Detailed Island Risk Assessment in Maldives
Volume III: Detailed Island Reports
H. dh. Kulhudhuffushi – 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
2 1. Geographic background
1.1 Location
Kulhudhuffushi is located on the eastern rim of Thiladhunmathi Atoll, at approximately 73° 04' 10"E and 6° 37' 24" N, about 276 km from the nations capital Male’ and 19 km from the nearest airport, Hanimaadhoo (Fig. 1.1). Kulhudhuffushi is the Atoll Capital of the administrative atoll Haa Dhaalu, amongst a group of 16 inhabited islands. It’s nearest inhabited islands are Nolhivaramu (4 km), and Kumundhoo (6 km). Kulhudhuffushi is amongst a group of 8 large islands, totalling 18km2, located along the north eastern rim of Thiladhunmathi, making the area one of the dense concentrations of land in Maldives. The island’s location in the northern exposes it to NE monsoon generated winds and waves, and occasional storm activities originating from the cyclone belt of Indian Ocean (UNDP, 2005).
E
E
' ' Baarah
5
0
1
0
°
°
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7
7
6° 45' N Hanimaadhoo (Airport)
South Thiladhunmathi Nolhivaranfaru (Haa Dhaalu Atol)
Nolhivaram
Kulhudhuffushi
Kumundhoo
Neykurendhoo
N 6° 30' N
Location Map Kan'ditheemu of Kulhudhuffushi 0 5 10 North Miladhunmadulu (Shaviyani Atoll) kilometers
Figure 1.1 Location map of Kulhudhuffushi
3 1.2 Physical Environment
Kulhudhuffushi is amongst the largest inhabited islands of Maldives with a length of 2530m and a width of 900 m at its widest point. The total surface area of the island is 195.5 Ha (1.95 km 2) which is almost the same size as the nations capital, Male’. The reef system has a surface area of 366 Ha (3.66 km 2) and the island occupies 54% of the system. The island is located closer to the oceanward reef edge where the distance on average is 70 m compared to the lagooward reef edge average distance of 400 m. The depth of the reef flat is quite shallow averaging less than -1m MSL on the oceanward reef flat and slightly deeper on the lagoonward side. The reef system and the island is oriented in a northwest- southeast direction with approximately 3.5 km of eastern coastline exposed to wave activity from East Indian Ocean.
Thiladhunmathi atoll can be considered a considerably open atoll due to the high proportion of atoll passes compared to the reefs, especially on the eastern rim. The depths within the atoll reach 70 m and have relatively few lagoonal reef systems. As a result waves are allowed to setup within the atoll during SW monsoon, affecting the eastern shoreline of Kulhudhuffushi during SW monsoon. Kulhudhufushi Island originally had about 0.5 km 2 of wetland areas (approximately 25% of the island) both on the northern and southern end of the island. Much of the southern wetland areas and a small proportion of the northern wetland areas have been reclaimed. At present the northern wetland areas comprise of an inland lake surrounded by mangrove vegetation and wetland areas covering 33 ha (0.3 km 2).
Kulhudhuffushi Island has very strong natural defensive system against ocean induced natural hazards along its oceanward coastline. This system is comprised of high ridges reaching +2.5 m MSL and a strong coastal vegetation belt with over 50 m width. The beach composition and geomorphology along the oceanward shoreline suggests that the area is exposed to strong wave energy
4 during NE monsoon or frequent storm activities. The island is generally low with an average elevation of +1.4 m MSL along the surveyed island topographic profiles. There is high coastal ridge extending right across the oceanward shoreline. The height of the ridge is highest along the central and southern shoreline and lowest on the northern shoreline. The vegetation cover on the island is moderate compared to the high population density on the island. Vegetation within the settlement mainly comprise of backyard tress which range from larger varieties such as breadfruit and mango to smaller fruit bearing varieties. A large proportion of the vegetation appears to comprise of introduced species.
Kulhudhuffushi is a highly urbanised settlement with a registered population over 7,500 inhabitants, and is the largest settlement in northern Maldives. The population density over dry land on the island is estimated at 52 persons per hectare. The high level of urbanization and functions of an Atoll Capital has also meant that the natural environment of the island is highly modified to meet the development requirements of the settlement and the atoll. Terrestrial modifications have been undertaken around the entire island, while coastal modifications have mainly been undertaken along the western and southern shoreline. Almost 70% of the western coastline has been modified through land reclamation, harbour development, coastal protection, dredging and quay wall development activities. Large area of wetland areas have so far been reclaimed for housing and are being considered for future reclamation. In contrast, the western coastline is very much in relatively pristine condition. The exceptions are the certain location where the reef area is cleared for recreational swimming. These areas are mostly at the end of major east west roads. There also appears to be a practice of removing the coastal ridge along the main roads, simply for aesthetic reasons. Much of the coastal vegetation has been kept intact and developments have been restricted close to the shoreline, mostly due to physical limitation caused by the geomorphology of the region. Kulhudhuffushi is
5 experiencing a land shortage and more land is expected to be reclaimed in the near future to meet the housing demands.
6 2. Natural hazards
This section provides the assessment of natural hazard exposure in Hdh.Kulhudhuffushi 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 Kulhudhuffushi 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 3.1 below lists the known events and their impacts on the island.
The historic hazardous events for Kulhudhuffushi showed that the island faced the following multiple hazards: 1) flooding caused by heavy rainfall, 2) windstorms, 3) Udha, 4) swell surges, and 5) tsunami. Impacts and frequency of these events vary significantly. Flooding caused by rainfall and windstorm events are the most commonly occurring hazard events. Udha have also been reported as frequent especially during the southwest monsoon but has very little intensity. Swell surges have been reported but very infrequent and as having little impact.
Table 2.1 List of historic hazard events of Kulhudhuffushi Metrological Dates of the Impacts hazard recorded events
Flooding caused Once in every few Flooding caused by heavy rainfall is limited by Heavy rainfall years to a few topographic low points on the island. Heavy rainfalls cause flooding of the houses in these low topographic areas and causes great inconvenience to the
7 people living in these areas. The rain floods have been reported to reach approximately 0.5m in these topographic low areas. The floods were reported to have flooded homes and kitchens which unable people to cook in their kitchens.
Flooding caused 18-20 June 2007 No established records but there are by swell surges No established geomorphic evidence at the coastal zone records that indicates there have been events of severe surges. Elders also report occasional tide surges on to the island although no dates could be determined. One such event was traced to (Bodu Vissaara) of 1955, an event spoken of by the elderly people of the most northern islands. The nation wide flood event of June 2007 destroyed parts of the harbour quay wall and flooded the houses within 40m of coastline.
Windstorms 9 July 19731 A single event was reported by the island 17 June 1975 office that caused severe damages to a 24 May 2005 few houses on the island. The damages included blowing off the roofs of the houses, falling of large trees and destruction to backyard crops. The elders report numerous reports of windstorms which had minor impacts on the structures on the island. No dates could be determined.
Droughts No major event have been reported
Earthquake No major event have been reported
Tsunami 26th Dec 2004 The tsunami of December 2004 flooded the inhabited areas on the western side of the island. The flooding caused by the Tsunami was reported to reach approximately 1m. This event damaged the boundary walls of the houses in the flooded area and damaged a lot of furniture and house hold goods in the flooded houses. The floods also destroyed backyard crops and some larger trees within the flooded areas.
1 Dates in italic were reported in MANIKU, H. A. (1990) Changes in the Topography of Maldives, Male', Forum of Writers on Environment of Maldives.
8 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 Kulhudhuffushi. • Windstorms • Heavy rainfall (flooding) • Swell waves and udha • Storm Surges • Tsunami • Earthquakes • Climate Change
2.2.1 Swell Waves and Udha
Studies on wave patterns 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)). Being located on the eastern rim of Thiladhunmathi Atoll, and on the eastern line of atolls with the archipelago, Kulhudhuffushi is relatively protected from predominant swell waves in the region. However, the island is still exposed to abnormal swell waves originating from intense storms in the southern hemisphere between 73°E and 130°E. Waves generated from such abnormal events could travel against the predominant swell propagation patterns in the Indian Ocean (Goda, 1998), causing flooding on the eastern rim island of Maldives.
9
Estimated wave propagation patterns around Kulhudhuffushi
0 20 40 kilometres
Kulhudhuffushi
s n e
o
SW monsoon v a o
s w
Wind waves n
d o
n sss i
M sss eee
vvveee W vvv E aaa
wwaaa N ll l w w eeellll l wweee sssww EEE sss SSSEEE ll l S SS aaalll rmrmrm ooormrmrm ooonnn bbbooo AAbbb
Funadhoo
SSS WW
S SS Residual Swell waves www eeelll penetrating through llll l ll l W W aaa atoll passes aaavvv vvveee sss
Fig. 2.2 Estimated (predominant) wave propagation patterns around Kulhudhuffushi.
