are based on 5 major stations and not at atoll

level or island level. Hence all hazard predictions for Gan are based on regional data

rather than localised data. Often the datasets available are short for accurate long term

prediction. Hence, it should be noted that there would be a high degree of estimation

and the actual hazard events could vary from what is described in this report. However,

the findings are the closest approximation possible based on available data and time,

and does represent a detailed although not a comprehensive picture of hazard exposure

in Gan.

References

ALI, S. (2005) December 26 2004 Tsunami Impact Assessment and a Tsunami Risk Assessment of the Maldives. School of Civil Engineering and the Envrionment. Southampton, United Kingdom, University of Southampton, .

BINNIE BLACK & VEATCH (2000) Enviromental / Technical study for dredging / reclamation works under Hulhumale' Project - Final Report. Male', Ministry of Construction and Public Works.

BUCKLEY, B. W. & LESLIE, L. M. (2004) Preliminary climatology and improved modelling of South Indian Ocean and southern ocean mid-latitude cyclones. International Journal of Climatology, 24, 1211-1230.

DEPARTMENT OF METEOROLOGY (DOM) (2005) Severe weather events in 2002 2003 and 2004. Accessed 1 November 2005, <http://www.meteorology.gov.mv/default.asp?pd=climate&id=3>, Department of Meteorology, Male', Maldives.

DHI (1999) Physical modelling on wave disturbance and breakwater stability, Fuvahmulah Port Project. Denmark, Port Consult.

GIORGI, F. & FRANCISCO, R. (2000) Uncertainties in regional climate change prediction: a regional analysis of ensemble simulations with HadCM2 coupled AOGCM. Climate Dynamics, 16, 169-182.

HAY, J. E. (2006) Climate Risk Profile for the Maldives. Male', Ministry of Envrionment Energy and Water, Maldives.

IPCC (2001) Climate Change 2001: The Scientific Basis, New York, Cambridge, United Kingdom and New York, NY, USA.

KATZFEY, J. J. & MCINNES, K. L. (1996) GCM simulation of eastern Australian cutoff lows. Journal of Climate, 2337-2355.

KENCH, P. S. & BRANDER, R. W. (2006) Wave processes on coral reef flats: Implications for Geomorphology using Australian Case Studies. Journal of Coastal Research, 22, 209-223.

KENCH, P. S., MCLEAN, R. F. & NICHOL, S. L. (2005) New model of reef-island evolution: Maldives, Indian Ocean. Geology, 33, 145-148.

KHAN, T. M. A., QUADIR, D. A., MURTY, T. S., KABIR, A., AKTAR, F. & SARKAR, M. A. (2002) Relative Sea Level Changes in Maldives and Vulnerability of Land Due to abnormal Coastal Inundation. Marine Geodesy, 25, 133–143.

KITOH, A., YUKIMOTO, S., NODA, A. & MOTOI, T. (1997) Simulated changes in the Asian summer monsoon at times of increased atmospheric CO2. Journal of Meteorological Society of Japan, 75, 1019-1031.

MANIKU, H. A. (1990) Changes in the Topography of Maldives, Male', Forum of Writers on Environment of Maldives.

MORNER, N.-A. (2004) The Maldives project: a future free from sea-level flooding. Contemporary South Asia, 13, 149-155.

MORNER, N.-A., TOOLEY, M. & POSSNERT, G. (2004) New perspectives for the future of the Maldives. Global and Planetary Change, 40, 177-182.

NASEER, A. (2003) The integrated growth response of coral reefs to environmental forcing: morphometric analysis of coral reefs of the Maldives. Halifax, Nova Scotia, Dalhousie University.

RICHTER, C. F. (1958) Elementary Seismology, San Francisco, W.H. Freeman and Company.

SHEPPARD, C. R. C. (2002) Island Elevations, Reef Condition and Sea Level Rise in Atolls of Chagos, British Indian Ocean Territory. IN LINDEN, O., D. SOUTER, D. WILHELMSSON, AND D. OBURA (Ed.) Coral degradation in the Indian Ocean: Status Report 2002. Kalmar, Sweden, CORDIO, Department of Biology and Environmental Science, University of Kalmar.

UNISYS & JTWC (2004) Tropical Cyclone Best Track Data (1945-2004). http://www.pdc.org/geodata/world/stormtracks.zip, Accessed 15 April 2005, Unisys Corporation and Joint Typhoon Warning Center.

WOODROFFE, C. D. (1993) Morphology and evolution of reef islands in the Maldives. Proceedings of the 7th International Coral Reef Symposium, 1992. Guam, University of Guam Marine Laboratory.

YOUNG, I. R. (1999) Seasonal variability of the global ocean wind and wave climate. International Journal of Climatology, 19, 931–950.

