The impacts of the 26th December 2004 Indian Ocean tsunami were examined on three separate coastal sectors in the west, north and east of Banda Aceh. The most vulnerable coasts are the soft coasts, such as mangroves, and the least vulnerable are the rocky headlands with the sandy coasts occupying a broad intermediate position. The extent of impact for each category of coasts appears to vary with the tsunami wave height and other characteristics. Coastal recovery was remarkably rapid, especially for sandy beaches. In some cases, foredunes returned to the coast. The impacts and recovery processes provide valuable lessons for coastal management, for example, in the replanting of mangroves and other coastal vegetation in the modified coastal environments and the questionable construction of seawalls on accreting coasts. In years to come, the tsunami impacts would disappear, except for modifications by human activities.
The 2004 Indian Ocean tsunami transported large boulders shoreward at Pakarang Cape, Thailand. To elucidate boulder transport processes using their original locations, initial tsunami waveform, and coastal profiles, we conducted a cross-sectional calculation. Our results indicate that the tsunami (trough arrives first) might have displaced boulders and cast some on the tidal bench. However, if the wave crest arrives first, only some reef-edge boulders are displaced and emplaced on the tidal bench. More and larger boulders are displaced and deposited on the tidal bench when the reef slope is gentle, as at Pakarang Cape, than for a steep slope case.
We investigated damage to mangroves from the 2004 Indian Ocean tsunami at Pakarang Cape and Namkem, Thailand. Visual inspection of remotely sensed images revealed that 12 and 20 ha of mangrove forests were damaged, respectively, at Pakarang Cape and Namkem. Field surveys revealed that mangrove trees were destroyed particularly around the river mouths and channels. Numerical simulation indicated that the flow concentrated at the river mouth and inundated mangrove forests through river channels. We concluded that the tsunami flow pattern was largely affected by local river mouth and channel topography. Damage to mangroves might be severe in such areas.
Three sandy beaches on Phuket and Kho Khao islands, Thailand, were monitored annually to study the short- and long-term impacts of the 2004 tsunami on their meiofauna assemblages and sediment characteristics. The sediment grain size compositions changed significantly within one year after the tsunami (improved sorting and less negatively skewed distributions), but meiofauna assemblages did not. The fast recolonization of the beaches after the tsunami confirmed that meiofauna is highly resilient to ecosystem disturbances. The tsunami was not observed to have a long-term impact on meiofaunal assemblages.
On 26D ecember 2004, a tsunami severely affected almost all the coastal villages of Kanyakumari District, India. It was one of the worst affected coastal sectors of South India. An attempt has been made here to assess the impact of the tsunami hazard on coastal landforms and the level of inundation using GIS techniques. The areas of inundation were surveyed and mapped by fixing regular transects along the coastal regions. The percentage of inundated area in the total area was estimated. It was found that inundation was higher on low-lying coasts and relatively less on elevated coasts. In some cases, the extent of inundation was a few kilometres in relation to other coasts, but the percentage of inundated area in the total coastal area was high. The extent of inundation along the study area varied from 50 m to 450 m. Inundation was minimal in coastal villages like Kanyakumari, Agastheeswaram, Madhysoodhanapuram and Dharmapuram, but extensive at Colachel. The percentage of inundated area in the total area ranges from 8% (Dharmapuram) to 39% (Colachel). The degree of inundation was controlled by coastal geomorphological features such as sand dunes, cliffs, coastal vegetation, nature and configuration of the beach, not to mention the angle and velocity of the invading tsunami surge.
On December 26th, 2004, a tsunami hit the Andaman Sea coast of Thailand, leaving bimodal tsunami deposits in the coastal zone. Granite boulders and sandy tsunami deposits were investigated near Thap Lamu Navy Base in Phang Nga Province, Thailand. Boulders (< 2.5m³) were mostly scattered close to a tidal inlet on a flat plain elevated 1-2m above the high tide water level, reaching up to 140m inland. Most boulders had oyster shell remnants over their surface, which suggests that they were dragged from the nearby shore. The tsunami also brought a sheet of medium to coarse grained sand, with thickness ranging from a few mm up to 37cm. The distribution of deposits was mainly controlled by the existing topography. Another group of granite boulders was found between 150 and 300m from the coastline, at elevations of 2m and more. Their size reached 5.5m³. This second group of boulders may have been transported by an ancient tsunami.
There have been very few quantitative studies of the intertidal and shallow water biota of the Andaman Coast of Thailand and thus it was very difficult to provide precise estimates of the impact of the tsunami on coastal resources. Some quantitative data from Laem Son National Park existed, having been collected by the present authors, and these indicated that the most severe impacts were on the intertidal sand beach fauna, on rocky shore assemblages and on the seaward edge of mangrove forests. Inside the forests there was heavy deposition of coarse sediment on the forest floor and this led to changes in the species composition of the infauna. Most, but not all, sea grass beds escaped serious damage. By 2008 intertidal sediment assemblages contained a similar number of individuals to that recorded before the tsunami. Pre-tsunami data indicate that open coast, estuarine and seagrasses assemblages are naturally highly variable and thus were well adapted to recovering from the tsunami disturbance. Offshore sediments lack pre-tsunami information, but they too appear to be normal. Size frequency analysis of a population of the heart urchin Brissopsis luzonicus indicate that some individuals survived the tsunami but that there is heavy domination by the first post-tsunami cohort suggesting heavy colonization of disturbed seafloor. The trees in the seaward fringe of the most exposed mangrove forests still have to recover from tsunami damage, although the benthic fauna within the forest has returned.