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Post-Tsunami Assessment in the coastal region between Kanyakumari and Ovari, Tamil Nadu – a case study S. Saravanan1 N. Chandrasekar1, C. Hentry3, M. Rajamanickam1 J. Loveson Immanuel1 and P. Siva Subramanian2 1. 2. 3.

Centre for Geo Technology, Manonmaniam Sundaranar University, Tirunelveli – 627 012 Marine Geochemistry Research Lab, Spic Research centre, V.O.C. College, Tuticorin – 628 008 Department of Physics, St. Jude’s College, Thoothoor – 629 176

ABSTRACT Coastal zones are dynamic areas that are constantly undergoing change in response to a multitude of factors including sea level rise, wave and current patterns, hurricanes and human influences. On 26 th December 2004, huge waves smashed across the shore between Kanyakumari and Ovari. As they crossed the beach, the waves up to 30 feet tall. Many people are dead due to crush and pull to sea and drowned as the mighty waves withdraw.

Many villages have been

obliterated, the death tole could exceed 300 but the damage to the property is very high. The size of the Tsunami is related to the area that moves on the ocean bottom and how far it moves. This region is manifested with marine terrace, sand dunes, beach ridges,

estuaries,

floodplains,

beaches,

mangroves,

peneplains,

uplands, sea cliff, etc., we have attempted the shoreline dynamics using beach profile survey, and coastal environment changes through on line survey, Govt. records and coastal geomorphological studies using remote sensing technique.

The major destructions were

identified in this paper. Key Words:- Tsunami, Waves, Ecological Impact.

1 INTRODUCTION 26th of December 2004, dawned silently like all the other mornings. It was so with the Coastal areas of Tamil Nadu. But, on that Sunday’s morning, all on a sudden, from Marina Beach, Chennai and down to the Coastal areas of Cuddalore, Nagapattinam and then down south to Colachel, the coastal area on the West side of Kanyakumari tip of India. In no time, the sea, in a sudden ferocious way rose high and got into the land covering two to three kilometres of areas with its watery net. In this process thousands of people were taken off, into the fold of the sea and killed. Whenever an earthquake occurs on land, the seismic energy released by it normally travels in waves resulting in damage to buildings and other structures(2). But the seismic energy released by the earthquake in ocean causes tsunamis which travel thousand of kilometers. The tsunamis hit the obstacles that come along their path with great ferocity and the east coast was the first obstacle where the huge tidal waves encountered, causing destruction all along the coast. When, We visited the affected coastal areas from Kanykumari to Ovari, the whole area gave a painful feeling on how the already deprived and the marginalized communities like the fisher folk, gets more and more victimized during such calamities, of natural or human made. All the areas remained like deserted battlefields with broken buildings, dead bodies, carcasses of animals, uprooted trees and deserted and lone houses and huts. The fishing boats could be seen damaged and lying in different faraway areas up to one to two kilometers away from the sea. The fishing nets were also seen lying in a stranded way. There were cries and wailings everywhere due to the

destruction made by the tsunami in the study area. The detailed studies of Post-tsunami assessment were made in this paper. 2 Tsunami and Study area The study are located between Latitude of N 80 04’ to N 80 17’ and Longitude of E 770 32’ to E 770 54’ at southern part of the Tamil Nadu. It encompasses district of Kanyakumari and Tirunelveli (Table 1). It is bounded by Bay of Bengal in the east, Western ghats in the west and Indian Ocean in the south being the southern most tip of India (Figure 1). Mostly Kanyakumari district made of Charnockite, Garnetiferous gneiss and Leptynite and Tirunelveli district made of mostly Garnite gneiss. The killer earthquake, which had its epicenter near Indonesia, claimed five lives in the district when tidal waves triggered by seismic activity entered nine coastal villages and caused extensive damage to fisherman’s property particularly catamarans and fishing nets. Of the nine coastal villages in the district – Koottapuli, Perumanal, Panjal, Idinthakarai, Thomaiyarpuram, Koothankuzhi, Uvari, Koottappanai and Kooduthaazhai

all under Radhapuram taluk and Koothankuzhi,

Idinthakarai and Koottapuli were the worst affected. However, no men and materials at the site of Kudankulam Nuclear Power Project were affected

or

damaged.

The

seawater,

which

started

entering

Kooththankuzhi around 9.30 am, invaded about 750 meters into the villages.

