Coastal resources, livelihoods and the 2004 Indian Ocean tsunami in Aceh, Indonesia
Highlights
► The impact of the 2004 Indian Ocean tsunami on coastal resources is investigated. ► Loss of mangrove and aquaculture farms impacted livelihoods and local economies. ► Mangroves did not mitigate the tsunami in west Banda Aceh. ► Mangroves are important for environmental, economic and disaster resiliency. ► Coastal management and Disaster Risk Reduction activities need to be integrated.
Introduction
On 26 December 2004, a magnitude 9.2 earthquake occurred along the Sunda Subduction Zone within 150 km of the Nanggroe Aceh Darussalam (NAD) province of Indonesia (Chlieh et al., 2007) (Fig. 1). This earthquake created a tsunami that propagated in a westward and eastward direction across the Indian Ocean. In Indonesia, onshore tsunami heights ranged from 1 to 30 m and inundated up to 5 km inland (Telford et al., 2006; Paris et al., 2007). A total of 811,409 people were displaced, 166,760 killed, 127,749 unaccounted for and greater than 1 million people affected (Athukorala and Resosudarmo, 2006).
Beaches, dunes, tidal creeks, river channels, coral reefs, mangroves, seagrass beds and coastal forests were all severely impacted by the tsunami (Srinivas and Nakagawa, 2008). It is estimated that 90% of mangroves within Aceh were destroyed by the tsunami (Chen et al., 2005). The aquaculture and fishing industries were significantly impacted with 9000 ha of aquaculture farms (tambak) severely damaged or swept into the sea, and the extensive loss of fishing boats, jetties and market facilities (Athukorala and Resosudarmo, 2006; FAO, 2005).
Beaches lost vast amounts of sand and sediment was deposited both off- and on-shore, particularly in topographic lows (Paris et al., 2007, 2010; Liew et al., 2010). Paris et al. (2009) found that sand barriers protecting lagoons or river mouths were completely eroded and that extensive bank erosion and widening of river channels occurred. At 6 months after the tsunami Meilianda et al. (2010) found that Ulee Lheue on the north coast of Aceh still showed significant signs of erosion while Lhok Nga on the west coast had regained 60% of the sediment lost during the tsunami (Fig. 1). Liew et al. (2010) found that from Lhok Nga south to Meulaboh (180 km southeast of Lhok Nga) most beaches were rebuilt to their approximate previous state by 13 months after the tsunami; however, tambak ponds still showed extensive signs of erosion.
In various post-disaster reports and articles erosion of the physical environment was correlated with the presence or absence of coral reefs, mangroves, sea grass beds, casuarina forests and dunes. These observations were not only made in Indonesia but have also come from Thailand, India and Sri Lanka (Danielsen et al., 2005; Kathiresan and Rajendran., 2005; UNEP, 2005; Chang et al., 2006; Chatenoux and Peduzzi., 2007; Iverson and Prasad, 2007; Umitsu et al., 2007; Mascarenhas and Jayakumar., 2008; Pari et al., 2008; Kaplan et al., 2009; Liew et al., 2010). These reports vary in detail and scope and have initiated a scientific debate about the effectiveness of coastal environments and ecosystems for tsunami mitigation purposes. While some authors advocate the effectiveness of coastal ecosystems within a hazard context (Danielsen et al., 2005; Kathiresan and Rajendran., 2005; UNEP, 2005; Chang et al., 2006; Iverson and Prasad, 2007; Mascarenhas and Jayakumar., 2008 Kaplan et al., 2009), others suggest this is limited to small scale events (Cochard et al., 2008; Yanagisawa et al., 2009). Other authors have critiqued articles that advocate mangroves as a tsunami mitigation measure due to a lack of rigor in their statistical analyses and interpretation of imagery (Kerr et al., 2006; Dahdouh-Guebas et al., 2006). Despite the uncertainty surrounding these observations, various mangrove and casuarina replantation programs were implemented in Aceh from the year 2005 motivated in part by tsunami mitigation needs (see UNEP, 2005; Wibisono and Suryadiputra, 2006).
