Executive summary In the morning hours of 26 December, 2004, huge seismic sea waves triggered by massive undersea earthquake in the Indian Ocean caused the death of many thousands of people, leaving tens of thousands homeless in India, Sri Lanka, Indonesia, Malaysia, Thailand and Maldives. Fishermen, tourists and people living on the coast were unprepared for the waves that rose upto 6 meters high throughout the Indian Ocean, Andaman Sea and Arabian Sea. The earthquake, had its epicenter 257 km south southwest of Banda Aceh in Sumatra, Indonesia. This was the most powerful earthquake experienced in the region during the last 40 years. 176 persons were killed in Kerala as tsunami waves rising over the Arabian Sea invaded the land, wreaking havoc and destruction in the coastal fishing hamlets in the southern districts of the state. This report presents the impact of tsunami on natural eco systems. The marine environment in the southwest coast between Thottapally and Muttam has been successfully affected as a result of the impact of Tsunami , as reflected by the following findings : The concentration of nutrients has been reduced at all transects just after tsunami. However, values gradually picked up in the period from January to May 2005. Primary productivity had been drastically reduced in the wake of tsunami, especially near Vizhinjam and Kolachel. This also has improved considerably evident from the samples collected in May 2005. There was a lowering of plankton species diversity just after tsunami period, in January 2005. The fish catch has been reduced subsequent to tsunami. This has shown considerable improvement now, as reported by the fishermen from that area. The drop observed off Muttam indicates flow of water along the sediments to develop certain channels in the ocean bed. The presence of factors resulting in this channelling needs to be checked up with earlier bathymetric data. The sediment samples collected offshore contain more coarse sand, indicating recent transportation of the material from the coast The presence of heavy minerals in the sediment samples collected as far as 25 km offshore indicate that these minerals have also been transported offshore due to high-energy backwash. The impact of tsunami was maximum at Vizhinjam, Kolachel, and Valiyazhikkal due to the geomorphological feature, which resemble inland basin. Impact was least from Veli to Quilon and north of Thottappally due to long stretches of coastal plains. There are indicators which show that the marine environment is slowly recovering from the impact of tsunami, as evident from the improvement in biological productivity of this coastal stretch. The marine ecosystem has undergone significant changes during the tsunami. Changes in the sediment characteristics has been observed, with heavy deposition of fine clay and silt at the 30m and 100m station all along the Kerala coast with possible changes in the community structure, abundance and distribution of the marine benthic fauna. Though algal blooms not has been recorded by FORV Sagar Sampada during January 2005, extensive blooms of the cyanobacteria and trichodesmium were observed all along the Kerala coast during March and April 2005. Evidence of bottom disturbances by the tsunami with consequent displacement of macrobenthic infauna have been recorded throughout the coast. In general, lighter macrobenthic forms seem to have been transported to deeper waters by the receding tsunami waves, whereas the heavier forms might have got settled along the shallower waters. As the macrobenthic fauna form an important component in the food of demersal fishes, the observed changes of the composition and distribution pattern of macrobenthos may have short term/long term impacts on demersal fishery of the coast. Among the physico-chemical parameters analysed, significant changes were observed only in surface silicate values, which were almost five times higher than normal values. Surface nitrate values were comparatively less indicating the possibility of increased surface primary production soon after the tsunami. The pre-tsunami beach profiles were taken on 14th November, 2004, i.e., 42 days before the event. Huge accretion has been taking place in the southern side of the Kayamkulam inlet due to the predominant northerly longshore currents, during fair weather. Erosion has taken place in the northern side due to the groin effect of the breakwater. Thus the beach in the southern side of the inlet must have got considerably accreted with respect to the pre-tsunami profile and thereafter till th epost tsunami beach profiling on 15.01.2005. The field signatures on both the sides of the inlet showed scouring and erosion. The bathymetric survey conducted by CESS confirms the erosional tendency of the tsunami waves. As in the case of beach, erosion is noticed in the innershelf also. The sediment distribution pattern correlates the findings of bathometric resources. The preliminary results indicate changes in the innershelf sediment characteristics with shoreward migration of sandy patch