Kulhudhuffushi is also partially exposed to residual swell waves approaching from a south westerly direction. Such waves could penetrate through the wide western reef passes and reach the western shoreline of Kulhudhuffushi. Intensity of so such waves is estimated to be moderate to low due to the partial protection offered by the western rim. However, their impacts should not be discounted as demonstrated by the swell wave event of May 2007, which affected the eastern coastline of Kulhudhuffushi up to 30 m inland and flooded houses with in the region.
The occurrence of abnormal swell waves on Kulhudhuffushi reef flat is dependent on a number of factors such as the wave height, location of the original storm event with in the South Indian Ocean, tide levels and reef
10 geometry. Figure 2.3 below illustrates the estimated wave propagation and behaviour patterns around Kulhudhuffushi. The orientation of the island in a N to S direction could facilitate wave run-up on the island from oceanward side, especially the southern side. Similarly the presence of a channel north of the island may cause waves to refract around the island and flood along the northeastern shoreline.
N
S
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R T S E S W S I E D L U L A ES W L V A A S W V W L E L S E SW L A M R NO B A SE
PREDICTED LOCALISED WAVE EXPOSURE REGIMES AROUND KULHUDHUFFUSHI
01,000 2,000 meters
Figure 2.3 Estimated behaviour of swell waves around Kulhudhuffushi.
It is often difficult to predict occurrence of such abnormal events as there is only a small probability, even within storm events of similar magnitude, to produce waves capable of flooding islands. Moreover, based on the current data available it is impossible to link the swell incidents to the known cyclonic events in the Indian Ocean. Detailed assessment using synoptic charts of the South Indian Ocean corresponding to major flooding events are required to delineate any specific trends and exposure thresholds for Kulhudhuffushi from southern swells.
11 Unfortunately this study does not have the resources and time to undertake such an assessment but is strongly recommended for any future detailed assessments. Unlike the swell waves, both the oceanward and lagoonward coastlines of Kulhudhuffushi are exposed to monsoonal wind waves. During the NE monsoon between November and March, the eastern (oceanward) coastline may receive strong waves. Wave studies done in similar settings have reported wave heights less than 2.0m and with wave periods of 2-4 seconds in the eastern side. The west coast is exposed to wind generated waves during SW monsoon, originating within the atoll lagoon. It is also likely that monsoonal wind waves originating in the open ocean may propagate through the wide reef passes and fuel the waves generated within the atoll lagoon. Wave heights are predicted to be less than 0.5 m.
Udha
Flooding is also known to be caused in Kulhudhuffushi 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 5-10m of coastline at less than 0.3 m height above the ground. It is not expected to be a high intensity hazard in the short-term.
The origins of the udha waves as yet remain scientifically unproven. 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
12 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. However, the strongest mean wind speeds in Hanimaadhoo has been observed for May, June and July (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 Kulhudhuffushi was located in a moderate storm surge hazard zone with probable maximum event reaching 0.6 m above MSL or 1.53 m with a storm tide. The combined historical records of nearby islands report major storms in the past which have caused extensive damages to inhabited island and changes to coastal features. The most notable events were reported as December 1918 and January 1955 events, which caused extensive damages and flooding in the northern region of Maldives. In fact the event of 1918 was named after the neighbouring Keylakunu Island, due to the extensive destruction it caused on the island. Keylakunu was an inhabited island during the event but had to be abandoned following the incident. Furthermore, there is geophysical evidence on the eastern coastline of Kulhudhuffushi and nearby islands that points significant wave events, most likely caused by a single or a series of storm surges. The location of Kulhudhuffushi in the northern half of Maldives and close to the northern Indian Ocean cyclone belt further increases the probability of surge events.
13 Similar to the swell waves, the occurrence of any storm surge on Kulhudhuffushi 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, abnormal swell related flooding events should be considered a serious hazard for Kulhudhuffushi. The island is expected to be exposed to storm waves mainly from south and south east as shown in the map below. Events beyond this arch may not influence the island due to the protection offered by surrounding atolls.
Possible range of swell wave direction in K.Thulusdhoo: SE to S
Historic storm events 1945 - 2007
Figure 2.4 Historical storm tracks (1945-2007) in Indian Ocean and possible direction of swell waves for Kulhudhuffushi Island
Due to the unpredictability of these swell events and lack of research into their impacts on Maldives, right now it is impossible to forecast the probability of swell
14 hazard event and their intensities. Assessment in Kulhudhuffushi 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 10 years with probable water heights above 0.6 m and every 5 years with probable water heights of 0.3 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 probability of storm surges occurring in Kulhudhuffushi is low but should be considered to belong to the group of islands most exposed to storm surges in Maldives. Figure 2.5 shows storm tracts in the regions and potential storm surge direction for Kulhudhuffushi.
15 INDIA
SRILANKA
Kulhudhuffushi
Funadhoo
Storm Tracks 1945-2007 Potential storm surge direction (larger triangles represent stronger surges for eastern islands)
Figure 2.5 Historical storm tracks (1945-2007) in Indian Ocean and possible direction of storm surges for Kulhudhuffushi Island.
The reclamation plans for Kulhudhuffushi were incomplete at the time of this study. The existing drafts show land reclamation on the western half of the island. After this development the reef flat width will be reduced to approximately 100m. However, since the reclamation is on the atoll lagoonward side and since appropriate coastal protection is planned for the new reclamation, the activities are unlikely to increase the occurrence of swell or udha related flooding.
Potential increase in frequency and intensity of flood events are 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
16 data from the three main meteorological stations (Fig. 2.6), HDh Hanimaadhoo, K. Hulhule and S Gan shows an increasing average rainfall from the northern regions to the southern regions of the country. The average rainfall at HDh Hanimadhoo is approximately 481 mm lower than that at S Gan.
3500
3000
2500
2000
1500
1000
Meanannual rainfall (mm) 500
0 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 Year
Gan Hulhule Hanimadhoo
Fig. 2.6 Map showing the mean annual rainfall across the Maldives archipelago.
The closest meteorological station is the Hanimadhoo Meterological Centre located 15 km north of Funadho . Unfortunately this study does not have access to daily data for Hanimaadhoo.
The mean annual rainfall in Hanimaadhoo is 1818.7 mm with a Standard Deviation of 316.4mm and the mean monthly rainfall is 151.5 mm. Rainfall varies throughout the year with mean highest rainfall during May to August and lowest between January to March (See Figure 2.7).
17
Fig. 2.7 Mean Monthly Rainfall in Hanimaadhoo (1992 to 2004).
Historic records of rainfall related flooding on the island of Kulhudhuffushi indicates that this island is often flooded and its intensity is comparatively high around present and reclaimed wetland areas. The overall intensity is usually moderate to low especially in most of the inhabited 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 the above mentioned sections of the island. Substantial topographic variations exist within the island, as is common on larger islands of Maldives. Heavy rainfall related flooding has been reported to reach up to 0.3m above the ground level in north and southern parts of the island which correspond to existing and reclaimed wetland areas.
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. Of particular importance is the location of Northern Secondary School in a flood prone location.
18 It would be possible to identify threshold levels for heavy rainfall for a single day that could cause flooding in Kulhudhuffushi, through observation of historic daily rainfall data. Unfortunately, we were unable to acquire complete daily historical data from Hanimaadhoo. Available limited severe weather reports published on the Department of Meteorology website is summarised below in Table 2.3. The values shows that Hanimaadhoo received a maximum precipitation of 95mm for a 24 hour period, between 2001 and 2007, on 23 July 2007 (DoM, 2005). Based on interviews with locals almost all these events had some form of impact on the island. However, they particularly highlighted the high intensity of 2001, 2002 and 2007 events, all of which had over 80mm for a 24 hour period. There may be minor discrepancies between recorded rainfall in Hanimaadhoo and actual rainfall in Kulhudhuffushi but is unlikely to vary substantially. Impacts from the reported events include flooding around existing northern wetlands and reclaimed southern wetland areas. School and houses located close to the wetland experienced flooding and disruption in school activities. Similarly some houses in southern half experienced flooding with damages to household and required evacuation. Businesses and daily activities on the island were also disrupted due flooding on roads.
Table 2.3 Maximum precipitation for 24 hour periods between 2001 and 2007 at Hanimaadhoo Weather Station. Year Maximum Rainfall (mm) Date 2001 89.4 13 may 2002 81.0 31 July 2003 72.9 12 June 2004 79.0 2 May 2005 62.9 29 May 2006 71.0 8 September 2007 95.0 23 July
The probable maximum precipitations predicted for Hanimaadhoo by UNDP (2006) are shown in Table 2.4.
19 Table 2.4 Probable Maximum Precipitation for various Return periods in Hanimaadhoo Weather Station. Return Period Station 50 year 100 year 200 year 500 year Hanimaadhoo 141.5 151.8 162.1 175.6
Based on the field observations and correlations with severe weather reports from Department of Meteorology the following threshold levels were identified for flooding. These figures must be revised once historical daily rainfall data becomes available.
