Detailed Island Risk Assessment in Maldives, S. Feydhoo – Part 1
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Detailed Island Risk Assessment in Maldives Volume III: Detailed Island Reports S. Feydhoo – 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 Feydhoo Island is located on the western rim of Addu atoll, at approximately 73° 08' 00"E and 0° 40' 52" S, about 542 km from the nations capital Male’ and 2 km from the nearest airport, Gan (Fig. 1.1). It is the southernmost inhabited island in Maldives. Feydhoo is one of the few inhabited islands facing the western Indian Ocean and exposed to the south west monsoon related wave action. Feydhoo is one of the six inhabited islands in the atoll and it’s nearest inhabited islands are Maradhoo Feydhoo and Maradhoo. Feydhoo forms part of a stretch of 5 islands connected though causeways and bridges and is the second largest group of islands connected in this manner. Addu Atoll is the southern most atoll of Maldives and is located south of the equator. It sits along the southern half of the laccadive-chagos ridge, exposing the entire atoll to direct wave action from Indian Ocean. 73° 15' E 73° Meedhoo Hithadhoo Hulhudhoo Addu Atoll (Seenu Atoll) Maradhoo Maradhoo-Feydhoo Viligilli 0° 40' S N Feydhoo Gan (Airport) Location Map of Thinadhoo 0 2.5 5 kilometers . Figure 1.1 Location map of Feydhoo. 1.2 Physical Environment Feydhoo is a fairly large island with a length of 1600 m and a width of 550 m at its widest point. The total surface area of the island is 62.5 Ha (0.62 km 2). It is the 4th largest island in Addu atoll amongst six inhabited islands. The reef of Feydhoo is large with a surface area of 4152 Ha (41.5 km 2) and cover the entire western rim of Addu Atoll, stretching to approximately 18km. The reef also hosts 3 large inhabited islands and the Airport island (Gan), totalling a 1011ha (10.1 km 2) of land. It is one of the largest concentrations of land in a single reef. The reef and the islands on them are is oriented in a northwest-southeast direction. Feydhoo is located on the southern half of the reef system, approximately 700m from the oceanward coastline and 255 m from the lagoonward coastline. There are a group of small uninhabited islands located on the oceanward reef flat of Feydhoo. They could be effectively considered barrier islands for Feydhoo Island, although the relatively small size and dispersed nature would probably mean that they do not necessarily perform the functions of a barrier island. Feydhoo is a highly urbanised settlement with a registered population over 4000 inhabitants, which is considered large in Maldivian context. The high level of urbanization also meant that the natural environment of the island is highly modified to meet the development requirements of the settlement. Majority of the present population of Feydhoo Island consist of the inhabitants from Gan Island, who migrated to Feydhoo in 1950’s during the development of Gan as an airbase for British Royal Air force. It should be noted that the vegetation cover in Feydhoo is quite substantial compared to other islands with similar population densities. At first glance, this appears to be due to the effectives of settlement planning, large plot sizes and possibly due to the high rainfall. Almost all islands have a substantial backyard area with a concentration of large trees. A number of infrastructure development and coastal modification activities has been undertaken in the island over the last 60 years resulting in substantial changes to the island environment. These include reclamation activities, coastal protection, beach replenishment and modifications to coastline resulting from the linking of nearby islands using causeways and bridges. Environmental issues associate with urbanisation are being experienced by its inhabitants including, ground water contamination, improper waste disposal, degradation of coastal areas, depletion of vegetation and coastal erosion. The island is currently facing a shortage of land for further development activities and residential development. Feydhoo has a high incidence of historical natural hazards and the present environmental characteristics in the island have a number of weaknesses which may expose the island to future hazards. 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 Feydhoo has been exposed to multiple hazards in the past. A natural hazard event history was reconstructed for Feydhoo 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. The historic hazard events for Feydhoo showed that the island faced the following multiple hazards: 1) flooding caused by heavy rainfall and 2) swell surges, 3) windstorms and 4) earthquakes. Impacts caused by these events and frequency of occurrence of the events vary significantly. Flooding caused by rainfall and swell surges are the most commonly occurring hazard events, which however, can only traced back 15-20 years, beyond which no reports of serious events are available. Windstorms have also been reported as frequent especially during the southwest monsoon. Since the elderly in the island cannot recall events beyond 1984, it is highly plausible that severe events came to the attention of inhabitants only with the rapid expansion of settlement especially towards the hazard prone western coastline of the island. Feydhoo is also one of the very few islands which have a recorded damage caused by an earthquake, although the damage was insignificant. Table 2.1 Known historic hazardous events of Feydhoo. Natural hazard Dates of the Impacts recorded events Flooding caused by • 27 th June 1997 Damage from rainfall related flooding was Heavy rainfall • 3rd May 2004 mostly limited to household goods and • 4th September backyard crops. These events are 2005 reported to cause flooding almost across the entire island. Flooding of the houses is increased by raised roads that drain the water from the roads into the houses alongside the roads. Rain related flooding on the island is reported to reach up to 0.4m from ground level. Measured values on walls showed 0.3m. Major impacts of these flooding are: Blocking of the sewerage networks within the flooded zones Severe damages to the backyard crops such as bananas, chillies etc. Damages to house furniture and other household goods. Reduction in mobility around the island leading to short term closure of economic and social institutions • Flooding • 8th May 1993 The island is reported to experience caused by swell • 5th June 1993 frequent (once every few years) flooding surges • 6th & 7 th April caused by wave surges and sometimes 1984 large swell waves generated far offshore • 6th November from the costs of the Maldives. These 1994 events are also reported to occur during • 15 th October mid SW monsoon. Surge waters often 1985 reaches up to 200m inland along much of • 2nd & 3 rd June the length of southern shoreline. These 1987 surge waters have flooded the impact zone • 20 th July 2001 (Figure 3.10) up to a height of 0.3m. The major impact of these events is damages • 3rd May 2004 to the backyard crops within the impact • 18 th September zone. 2005 • 4th September 2006 • 30 th November 2006 • Windstorms • 17 th October Rare incidents of strong winds have also 1995 been reported for the island. The recorded • 20 th May 2000 event of strong winds and rain affected • 20 th July 2003 caused damages to the roofs of some • 3rd May 2004 houses were blown off and trees such as • 30 th November papaw, banana, coconut palms, etc. The 2006 effect of this event was felt across the entire island. Droughts No major event have been reported Earthquake 16 th July 2003 (1:25 The only earthquake that has been – 1:30am) recorded to have caused damages to the island was in 2003. This earthquake cracked some buildings and houses on the island. These included Feydhoo School and Feydhoo Office but the damage was minimal and there was no functional loss at any of these two facilities Tsunami 26 th Dec 2004 There have been one noticed event but this event did not flood the island of Feydhoo. 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 Feydhoo. • Swell waves and wind waves • Heavy rainfall (flooding) • Windstorms • Tsunami • Earthquakes • Climate Change 2.2.1 Swell Waves and Wind Waves Origins and Occurrence of waves in Feydhoo The wave regime around Maldives, especially around the western line of atolls is partially influenced by swell waves originating from the Southern Indian Ocean (Kench et.