Reconstructions of the coastal impact of the 2004 Indian Ocean tsunami in the Khao Lak area, Thailand

Abstract

[1] Khao Lak, SW Thailand was severely affected by the tsunami on 26 December 2004. Here we present reconstructions of its coastal impact in this area. These are based on (1) eyewitness reports alone and (2) eyewitness reports supported by videos and photos of the tsunami and the damage it caused, field measurements, and satellite imagery. On the basis of eyewitness reports, we estimated that the sea began retreating at 1000 local time (LT) and, based also on photos, that the tsunami arrived at 1026-1029 LT. On the basis of videos of the tsunami, we estimated an offshore wave direction of 083 ± 3°and on the basis of the paths by which eyewitnesses were carried, we estimated an onshore direction of 088 ± 6°. On the basis of videos, we calculated that the velocity of the wavefront on its final approach was 33 ± 4 km/h. We obtained tsunami heights of 7.3 ± 0.8 m (relative to ground level) on the basis of eyewitness reports and 8.0 ± 0.6 m (relative to mean sea level) on the basis of field and photographic data. On the basis of eyewitness reports and photos, we concluded that Khao Lak experienced at least two main waves with a period >40 min. From eyewitness reports and satellite imagery, we measured maximum inundation 0.5 km in the southern part of the area, which is confined by a steeply sloping hinterland, and 1.5 km in the more gently sloping northern part. Comparison between these reconstructions supports the reliability of eyewitness reports as a source of quantitative data, and comparison with the numerical simulation by Ioualalen et al. (2007) supports the validity of the simulation.

26 December 2004 tsunami deposits left in areas of various tsunami run up in coastal zone of Thailand

“…Altogether, up to 7 waves were reported by eyewitnesses (Mård Karlsson et al, 2009). Some of the witnesses reported a smaller wave arriving a few minutes before the main wave (Mård Karlsson et al, 2009). Alternatively, some witnesses reported several waves inundating the land in periods of a few minutes without intervening water withdrawals (Choowong et al, 2008b).…”

“…Most of the eyewitness reports documented two major waves, with a period of approximately 40 minutes, inundating the coastal zone; several smaller waves were also documented. Altogether, up to 7 waves were reported by eyewitnesses (Mård Karlsson et al, 2009). Some of the witnesses reported a smaller wave arriving a few minutes before the main wave (Mård Karlsson et al, 2009).…”

The influence of land cover roughness on the results of high resolution tsunami inundation modeling

“…The area is characterized by several tidal inlets and large patches of dense tropical vegetation like mangroves, casuarinas forests, or coconut plantations. Khao Lak was the most heavily impacted area in Thailand during the 2004 tsunami, in which 80 % of the hotel capacity was lost (Mård Karlsson et al, 2009). The study area located south of Pakarang Cape comprises the largest mangrove patch in Khao Lak, a tidal inlet, aquaculture, coastal forests and hotel resorts.…”

Reproducing an extreme flood with uncertain post-event information

“…These can be done through eye-witness accounts and field campaigns (Brandimarte and Di Baldassarre, 2012;Ciervo et al, 2015;Gaume and Borga, 2008;Horritt et al, 2010;JICA, 2002;Smith et al, 2002), sometimes in combination with additional methods such as searches into historical documentation and paleo-flood techniques (Mård Karlsson et al, 2009;Smith et al, 2012;Valyrakis et al, 2015). Such surveys have been useful to estimate hydrometric data of the floods.…”