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 Table 2.6.
Table 2.6 Threshold levels for rainfall related flooding in Kulhudhuffushi Threshold level Impact (daily rainfall) 50mm Puddles on road, flooding in low houses, minor damage to household goods in most vulnerable locations, disruption to businesses and schools in low areas; stadium unusable for over 24 hours. 100mm Moderate flooding in low houses; all low lying roads flooded; moderate damage to household items especially in the backyard areas; school closure 150mm Widespread flooding on roads and low lying houses. Moderate to major damage to household goods, School closure. 200mm Widespread flooding on roads and houses. Major damages to household goods, sewerage network, backyard crops, school closure, gullies created along shoreline, possible damage to road infrastructure. 250+mm Widespread flooding around the island. Major damages to household goods and housing structure, schools closed, businesses closed, damage to crops, damage to road infrastructure, sewerage network and quay wall.
2.2.3 Wind storms and cyclones
20 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 (UNDP, 2006). However, Kulhudhuffushi falls within the most hazardous zone for cyclone related hazards in Maldives and has a maximum predicted cyclonic wind speeds of 96.8 Kts (see Figure 2.8). There are no records of such high wind intensity resulting from a cyclone for the northern region in the recent past, although a number of gale force winds have been recorded due to low depressions and South west monsoon in the region. Winds exceeding 35 knots (gale to strong gale winds) were common occurrences during south west monsoon over the last 7 years. In general the wind speeds are higher in the north than the central and southern areas during SW monsoon (DoM, 2005). Peak wind speeds in Hanimaadhoo between 2006 and 2007 showed 10 events above gale to strong gale winds (above 35 Knots) and within them 6 events were above 40 knots. During the past 7 years the highest peak wind speed was recorded as 46 knots on 21 June 2007. In addition historical records show that the northern region was hit by a number of major storms which combined high wind speeds, heavy rainfall and strong seas. As noted above, the most significant two events occurred during 1918 and 1955 both which led to extensive damage and abandonment of a number of inhabited islands.
Moreover, 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 events of 22 June 2003, 12 July 2003, 22 June 2006 and 21 June 2007 have been reported to have caused moderate to extensive damage to crops, vegetation and housing structures. All these events had wind speeds over 40 knots.
21 Kulhudhufushi Fonadhoo
Thulusdhoo
Kudahuvadhoo Vilufushi Gan
probable maximum Hazard Zones cyclone wind speed (kts) Villingili 5 96.8 Thinadhoo 4 84.2 3 69.6 2 55.9 Hithadhoo Feydhoo 1 0.0
Fig. 2.8 Cyclone hazard zones of the Maldives as defined by UNDP (2006).
Hence, wind speeds close to near gale winds (see Table 2.8) have caused moderate damage to property and trees on the island. Kulhudhuffushi now have sparse vegetation cover, resulting primarily from settlement expansion related clearing. Moreover, the remaining large trees within the settlement contain a large proportion of wind vulnerable species, especially breadfruit trees (Artocarpus altilis).
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 2.8 Beaufort scale and the categorisation of wind speeds.
22 Average wind Cyclone Average wind speed Beau- fort No Description Specifications for estimating speed over land category speed (Knots) (kilometres per hour)
0 Calm Less than 1 less than 1 Calm, smoke rises vertically. Direction of wind shown by smoke drift, but not by wind 1 Light Air 1 -3 1 - 5 vanes. Wind felt on face; leaves rustle; ordinary wind vane moved 2 Light breeze 4 - 6 6 - 11 by wind. Leaves and small twigs in constant motion; wind extends 3 Gentle breeze 7 - 10 12 - 19 light flag. Moderate 4 breeze 11 - 16 20 - 28 Raises dust and loose paper; small branches moved. Small trees in leaf begin to sway; crested wavelets form on 5 Fresh breeze 17 -21 29 - 38 inland waters. Large branches in motion; whistling heard in telegraph 6 Strong breeze 22 - 27 39 - 49 wires; umbrellas used with difficulty. Whole trees in motion; inconvenience felt when walking 7 Near gale 28 - 33 50 - 61 against the wind.
8 Gale Category 1 34 - 40 62 - 74 Breaks twigs off trees; generally impedes progress. Slight structural damage occurs (chimney pots and slates 9 Strong gale Category 1 41 - 47 75 - 88 removed). Seldom experienced inland; trees uprooted; considerable 10 Storm Category 2 48 - 55 89 - 102 structural damage occurs. Very rarely experienced; accompanied by widespread 11 Violent storm Category 2 56 - 63 103 - 117 damage. 12 Hurricane Category 3,4,5 64 and over 118 and over Severe and extensive damage.
The threshold levels for damage (Table 2.9) are predicted based on interviews with locals and housing structural assessments provided by risk assessment report (UNDP, 2006). Table 2.9 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 Kulhudhufushi is geographically located to be a high tsunami hazard zone. However the impact of tsunami of December
23 2004 on Kulhudhufushi was limited to a relatively small area of the island. The relatively limited flooding caused by the tsunami of December 2004 is believed to be a result of the high coastal ridge system formed on the oceanward side of the island. The nearest tide gauge at Hanimaadhoo Airport recorded the tsunami of December 2004 as a wave of height 2.5 m within the atoll lagoon (Fig. 2). The maximum water level recorded at Hanimaadhoo tide gauge (1.83m +MSL) indicated the rise in water level induced by the tsunami within the atoll lagoon of the northern atolls. Flooding from the western side of Kulhudhufushi was caused by the refracted wave that rapped around the island and thus flooding the island along lowest parts of the western coastline.
UNDP (2006) reported the region where Kulhudhuffushi is geographically located to be a very high tsunami hazard zone. According to official reports 20% of the island was flooded during the 2004 tsunami. Flooding occurred mainly from the southern and western side and penetrated more than 200 m inland. Flood waters only approached from the lagoonward side due to refraction and the tsunami related tide surge. The relatively limited flooding during December 2004 tsunami is attributed to the high coastal ridge system on the oceanward side of the island, which prevent run-up on the island. As a result, the event did not have a major impact on Kulhudhuffushi.
The nearest tide gauge at Hanimaadhoo Airport recorded the tsunami of December 2004 as a wave of height 2.5 m within the atoll lagoon (Fig. 2.9). The maximum water level recorded at Hanimaadhoo tide gauge (1.83 m +MSL) indicated the rise in water level induced by the tsunami within the atoll lagoon of the northern atolls.
24 200
150
100
50
0
-50
-100 0 100 200 300 400 500 600 700 800 900 1000 1100 Elapsed time (min) since 00:00hrs (UTC) of 26-12-2004
Fig. 2.9 Water level recordings from the tide gauge at Hanimaadhoo indicating the wave height of tsunami 2004.
The December 2004 event caused limited structural damages close to the western coastline including damage break water, quay wall and house damages. Further damages include loss of personal property, backyard crops, damage to vegetation, salinisation of groundwater for a week, partial damage to sewerage network and business establishments.
The tsunami run-up height on the western and southern shoreline was reported at 1.0 m reducing to 0.1 m around 200-250 m inland. Figure 2.10 and 2.11 below shows topographic profiles across east-west and north-south. Tide related flood waters failed to reach beyond the high oceanward coastal ridges while they managed to flood parts of western and southern coastline.
25 m 5 P4
4 P2 Tsunami Induced tide level Extent of Flooding P3 at the nearest tide station P1 3 (December 2004 tsunami) N
2
1
-0 0 100 200 300 400 500 600 700 800 900
-1 Oceanward Side Lagoonward Side (east) (west)
Fig. 2.10 Maximum water level within the atoll lagoon induced by tsunami of December 2004 plotted across Kulhudhuffushi’s east-west topographic profile.
P4 P2 P3 P1
N m 4 Tsunami Induced tide level at the nearest tide station 3 Extent of Flooding (December 2004 tsunami)
2
1
0 500 1000 1500 2000 SOUTH NORTH -1
Fig. 2.11 Maximum water level within the atoll lagoon induced by tsunami of December 2004 plotted across Kulhudhuffushi’s east-west topographic.
The predicted probable maximum tsunami wave height for the area where Kulhudhuffushi is located is 4.5 m (UNDP, 2006). Examination of the flooding that will be caused by a wave run-up of 4.5 m for the island indicates that such a magnitude wave will flood at least 300- 400m inland from the oceanward shoreline. The first 50 – 100 m from the shoreline will be a severely destructive zone (Fig. 2.12). The theoretical tsunami flood decay curve was plotted for a wave that is applied only for the direct wave from the oceanward side of the island. However, it 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. Rising
26 of water level in the atoll lagoon would also cause flooding of the island from the lagoonward side of the island, if the atoll lagoon water level rises above the height of the island. Hence the entire island is predicted to be flooded with a maximum predicted tsunami.
