Detailed Island Risk Assessment in Maldives, Dh. Kudahuvadhoo
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Detailed Island Risk Assessment in Maldives Volume III: Detailed Island Reports Dh. Kudahuvadhoo – Part 1 DIRAM team Disaster Risk Management Programme UNDP Maldives December 2007 Table of contents 1. Geographic background 1.1 Location 1.2 Physical Environment 2. Natural hazards 2.1 Historic events 2.2 Major hazards 2.3 Event Scenarios 2.4 Hazard zones 2.5 Recommendation for future study 3. Environment Vulnerabilities and Impacts 3.1 General environmental conditions 3.2 Environmental mitigation against historical hazard events 3.3 Environmental vulnerabilities to natural hazards 3.4 Environmental assets to hazard mitigation 3.5 Predicted environmental impacts from natural hazards 3.6 Findings and recommendations for safe island development 3.7 Recommendations for further study 4. Structural vulnerability and impacts 4.1 House vulnerability 4.2 Houses at risk 4.3 Critical facilities at risk 4.4 Functioning impacts 4.5 Recommendations for risk reduction 1. Geographic background 1.1 Location Kudahuvadhoo is located on the southern end of South Nilandhe Atoll (Dhaalu Atoll), next to the Kudahuvadhoo Kanduolhi (reef pass) at approximately 73° 39' 3"E and 4° 22' 28" N (Figure 1.1). It is located at about 181 km from the nation’s capital Male’ and about 113 km from the nearest Airport Laamu Atoll, Kadhoo. Kudahuvadhoo is the Atoll Capital of Dhaalu Atoll, amongst a group of 7 inhabited islands. It’s nearest inhabited islands are Maaenboodhoo (8 km), and Vaanee (13 km). Dhaalu atoll is located along the western line of atolls. 3° 00' N Meedhoo Ban'didhoo Rin'budhoo Hulhudheli South Nilandhe Atoll (Dhaalu Atoll) 2° 45' N N Vaanee Location Map of Kudahuvadhoo Maaen'boodhoo 0 5 10 E ' 0 kilometers Kudahuvadhoo 0 ° 3 7 Figure 1.1 Location map of Kudahuvadhoo. 1.2 Physical Environment Kudahuvadhoo is a fairly large island with a length of 1040m and a width of 880 m at its widest point. The total surface area of the island is 69.7 Ha (0.69 km 2). The reef of Kudahuvadhoo is one of largest in Maldives with a surface area of 5601 Ha (56.01 km 2). The reef also hosts 3 other uninhabited islands. Kudahuvadhoo is located at the southern tip of the reef system, approximately 450m from the southern wave break zone and 320m from the eastern reef edge. The depth of the reef flat is quite shallow averaging less than -1m MSL. The island has an elevation ranging from +0.45 to +1.5m MSL along the island topographic profile survey line. The island could be describes as located on an east west orientation and appears to be growing towards west. Kudahuvadhoo has a natural harbour due the extensive lagoon on the western side of the island. The lagoon extends to about 12km within the reef. The growth of the island towards west has meant that sand is constantly deposited within the deep lagoon creating a steep underwater slope on its western end and allowing vessels to approach close to the shoreline. The island had large areas of undeveloped land allowing the presence of strong vegetation cover on its southern side. Much of this new land is now being developed for Tsunami related resettlement schemes, agriculture, recreation and is predicted to be depleted in the near future. The existing natural environment of the island has been modified, especially in the northern side, although the extent of coastal modifications is small compared to most other inhabited islands. Major modifications include development of a harbour, land reclamation from the excess dredge material during harbour development and clearing of vegetation. 2. Natural hazards This section provides the assessment of natural hazard exposure in Feydhoo Island. A severe event history is reconstructed and the main natural hazards are discussed in detail. The final two sections provide the hazard scenarios and hazard zone maps which are used by the other components of this study as a major input. 2.1 Historic events The island of Kudahuvadhoo has been exposed to multiple hazards in the past although its exposure has been limited. A natural hazard event history was reconstructed for the island based on known historical events. As highlighted in methodology section, this was achieved using field interviews and historical records review. Table 2.1 below lists the known events and a summary of their impacts on the island. Table 2.1 Known historic hazard events of Kudahuvadhoo. Me trological Dates of the Impacts hazard recorded events Flooding caused • Frequent events Flooding limited to a few topographic low by Heavy rainfall commonly areas on the island. The magnitudes and occurring during impacts of these floods are small with SW monsoon. water levels barely exceeding 0.3m. However, disruptions to socio-economic activities have occurred in the past with schools and shops being closed for over 24 hours. Flooding caused No records of major - by swells or incidents surges Flooding caused Annually Impact limited to 10 m from shoreline. In by monsoonal intensity is very low and rarely effects wind waves or property or human well-being Udha Windstorms • 24 June 1987 1 Windstorms are common on the island. • 18-20 Dec 1992 2 These events affect housing structures, 1 All dates in italics are adopted from MANIKU, H. A. (1990) Changes in the Topography of Maldives, Male', Forum of Writers on Environment of Maldives. and news paper reports. 