off Kayamkulam. A deterioration in the quality of groundwater was noted soon after tsunami. It may be presumed that the pressure of the wave was transmitted underground through the coastal aquifer ahead of the surface wave. Salinization of shallow fresh groundwater, reduction in volume of freshwater lenses, landward shift of freshwater/saltwater mixing zones, pollution of groundwater by chemicals and other contaminants mobilized by flooding seawater were noticed. It is found, that after a month of the occurrence of Tsunami, that more than 80% of the wells showed reduced values in salinity when compared to the samples collected just after the impact of the tidal waves of Tsunami. It was also noted that during dry summer months of 2005, salt swings back to the surface soil again by capillary rise. The trapped salts will vertically oscillate between the perched ground water lens and the soil horizons for many years before being completely removed. Thus, the deleterious repercussions of sea wave intrusion are bound to last for a long time to come, and hence necessitates monitoring of the quality of water periodically. It may be mentioned that the entire island relies on deep ground water pumped day in and day out to meet the fresh water needs. Groundwater is steadily being pumped out for the last fifty years. The grave environmental impacts thereof have not been assessed. Tsunami had a mild but definite influence on the water quality as well as the characteristics of the sediments of the region. Surface water quality parameters (chlorophyte and suspended solids) showed definite changes, just after tsunami and later recovered over a period of time. This may be due to energetic mixing of coastal waters and the freshwater flown in from the rivers. The bottom sediments have also undergone some amount of churning leading to the release of organic mater associated with the undisturbed bottom mud. The effect of tsunami on the vegetation was also studied. It was noted that man- made plantations of coconut (Cocos nucifera) intermixed with jack (Artocarpus heterophylla), poovarasu (Thespesia populneoides) and Indian almond (Terminalia catappa) constitute the dominant sylvan landscape of the coastal vegetation and meager casualties of tree crops, especially coconut trees, were observed as the larger tree populations escaped the onslaught of the killer waves. The estuarine coastal belt and its associated natural mangrove vegetation are highly dissected due to various anthropogenic activities. As a result, extensive mangrove vegetations expected of the inter-tidal areas are missing and are in a highly degraded state, having transformed into a thicket-physiognomy. Nevertheless, the mangrove patches were found only slightly affected by the tsunami waves; a few instances of toppled coconut trees and some uprooted shrubs were the only detectable impact. In other words, the impact on mangroves was not specific to any individual plant species. Elsewhere, it has been pointed out that the presence of shelterbelts and mangrove vegetation helped in reducing the impact of coastal disasters. In addition to helping in breaking the force of the tidal waves, these trees served as escape routes for a number of individuals who took shelter in these trees to rescue themselves. Satellite imageries were used for assessing the damage. There was not much damage to the vegetation detected in IRS imageries. However, the shoreline changes with reference to sea shallowness are remarkable. An attempt to evaluate the sea shore changes with regard to the depth of sea, based on the soil reflectance value from the sea bottom, indicated that because of the increase in sea depth, in future the impact of the waves during monsoon may be of higher order in future. The water spread area has widened after the tsunami as seen in the imagery. Despite the massive structure, the sea walls were less effective being a structure in continuum, without break or openings permitting water to dissipate and the tidal force to dampen. Had the sea walls been discontinuous with occasional gaps, coupled with shelterbelt plantations of tree crops/mangrove vegetation might have diminished the disaster impact, as the vegetation would have served as a porous and effective barrier than the continuous engineering structures like sea walls. It was very evident that the populations along the beaches were directly affected by the tsunami. The worries of the people along the coast need to be addressed and a mitigation strategy need to be evolved. Coastal hazard zonation map need to be prepared and a vulnerability line need to be demarcated on the coast. Massive awareness among community need to be carried out for capacity building in the area. Chapter I Tsunami 1.1 Introduction The Tsunami which struck the Kerala coast on 26th December 2004 has created wide spread havoc on human life and property. It took away many valuable life and coastal destruction and damages to life supporting structures all along the coastal belt of Thiruvananthapuram, Kollam, Alappuzha, Eranakulam and Thrissur.