3. Environment Vulnerabilities and Impacts

3.1 Environment Settings

3.1.1 Terrestrial Environment

Topography

The topography of Kudahuvadhoo was assessed using three topographic profiles (see

Figure 3.1). Given below are the general findings from this assessment.

Location of

w ells

Topographic

Profiles

P3 Profile Number

300

Topographic Survey

Locations

0

metres

150

P3

P2

P1

72.8

93°E

72.8

975

°E

2.67549°N

2.671°N

2.6665°N

Figure 3.1 Topography field survey locations

The island is generally low lying with an average elevation of +0.88 m MSL along the

surveyed island profiles. This finding was reconfirmed from the shallow depths of ground

water table around the island (on average approximately 1 m at median tide). As

characteristic of large islands, considerable variations in topography were observed in

Kudahuvadhoo.

The main topographic features along Profile 1 (P1) are the coastal ridge on the

oceanward side (+1.5 m), a 75m wide low area (+0.45m) and higher ridge like feature

approximately 300 m from coastline (see Figure 3.2). The settlement area is generally

low at about +0.8 m MSL. The high ridge like feature may perhaps represent an old

shoreline during the evolution of the island. The adjacent low area and the present ridge

system are reminiscent of an island undergoing a long period of accretion and

subsequent stabilisation. The area nonetheless appears to be a major natural asset of

the island against flooding events due to the double ridge and low drainage zone. The

low areas were reported to be regular flood zone during heavy rainfall. At present no

developments have been made in the area, except agricultural plots, which appears to

be thriving in the area. Future housing developments have been planned within the low

area and may have implications during major flooding events. These issues will be

discussed in a latter section. Low areas were identified in the existing settlements which

corresponded with reported rainfall related flood zone. Most notable of these were the

areas around the Atoll Education Centre and Pre-school.

0 100 200 300 400 500 600 700 800

G G’

900

Approximate Mean Sea Level

1m

0

Oceanward SideLagoonward Side

G

G’ Profile P1

Oceanward Ridge

(+1.5m)

Low Area(+0.475)

Existing settlement

HarbourQuay Wall

Extent ofreclaimed land

Extent ofExisting Settlement

High point(+1.2m)

Possibly and

old ridge

*

*No clear sight. Deviation of 5 . The length does not reflect the island width but accurately represents depth variationso

Figure 3.2 Topographic profile P1.

The main topographic features along Profile 2 (P2) are the consistent low elevation (less

than 1.0 m MSL and the presence of a ridge like feature approximately 250 m inland

(see figure 3.3). This high area could be part of the old ridge system described above for

P1since it has a similar heights and distance from coastline. It may be possible that this

ridge extends around the south and east sides of the island. The oceanward ridge along

the survey line has been considerably cleared and modified during the construction of a

waste management centre. Hence, the height of 1.3m may not represent the actual ridge

height. However, observations of coastline further south and north of the area showed

no significant changes in height. If ridge height is a crude indicator of wave power, the

area is considerably less exposed to strong wave action compared to the coastline

facing the southern reef edge.

In general the coastline topography and geomorphology around the island is reminiscent

of islands in low energy settings around Maldives. Hence, it is very likely that

Kudahuvadhoo has low exposure to strong wave action. Some possible reasons for lack

of exposure include island location within the reef, atoll and the archipelago, which on

initial observation appears to protect the island from high energy events and seasonal

wave action.

0 200 400 600 800 1000 1200

1m

0

Approximate Mean Sea Level

Oceanward SideLagoonward Side

G G’

G

Profile P2

G’

Oceanward Ridge

(+1.3m)Area modifiedfor wastesite constructionLow area

(+0.8m)High Point

(+1.2m)Low area(+0.8m)

Relatively young

Low area(+0.5m) New Settlement

Figure 3.3 Topographic Profile P2.

Based on the topographic profiles, a crude estimate of the island topography was

developed. Figure 3.4 shows the predicted main high and low areas of the island.

Topographic Survey

Locations

metres

1500 300

High areas

Low areas

Figure 3.4 Predicted high and low areas of Kudahuvadhoo.

Vegetation

Despite being a large island, the vegetation of Kudahuvadhoo is rapidly being depleted.

At present 50% of the island comprises of moderate to dense vegetation. However,

approximately half of the vegetated area is currently being utilised for agriculture and

various human activities. Hence, much of the vegetation cover is low and the amount of

dense vegetation cover is limited to 20% (see Figure 3.5). Much of the undeveloped

areas on the southern half of the island have been cleared for agricultural activities. New

housing developments in the areas have also resulted in vegetation cover to be reduced.

