Coastal resources, livelihoods and the 2004 Indian Ocean tsunami in Aceh, Indonesia

Abstract

The 2004 Indian Ocean tsunami drastically altered the coastal zone of Aceh, Indonesia. Tsunami induced erosion of the coast, including aquaculture farms (tambak) and mangrove forests, destroyed livelihood opportunities and access to coastal resources. The following paper discusses impacts of the tsunami on coastal resources and the associated coastal and disaster management implications. Data is drawn from a time series of digitised mean high water marks (MHWM's) sourced from Google Earth imagery, along with areal measurements of tambak, mangrove and casuarina cover and qualitative interviews with local residents. Two sites, namely, the Banda Aceh west coast and Lhok Nga Bay were studied. The results reveal that within these study sites 68% of mangroves and 92% of tambak ponds have not recovered since the tsunami resulting in the loss of between 241 and 725 tambak livelihoods and mangrove supplied resources including food, wood and shelter. Unique coastal environments respond to, and recover from, tsunami differently depending on factors such as tsunami characteristics, wave climate, sediment supply, vegetation, morphology and level of pre-disturbance human modification. While the study supports recent findings that mangrove and casuarina forests do not substantially mitigate the impact of large tsunamis, it strongly encourages their conservation for the environmental and economic sustainability of coastal communities. The study recommends that better integrated management of coastal resources such as mangroves and tambak, considering disaster management, environmental and economic concerns, will strengthen the resiliency of vulnerable coastal communities such as those in Aceh to future disaster.

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.