The coastal ridge on the oceanward side of the island acts as a barrier against abnormal wave events and is expected mitigate the impacts of tsunamis below 3.0 m height. Furthermore impacts from very high intensity tsunamis up to 4.5 m will be drastically reduced, although not eliminated.
m 5 P4 Extent of most P2 P3
destructive zone P1
4 N
3
2
1
-0 0 100 200 300 400 500 600 700 800 900 Oceanward Side -1 Lagoonward Side
Fig. 2.12 Tsunami related flooding predicted for Funadhoo based upon theoretical flood decay curve and the maximum probable tsunami wave height.
2.2.5 Earthquakes
There hasn’t been any major earthquake related incident recorded in the history of Kulhudhuffshi 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 Male’ 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
27 the zone 1 in which Kulhudhuffshi is located has a value less than 0.04 for a 475 years return period (see Table 2.10). PGA values provided in the report have been converted to Modified Mercalli Intensity (MMI) scale (see column ‘MMI’ in table 3.9 table below). The MMI is a measure of the local damage potential of the earthquake. See Table 2.11 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 Kulhudhuffshi Island as time was limited for such a detailed assessment. Instead, the findings of UNDP (2006) were used.
According to these findings it is unlikely that Kulhudhuffshi 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.
Table 2.10 Probable maximum PGA values in each seismic hazard zone of Maldives (modified from UNDP, 2006). Seismic hazard PGA values for 475yrs return MMI2 zone period 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 2.11 Modified Mercalli Intensity description (Richter, 1958). MMI Shaking Description of Damage Value Severity 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.
2 Based on KATZFEY, J. J. & MCINNES, K. L. (1996) GCM simulation of eastern Australian cutoff lows. Journal of Climate , 2337-2355.
28 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 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 - Light to total destruction Catastrophe
. 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) analysis of tidal data for Hulhule’, Male’ Atoll shows the overall trend of Mean Tidal Level (MTL) is increasing in the southern atolls of Maldives. Their analysis
29 shows an increasing annual MTL at Hulhule’ of 4.1 mm/year. These findings have also been backed by a slightly higher increase reported for Diego Garcia south of Addu Atoll (Sheppard, 2002). Moreover, IPCC (2001) predict a likely acceleration as time passes. Hence, this indicates that the MTL at Hulhule’ by 2100 will be nearly 0.5m above the present day MTL.
Similarly, Khan et al. (2002) reported air temperature at Male’ Atoll is expected to rise at a rate of 0.5°C per year, while the rate of rise in SST is 1.1°C.
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 Kulhudhuffushi 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 (Fig 2.13).
30 12
10
8
6 Rate of increase = 0.135% per year 4
2
Increase of precipitation (%) 0 2010 2020 2030 2040 2050 2060 2070 2080 2090 Year
Fig. 2.13 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 Kulhudhuffushi 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 Kulhudhuffushi and surrounding region is summarised below. 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.
31 Table 2.12 Summary of climate change related parameters for various hazards. Element Predicted Predicted change (overall rise) Possible impacts on rate of Best Case Worst Case Hazards in change Kulhudhuffushi SLR 4.1-5.0mm Yr 2050: Yr 2050: +0.4m Tidal flooding, increase /yr +0.2m Yr 2100: +0.88m in swell wave flooding, Yr 2100: reef drowning +0.4m Air Temp 0.5°C / Yr 2050: decade +2.15° Yr 2100: +4.65° SST 1.1°C / Yr 2050: Increase in storm decade +4.73° surges and swell wave Yr 2100: related flooding, Coral +10.3° bleaching & reduction in coral defences Rainfall +0.14% / Yr 2050: Increased flooding, yr (or +1204mm Could affect coral reef +28mm/yr) Yr 2100: growth +2604mm Wind gusts 5% and Yr 2050: +3.8 Yr 2050: Increased windstorms, 10% / Knots +7.7Knots Increase in swell wave degree of Yr 2100: +8.3 Yr 2100: +16.7 related flooding. warming Knots Knots Swell Frequency Increase in swell wave Waves expected related flooding. to change. Wave height in reef expected to be high
2.3 Event Scenarios
Based on the discussion in section 2.2 above, the following event scenarios have been estimated for Kulhudhuffushi Island (Tables 2.13, 2.14, 2.15).
Table 2.13 Rapid onset flooding hazards. Hazard Max Impact thresholds Probability of Occurrence Prediction Low Moderat Sever Low Moderate Severe e e Impact Impact Impact Swell Waves NA < > 2.3m > High Moderate Low (wave heights 2.3m 3.0m on reef flat –
32 Average Island ridge height +2.0m above reef flat; barrier island ridge is 2.3m) Tsunami 4.5m < > 2.5m > Moder Low Very (wave heights 2.5m 3.0m ate low on reef flat) SW monsoon 0.5m < > 2.5m > High Very low Unlikel high seas 2.5m 3.0m y
Heavy Rainfall 241mm <60m > 60mm >150 High Moderate Low (For a 24 hour m mm period)
Table 2.14 Slow onset flooding hazards (medium term scenario – year 2050) Hazard Impact thresholds Probability of Occurrence Low Moderate Severe Low Moderate Severe SLR: Tidal < 2.5m > 2.5m > 3.0m Moderate Very Low Very Flooding Low SLR: Swell < 2.5m > 2.5m > 3.0m Very high Moderate Low Waves SLR: Heavy <60mm >60mm >150mm Very Moderate Low Rainfall High
Table 2.14 Other rapid onset events. Hazard Max Impact thresholds Probability of Occurrence Prediction Low Moderate Severe Low Moderate Severe Wind storm NA <30 > 30 knts > Very High Moderate knts 45Knts High Earthquake I < IV > IV > VI Very Unlikely none (MMI Low value3)
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
3 Refer to earthquake section above
33 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 wave, storm surges and SW monsoon high waves
The intensity of swell waves is predicted to be highest along southern, northern and eastern coastline (see Fig. 2.14). Severe events could cause flooding up to 450m inland along southern coastline with high intensities along the first 100m. Flood run up would be facilitated by the low topography in the region owing to lowly reclaimed wetlands. Such an impact is only possible of the origin of the storm lies in a south to easterly direction from the island.
Severe flooding could also occur along the northern coastline especially during a storm surge. The relatively lower ridge combined with a downward sloping topography towards the wetland area could facilitate water run-up. At present no housing structures are planned but economic activities are planned in the zone.
The western coastline is particularly exposed to abnormal swell waves approaching from the south west of South Indian Ocean. Waves could penetrate through the open reef passes along the western rim and cause flooding. Wave height could reach 1.0-1.5 m during severe events and could penetrate 300m inland. The high intensity zone is predicted to be the first 50-100 m.
The eastern shoreline fairly protected from abnormal wave activity due to the geophysical characteristics of the ocean ward ridge. The ridges are capable of mitigating wave events up to 2.5 m above MSL. Impacts in this zone are
34 expected to be limited to 100 m with the first 10-30 m being the high intensity zone.
SW monsoon udha events are expected to have limited impact on the island and are predicted to be confined to 10-50 m from the eastern and southern coastline. .
Hazard Zoning Map Swell waves, Storm surge and Udha
Intensity Index
Low 1 2 3 4 5 High Contour lines represent intensity index based on severe event scenarios
0 300 600 meters
Figure 2.14 Hazard zoning map for swell wave, storm surges and southwest monsoon high seas.
35 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 flooded. If the waves reach beyond 4.0 m MSL 90% of the island is highly 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 lagoon, flooding from the western shoreline. The intensity of flood waters will be highest 100-150 m from the shoreline.
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.
The presence of high ridges on the eastern side will control much of the energy from a severe tsunami but may not entirely prevent flooding. The northern and southern ends of the island are more exposed to tsunamis.
36 Hazard Zoning Map Tsunami
Intensity Index
Low 1 2 3 4 5 High Contour lines represent intensity index based on severe event scenarios
0 300 600 meters
Figure 2.15 Hazard zoning map for tsunami flooding.
2.4.3 Heavy Rainfall
Heavy rainfall above the severe threshold is expected to flood low lying area of the settlement. Low areas in the north are located around the exiting wetland area and low areas in the south are located on reclaimed wetland areas. Areas adjacent to the high ridges and harbour are also exposed to flooding due to the topographic low and existing drainage system. The areas predicted for severe
37 intensity are mostly located outside the existing settlement footprint. However, reclaimed areas in the south are particularly exposed severe impacts.
Hazard Zoning Map Heavy Rainfall
Intensity Index
Low 1 2 3 4 5 High Contour lines represent intensity index based on severe event scenarios
0 300 600 meters
Fig. 2.16 Hazard zoning map for heavy rainfall related flooding.
The intensity is generally expected to be low in most locations with floods reaching between 0.3-0.5m in the southern and northern ends.
38 The hazard zone presented in the map below is based on limited 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.
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. Given the intensity of historic storm events in the region there is a real risk of severe damage during such an event. 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.