The growing debate surrounding coastal ecosystems and tsunami impact has significant implications for Disaster Risk Reduction (DRR) activities. DRR is defined by the United Nation's International Strategy for Disaster Reduction (UNISDR) as “the concept and practice of reducing disaster risks through systematic efforts to analyse and manage the causal factors of disasters, including through reduced exposure to hazards, lessened vulnerability of people and property, wise management of land and the environment, and improved preparedness for adverse events”. There is a growing concern that rehabilitating mangroves or other ecosystems for the direct mitigation of tsunami events will divert resources away from more effective disaster mitigation and DRR activities (Cochard et al., 2008). This may then instill a false sense of security in communities and ultimately lead to greater impacts in the event of a future disaster.
The relationship between coastal environments and natural hazards needs to be better understood to ensure that coastal management decisions consider DRR issues and vice versa. Understanding this relationship forms the focus of this paper. The impact of the tsunami on coastal resources, including mangroves, casuarina and tambak, is investigated and the subsequent social and management implications discussed.
Section snippets
Study sites
Two sites were chosen to measure tsunami induced coastal erosion and environmental change. These are the Banda Aceh west coast, study site 1, and the northern section of Lhok Nga Bay, study site 2 (Fig. 1).
Study site 1 spans the Banda Aceh west coast and includes the Cangkoi estuary, Ulee Lheue Harbour and estuarine plain adjacent to the village of Pande. Study site 1 was selected as it is a low lying, low energy deltaic environment (Meilianda et al., 2010) that has been artificially modified
Methods
Coastal morphological change and recovery pre- and post-tsunami was measured using a time series of historic imagery sourced from Google Earth. Imagery from 1 year prior to, and up to 6 years after the tsunami, was used in the assessment. A mean high water mark (MHWM) line was digitised for 4 dates at study site 1 and for 5 dates at study site 2 (Table 1). The series of MWHMs were digitised at a scale of 1:2000 and represent the wet–dry transition on the beach. This scale was used as it
Study site 1
At study site 1, tsunami induced erosion was extensive. The beach barrier systems at Cangkoi estuary and Pande village that prior to the tsunami enclosed vast expanses of tambak were completely eroded (Fig. 2, Fig. 3, Fig. 4, Fig. 5). At Cangkoi estuary the maximum extent of this erosion measured 1 km inland (Fig. 3). Over the past 6 years this beach barrier has begun to rebuild, with a maximum accretion of 30 m measured between May 2009 and July 2010. Despite this accretion the present day
Discussion
The impact of the tsunami at two sites in Aceh shows that different coastal environments respond differently to tsunami events. The study shows that the high energy, sediment rich and undisturbed coastal system of study site 2 (Lhok Nga Bay) recovered most quickly from the large tsunami induced disturbance (Figs. 7 and 9). Conversely, the low energy, sediment poor and anthropogenically modified coastal zone of study site 1 (Banda Aceh west coast) sustained long-term to permanent loss of land (
Conclusions
The Indian Ocean tsunami that struck the coastline of Aceh on 26 December 2004 drastically changed the landscape configuration of the coastal zone. This change impacted livelihood opportunities and the quantity of coastal resources available to the residents of Aceh. Study site 1 (Banda Aceh west coast), an anthropogenically modified coastline used extensively for tambak farming, has not recovered from the tsunami. In comparison, the beaches of study site 2 (Lhok Nga Bay) have recovered to a
Acknowledgements
We would like to acknowledge the valued assistance of Dr Syamsidik and Bustamam Koetapangwa from the Tsunami and Disaster Mitigation Research Centre in Banda Aceh. We would also like to thank Era Maida for her translation work and the residents of Pande village who participated in the interviews. We would like to acknowledge Dr Sara Pozgay-Rawlinson for her guidance in formulating this research topic and the valued input of 2 anonymous reviewers.
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