The coastal vegetation on the island is dense but narrow in most locations, especially

along the southern coastline. This has been a result of agricultural plots encroaching

coastal vegetation. Coastal erosion has further narrowed the vegetation strip in the

southern coastline. There is a strong presence of vegetation in both the southeast and

southwest corner of the island, crucial for keeping the erosion prone areas stable. The

planned new developments would remove much of this vegetation, however.

Major vegetation

patches

Agricultural

land and

recreational areas

Settlement in

2004

Reclaimed

land

Current Tsunami

housing project

300

Vegetation Distribution

0

metres

150

Planned expansion

of settlement

Figure 3.5 Distribution of Vegetation.

Ground Water and Soil

Kudahuvadhoo is expected to have a substantial layer of fresh water. Water lens depth

varies across the island based on topography. Generally the water table could be

reached with less than 1m at median tide. This could decrease to 0.5m during spring

high tides or more during heavy rainfall. There are no areas above water table or

wetland areas within Kudahuvadhoo.

Kudahuvadhoo’s ground water was reported to be in generally in good quality (MPND,

2005). The inhabitants reported no shortages of drinking water in the past due to the

good quality of ground water. However, the settlement were reported be experiencing

gradual decline in quality due to contamination and over extraction. The Friday Mosque,

located away for the settlement is still used as a source of ground water during periods

of low rainfall. Rainwater is the main source of drinking water in 2004 (MPND, 2005).

The soil conditions varied from north to south. The main observation was that the

southern half of the island had a large humus layer while the northern parts had

comparatively small humus layer. This finding may generally be explained by the

presence of settlement in the north and agricultural or undeveloped land in the south.

3.1.2 Coastal Environment

Beach and Beach Erosion

Kudahuvadhoo island beach environment has remained relatively stable over the past

45 years. Currently the islands western and southern shorelines are very active while the

northern and eastern shorelines have undergone a reduction in mobility due to coastal

developments. The western shoreline appears to be growing despite the coastal

development in the north. This may be related to the constant sediment supply from the

south, especially during the northeast monsoon, which is considered the most dominant

supply route. It is also highly likely that the major island building processes takes place

during northeast monsoon.

Beach rock was found along an 800m stretch of the southern shoreline (see Figure 3.6).

Part of the beachrock was covered with accretion, indicating seasonal variation in

beachrock exposure. The beachrock areas were located 2-5m away from the present

shoreline further indicating the seasonal nature of erosion.

There are areas of accretion on the west and east sides and areas of erosion on north,

south and east sides. Erosion on north side may not cease in the short-term, as it could

be related to the stabilisation process after land reclamation. The islanders did not

identify erosion as a major problem.

1969 Beach Line

2004 Island Area

2000 New ly Reclaimed Land

1969 Vegetation Line

Exposed Beach Rock

Erosion

Accretion

Figure 3.6 Erosion and accretion in Kudahuvadhoo.

3.1.3 Marine environment

General Reef Conditions

General historical changes to reef conditions were assessed anecdotally, though

interviews with a number of fishermen and young snorkelers. The general agreement

amongst the interviewees were that the quality of reef areas on the southern reef line

had declined considerably over the past 50 years with a lowering of coral cover and

reduction in fish numbers. Reef conditions on the northern reef line were reported to be

in relatively good condition as is the areas of the reef away from Kudahuvadhoo.

Patches of seagrass can be found on the eastern and southern side of the island and

could soon spread to the western side of the island. Overgrowth of seagrass may

become a major nuisance in the future due to the low currents observed in the region.

3.1.4 Modifications to Natural Environment

Coastal Modifications

300

Coastal Developments

metres

1500

Dredged area

(boat landing area)

Breakwaters

Harbour and

entrance dredgingLand ReclamationPiled Jetty

Piled Jetty

Figure 3.7 Coastal modifications in Kudahuvadhoo.

• As in most inhabited islands of Maldives, access infrastructure has been

developed in Kudahuvadhoo Island. These include a harbour, harbour entrance

channel, breakwaters, dredged areas for boat landing and land reclamation as a

method of dredge material disposal. Two piled jetties were also developed on the

western side of the island prior to the development of harbour. Almost all the

development activities have been located in the northern half of the island.

• No coastal developments were undertaken on the southern side of the island

• As a result of these modifications, coastal processes in the northern part of the

island appear to have altered considerably.

Terrestrial Modifications

• As presented earlier, substantial changes to the vegetation was necessitated due

to the expanding human settlement. Vegetation cover comprising larger trees

have been reduced by almost 50% within the last 45 years and are predicted to

decline further due to the planned settlement expansion and lack of re-vegetation

policies.

• Coastal vegetation has been considerably reduced over the past 10 years and

may continue to do so with the planned expansion.

• The modification to topography, especially from road maintenance activities is

minimal. Parts of the eastern coastline have had considerable modifications

along the ridge areas close to shoreline due to past and current waste

management activities.