3.4.6 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.
2.4.7 Composite Hazard Zones
39 A composite hazard zone map was produced using a GIS based on the above hazard zoning and intensity index. The coastal zone approximately 150 m from the oceanward coastline, 100 m from the lagoonward coastline and the topographic lows 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 and tsunamis.
Hazard Zoning Map Tsunami
Intensity Index
Low 1 2 3 4 5 High Contour lines represent intensity index based on severe event scenarios
0 300 600 meters
Fig. 2.17 Composite hazard zone map.
40 2.5 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 carry out 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 at least 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.
41
The meteorological records in Maldives are based on 5 major stations and not at atoll level or island level. Hence all hazard predictions for Kulhudhuffushi 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 Kulhudhuffushi.
REFERENCES
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,
42 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., 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.
43 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.
44 3. Environment Vulnerabilities and Impacts
3.1 Environment Settings
3.1.1 Terrestrial Environment
Topography
The topography of Kulhudhuffushi was assessed using 3 island profiles (see Figure 3.1). Given below are the general findings from this assessment.
P2 0 300 600 meters
TOPOGRAPHIC SURVEY PROFILES
6.62803°N
P1
6.61904°N
P4
P3 3 0632°E73. 73.0813°E
Figure 3.1 Topographic survey locations of Kulhudhuffushi.
45 Kulhudhuffushi has one of the highest elevations in Maldives along its eastern shoreline (see Figures 3.2, 3.3, and 3.4). The ridge system which is believed to be a response to high wave and wind energy in the area reaches to +2.6 m MSL along the surveyed lines. The average height of the ridge system is estimated at +2.4 m MSL and the average width is estimated at 50m. The height of the ridge decreases northwards and is estimated to be around +1.6-2.0 m. The ridge system stands out prominently in the island section profile and is +1.2 m higher than the average elevation of the island.
Oceanward End of Beach Ridge ridge rock (+2.6m) system
Main Road (+1.3m) Harbour Quay wall
G R o a d l e v e l l e d G’
1m
0 Approximate Mean Sea Level Oceanward Side Lagoonward Side
0 100 200 300 400 500 600 700 800 900
Figure 3.2 Topographic profile P1.
Elevation (+0.8m) P2 Modified Elevation Modified P3
P1 Oceanward Oceanward High area (+1.4m) Edge Reclaimed Ridge Main Road Ridge in original wetland (+1.3m) original road (Construction wetland (+0.8m) (+1.6m) Debris) +1.2m
1m
Wetland Wetland Wetland 0 SOUTH Approximate Mean Sea Level NORTH
0 500 1000 1500 2000 2250m
Figure 3.3 Topographic profile P2.
46 Oceanward P4
Ridge End of P2 (+2.7m) ridge P3
Beach P1 system Very low area rock N (water table at 0.1m at high tide)
1m
0
0 20 40 60 80 100 120 140 160 180 200
Figure 3.4 Topographic profile P3.
Apart from the coastal ridge, the island is generally low lying with an average elevation of +1.4 m MSL along the surveyed island profiles (see Figures 3.2-4). This finding was reconfirmed from shallow depths of ground water lens around the island and considerably deeper depths along the ridge. The actual topographic measurements may have an error of +0.1-0.3 along the main roads as the roads have been raised as part of road maintenance. The lowest elevation on dry land (+0.8 m) is found along the newly reclaimed areas of the south which (see Figure 3.3). The reclaimed areas along the wetlands were found to be -0.4 m lower than the natural island elevation causing drainage into these zones and potential flooding.
There are two major low areas on the island: the inland lakes and wetlands in the north and reclaimed wetland areas in the south (see Figure 3.3 and 3.5). These areas appears to have a major influence on the drainage system of the island and this pattern is further enhanced since the eastern side of the island is substantially higher the western side. The fact that the original wetland areas were reclaimed at a lower elevation than the surrounding land causes water runoff into these zones during heavy rainfall and eventually leads to flooding.
47 73.0632°E 73.0813°E
6.62803°N
6.61904°N
Reclaimed Wetland Reclaimed Reef
Figure 3.5 Predicted drainage patterns.
Vegetation
The vegetation cover in Kulhudhuffushi Island is high compared to islands with similar population densities. Figure 3.6 shows the dominant patterns in vegetation distribution. Much of the vegetation in the settlement area is located within the backyard and comprises of fruit bearing or ‘shade’ trees such as mango and breadfruit. The settlement area of the island is sparsely vegetated.
48 The northern wetland area is surrounded by a healthy stretch of mangrove vegetation. Much of this vegetation is located inland surrounding the lake. The rest of the area around the wetland region is dominated by low vegetation species which are more representative of coastal vegetation.
The coastal vegetation around the island, apart from the modified eastern shoreline is very dense and mostly in their natural state. On average the coastal vegetation belt is 70m wide with some areas reaching over 80-120m. All in all, the coastal vegetation system is healthy and functioning well compared to most other inhabited islands with similar population densities. However, certain parts of the vegetation system close to the settlement have had their undergrowth removed for aesthetic reasons and only larger trees such as coconut palms remain. Coastal vegetation clearing is most prominent at the end of the roads where vegetation is cleared more for aesthetic than functional reasons.
49 0 300 600 meters
Vegetation Distribution
6.62803°N Mangroves Strong Coastal Larger trees Low coastal
6.61904°N 3 0632°E73. 73.0813°E
Figure 3.6 Distribution of Vegetation.
The low coastal vegetation on the southeast corner of the island has some peculiar characteristics. The area doesn’t seem to accommodate growth of the usual coastal vegetation species and neither does it have any natural growth of larger trees. The dominant vegetation in the area was found to be a grass species. According to the islanders, it was mainly due to natural causes than human interference. It is unclear what causes this, but observation of historical aerial photographs confirms the information given by the inhabitants. Furthermore, on close observation of the geomorphology of the area, it was observed that the area had thick layer of large coral conglomerates and a very thin layer of fine sediments. It was also observed that the area contained a
50 stratum of consolidated corals (similar to beach rock), at about 1m below ground level. The area has not been considered for agricultural activity or even housing due these geomorphologic characteristics.
The vegetation cover on the island is predicted to decline due to the high demand for land. So far the authorities have resisted giving plots closer to the western shoreline, but the latest plot allocation suggests that these areas may also be considered. Hence, there is a possibility that the exiting strong coastal vegetation strip may be reduced in the future.
Ground Water and Soil
Kulhudhuffushi Island has a substantial layer of fresh water (MoFT, 1999). Water lens depth varies across the island based on topography. Generally the water table could be reached with less than 1.3m at median tide in all areas other than the ridge system. This could decrease to 0.7 m during spring high tides or more during heavy rainfall, especially in reclaimed wetland areas.
Kulhudhuffushi’s ground water was reported to be in generally good condition although traces of contamination were reported in some parts of the island due to the sewerage disposal methods (MoFT, 1999). There were reported occasional shortages of potable water in the past due to ground water contamination and relatively low rainfall in some periods.
The soil conditions were not assessed across the island due to time limitation. Kulhudhuffushi is expected to have comparatively good soil due to vast size of the island and the general low elevation of the island. The reclaimed wetland areas do not seem to be particularly fertile compared to similar reclamations in Seenu Hithadhoo and Gaafu Alifu Viligilli. It seemed the conditions were similar to that of Gaafu Dhaalu Thinadhoo, where natural vegetation growth was minimal. In both Thinadhoo and Kulhudhuffushi, reclamation of wetlands was done using
51 heavy machinery and using dredge material from the lagoon while reclamation of wetlands in Viligilli and Hithadhoo were undertaken manually in an adhoc basis. Hence, it is highly likely that the former method retains the effects of salt in the soil for a longer period.
3.1.2 Coastal Environment
General environment
The coastal environment of Kulhudhuffushi has contrasting characteristics on its eastern and western shoreline. Figure 3.7 summarises these coastal characteristics. The western shoreline, which is less exposed to natural hazards, has been largely modified by development activities. The coastal processes on the eastern shoreline, especially the south-western, end no longer functions properly due to obstructions such as sand pier, coastal protection and dredging activities. The eastern shoreline on the other hand is very much in its natural state with a functioning coastal system.
52 73.0813°E 73.0632°E
Weak coastal vegetation Severe erosion Lower ridges (<2.0m) Vegetation cleared in the past and and redige modified only 5m wide beach seperates mangrove %%%%%% from lagoon %% Narrow (70m) & shallow reef flat (<1.0m)
6.62803°N Extensive beach rock areas %%%%%% Strong Coastal Vegetation (width 90m) High ridges (+2.6m) %%%%%%%
Major coastal Ridge modified modifications for aesthetic 6.61904°N reasons %%%%%%
Extensive beach rock areas Weak coastal vegetation Higher ridges (+2.6m)
Narrow stretch %%%%%%% of coastal vegetation remain 0 300 600 meters Coastal Features
Figure 3.7 Main coastal characteristics of Kulhudhuffushi.
