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Serving Sri Lanka

This web log is a news and views blog. The primary aim is to provide an avenue for the expression and collection of ideas on sustainable, fair, and just, grassroot level development. Some of the topics that the blog will specifically address are: poverty reduction, rural development, educational issues, social empowerment, post-Tsunami relief and reconstruction, livelihood development, environmental conservation and bio-diversity. 

Thursday, March 31, 2005

Tsunamis, earthquakes, their intensity and periodicity

Online edition of the Island: Feature: by A. Denis N. Fernando. Fellow of the National Academy of Sciences

The Geomorphology of the island reflects the different natural forces that operated on it over geological time that resulted in determining its present shape and form. The high degree of correlation between lithology, landform, soil vegetation etc provides us not only the information of the interior of the Island but also its coastline. MAP I indicates the Geomorphology of the Island. It comprises plains, ridge and valley systems, and Valley systems, plateaus, and mountains. It is the coastal plains that play the key role in the study of the effect of Tsunami. The boundary between the land and the ocean is not static but dynamic, it moves with the tide and cyclonic storm surges and other forces that act upon it like earthquakes and Tsunamies caused by underwater earthquakes.

The Island has a building coastline in the eastern, seaboard from Panama northwards up to the Jaffna Peninsula. Similarly the Western seaboard a building coastline northwards of Chilaw to the Jaffna Peninsula, while the Southern coastline is an and submerging coastline, clearly reflected when we study the river profiles especially at its mouths. In addition in the southern sea bed we have enormous submerged canyons from Panadura, to Yala also confirming the subsidence of the southern coastline.. The coastline of Sri Lanka indicates varying coastal Geomorphological features clearly seen on the Aerial Photographs and satellite imagery. We notice the river mouths , spits, lagoons , swamps, wetlands dunes estuaries etc that react differently to the storm surges and cyclonic activity and other ingress from the sea because of their different natural resistance, when the sea overtops the high tide level and proceeds inland.

A short digression to history reveals that after the change ‘in the river course of the Mahaweli Ganga in the 13th century the Dry zone was virtually abandoned the people shifted from the Ancient Hydraulic Civilization in the Dry Zone to the Wet Zone and built new capitals in Dambadeniya, Yapahuwa, Kotte finally in Kandy. In the meantime there were foreign incursions and in, the time of Parakramabahu VI 14th century) these incursions were suppressed. The warriors who suppressed them were settled by the King along the coast, which they even occupy today. During the Colonial period all the Forts and manor houses of the period were also located in the coastal regions. With the development these areas in more recent times they were also occupied by other citizens, while- in more recent times were drawn by the hotel industry displacing the poorer sections of the traditional coastal dwellers.

Today the Population of Sri Lanka is about 20 million and the coastal Zone comprises about a fourth of the countries population and a fifth of the country’s land area. Fisheries activity has been the economic activity from which about a on people are dependent on it and derive their livelihood from the sea. In more recent times with the development of the Tourist industry sponsored by local and foreign entrepreneurs there is competition for the sea shore for recreational purposes and entertainment. In the process the government sponsors the new Tourist industry as it brings more foreign exchange at the expense of the fishing industry from which the poorest of the people deprive their sustenance, and we cannot sacrifice industry and people involved in it to earn 30 pieces of silver from the tourist industry.. One must not forget that Marine fishery accounts for nearly 100 % of the counties fish production and about a on persons deriving their lively hood from economic activities of this zone and we cannot therefore afford to deprive them of their livelihood to earn a few dollars from the tourist and the entertainment industry that benefits and affects only the upperclasses of society.

I would give Just two examples to illustrate It. In Negombo, which is well known for its fisheries activity, from time immemorial there was a special quarter where the fisherman used to dry their fish and nets. This was acquired by the Brown's Beach hotel and the land appropriated for its use right up to the sea, The fisherman had no place either to dry their fish or their nets. They stared to use the famous seabeach beside the Negombo Fort and the Rest house depriving the Towns folk of the seabeach for recreation and the weekly music entertainment they enjoyed for generations, as the beach was used thence as a fish market and the drying of fish that emanates and unusual stink which kept the citizens away. In course of time the Lagoon also became a mass sewerage pit with no plans for even developing a harbour for the several boats that used it. Though plans have been drawn to develop the lagoon by opening the ancient second outlet to the sea so as to flush the lagoon using the tides from ancient times, but nothing has been done.