• Saltwater intrusion in the water lens was not reported as an issue on the island.

3.2 Environmental mitigation against historical hazard events

3.2.1 Natural Adaptation

There is little evidence that Kudahuvadhoo was in the past exposed to severe storm

events or intense wave activity. The presence of multiple ridges on the southern part of

the island does indicate abrupt changes to coastline in response to changing wave

conditions, however. The height of these ridges is quite low and material quite fine,

indicating a possible lack of intense storm activity or strong wave action.

It is apparent from Kudahuvadhoo’s observation that the island adapts to the limited

long-term hazards it experiences and mitigates them naturally but is still exposed to

infrequent high impact hazards. In this sense the southern coastline is critical zone for

future natural adaptation of the island.

3.2.1 Human Adaptation

Kudahuvadhoo has no major mitigation measures undertaken to prevent exposure to

natural hazards. The main activities include construction of breakwaters to protect the

harbour and the use of coastal protection measures to prevent erosion in the reclaimed

area. Additionally some roads works have been undertaken in the past to mitigate

rainfall related flooding, but there is no continuous road maintenance programme. The

lack of both natural and human adaptation measures could be taken as crude indicator

of the historical exposure of the island to natural hazards, specifically climate related

hazards.

3.3 Environmental vulnerabilities to natural hazards

3.3.1 Natural Vulnerabilities

• Island is generally low lying and therefore exposed to flooding from the southern

and north eastern side of the island.

• Topographic variations within the island exposes certain areas to heavy rainfall

associated flooding and creates condition for flood run-up during ocean induced

flooding events. Currently the low areas experience heavy rainfall related

flooding almost regularly, effecting island functions such as schools and

economic activities. There are major low areas in the present uninhabited areas

of the island and could become a major issue due to settlement expansion.

Analysis of flood extents during tsunami shows that the effects of topographic

lows were prominent in the wave run up.

• The ridges around the island and more importantly on the southern side are not

high enough to prevent the +1.82 or +2.30m storm surges predicted in the

hazard scenarios.

• Its location facing the Veymandoo Channel and bathymetric features off the

eastern coastline of Maldives exposes the island to effects of tsunamis.

3.3.2 Human induced vulnerabilities

• The lack of coastal vegetation in certain parts of the coastline is a major concern

in terms of exposure to natural hazards. Coastal vegetation including the

undergrowth acts as natural barrier against tsunami’s, other ocean induced

flooding events and wind storms. A wider coastal vegetation belt would absorb

wave energy from a tsunami or a flooding event reducing the impact on

infrastructure and human settlement. This has been proven from findings across

the nine islands studied under this project. In Kudahuvadhoo Island itself, coastal

vegetation is predicted to have played a major role in preventing the wave run-up

on land due to the vegetation belt and agricultural crops. Stronger coastal

vegetation also reduces wind energy during wind storms and protects settlement

areas near the coastline. Coastal vegetation also plays a critical role in stabilising

the beach areas and assists in controlling erosion. Hence consistent decline in

coastal vegetation along the southern and western shoreline exposes these

areas to above mentioned hazards.

• Similar to the lack of coastal vegetation, the removal of vegetation from the

settlement area exposes the structures to the direct effects of strong wind. The

effects of climate change and global warming could be felt more strongly due to

the apparent increase in temperature within the settlement area.

• The northern coastline of the island has been modified to develop a harbour.

Since its development, it was observed that considerable erosion was

experienced by the newly reclaimed land, probably in search of equilibrium in

coastal processes of the region. It was also observed that the southern half of the

island remains more exposed during both monsoons. Developments in northern

coastline would have implications for the stability of southern coastline if enough

sediment is not transported to the southern side during SW monsoon. It may be a

long time before the coastline adapts to the new modifications, by which time it is

highly likely that mitigation measures for coastal erosion will be put in place,

further changing the coastal processes.

• Reefs form the first line of defence in coral islands against waves and predicted

sea level rise. A functioning and healthy reef is essential for a number of

geomorphologic functions such as sediment production and reef adaptation to

rising sea levels. The natural history of Maldives bears evidence of the role reefs

played in natural adaptation to varying sea levels. The fact that the southern side

of the reef of Kudahuvadhoo is in good condition is an asset. However, the past

inappropriate human activities in the reef such as coral mining and the gradual

decline of reef condition on the eastern and northern ends probably would

increase the sea level rise hazard in Kudahuvadhoo.

3.4 Environmental assets to hazard mitigation

• The relatively large size of Kudahuvadhoo is its main asset against natural

hazards. During ocean induced flooding events, the extent of impact on the

settlement may be considerably reduced due the limited extent of inundation, as

has been demonstrated by the tsunami of 2004 and other flooding events (see

Natural Hazards Section).

