Detailed Island Risk Assessment in Maldives Volume III: Detailed Island Reports Ga. Viligilli – Part 1 DIRAM team Disaster Risk Management Programme UNDP Maldives December 2007 1 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 Viligilli Island is located on the eastern rim of Gaafu Alifu atoll, at approximately 73° 26' 5"E and 0° 45' 22" N, about 380km from the nations capital Male’ and 72 km from the nearest airport, Gaafu Dhaalu Kadedhdhoo (Figure 1.1). The island forms part of the natural atoll called Huvadhoo Atoll, which is considered the second largest atoll in the world. Viligilli is the atoll capital amongst 10 other inhabited islands. It’s nearest inhabited islands are Maamendhoo (4 km) and Dhaandhoo (12.5 km). Villigili is also just 2 km from Koodoo, the main fish processing centre in the southern region of Maldives. Huvadhoo atoll is the nearest atoll in Maldives to the equator and sits along the southern half of the laccadive-chargoes ridge, exposing the entire atoll to direct wave action in Indian Ocean. However, it location in the heart of the doldrums makes the island relatively safe from major climatic hazard events. 73.25°E 73.5°E Kolamaafushi 0.75°N Viligilli Maamendhoo N Nilandhoo Location Map North Huvadhu Atoll Dhaandhoo of Viligilli (Gaafu Alifu Atoll) 0 5 10 kilometers Dhevvadhoo 0.5°N Kon'dey Dhiyadhoo Gemanafushi Kanduhulhudhoo Figure 1.1 Location map of Viligilli. 3 1.2 Physical Environment Viligilli is a narrow and elongated island with a width ranging from 600 m to 180 m and a length of 1846 m. The total surface area of the island is 54.8 Ha (0.55 km 2). The island is oriented in a north south direction and the width of the island narrows northwards. The reef of Viligilli is large with a surface area of 3000 Ha (30 km 2) extending to about 20.5 km. The reef also hosts three other uninhabited islands. Viligilli is located on the southern tip of reef system, next to a major reef entrance (Viligilli Kandu). The island of Falhuverreha, located off the north-eastern tip of the island is separated by a mere 20m ‘mini channel’. The depth of the reef flat is quite shallow averaging less than -1m MSL (EDC, 2006). The distance between the island shoreline and oceanward reef rim varies from 100m in the south to 750 m in the north. The average distance to reef edge is approximately 300 m. Viligilli appears to have grown northwards and continues to do so with the constant supply of sediments and due to the funnelling effect caused by the orientation and location of Falhuverreha Island. Much of the original island was covered with wetland areas which have now been reclaimed on an adhoc basis by the inhabitants. Remnants of these wetland areas can still be found in the northern and southern part of the island. Hence, much of the settlement is located in low lying reclaimed areas. Over the years these fertile low areas of the island have become productive areas for vegetation and backyard agriculture. Much of the larger trees in the island, especially 95% of the mango trees are located in these low areas. Viligilli, in spite of its size is highly urbanised. Due to the narrow width of the island, settlement has already expanded to the edges of coastline and new plots are still being developed. It was reported that Viligilli was facing land shortages for housing purposes. The island only had thin layer of depleted coastal vegetation around its settlement and the remaining vegetation could be further depleted with planned expansion of settlement. The coastal areas of the island have been heavily modified in the past, especially the northern western coastline of the island where harbour construction and reclamation activities have been undertaken twice. 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. 4 The tsunami of 2004 had a major impact on the islands terrestrial environment and entire settlement. The most notable environmental damages were the negative impacts on 50% of the island’s larger trees, including loss of 90% of all mango trees. The existing environmental characteristics and features of Viligilli appear to play a major role in exposing the island to natural hazards, especially flooding. 5 2. Natural hazards This section provides the assessment of natural hazard exposure in G.A Viligilli 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 Viligilli has been exposed to multiple hazards in the past. 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 a summary of their impacts on the island. The historic hazardous events for Viligilli showed that the island faced the following hazards: 1) flooding caused by heavy rainfall and 2) swell surges, 3) windstorms and 4) tsunami. Impacts and frequency of these events vary significantly. Flooding caused by rainfall and swell surges are the most commonly occurring hazard events. Windstorms have also been reported as frequent especially during the southwest monsoon. Since the elders from the island cannot recall events beyond 1978, it is 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 and due to land reclamation activities. Table 2.1: Known historic hazard events of Viligilli. Metrological Dates of the Impacts hazard recorded events Flooding caused • Very frequent According to the island office records by Heavy rainfall (almost yearly heavy rainfall is most common during events) events mid to late South West (SW) monsoon. commonly These events are reported to cause occurring during heavy flooding of the old marsh (now SW monsoon. reclaimed) area in the central region of the island, which is approximately 30% of the presently populated area of the island. Heavy rainfalls are reported to cause flooding within this zone up to a height of 0.3m – 0.6m. It has been reported that the flood waters sometimes have lasted between 3 – 5 days. The major impacts of these flooding are: 6 - Blocking of the sewerage networks within the flooded zones (up to 75% of the houses could not flush their toilets during these floods) - Severe damages to the backyard crops such as bananas, chillies etc. - Damages to house furniture, children’s text books and other household goods. Flooding caused • 5 July 1966 1 The island is reported to experience by swell surges • 24 August 1975 frequent (once every few years) flooding • 8 August 1979 caused by wave surges and sometimes • 17 Sept 1979 large swell waves generated far offshore • 14 July 1983 from the coasts of the Maldives. These • 06 April 1984 events are also reported to occur during • 28 June 1987 mid SW monsoon. Surge waters often reach more than 50m inland along much • June 2006 of the length of eastern shoreline to a maximum of 200m. The major impact of these events is damages to the backyard crops within the impact zone. Windstorms • 28 Sept 1984 A number of windstorm events were • 27 March 1988 reported by elders; however, no dates could be determined. Major damages include falling trees, damage to crops, and structural damage to roofs. Droughts No major event have been reported Earthquake No major event have been reported Tsunami 26 th Dec 2004 There has be en only one known event. This event flooded a large area of the island with great force. The tsunami wave was reported to have a height of approximately 3m when it reached the eastern shoreline of the island. Villingili is one of the most effected islands in the southern atolls. The impacts of the tsunami include: - Salinisation of groundwater - Damage to the sewerage network - Damage to large trees such as mangos, breadfruit, etc. 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. 7 - Destroyed backyard crops - Severe to minor structural damage to many houses 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 Viligilli. • Heavy rainfall (flooding) • Swell waves and wind waves • Windstorms • Tsunami • Earthquakes • Climate Change 2.2.1 Swell Waves and Wind Waves Being located on the eastern rim of Huvadhoo atoll, Viligilli is relatively protected from the year round swell waves approaching from a west to southerly direction.