The eastern coastline has one of the most well established defence systems against sea induced natural hazards. The +2.5 m high ridges have been developed over time due to strong wind and very high wave energy, which could be either due to strong wind generated waves during northeast monsoons or storm activities in the region. The fact that the other neighbouring islands such as Nolhivaramu, Nolhivaranfaru and Kumundhoo has similar high ridge systems on
53 the eastern shoreline, supports the assumption that the ridge formation is associated with storm and wave activity in the region.
The beach composition on the island generally varies from north to south along the eastern shoreline. The northern half, especially the northeast corner is characterised by coarser sediments while the central areas had comparatively higher proportion of finer sediments. Similar trends were also observed towards south west corner of the island. This pattern usually indicates two natural processes: 1) the areas are exposed to strong wave energy from severe storm activity or wind generated waves, and 2) the coral decomposing organisms in the area are low. Judging from the geomorphic features such as ridges, it is very likely that the area is both exposed to strong wave energy and lacks decomposing organisms.
The high ridges along with the strong coastal vegetation belt form the natural defensive system of the island against future sea induced flooding events.
Beach and Beach Erosion
Erosion and accretion in Maldivian coral islands is a natural process which is largely dictated by natural forces, especially prevailing climatic conditions. Erosion in Maldives is generally caused by natural and human alterations to coastal processes, which may be either seasonal, cyclic or long term changes (Kench 2001). Impacts of human alterations are more prominent in inhabited islands where coastal modifications have been undertaken (Kench, Parnell et al. 2003).
Kulhudhuffushi has undergone significant coastal erosion over the last 40 years (see figure 8). Between 1969 and 2004, it was estimated that about 8 ha of land was lost to erosion while 5 ha of new land was added through accretion. Much of the erosion took place on the northwest corner of the island near the wetland
54 area. During 1969 a 150m buffer existed between the wetland area and the shoreline. By 2004 the distance was reduced to a mere 5m which forms a narrow strip between the inland lake and the lagoon (see Figure 3.8). It is highly unlikely that this strip would be breached naturally, and even if it does, it is highly unlikely that the area will remain open for long due to the deposition patterns in the region. In general, it appears that the eastern shoreline undergoes seasonal and periodic erosion cycles. Large stretches of coastline showed evidence of past erosion due to the presence of beach berms, exposed roots of vegetation and beach rock. Erosion in one area is associated with proportional accretion along another part of the coastline. During field observations, the northern areas along the eastern shoreline were seen to be undergoing moderate erosion while the northwestern areas were undergoing accretion. The coastal modifications, especially the sand pier, along the eastern shoreline appear to have prevented the natural erosion and accretion cycles to function properly. The pier is also causing permanent erosion on its southern side.
55 0 300 600 meters Erosion and accretion patterns
6.62803°N Areas lost since 1969 Areas gained since 1969
Current erosion
Current Accretion
6.61904°N 3 0632°E73. 73.0813°E
Figure 3.8 Erosion and Accretion Patterns in Kulhudhuffushi.
3.1.3 Marine environment
General historical changes to reef conditions were assessed anecdotally, through interviews with a number of fishermen. The general agreement amongst the interviewees was that the quality of reef areas around the island declined considerably over the past 50 years. During this period lowering of coral cover and reduction in fish numbers, were reported. Reef conditions on the oceanward reef line were reported to be comparatively better than the lagoon wards side. No overgrowth of sea grass patches were observed during the survey.
56 3.1.3 Modifications to Natural Environment
3.1.3.1 Coastal Modifications
73.0813°E 3 0632°E73. Vegetation cleared and ridge reduced for road development
%%%%%% Reclaimed road over mangrove area
Reclaimed wetland Reclaimed area %% %%%%%%% %%%%%%% mangrove area 6.62803°N low lying
Sand pier used %%%%%% At the end of major to mine sand %% %%%%%%% roads corals cleared of lagoon for for recreational road maintenance swimming %%%%%%%
%%%%%% Breakwater Ridge reduced by 1m for 6.61904°N aesthetic reasons
%%%%%% Vegetation cleared %%%%%% to some extent %%%%%% Remanants of wetland still exists %%%%%% Coastal vegetation effected by waste site
0 300 600 Reclaimed Wetland meters Coastline stabilised Reclaimed Reef Coastal Modifications with construction debris
Figure 3.9 Coastal and terrestrial modifications in Kulhudhuffushi.
As noted earlier, much of the coastal modifications have been undertaken on the western shoreline of the island. Below is a summary of major modifications.
57 The major coastal modifications undertaken on Kulhudhuffushi are associated with the development of the commercial harbour and local harbour. The commercial harbour development involved major dredging activities, land reclamation and construction of breakwaters. The local harbour development involved dredging and coastal protection activities. The present harbour is reported to be inadequate and a new harbour is planned. The two harbours have ceased the coastal processes along the coastline including transport of sediments and island building processes in the area.
The reclamation of a sand pier along the western coastline has interrupted the flow of sediments along the highly volatile north-western corner of the island. The area had recently undergone erosion and may have been part of an erosion cycle where the next stage could have involved accretion. Since, the coastal processes no longer functions well in the area, it may be a long time before the area is stabilised.
The southern coastline has been largely modified due to the land reclamation activities in the southwest corner. Some of the changes may be explained by the rapid natural changes that followed reclamation while other areas were directly modified through further human activities such as dumping of construction waste in the region. Severe coastal erosion was prominent in the region following land reclamation and construction waste is being used as a coastal protection measure against erosion. The area is no longer conducive for natural forces to operate.
The location of the waste site at the south east corner of the island within a few meters of the coastline may have future implications for the coastal environment through pollution. Furthermore, there is concern that the narrow strip of land and vegetation between the coastline and waste site may be breached as part of the natural shifts in the coastline.
58 Further developments have been planned in the western coastline as part of the safe island development programme. These include reclamation of 75% of the lagoon, construction of a harbour and breakwaters stretching over a kilometre. These developments will convert the western coastline from a semi-artificial to a completely artificial area.
3.1.3.2 Terrestrial Modifications
The terrestrial environment of the island has been considerably modified due to the settlement expansion. Vegetation has been drastically reduced in the settlement area, but the vegetation cover is considered to be higher than similar high density settlements.
Much of the coastal vegetation on the western coastline is intact, but there are areas where the coastal vegetation has been encroached by development activities, especially the construction of new houses.
Land reclamation of wetland areas without considering the elevations and impacts on drainage systems has caused such areas to flood regularly during heavy rainfall.
The increase in rainfall related flooding in the low areas of the island prompted the authorities to undertake road maintenance activities, which primarily involved levelling and raising roads. This has led to some houses in the island to be lower than the road, especially in the low lying areas, causing flooding in these houses during heavy rainfall. It has to be noted that the proportion of houses effected in this manner is small compared to other islands such as Gaafu Dhaalu Thinadhoo and Gaafu alifu Viligilli.
The newly reclaimed areas from the reef and southern wetland areas have poor vegetation cover. This pattern is typical in reclaimed reef areas across Maldives.
59 This may be partly due to the high alkalinity of the soil following reclamation and partly due to lack of re-vegetation activities following land reclamation projects.
3.2 Environmental mitigation against historical hazard events
3.2.1 Natural Adaptation
Kulhudhuffushi is a good example of how the large islands in the north along the eastern rim of atoll adapts naturally to prevailing stormy conditions of the region. The adjustment of ridges, coastal processes and drainage patterns are evident from initial assessments and require further empirical assessments to understand the adaptation processes. The defensive mechanisms established for the storms are critical for mitigating a number of other sea induced hazards as well. Preservation of this these natural defensive mechanisms and minimal alteration of physical processes that help develop these systems are critical in natural hazard mitigation planning.
3.3.2 Human Adaptation
Kulhudhuffushi has relatively few modifications undertaken to directly prevent natural hazards. The main activities include use of construction debris to mitigate coastal erosion in the southern end of the island, construction to breakwaters along the commercial port and local port to minimise the impact of wave activity and to prevent wave overtopping into the port areas. Actions have also been undertaken to prevent rainfall relation flooding in newly reclaimed low areas and the main roads by raising the road surface.
3.3 Environmental vulnerabilities to natural hazards
3.3.1 Natural Vulnerabilities
60 The northwest-southeast orientation along with reef distance and reef shape exposes the majority of the island’s eastern shoreline to tsunami related flooding hazards and sea level rise.
There are substantial topographic variations within Kulhudhuffushi and naturally established drainage system. During times of heavy rainfall the drainage patterns causes flooding in structures and roads around low areas especially close to the present and reclaimed wetland areas.
Kuhudhuffushi is located in a major storm zone (UNDP, 2005) and hence is prone to strong winds and storm surges from both sides (see section 3).