• The location of the island on the western line of atolls and on the southern end of

Dhaalu Atoll has meant that the island is relatively less exposed to major ocean

induced hazards. It is relatively protected from the long distant swell waves

coming from the east and the monsoon driven waves coming from the west.

Evidence from the ridge heights also shows that the island has not been exposed

to strong wave action or storm activity in the past. Location within the archipelago

has also meant that Kudahuvadhoo is less exposed to storm surges and strong

winds. However, the island is exposed to tsunami due to the ocean topography

off the eastern rim of Maldives towards Kudahuvadhoo (Shifaz, 2004).

• The east-west orientation of the island can generally be regarded as an asset in

terms of exposure to ocean induced hazards and strong wind related hazards. It

has been found that islands on an east west orientation experienced far less

impacts during the tsunami of 2004 and in previous flooding events.

• Strong coastal vegetation along the majority of the island’s coastline act as a

strong defence line against ocean induced floods and strong winds.

• The present agricultural land acts as a buffer between the settlement and

oceanward coastline, protecting the settlement from sea induced floods. The

protection however comes at an expense to the agricultural crops. The tsunami

of 2004 failed to affect the settlement area due the presence of this wide

vegetation belt, but also destroyed much of the agricultural crops.

• Kudahuvadhoo appears to have two major routes for sediment supply due to its

location on the reef system. This has allowed the island to grow westward

consistently in spite of the presence of a deep lagoon. This also has probably

meant a reduced but a consistent supply of sediments from the southern route

(see existing environment section) even after the construction of the harbour.

More detailed studies are required to confirm this finding.

• Kudahuvadhoo Island’s coastal environment has remained predominantly stable

over the past 50 years (based on historical information and field evidence).

Perhaps this stability is largely due to a consistent sediment supply and due the

location of the island within the archipelago and reef system. Changes after the

construction of the harbour have not been monitored well, but thus far does not

seem to have led to major net erosion in the original island.

• The topographic lows on the southern half of the island may act as a drain during

flooding events, preventing wave run-up further inland.

• Reef width appears to play an important role increasing or decreasing the

impacts of ocean induced wave activity. The impact of gravity waves such as

tsunami’s for example has its impacts reduced based on the length of reef. As

has been discussed in the natural hazards chapter, these findings are preliminary

and needs further inquiry using detailed empirical research.

3.5 Predicted environmental impacts from natural hazards

The natural environment of Kudahuvadhoo and islands in Maldives archipelago in

general appear to be resilient to most natural hazards. The impacts on island

environments from major hazard events are usually short-term and insignificant in terms

of the natural or geological timeframe. Natural timeframes are measured in 100’s of

years which provides ample time for an island to recover from major events such as

tsunamis. The recovery of island environments, especially vegetation, ground water and

geomorphologic features in tsunami effected islands like Laamu Gan provides evidence

of such rapid recovery. Different aspects of the natural environment may differ in their

recovery. Impacts on marine environment and coastal processes may take longer to

recover as their natural development processes are slow. In comparison, impacts on

terrestrial environment, such as vegetation and groundwater may be more rapid.

However, the speed of recovery of all these aspects will be dependent on the prevailing

climatic conditions.

The resilience of coral islands to impacts from long-term events, especially predicted sea

level rise is more difficult to predict. On the one hand it is generally argued that the

outlook for low lying coral island is ‘catastrophic’ under the predicted worst case

scenarios of sea level rise (IPCC 1990; IPCC 2001), with the entire Maldives predicted

to disappear in 150-200 years. On the other hand new research in Maldives suggests

that ‘contrary to most established commentaries on the precarious nature of atoll islands

Maldivian islands have existed for 5000 yr, are morphologically resilient rather than

fragile systems, and are expected to persist under current scenarios of future climate

change and sea-level rise’ (Kench, McLean et al. 2005). A number of prominent

scientists have similar views to the latter (for example, Woodroffe (1993), Morner

(1994)).

In this respect, it is plausible that Kudahuvadhoo may continue to naturally adapt to

rising sea level. There are two scenarios for geological impacts on Kudahuvadhoo. First,

if the sea level continues to rise as projected and the coral reef system keep up with the

rising sea level and survive the rise in Sea Surface Temperatures, then the negative

geological impacts are expected to be negligible, based on the natural history of

Maldives (based on findings by Kench et. al (2005), Woodroffe (1993)). Second, if the

sea level continues to rise as projected and the coral reefs fail to keep-up, then their

could be substantial changes to the land and beaches of Kudahuvadhoo (based on

(Yamano 2000)). The question whether the coral islands could adjust to the latter

scenario may not be answered convincingly based on current research. However, it is

clear that the highly, environments of Kudahuvadhoo, especially the northern coastline,

stands to undergo substantial change or damage (even during the potential long term

geological adjustments), due to potential loss of land through erosion, increased

inundations, and salt water intrusion into water lens (based on Pernetta and Sestini

(1989), Woodroffe (1989), Kench and Cowell (2002)).