The intense tides, which entered more than six times

between 9.30 am and 1 pm. Capsized fiberglass boats with huge holes could be seen floating at a distance from the shore.

Around 30

catamarans were pushed up to the bridge, nearly a km away form the sea Seawater swelled around 9.30 am and moved nearly 250-400 meters into the land. When it receded, it retreated one km beyond the

normal point, leaving a huge stretch of dump land.

However, the

retreat and invasion of heavy tides continued in frequent intervals. Vivekananda Memorial Rock and near the Tiruvalluvar Statue at Kanayakumari, the waves were boost up above a height of 33m. Compared to Western coast of Tamilnadu not a lot of Casualties not much occured in Southern Coast of Tamil Nadu. 3. Tsunami wave approachs along the study area In Tamil Nadu, the “shadow” coastal regions of Tuticorin, Rameswaram, Kanyakumari, and Tiruchendur were relatively less afftected.

In these areas, the effects were generated by diffracted

waves, which were less intense than the direct impact of tsunamis. When a wave encountered a large barrier, its motion penetrated the region of the geometric shadow by a process of scattering of wave diffraction. When the waves were diffracted by a large leading body, their

height

gets

progressively

diminished,

resulting

continued

reduction in wave energy flux until it met with another boundary of the trailing

body.

Understanding

this

phenomenon

could

have

considerable practical significance in establishing the wave action behind large breakwaters or offshore structures and around small islands(5). The speed of the tsunami was governed by the water depth. Speed reduces and wave height.

Speed reduces and wave height

increased as it approached the shore (Fig.2) 4. Methodology 4.1. Data and field inspection

Most of the data and information were gathered from field inspection of shoreline morphology as well as from eyewitnesses and survivors through interviews. True wave heights of tsunami were measured and/or estimated from the accounts of the interviewees (i.e. relative to their body or height of watermarks) and landmarks such as trees, rocks, coral reefs, dikes, riverbanks and other natural features found in the area. municipalities

we

Existing records from collector office and gathered

information

wherever

possible

for

verification purposes, particularly in terms of damages related to tsunami inundation. During interviews, information was extracted from the interviews through

a patterned set of questions and through their own

spontaneous accounts from the time they felt the strong ground shaking until the tsunami waves receded to its normal level. Interview was conducted at least every 2 to 5 kilometers for a uniform sampling point between municipalities and communities along the coast. Each tsunami intensity measurement for all the areas visited is based on the Tsunami Intensity Scale (Ambrasey, 1962). 4.2. Tsunami Height The change in tsunami height with distance from the shoreline is important information for determining how the tsunami lost energy as it moved inland. Casualties and damage to structures were strongly related to the height of a tsunami not only at the shoreline, but also how it decreases inland. There were structures and trees remaining in many locations, where the tsunami was large. Tsunami height information is one of the best data set ever collected on how a tsunami looses energy moving inland. Water levels were usually greatest near the shoreline and

decrease to zero at the limit of tsunami penetration where all the energy of the tsunami was expended (Fig.3). Water levels near the shoreline measured varied from less than 3 meters to more than 10 meters. In general, water levels, and by inference tsunami height, near the shoreline increased on the North toward the South. There was, however, considerable variability caused by a number of factors including underwater topography (focusing or defocusing of tsunami energy, removal of energy by drag on the bottom and breaking) and orientation of the coastline. In areas where the there were no structures or trees left standing after the tsunami, tsunami height will be modeled using inundation distance, run-up elevation, and topographic data.

Fig.3:- Schematic diagram showing the Tsunami height

4.3. Inundation distance - The distance from the shoreline to the limit of tsunami penetration Inundation distance measured varied from less than 100 meters to more than 1 kilometer. (Table. 2) In general, inundation distance increased on the Northern coast of Tamil Nadu towards the South. However there was considerable variability caused by a number of factors, including slope of the land (greater inundation distances in flatter areas), underwater topography, and orientation of the coastline. The South and West coasts of Tamil Nadu are characterized by rocky headlands and intervening embayment with narrow beaches and low, coastal plain topography. Tsunami inundation was greatest in the embayment. Measured inundation distances will be compared to predictions to improve the ability to model future tsunamis in Sri Lanka and elsewhere(4) . Generally, tsunami inundation varied from several centimeters and reached as far as 100 to 1000 meters inland wherein the coast between Kanyakumari and Ovari suffered the worst where many houses and boats were totally destroyed and/or washed away into the open sea.

