Investigating beach erosion related with its recovery at Phra Thong Island, Thailand caused by the 2004 Indian Ocean tsunami

Abstract

Abstract. The 2004 Indian Ocean Tsunami and the 2011 Great East Japan earthquake and tsunami caused large-scale topographic changes in coastal areas. Whereas much research has focused on coastlines that have or had large human populations, little focus has been paid on coastlines that have little or no infrastructure. The importance of examining erosional and depositional mechanisms of tsunami events lies in the rapid reorganisation that coastlines must undertake immediately after an event. Through understanding the precursor conditions to this reorganisation is paramount to the reconstruction of the coastal environment. This study examines the locations of sediment erosion and deposition during the 2004 Indian Ocean Tsunami event on the relatively pristine Phra Thong Island, Thailand. Coupled with satellite imagery, we use numerical simulations and sediment transportation models to determine the locations of significant erosion and the areas where much of that sediment was redeposited during the tsunami inundation and backwash processes. Our modelling approach confirms that beaches on Phra Thong Island were significantly eroded by the 2004 tsunami, predominantly during the backwash phase of the first and largest wave to strike the island. Although 2004 tsunami sediment deposits are found on the island, we demonstrate that most of the sediment was deposited in the shallow coastal area, facilitating quick recovery of the beach when normal coastal processes resume.

Reconstruction of flow conditions from 2004 Indian Ocean tsunami deposits at the Phra Thong island using a deep neural network inverse model

“…While the inverse analysis of tsunami deposits provides estimates of the flow characteristics in specific regions, two or three dimensional forward modeling is required to infer the spatial distribution of the flow parameters on a regional scale (Masaya et al, 2019;Li et al, 2012). The horizontal two dimensional forward model TUNAMI-N2 was applied to the Phra Thong island, to estimate the spatial distribution of the maximum flow depth in this area (Masaya et al, 2019). However, model appeared to have overestimated the maximum flow depth when compared with the measured values obtained by the KSCOE group (Choi et al, 2006), ), with the former returning a flow depth of 6-8 m and the latter returning a depth of 4.2-3.8 m.…”

“…The model's results strongly depend on these fault parameters which should be iteratively modified to fit the measurement or distribution of the actual tsunami deposits. Moreover, the model of Masaya et al (2019) employed single grainsize class for the reconstruction of the parameters from a larger area, which could have resulted in an erroneous estimation as the distribution of grain-size of tsunami deposits varies due to sediment transportation and deposition (Sugawara et al, 2014).…”

“…On December 26, 2004, a Mw 9.1 earthquake triggered a devastating tsunami that affected the coastal areas and cities adjacent to the Indian Ocean, which resulted in extensive socio-economic damage and numerous fatalities in several countries including Thailand, Indonesia, Srilanka, India, Myanmar (Rossetto et al, 2007;Satake et al, 2006;Sinadinovski, 2006;Philibosian et al, 2017;Satake, 2014;Pari et al, 2008). In Thailand, 8300 people lost their lives, with 70 lives and a village of households were lost on the Phra Thong island in Phang-Nga province (Satake et al, 2006;Masaya et al, 2019). The total damage was estimated to amount to around USD 508 million, which equates to 2.2% of GDP which while the number of deaths was 4225, with the injured and missing cases and the cost reconstructing properties much lower than the overall damage value (Jayasuriya and McCawley, 2010;Suppasri et al, 2012).…”

“…To obtain the onsite flow conditions essential to tsunami hazard mitigation in terms of devising future structural measures and levee construction, investigating tsunami deposits, which provide crucial information on the flow discharge and the extent of the tsunami inundation (Dawson and Shi, 2000;Udo et al, 2016;Sugawara and Goto, 2012;Furusato and Tanaka, 2014;Sugawara et al, 2014;Koiwa et al, 2018;Masaya et al, 2019), is important. It has been suggested that, after distinguishing tsunami deposits from other deposits such as flood or storm deposits through their sedimentological characteristics (Morton et al, 2007;Switzer and Jones, 2008;Szczuciński et al, 2012), they can be used to reconstruct tsunami flow conditions (Jaffe and Gelfenbuam, 2007;Smith et al, 2007;Paris et al, 2009;Sugawara and Goto, 2012;Naruse and Abe, 2017;Tang et al, 2018).…”

“…The island is a historically important location for the study of tsunami deposits, with pre-2004 tsunami deposits preserved in inter-ridge swales and an overall extensive distribution of paleotsunami deposits having been reported (Jankaew et al, 2008;Fujino et al, 2009). In fact, palaetsunami deposits have been identified at Phra Thong isalnd, Thailand were identified by several research teams (Jankaew et al, 2008;Sawai et al, 2009;Fujino et al, 2008Fujino et al, , 2010Brill et al, 2012b;Pham et al, 2017;Gouramanis et al, 2017;Masaya et al, 2019).…”