The wetland areas in the north could expand with the projected sea level rise and associate rise in water table, leading to more frequent rainfall induced flooding events.
The wetland areas in the north are separated from the ocean only by a narrow stretch of coral deposits. This rim could be breached or enhanced by a major storm event in the future.
The relatively low elevation of the north eastern area and southern area exposes the areas to wave over-topping during sea induced flooding events.
3.3.2 Human induced vulnerabilities
The major impacts from human induced activities have come from improper land reclamation on the eastern side of the island (port development) and improper reclamation of wetland areas in the south. The impacts have mainly resulted from lack of consideration for island topography and general failure to assess the impacts of reclamation on surrounding environment. Increased exposure to the following hazards was identified:
61
Lack of consideration for island topography has resulted in the newly reclaimed land in the south to be lower than the existing island. This has exposed the newly reclaimed areas to rainfall related flooding due the absence of an artificial drainage system. The low rainfall in the region compared to the southern Maldives has presently kept the rainfall related hazard events to a minimum. The reclamation activities on the western side have caused changes in the coastal processes exposing the area to coastal erosion and decline in adaptive capacity to ocean induced hazards.
The quality of reef on the western side of the island has been reported to have declined considerably following development activities. Interviews with fishermen revealed a decline in live coral cover over the past 40 years probably owing to the human activities and over exploitation of reef resources. The quality of reef on the eastern side of the island has been reported to be in a better condition. Decline in reef quality will have implications on how the reef system and the island can adapt to sea level changes.
Almost 70% of Kulhuduffushi’s western coastline does not have proper coastal vegetation on them. This is primarily due to the development activities in the area. Artificial structures are required in the area to mitigate flood exposure although the probability of floods on the western coastline is low.
The western coastline is now an artificial environment due to dredging activities, quay walls and reclamation activities. The island building processes no longer functions properly in this region. It would require continuous human intervention to mitigate natural hazards such as erosion.
Encroachment of settlement areas close to wetland areas has caused some housing plots to be located along the natural drainage zone. This has in the past exposed such plots to rainfall induced flooding. This pattern was most noticeable
62 in the northern parts of the island and close to the southern wetland areas. The extent of flooding however remains low.
Past and current road maintenance activities on the island to mitigate rainfall flooding have caused the road to be raised higher than the surrounding housing plots. As a result, in some areas of the island, the surrounding houses have experienced flooding during heavy rainfall.
The strong vegetation belt on the eastern shoreline is being encroached to develop new plots. Additionally, the undergrowth has been consistently cleared from the coastal vegetation to create ‘better views’. These activities will gradually reduce the defensive function of coastal vegetation against sea induced flooding events and coastal erosion.
Levelling of coastal ridge to the central island level was observed on the eastern side of the island along the two of the main east-west roads. We have not been unable to get a clear reason for this clearing but according to locals the clearing was done by heavy machinery and was simply to create a ‘better view’ across the main roads. Such activities have serious consequences for hazard exposure as they reduce the functions of natural defensive systems in the island. The eastern areas of the two roads are now exposed to sea induced flooding. Similar observations were also made along the north-south main road and few other roads.
3.4 Environmental assets to hazard mitigation
The size of Kulhudhuffushi could be considered its biggest asset against ocean induced flooding events.
The island has a high natural ridge which is commonly found in large northern islands on eastern rim of the atoll. These ridges are believed to be a response to
63 major storm events or continued exposure to strong wave action in the region. Although a response to frequent wave induced hazards these ridges are capable of mitigating sea induced flooding events up to 2.5m high. Hence, these ridges are one of the main defensive assets of Kulhudhuffushi against sea induced hazards.
Strong coastal vegetation systems have the ability to reduce wave energy and block the flow of debris into the settlement during major flooding events such as tsunamis. Kulhudhuffushi also has one of the strongest coastal vegetation belt found in the nine islands studied in this project. Along with the high ridge, the strong coastal vegetation belt forms a formidable defensive system against ocean induced flooding and strong wind. Much of the Kulhudhuffushi’s eastern coastline is very likely to naturally mitigate flood events of up to +3.0m above MSL.
There is a well established drainage system, dominated by wetland areas in the north and south reducing the impact of rainfall related flooding.
The coastal processes along the eastern coastline of the island appear to be functioning well and help to maintain the natural processes responsible for natural hazard mitigation intact.
The small distance to reef along with a high ridge may be an asset against certain types of ocean induced hazards as it reduces the run-up for waves (see section 3).
The geographic location of Kulhudhuffushi in the archipelago has considerably reduced the exposure to earthquake hazards (UNDP, 2005).
3.5 Predicted environmental impacts from natural hazards
64 The natural environment of Kulhudhuffushi and islands Maldives archipelago in general are appear to be resilient to most natural hazards. The impacts on island environments 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 impacts 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 Kulhudhuffushi may continue to naturally adapt to rising sea level. There are two scenarios for geological impacts on Kulhudhuffushi. 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
65 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 Kulhudhuffushi (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, modified environments of Kulhudhuffushi 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)).
Kulhudhuffushi has particular vulnerability to sea level rise due to the presence of wetland areas. Since wetland areas in coral islands are linked to the tide and sea level, an increase in sea level may result in increase in size of such areas and a subsequent reduction in land (Woodroffe 1989).
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 Kulhudhuffushi.
Hazard Scenario Probability at Potential Major Environmental Impacts Location Tsunami (maximum scenario) 4.5m 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. Salt water intrusion into wetland areas and island water lens causing loss of some flora and fauna. Contamination of ground water if the sewerage system is damaged or if liquid contaminants such as diesel and chemicals in the boat yard are leaked. Damage to waste management site and subsequent
66 Hazard Scenario Probability at Potential Major Environmental Impacts Location dispersion of debris in southern half of the island and pollution (land and ground water) Salinisation of ground water lens to a short period of time causing ground water shortage. If the rainwater collection facilities are destroyed, potable water shortage would be critical. Widespread damage to backyard crops (short-term) Widespread damage to coastal protection and island access infrastructure such as breakwaters and ports. Short-medium term loss of soil productivity Moderate damage to coral reefs (based on UNEP (2005)) Storm Surge (based on UNDP, (2005)) 0.60m (1.53m storm Low Minor damage to coastal vegetation tide) Minor loss of crops Minor to moderate damage to coastal protection infrastructure Minor geomorphologic changes in the north western shoreline and lagoon 1.32m (2.30m storm Very Low Moderate damage to coastal vegetation especially tide) in the north eastern region Minor damage to selected inland vegetation especially common backyard species such as mango and breadfruit trees. Salt water intrusion into northern wetland areas and island water lens causing minor loss of some flora and fauna. Contamination of ground water if the sewerage system is damaged or if liquid contaminants such as diesel and chemicals in the boat yard are leaked. Salinisation of ground water lens to a short period of time causing ground water shortage in the northern part of the island. Minor damage to waste management site and potential dispersion of debris in southern half of the island causing pollution (land and ground water) Minor-moderate damage to coastal protection and island access infrastructure Minor geomorphologic changes in the north western shoreline and lagoon Minor-moderate damage to coral reefs 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.
67 Hazard Scenario Probability at Potential Major Environmental Impacts Location Minor changes to coastal ridges
Heavy rainfall 187mm Moderate Minor to moderate flooding in low areas, including roads and houses. 240mm Very Low Widespread flooding but restricted to low areas of the island. Drought Minor damage to backyard fruit trees Earthquake Minor-moderate geomorphologic changes Sea Level Rise by year 2100 (effects of single flood event) Medium (0.41m) Moderate Widespread flooding during high tides and storm surges. Loss of land due to erosion. Loss of coastal vegetation Major changes to coastal geomorphology. Saltwater intrusion into wetland areas and salinisation of ground water leading to water shortage and loss of flora and fauna. Minor to moderate expansion of wetland areas
3.7 Findings and Recommendations for safe island development
At the time of this study, no detailed plans have been developed for establishing Kulhudhuffushi as a safe island, except a new land use plan has been developed in August 2006. Presented below are some of the considerations that need to be made in developing Kulhudhuffushi as a safe island in the future. Assessment has also been made based on the existing land use plan.
Kulhudhuffushi has a well established defensive system against sea induced natural hazards on its eastern coastal line. It is made of a high and wide ridge system, and a strong coastal vegetation belt. It is vital that this system be maintained and enhanced in the new safe island development plan. Specific attention should be given in the land use plan to avoid developments within this zone, including coastal protection. Present land use plan reduces the width of the coastal vegetation belt with the development of a new ‘ring road’. Alternate options may need to be developed to maintain the vegetation belt. If not the exposure to sea induced flooding and windstorm hazards may be considerably increased.
68
The proposed new land reclamation under the present land use plan is expected to have implication on island environment and island exposure to natural hazards. The following points were noted on the proposed reclamation project.