As noted earlier, environmental impacts from natural hazards will be apparent in the

short-term and will appear as a major problem in inhabited islands due to a mismatch in

assessment timeframes for natural and socio-economic impacts. The following table

presents the short-term impacts from hazard event scenarios predicted for

Kudahuvadhoo.

Hazard Scenario Probability at Location

Potential Major Environmental Impacts

Tsunami (maximum scenario) 3.2m Low • Widespread damage to coastal vegetation

(Short-term)

• Long term or permanent damage to selected inland vegetation especially common backyard species such as mango and breadfruit trees.

• Contamination of ground water if the sewerage systems are damaged or if liquid contaminants such as diesel and chemicals in the boat yard are leaked.

• Salinisation of ground water lens to a considerable period of time causing ground water shortage. If the rainwater collection

Hazard Scenario Probability at Location

Potential Major Environmental Impacts

facilities are destroyed, potable water shortage would be critical.

• Widespread damage to crops

• Moderate to major damage to coastal protection and island access infrastructure such as breakwaters and quay walls.

• Short-medium term loss of soil productivity (southern agricultural zone)

• Minor damage to coral reefs (based on UNEP (2005))

Storm Surge (based on UNDP, (2005)) 0.60m (1.53m

storm tide) Very Low • Minor damage to coastal vegetation

• Minor loss of crops

• Minor damage to coastal protection infrastructure

• Minor geomorphologic changes in the southern oceanward shoreline and lagoon

Strong Wind 28-33 Knots Very High • Minor damage to very old and young fruit

trees

• Debris dispersion near waste sites.

• Minor damage to open field crops 34-65 Knots Low • Moderate damage to vegetation with falling

branches and occasionally whole trees

• Debris dispersion near waste sites.

• Moderate-high damage to open field crops

• Minor changes to coastal ridges 65+ Knots Very Low • Widespread damage to inland vegetation

• Debris dispersion near waste sites.

• Minor changes to coastal ridges Heavy rainfall

187mm Moderate • Minor to moderate flooding in low areas, including roads and houses.

242mm Low • Widespread flooding but restricted to low areas of the island.

Drought Low • Minor damage to backyard fruit trees and crops

Earthquake Low • Minor geomorphologic changes to land and reef system.

Sea Level Rise by year 2100 (effects of single flood event) Medium

(0.41m) Moderate • Widespread flooding during high tides and

surges.

• Loss of land due to erosion.

• Loss of coastal vegetation

• Major changes to coastal geomorphology.

• Saltwater intrusion into water lens and salinisation of ground water leading to water

Hazard Scenario Probability at Location

Potential Major Environmental Impacts

shortage and loss of flora and fauna.

• Minor to moderate expansion of wetland areas

3.6 Findings and Recommendations for safe island development plan

• A coral islands main defensive ability against frequent natural hazards is perhaps

its robust natural adaptive capacity. In order to retain this ability against ocean

induced hazards, a proper and functioning coastal environment is essential. It

takes a number of years in term of geological time for an island to stabilise and

achieve equilibrium in processes around the island. Once established the island

evolves and adapts to the prevailing conditions. The natural history of Maldives

bears evidence to such natural adaptation, including the survival through a 2.5m

rise in sea level (Kench et.al, 2004). It is perhaps the foremost reason why the

coral islands of Maldives have survived thus far.

• The proposed safe island development in Kudahuvadhoo proposes to change a

functioning coastal environment into a more artificial environment. The

implications of this change are numerous especially in the short term. The

proposed modifications may require considerable time for the island to achieve

equilibrium in different forces controlling coastal processes. During this period

considerable changes to the existing coastal environment may be imminent. In

the absence of coastal protection, these changes would be more noticeable.

There is a high probability that the proposed coastal modifications would expose

Kudahuvadhoo to the following ocean induced hazards.

There could be a rapid onset of erosion in specific areas of the island in the

short-term until the coastal environment achieves an equilibrium. The present

shape of the coastline is a result of the prevailing condition within the reef.

Considerable changes to unaltered zones of the island are highly probable.

Hence, coastal erosion hazards may in general be increased.

• Island topography and resulting drainage systems are critical features of an

island in relation to exposure to natural hazards. Safe island development plan of

Kudahuvadhoo should consider the existing topography and implications of

modifying the topography on the rainfall related flooding. Such activities include

reclamation activities proposed in the southern end of the island.