Based on inundation distance, prepared the Tsunami

Classification map (Fig. 4). 4.4. Run-up elevation—the elevation above sea level of a tsunami at the limit of penetration.

Run-up elevation measured varied from less than 3 meters to more than 12 meters. In general, run-up elevation increased towards the South. On the South coasts run-up elevation typically was greatest at the headlands. There was, however, considerable variability caused by a number of factors, including slope of the land (lower run-up elevations in flatter areas), underwater topography, and orientation of the coastline. Measured run-up elevations will be compared to predict and to improve the ability to model future tsunamis in Tamil Nadu and elsewhere. 4.5. Tsunami Sand Deposits The tsunami in Tamil Nadu carried sand from the beach and ocean floor and deposited it in buildings, on top of boulders, and on the ground. Tsunami sand deposits were found at all sites. Although tsunamis were capable of eroding the land, erosion in Tamil Nadu was often concentrated in a relatively narrow zone near the coast. (MidTide region). The sand eroded was transported both onshore and offshore. The sand transported onshore formed a recognizable tsunami sand deposit. Tsunami sand deposits started about 50 meters inland, and decreased in thickness from about 10 centimeter total thickness to about 2 cm thickness at about 250 meters inland. Tsunami sediments were dumped in very few places. Most of these deposits were eroded or washed away by the waves of the same tsunami event or the succeeding big waves of typhoons and the usual high tides. The only place where the deposit is still available for future and further studies in Chinna muttam, Rasthakaddu, Kuttapuli, Navaladi and Perumanal (Figure. 5 ). In other locations where the tsunami was larger, both the width of the erosion zone and the tsunami deposit were larger. The tsunami sand deposits often contained two or more layers. These layers were

formed by different tsunami waves and by variations in flow within a wave(3) . 4.6. Changes in Beach Morphology and sediments Sand dunes may have totally disappeared or remnants may be left with a vertical seaward slope and bereft of vegetation (Herbs). In small sandy bays, all the sand may have been moved to the end of the beach. Beach Profile was completely changed in some places (figure. 6). And also, Beach width, Beach slope also varied after tsunami. (Table. 3) Whenever, the sea is inward, the deposition is taken place. After Tsunami, heavy mineral deposition is present significantly. 3m – 4m sea level rise leading to erosion activities changed in the beach slope variation. Many gentle slope regions have been transformed into steep slope region and flat regions also transformed into gentle slope regions. Heavy mineral deposits in sand washed ashore from the deep sea by the tsunami seismic waves from mining area along the coast of Kanyakumari and Tirunelveli district. 5. Analysis and Discussions for Post-tsunami assessment Out of nineteen (19) towns and communities that were visited, only nine sites were directly affected by the tsunami event. These sites were located mainly along the coastal areas of Tamil Nadu. True heights were measured in all locations together with the arrival times and

period

of

tsunami

waves.

Other

observable

features

like

subsidence, uplift, erosion etc. were likewise noted. During the field visit, it was seen that as the waves approach the shores of Kanyakumari at about 100m from the shore, the wave height is about 20cm to about 50cm. But as it enters the concave-shaped

coastline the wave increase its size to almost double or triple as it breaks on the shore. Such increase in wave height is an indication of the presence of features that enhance the unusual wave height. The cause of the unusual height of the tsunami in this area is most probably due to one or combination of these features: the direction of the wave as it approaches the shore, submarine topography and the concave-shaped of the shore fronting Tiruchendure (Figure.7). However, based on tsunami time arrival, the earliest wave reached in Ovari region, that is located about 60km north of the town. The tsunami arrived in this area nippy relative to Kanyakumari. Wave time arrivals in the southern area have some variations.

Generally, the

tsunami was preceded by lowering of sea water level from about 50250m exposing corals and other submarine features. Further, this coastal area remained flooded at about a meter higher than the usual. On the other hand, only few areas like Kanyakumari were affected by erosion due to the passage of tsunami waves. It can be deduced as well that the amount of sediment dumped by the tsunami wave is not significant enough to cause any noticeable local lowering of water level or increase in land elevation relative to the previous mean sea level. Among the coastal features observed, the coral reef located between 100-200m from the shore is the most significant. Residents noted that the tsunami wave broken as it encountered the reefs and decreased in height before it reached the shorelines of Southern Tamil Nadu.

Without coral reefs, the tsunami wave could

have reached the shorelines with a much higher and in more destructive height.