The reclamation is highly likely to cause further damage to the outer reef and the protected areas due to its proximity and current land reclamation practices. This may reduce the defensive capacity of the reef system and expose Kulhudhuffushi to long term climate hazards. Proper reclamation practices need to be put in place prior to considering reclamation activities.
The soil composition of a reclaimed area may need to be properly established. Soil in coral islands of Maldives has specific profiles which dictate the suitability vegetation and perhaps drainage.
The elevation of the newly reclaimed area should be inline with the existing island topography or should consider establishing a functioning drainage system to mitigate flooding hazards resulting from modified topography, especially where the new reclamation joins the existing island. Special consideration may need to be given to maintain the existing drainage towards the northern wetland area. If the proper drainage flow and topography is not maintained, it is possible that existing flow with the island may be diverted to the newly reclaimed land leading rainfall related flooding.
The elevations and desired topography for the proposed reclamation needs to be determined.
A re-vegetation plan needs to be incorporated into the safe island development plan, especially to the proposed reclaimed zone, to ensure minimal exposure to strong winds and future climate change related temperature increases.
69 Although the western side of the island is considered the atoll ward side of the island, the openness of the atoll and prevalence of storm activity in the North Indian Ocean, exposes the eastern side of the island to potential storm surges. It should be noted that the probability of a major event on the western side of the island is low but not nil.
Structures located close to the wetland area and in the reclaimed wetland zone have a higher probability of flooding during rainfall flooding and possibly during the tsunami, as the wetland area is generally low.
70 3.6 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 three 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
71 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.
72 References
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. (2001). Maldives erosion assessment and management. Report prepared for UNDP as part of the Republic of Maldives Climate Change Enabling Activity Project. MDV/95/G32/A/1G/99. Male', UNDP and Ministry of Home Affairs, Housing and Environment.
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.
Kench, P. S., K. E. Parnell, et al. (2003). A process based assessment of engineered structures on reef islands of the Maldives. Proceedings, Coasts and Ports Australasian Conference 2003, Auckland, Coasts and Ports Australasian Conference Organising Committee Paper 74.
Ministry of Finance and Treasury (MoFT) (1999). Final Report for the Atoll Development Project. Atoll Development Project, Volume 2: Working Papers.
73 Opus International Consultants Limited. Male', Ministry of Finance and Treasury, Government of Maldives.
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.
74 4. Structural vulnerability and impacts
Kulhudhuffushi is exposed to all three major flood types prevailing in the Maldives, but only tsunami inundation prevailing on the western and south- western coast may have some effects. The eastern coast of the island is well protected from tsunami waves by a wide dense green belt and a high ridge, one of the strongest coastal vegetation belt found in the nine islands studied in this project. Along with the high ridge, the strong coastal vegetation belt forms a formidable defensive system against ocean induced flooding and strong wind. In the northern part of the island, rainfall floods may prevail.
4.1 House vulnerability
Around 60 houses, accounting for about 6% of the total existing houses on Kulhudhuffushi Island, are identified as vulnerable in terms of their physical conditions, protection, and plinth level. The house vulnerability of the Island is dominantly attributed to weak physical structure (Fig. 4.1 and Fig. 4.2). Almost all the vulnerable houses identified are located in the central part of the island, a flood-free zone.
100.0
80.0
60.0
40.0 Houses
20.0
%of Total Vulnerable 0.0 WB PP LE Indicator group
Fig. 4.1 Type of house vulnerability.
75
Kulhudhuffushi WB
WBPP 0%0%0%0%0%0% WBLE
WBPPLE
PP
LE
100% PPLE
Fig. 4.2 Type distribution of vulnerable houses.
4.2 Houses at risk
Houses on Kulhudhuffushi Island are exposed to both rainfall and tsunami floods. However, no houses are found exposed to ocean-originated floods on the eastern coast of the island due to a wide dense green belt with a high ridge. As shown in Fig. 5.3 (left), around 280 existing houses are located in the tsunami flood zone on the western coast of the island, of which only 7.5% (21 houses) are weak in physical structure and vulnerable to flooding. Given a water depth of 0.5- 1.5 m, 1.5% of the exposed houses may be subjected to moderate damage, and 6% to slight damage. The rest of the exposed are affected in their contents. As a result, only 0.15% of the total population may be displaced.
The exposure of houses to tsunami floods will increase in the future. According to the new land use plan of Kulhudhuffushi Island, around 300 new houses will be built in the new tsunami flood-prone area, although the exposure of existing houses will be significantly reduced (by 26%) after land reclamation.
The exposure of houses to rainfall floods is minor, accounting for less than 10% of the total houses and no vulnerable houses are found in the rainfall flood-prone areas. However, the exposure will increase dramatically. According to the new
76 land use plan, 160 houses will be added to the rainfall flood area in the northern part of the island, where the land is reclaimed from the wetland. On the other hand, the wetland areas in the north of the island could expand with the projected sea level rise and associate rise in water table, leading to more frequent rainfall flooding events.
Generally, most houses on Kulhudhuffushi are not vulnerable to earthquakes, located in Seismic hazard zone 1. However, houses with weak physical conditions may be subjected to slight damage in response to a PGA of 0.04. In addition, these weak houses may be affected by strong winds as well.
Table 4.1 Houses at risk on G.dh. Kulhudhuffushi. Exposed Vulnerable Potential Damage Hazard houses houses Serious Moderate Slight Content type # % # % # % # % # % # % TS(p) 279 28 21 7.5 0 0 4 1.4 17 6.1 258 92.5 TS(f) 15 1.5 0 0 0 0 0 0 0 0 15 100
W/S 0 0 0 0 0 0 0 0 0 0 0 0 RF(p) 85 8.5 0 0 0 0 0 0 0 0 85 100 RF(f) 85 8.5 0 0 0 0 0 0 0 0 85 100 Flood Earthquake 995 100 62 6.2 0 0 0 0 0 0 0 0 Wind 995 100 62 6.2 ------Erosion
77
Fig. 4.3 Houses at risk associated with rainfall floods.
78
Fig. 4.4 Houses at risk associated with tsunami floods.
79 4.3 Critical facilities at risk
Many critical facilities on Kulhudhuffushi Island, i.e. NSS, hospital, school, mosques, power house, and waste site, are located in the tsunami flood-prone area on the western coast and exposed to potential inundations of 0.5-1.5 m water depth (Fig. 4.5). However, MCPW may be at low risk. Located in the destructive tsunami hazard zone on the southern end of the island, MCPW is only 20 m far away from shoreline and not well protected. Its boundary wall is 60 cm high only.
The waste disposal site of the island is at risk as well, exposed to ocean- originated floods. The current waste site used to be a low-lying place of the island. The inundation of the site may cause secondary contamination to its surrounding environment. Power house may be affected by 0.5 m flooding. However, no physical damage is expected.
In the future, with the island land being reclaimed westwards, some critical facilities, such as NSS, hospital, are no longer exposed to tsunami inundation (Fig. 4.5, right). However, the exposure of power house, MCPW, and waste site remains same.
Few critical facilities are exposed to rainfall floods, except for part of the secondary school in the northern part of the island and all buildings of critical facilities are earthquake-resistant, given a PGA of 0.04.
4.4 Functioning impacts
The impacts on the functioning of critical facilities are minor. In worse cases, critical facilities such as hospital, mosques, and power house may be disrupted for hours. And the secondary contamination caused by the flooding of waste site may take days to clean up.
80 Table 4.2 Critical facilities at risk on Kulhudhuffushi Island. Critical facilities Potential damage/loss Hazard type Physical Monetary Exposed Vulnerable damage value NSS, hospital, 2 MCPW, Slight to - school, 2 power moderate Tsunami mosque, MCPW, house, damage to power house, waste site MCPW and waste site power house Part of a waste No Content-affected N/A Wave/Surge disposal site Rainfall Part of a school No Content-affected N/A Flood Earthquake All facilities No No No
Wind - - - -
Erosion - - - - Note: “-“ means “not applicable”.
Table 4.3 Potential functioning impact matrix. Flood Function Earthquake Wind Tsunami Wave/surge Rainfall Administration 1)
Health care
Education
Religion
Housing
Sanitation 3) A few A day days Water supply
Power supply A day
Transportation
Communication 2)
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.
81 4.5 Recommendations for risk reduction
Overall, both houses and critical facilities on Kulhudhuffushi Island are at very low risk. However, there are several advisory recommendations as follows:
• Enhance building codes in the rainfall flood-prone area in the northern part of the island, specifically, a plinth level of 0.5 m high above ground is strongly recommended for new houses considering 30-50 cm sea-level rise. • Set up an EPZ with a proper high ridge (not definitely 2.4+) at the southern end of the island to protect power house, waste site, and MCPW, or • Retrofit power house, waste site and MCPW.
82
Fig. 4.5 Critical facilities at risk associated with rainfall floods.
83
Fig. 4.6 Critical facilities at risk associated with tsunami floods.
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