• Kudahuvadhoo has considerable topographic variations. The proposed new

settlement expansion areas fall into significant low areas of the island which in

the future may be exposed to rainfall related flooding. Similarly, the function of

the low drainage areas in the Environment Protection Zone (EPZ) needs to be

reviewed. Given the topographic variations within Kudahuvadhoo , the proposed

0.1m variation in the drainage area may not have the desired effects on flood

control. In the southern areas where there are multiple ridges, the proposed

drainage area simply may have no function while in the western areas it may

lead to rainfall related flooding unless siltation-proof drainage systems are

installed.

• Based on the 9 islands studies in this project, it has been observed that strong

coastal vegetation is amongst most reliable natural defences of an island at times

of ocean induced flooding, strong winds and against coastal erosion. The design

of EPZ zone needs to be reviewed to consider the important characteristics of

coastal vegetation system that is required to be replicated in the safe island

design. The width of the vegetation belt, the composition and layering of plant

species and vegetation density needs to be specifically looked into, if the desired

outcome from the EPZ is to replicate the coastal vegetation function of a natural

system. Based on our observations, the proposed width of coastal vegetation in

the standard Safe Island Design may not be appropriate for reducing certain

ocean induced hazard exposures. The timing of vegetation establishment also

needs to be clearly identified in the safe island development plan.

3.7 Limitations and recommendations for further study

• The main limitation of this study is the lack of time to undertake more empirical

and detailed assessments of the island. The consequence of the short time limit

is the semi-empirical mode of assessment and the generalised nature of findings.

• The lack of existing survey data on critical characteristics of the island and reef,

such as topography and bathymetry data, and the lack of long term survey data

such as that of wave on current data, limits the amount of empirical assessments

that could be done within the short timeframe.

• The topographic data used in this study shows the variations along two main

roads of the island. Such a limited survey will not capture all the low and high

areas of the island. Hence, the hazard zones identified may be incomplete due to

this limitation.

• This study however is a major contribution to the risk assessment of safe islands.

It has highlighted several leads in risk assessment and areas to concentrate on

future more detailed assessment of safe islands. This study has also highlighted

some of the limitations in existing safe island concept and possible ways to go

about finding solutions to enhance the concept. In this sense, this study is the

foundation for further detailed risk assessment of safe islands.

• There is a time scale mismatch between environmental changes and socio-

economic developments. While we project environmental changes for the next

100 years, the longest period that a detailed socio-economic scenario is credible

is about 10 years.

• Uncertainties in climatic predictions, especially those related Sea Level Rise and

Sea Surface Temperature increases. It is predicted that intensity and frequency

of storms will increase in the India Ocean with the predicted climate change, but

the extent is unclear. The predictions that can be used in this study are

based on specific assumptions which may or may not be realized.

• The following data and assessments need to be included in future detailed

environmental risk assessment of safe islands.

� A topographic and bathymetric survey for all assessment islands prior to

the risk assessment. The survey should be at least at 0.5m resolution for

land and 1.0m in water.

� Coral reef conditions data of the ‘house reef’ including live coral cover,

fish abundance and coral growth rates.

� At least a years data on island coastal processes in selected locations of

Maldives including sediment movement patterns, shoreline changes,

current data and wave data.

� Detailed GIS basemaps for the assessment islands.

� Coastal change, flood risk and climate change risk modeling using GIS.

� Quantitative hydrological impact assessment.

� Coral reef surveys

� Wave run-up modelling on reef flats and on land for gravity waves and

surges.

References

UNDP (2006), Disaster risk profile of Maldives IDPA report IPCC (1990). Strategies for Adaptation to Sea-Level Rise: Report of the Coastal Management Subgroup. Strategies for Adaptation to Sea-Level Rise: Report of the Coastal Management Subgroup. IPCC Response Strategies Working Group. Cambridge, University of Cambridge. IPCC (2001). Climate Change 2001: Impacts, Adaptation, and Vulnerability. Cambridge, United Kingdom and New York, NY, USA, Cambridge University Press. Kench, P. S. and P. J. Cowell (2002). "Erosion of low- lying reef islands." Tiempo 46: 6-12. Kench, P. S., R. F. McLean, et al. (2005). "New model of reef-island evolution: Maldives, Indian Ocean." Geology 33(2): 145-148. Ministry of Planning and National Development (MPND) (2005). Infrastructure Development for Poverty Alleviation, Volume II - L.Gan. Male', Maldives, Ministry of Planning and National Development. Pernetta, J. and G. Sestini (1989). The Maldives and the impact of expected climatic changes. UNEP Regional Seas Reports and Studies No. 104. Nairobi, UNEP. UNEP (2005). Maldives: Post-Tsunami Environmental Assessment, United Nations Environment Programme. United Nations Development Programme (UNDP) (2005). Disaster Risk Profile for Maldives. Male', UNDP and Government of Maldives. Woodroffe, C. D. (1989). Maldives and Sea Level Rise: An Environmental Perspective. Male', Ministry of Planning and Environment: 63.