From our investigation mainly tsunami impacts

more in lowland area and inland areas like estuaries, tidal inlets and channels. (Figure 8).

Lastly, it was noted that based on the interviews, only one strong ground shaking was observed by the residents. Considering the magnitude and location of the event at that time, we can somehow infer the most probable event that was felt and tsunami damages in the south. The tsunami wave propagated in the southern part of Tamil Nadu based on their fault zone present along these sites. Furthermore, much have to be done in terms of seismic analysis to confirm the above mentioned probabilities. 6. The environmental impact of tsunamis Reports

about

the

tsunamis

understandably

have

been

dominated by tales of death, suffering and the physical destruction of infrastructure. But man was not alone in feeling the impact. But, ecosystems and other species were also affected. Saltwater intrusion in ground water was disappearance or relocation of beaches have also observed. Tsunamis may make small, low islands uninhabitable. Vegetation in large stretches of lowland can be hurt substantially as saltwater-tolerant mangroves and grasses take over from other species. For rare animals with specific reproduction sites, like marine turtles, the tsunamis effects could spell extinction. Whereas the damage to the environment on land can be seen and the ravages imposed on the marine environment are hidden. Obviously, when extremely strong waves hit coral reefs, some coral breaks off. But this is a comparatively small problem. The surface of coral is highly sensitive, and will now be exposed to major damage from all sorts of silt and debris carried back by water receding from flooded land. At the same time, the materials brought back from land to sea include nutrients and trace elements that cause a boom among plankton, which in turn feed other marine biota. Locally, but sometimes

still at a grand scale, the shock waves cause major sediment slides on steep underwater slopes such as those of the continental shelves. Closer to the shore, many natural ecosystems, most notably coral reefs and mangroves, act as natural shock absorbers and wave breakers. During the past several decades, these ecosystems have been damaged and reduced in most countries along the Indian Ocean. Indeed, the damage from the tsunami waves was far more devastating than it would have been had they still been intact. The situation on Sumatra is similarly grim, and it is even worse in the Tamil Nadu, where not only fishermen and boats were lost, but harbours were ruined. Such major losses in fishing capacity, with their far-reaching negative socio-economic consequences on the human populations and bound to have major, mostly favourable, effects on the fish stocks (Table 4).

The reason is simple: with most fish

populations nowadays hit hard by over-fishing. Another factor that fish stocks is a religiously motivated by the public in some areas to eat marine fish, as they are perceived to have fed on human corpses washed to sea (Table 5). 7. The ecological programme demands the following a) Promote peoples' participation in the conservation and enhancement of mangrove and other coastal wetlands, as well as coral reefs and coastal and marine biodiversity; A participatory mangrove forest management programme based on the guidelines already developed. It is based on the successful model of joint forest management that is in progress in most parts of India.

b) Promote the organization of community nurseries of mangrove and other appropriate tree species chosen under the coastal bio-shield and agro-forestry programmes. c) Regenerate fisheries and foster a sustainable fisheries programme. The new fishing vessels and nets should be designed. So that they do not disrupt the fish life cycle by catching young ones and also do not destroy sea grass beds that serve as habitats for dugongs. d) Provide landward housing sites for fisher families: The new houses should respect the 500 meter restriction and should be ecologically designed. Had all fisherfolk been given housing sites on the landward side of coastal roads, the death toll from the tsunami would have been much lower. Anticipatory action against sea level rise also demands a human security driven design of coastal habitations. e) The third medium - and long-term programme is establishing a network of rural knowledge centers. The crucial importance of timely information in averting loss of life during natural calamities is not widely recognized. A network of rural knowledge centers must be established all along the coat as soon as possible. Such centers will use in an integrated way in the internet, community (FM) radio, cable TV, and the Indian language press. They will provide generic as well as dynamic information, and help disseminate locale-specific and demand driven information. f)

A

resource

center

for

mangrove

forest

conservation,

rehabilitation, and expansion is urgently needed. Further, training modules must be prepared in local languages on a wide range of topics relating to both ecological and livelihood security. 8. HOW TO PREVENT OR REDUCE THE TSUNAMI IMPACT

8.1. Groynes did their bit Royapuram-Thiruvottriyur belt, has witnessed severe coastal erosion for decades, but did not suffer due to the groynes being constructed. As many as 10 groynes have been proposed along this belt, of which four have been completed.