2 Unnamed tropical depression passing over Dhaalu atoll between 18-20 December 1992. Source: UNISYS & JTWC (2004) Tropical Cyclone Best Track Data (1945-2004). http://www.pdc.org/geodata/world/stormtracks.zip, Accessed 15 April 2005, Unisys Corporation and Joint Typhoon Warning Center. • 5 other major vegetation and crops. The island is events since generally protected from thick coastal 1980’s (dates vegetation but even before the settlements unknown). expanded, there were reports of windstorm related damages. The effect of wind storm is spread across the entire island. Droughts No major event have been reported Earthquake No major event have been reported Tsunami 26 th Dec 2004 The effect of tsunami 2004 was limited on this island. Flooding occurred on the southern and parts of eastern side. There were no major structures in this area and as a result lost was very little. The flood itself came only about 150m on the southern side and up to a 300m on the eastern side. All these areas were uninhabited. Tsunami floods destroyed a number of agricultural fields, however. One farmer reported a loss of MRF 30,000 worth of crops. The repercussions for the damage were far reaching. He supplied vegetables to a number of islands within the atoll and employs 12 staff seasonally. The staff and the farmer therefore endured loss of income. Apart from the agricultural fields; the only notable damage to the island was to its Harbour. The outer harbour walls collapsed and part of the quay wall was damaged beyond repair. It is still in use but appears unstable. The historic hazardous events for Kudahuvadhoo showed that the island faced the following hazards: 1) windstorms, 2) flooding caused by heavy rainfall, and 3) tsunami. Impacts and frequency of these events vary significantly. Windstorms are the most commonly occurring events followed by flooding due to heavy rainfall. The occurrence of windstorms is usually limited to SW monsoon although occasional localised ‘freak storms’ due to low pressure systems forming above Maldives effects the island during NE monsoon. It is noteworthy that in spite of the exposure to southern Indian Ocean swell waves, flooding from swell waves or storm surges are almost non-existent in the historical records. The absence of historical records on swell related flood events in nearby islands with similar geographic settings such as Nilandhoo and Magoodhoo, further enhances this finding. The tsunami of 2004 is by far the most significant hazard event in Kudahuvadhoo with substantial economic damage. However, despite its location in a high tsunami hazard zone, the scale of impacts in Kudahuvadhoo is small compared to the other nearby islands such as Vilufushi, Kolhufushi, and Vaanee. The reasons behind the lack of impacts will be explored in latter sections. 2.2 Major hazards Based on the historical records, meteorological records, field assessment and Risk Assessment Report of Maldives (UNDP, 2006) the following meteorological, oceanic and geological hazards have been identified for Kudahuvadhoo. • Windstorms • Heavy rainfall (flooding) • Tsunami • Long distance swell waves and local wind waves • Earthquakes • Climate Change 2.2.1 Swell Waves and Wind Waves Long distance swell waves Kudahuvadhoo Island is exposed to effects of swell waves approaching from the Southern Indian Ocean. No site specific wave studies have been undertaken for Kudahuvadhoo but studies undertaken around the country reports a predominantly southwest to a southerly direction for swell waves (Kench et. al (2006), Young (1999), DHI(1999) and Binnie Black & Veatch (2000)). As a result the island is directly in the path of these long distance waves which occasionally reaches abnormal levels capable of flooding (see Figure 2.1). Kudahuvadhoo SW monsoon Wind waves Dhaalu Atoll S SSSS Meemu Atoll SSSS W WWWW WWWW S S SSS SSSS w wwww wwww e eeee eeee lll llllll llllll ll l W W WWW WWWW a aaaa aaaa vvv vvvvv NE Monsoon v e eeee eeee s s s s s s s s s Thaa Atoll Wind waves Laamu Atoll Figure 2.1 Estimated (predominant) wave propagation AAAbbbooonnnooorrrrmmmaaalllll l S SSEEE s sswwweeelllllllll l w wwaaavvveees ss Kudahuvadhoo. The shape of the reef and island, and location of t appears to control the flow of wave energy reaching Estimated wave propogation Hence, unlike islands located on the western rim of patterns around Kudahuvadhoo Thinadhoo), Kudahuvadhoo enjoys more protection due southern rim.