Woodroffe, C. D. (1993). Morphology and evolution of reef islands in the Maldives. Proceedings of the 7th International Coral Reef Symposium, 1992. Guam, University of Guam Marine Laboratory. 2: 1217-1226. Yamano, H. (2000). Sensitivity of reef flats and reef islands to sea level change. Bali, Indonesia.

4. Structural vulnerability and impacts

4.1 House vulnerability

Not surveyed.

4.2 Houses at risk

As shown in Fig. 4.1 and Fig. 4.2, no houses are exposed to flooding for the time

being. However, the situation will be subjected to a small change in the further

after the establishment of new settlements in the eastern side of the island,

according to a new land use plan updated most recently. Even if it is the case,

the exposure of houses to major flood hazards is very limited. Still no houses are

located in the swell wave / surge flood-prone area and only about 19 houses,

accounting for less than 1% of the total houses, are exposed to tsunami floods.

More houses (more than 20%) are affected by rainfall floods, but damage is very

limited due to the low intensity of rainfall floods (Table 4.1). only the contents of

exposed houses may be subjected to some degree affected. In all, houses on

Kudahuvadhoo Island are at very low risk.

Table 4.1 Houses at risk on Dh. Kudahuvadhoo.

Hazard

type

Exposed

houses

Vulnerable

houses

Potential Damage

Serious Moderate Slight Content

# % # % # % # % # % # %

Flo

od

TS 19 8

W/S 0 0 0 0 0 0 0 0 0 0 0 0

RF 53 22.5

Earthquake 236 100

Wind 236 100

Erosion

Fig. 4.1 Houses at risk associated with Tsunami floods.

Fig. 4.2 Houses at risk associated with rainfall floods (left) and wave / surge floods (right).

4.3 Critical facilities at risk

As shown in Fig. 4.3 and 4.4, critical facilities that are exposed to floods are 2

schools, a mosque, a power house, and a proposed waste disposal site and

waster water treatment plant. Located in the low-lying center of the island, 2

schools and a mosque may be subjected to rainfall floods of very low intensity,

but no physical damage is expected, given the physical conditions at present.

Located in the eastern coast, power house is exposed to ocean-originated floods.

Although no physical damage is expected, its contents may be subjected to

flooding. In addition, two waster processing facilities, proposed to be located in

the southern side of the island, will be subjected to ocean-originated flooding as

well. Flooding of these two facilities may cause secondary contamination to

groundwater system and sewerage system.

In all, critical facilities on Kudahuvadhoo Island are at low risk, although located

in hazard-prone areas. However, some mitigation measures are necessary to

retrofit power house and waste sites or reconsider the location of waste sites.

Table 4.2 Critical facilities at risk on Kudahuvadhoo Island.

Hazard type

Critical facilities Potential damage/loss

Exposed Vulnerable Physical damage Monetary

value

Flo

od

Tsunami Power house, waste

site, boat repair

none Content-affected N/A

Wave/Surge Power house, waste

site, boat repair

none Content-affected N/A

Rainfall 2 schools, 1 mosque none No N/A

Earthquake - - - -

Wind - - - -

Erosion - - - -

Fig. 4.3 Critical facilities at risk associated with rainfall floods.

Fig. 4.4 Critical facilities at risk associated with swell wave/surge and tsunami floods.

4.4 Functioning impacts

Although causing no physical damage to most critical facility buildings, major

flooding events may impact the functioning of critical facilities (Table 5.3). For

example, power house and associated distribution network may fail to operate for

days wave/surge and tsunami flooding; Inundation of the waste disposal site can

cause a secondary contamination to the sensitive groundwater system of the

island, which further affect the supply of potable water supply.School activities

may be interrupted for days by rainfall floods as well.

Table 4.3 Potential functioning impacts

Function Flood

Earthquake Wind Tsunami Wave/surge Rainfall

Administration1)

Health care

Education days

Religion

Housing

Sanitation3)

Secondary contamination

Water supply

Power supply A day

Transportation

Communication2)

Note: 1) Administration including routine community management, police, court, fire fighting; 2) Communication refers to

telecommunication and TV; 3) Sanitation issues caused by failure of sewerage system and waste disposal.

4.5 Recommendations for risk reduction

According to the physical vulnerability and impacts in the previous sections, the

following options are recommended for risk reduction of Kudahuvadhoo:

• Avoid locating proposed waste disposal site and waste water plant

in the flood-prone area;

• Retrofit the power house on the northeastern coast.