“The construction of the

groynes has led to the formation of smaller beaches in and around them. Though the full benefits of the groynes will be realized later, the fact that they ensured virtually nil damage in these during tsunami. The similar structure can be recommended based on the other nearshore parameter to the Tsunami vulnerability zone.

Which is a

sign of their success. 8.2. Mangroves can act as shield against Tsunami Tsunami is a rare phenomenon. Though we can not prevent the occurrence of such natural calamities, our anticipatory research work to preserve mangrove ecosystems as the first line of defense against devastating tidal waves on the eastern coast line has proved very relevant today. The dense mangrove forests stood like a wall to save coastal

communities

living

behind

them.

The

mangroves

in

Pichavaram and Muthupet region acted like a shield and bore the brunt of the tsunami. The impact was mitigated and lives and property of the communities inhabiting the region were saved. One is to conserve and regenerate coastal mangroves along the eastern coast of the country, and the second is transfer of salt-tolerant genes from the mangroves to the selected crops grown in the coastal regions. It is not found that wherever the mangroves have been regenerated, especially in the Orissa coast, the damage due to tsunami is minimal. Tsunami and mangroves are high-lighting the need to conserve and rehabilitate mangroves as the frontline defense against tidal forces.

9. DISCUSSION AND CONCLUSIONS Based on field investigations and interviews, people observed the tsunami between 1-10 minutes after the strong ground shaking related to the event. The water level retreated to about 50-250m several minutes before the tsunami waves arrived. True wave height varied from several centimeters up to 6 meters in some areas. The most common observations showed that the wave related to the tsunami oscillated for several minutes and the first wave was usually the biggest among the waves. The unusual height at Kanyakumari is probably the result of the combined effects of wave direction, submarine topography and shoreline shape of Kanyakumari. Based on the overall true height of the tsunami, the average height of tsunami is about a 5-7m meter high.

Tsunami inundation varied from several

centimeters and reached as far as 200-500 meters above in inland. There was no unusual uplift and/or subsidence observed in the northern coast. During the above field visits, at least two places were identified for future stratigraphic logging or trenching of tsunami deposit. Existing coral reefs somehow played an important role in attenuating the tsunami heights, thus reducing its destructive effects. Future activities to occur at any time in the coast to elucidate the tsunamigenic event are recommended. Trenching of tsunami deposit, review of historical events, and detailed mapping of shoreline morphology would be very helpful. Furthermore, seismic analysis and simulations might explain some anomalous observations. 10. RECOMMENDATIONS

Based on the above observations, the following activities are suggested: 1.

Trenching work or agur sampling from tsunami deposits to get more information about the tsunami as well as the other possible previous tsunami events.

2.

Review other big historical events in the area for future tsunami by simulations and correlation with regional geodetic database.

3.

Detailed study of morphological features along these areas to identify possible areas that could generate unusually high tsunami waves.

4.

Closer analysis of seismic record to clearly explain why there was only one Strong ground shaking felt and/or to identify which event.

5.

Grow the mangroves or coral reefs and most of the construction is on beaches or close to high tide region.

6. Build the groins in vulnerable Coastal villages to control the tsunami effect.

Acknowledgement: The authors are thankful to Dr. Bhoop Singh, Director, NRDMS, Department of Science and Technology, New Delhi for his kind help in preparing the manuscript and generating the data from field.

The

authors are thankful to Department of Science and Technology, New Delhi for providing the financial assistance under NRDMS Scheme (ES/11/526/2000) and (ES/11/936(5)/2005). References:

1)

Ambrasey, N.N., 1962. Data for the investigation of the seismic sea-waves

in

the

Eastern

Medditerranean.

Bulletin

of

Seismological Society of America 52(4): 895-913. 2)

Besana, G. M., M. T. Mirabueno, G. Quiambao, and P. Reniva, Final Report of 1992, Bislig.

3)

Daligdig, J.A. and Tungol, N.M. 1992. The May 17, 1992 Mindanao Earthquake, PHIVOLCS, Annual Report.

4)

Lander, J.F., Whiteside, L.S. and Lockridge, P.A., 2003. Two decades of Global tsunamis 1982-2002, Sceince of Tsunami Hazards, The International Journal of the Tsunami Society, 21(1): 3-88.

5)

Narag, I. C., Lanuza, A. G., Diongzon, N. F., Peñarubia, H. C. and Marte, F. A., 1992 Quick Response Team Report, PHIVOLCS.