The second example is the development of the tourist complex at Bentota. I was commissioned and assigned the task of conducting a Hydrographic Survey of the- Bentota shoreline in the mid 60’s which comprised an area of 5 miles of coastline and stretching half a mile into the sea. The report recommended that the, spit of the river not to be built upon .However the first that the Tourist Board did was to build hotels on the spit And today the Tsunami has done the need for not taking scientific advice into consideration.. Today it is unfortunate that with thirty pieces of silver one could do anything that is not socially desirable by looking after the interests of foreign entrepreneurs and local investors whose interest is only to make a quick buck.

In 1982 I compiled a book on the Ancient Hydraulic Civilization of Sri Lanka which was published by the Sri Lanka Branch of the Royal Asiatic Society. This contained MAP 2 a map showing the distribution of Earthquakes epicentres around Sri Lanka compiled by the National Earthquakes Information Service of the US Department of the Interior up to 1979. This contained 15 epicentres of Earthquakes around Sri Lanka of which 4 Earthquakes had intensities between 5 and 6 on the Richter Scale. As- there was no indication of an intensity more seven which is usually destructive that causes the damage. I had therefore to turn to the historical records that recorded the severe damage by Earthquakes in Sri Lanka in the 2nd century BC, as well as the devastating effect of the change in river course of the Mahaweli Ganga in the 13 the century.

History records that in the century B.C. in the Eastern. Seaboard in Kalyani Kanika in the time of King Kelanitissa Tsunami occurred inundating that several townships had been destroyed and is recorded in me Mahawamsa. The location of Kalyani Kanika has been established using scientific evidence including coastal hydraulics sea currents and its location determined in the eastern southern seaboard. History records that Viharamahadevi the daughter of King Kelanitissa was set afloat at Kalyani Kanika to appease the Gods and was brought to shore by sea currents, which landed her in Kirinda. King Kavantissa thereafter married her and a new dynasty of mixed parentage was established between the Naga Dynasty the Greek Bachies.

A closer examination of Ptolemys’s Taprobane indicates Kirinda is in the Bay of Cetcum promotorium and the names and the locations of townships of the people who inhabited this area is indicated therein.

However today this promontory is no more and comprises the rock outcrops of the Little Great Bassess. Map 3 indicates the southern seaboard and the inundated area of the Kalyani Kanika Kingdom of King Kelanitissa the that of King Kavantissa, which coastline has now been washed away and is indicated in red. Statistically the return period of such an event is of the order of 2200 years.

It must also be recorded here that the Eastern Sea board is also subject to Cyclonic winds during the Northeast monsoon which strike this area severely with a periodicity of about a quarter of a century which have been recorded by the Meteorological Department. I was witness to one of the severest to hit the south eastern coast in 1978 where the eastern coastline from Batticaloa up to the interior of Maduruoya Dam site was affected where even the elephants had no fodder to eat and had to resort to eating the teak plantations for the first time. Some action has to taken by government like an effective warning and evacuation plan designed to be followed by the people of the area during such times.

The 13th century change in the river course of the Mahaweli Ganga due to an Earthquake resulting in the abandonment of the dry zone by the people and the shifting of the capital from Polonnaruwa to the Intermediate and Wet Zones to Dambadeniya, Yapahuwa, Kotte etc.

The accompanying aerial photograph indicate the old and present river course of the Mahaweli Ganga that changed course in the 13th century.

Aerial Photograph showing old and present river course of Mahaweli Ganga

Ancient Mahaweli flowing from West to East and Present Mahaweli flowing from South to North at Somawathiya

While Map 4 indicates the ancient chaityas prior to the 13th century that lay beside the old Mahaweli Ganga called Phasis fluvius or the River of the Persians by Ptolemy. These ancient Chitiyas lay like a string of pearls abandoned beside the old Mahaweli Ganga, with not a single chaitiya beside the present river north of Polonnaruwa. The return period of such an event occurring again of the order of over 2000 years.


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