Sea levels, surveys and sovereignty


By Somasiri Devendra


After working in many places – where I did more learning than contributing – I finally ended up introducing Maritime Archaeology in Sri Lanka. This new field of activity opened new vistas of experience and knowledge. Naturally, I was involved in the maritime archaeological explorations and excavations throughout the 1990s, and early 2000s. The story I relate, and line of search that followed, are just one example of how a seemingly random observation turned out to be an obsession.

While the rest of the team was under water doing all the useful work I, no longer fit to dive, would wonder around Galle Fort teasing out its many secrets. The old gateway from the Fort, through the "pakhuis" to the quay (originally of wood but now replicated in concrete) fascinated me. One day, looking at the details on its various faces I saw a stone block set into the outer wall, on my right if I faced the harbour. It was not polished but well engraved with the letters "GTS" and, below them "BM". No one in the Archaeological Dept. or Central Cultural Fund in Galle, or even in Kachcheri circles was able to explain it and I filed it away knowing that it was something special. Once, we had to visit the Survey Dept., Galle, in search of old maps of the Fort, we were referred to an officer who had been serving there a long time. After he had attended to us I asked him whether he knew about the tablet. He laughed, and said that I was the first person who had asked him!

"Of course", he said, "our Dept. has to do an annual inspection of it. We dig down below it till we come to a Survey Bench Mark (the "BM") which marks the "Mean Sea Level" (i.e.the midpoint between the high and low tides) to see that it is intact. " It was placed there", he continued, "when the first Surveys were done under the "Greater India Triangulation Survey" ("GTS") in the 19th.century."

We had got him going on a favourite topic, and he continued that there were similar bench marks in Colombo and Trincomalee and, he added. there was also a similar one on Kachchathivu Island: the Dept. had used that as evidence of sovereign ownership when India was disputing Sri Lanka’s claim to that island.

All this was new to me, and pieces of a jig-saw were assembling in mind in a random and highly disorganized way. I was able to see the full picture only very recently.

Next, in our 1996-7 Report on "The Galle Harbour Project", there is a Note by Jeremy Green where he explains the method of converting positions from Latitude and Longitude ("UTM", or Universal Transverse Mercator, used on GPS) to Sri Lanka Survey Dept. maps which used on a survey datum called "Ceylon 1933( Kandawela-Everest)". "Everest" was a link to GTS, I thought, and must be the mountain and "Kandawala" must be Sir John Kotelawela’s estate at Ratmalana, now the KDU. In my ignorance I guessed wrong: "Kandawala" was not in Ratmalana but a suburb of Negombo and "Everest" was not the mountain!

In Galle, I would spend time with the Asst.Harbour Master, Galle, Capt. Athula Hewavitarna (now the Harbour Master in Colombo) a most enjoyable and knowledgeable man with whom I used to swap information. I told him about the Benchmark and he was surprised. He had not known. The information did come very handy for him later when, after the tsunami, the Indian Hydrographers had come to check on the old BMs – and he was able to show this to them! He also told me that these benchmarks were originally placed to help in calculating the high and low tides. While there were the more accurate measurements these days, these were the first ones.

So much for the benchmark in Galle. The one in Trincomalee I had not heard about in my days there. Described as "2.3 metres below a B.M. cut in a brass plate set flush in the SW, wall of the hut in the NE. side of dockyard", it has been located, I understand, from Commodore Y.N.Jayaratne, and is under the care of the Navy.

I searched for the one in Colombo when I was involved with an EIA at Colombo South Port Project, and though I was able to find its location, I did not get to see it. My informant was the Librarian, and the description is: "2.77 metres below a benchmark, 0.2 metres below ground level, under the outer wall of the double flight of steps leading to the Customs-house." But "The Ceylon Manual for the year 1910" gives a fuller but somewhat more confusing description of the site. "The height of the datum is embedded 9 inches underground and he datum is 1.24 feet below the mean level of the sea or 0.98 above the zero of the gauge, or 9.09 below the benchmark of reference which consists of a stone engraved G.T.S. B.M embedded 6 inches underground in a block of masonry about 3-foot cube, situated close under the outer wall of the double flight of steps leading (on the harbor side) to the Custom’s House and Master Attendant’s Office and 10 1/2 feet east of the lowest step of the western flight. Just above it there is a slab of cement let into the wall bearing the inscription G.T.S. B.M."

But I have, since, found a photograph of it titled: "Locating a long-hidden Tide Gauge Bench Mark at Colombo" (fig.2.1 in "Sea Level Science: Understanding Tides, Surges, Tsunamis and Mean Sea Level" by David Pugh and Phillip Woodworth: unfortunately I am unable to reproduce it but it is there on the Internet).

So much for the three Tide Gauge Benchmarks (for this is what they are) that figure in Tide Tables: Colombo, Galle and Trincomalee. But what about the one said to have been in uninhabitable Kachchathivu? It is not reflected in the list of BMs shown by the Indian Hydrographers to Capt. Hewavitharna nor is it shown in "The Indian Tide Tables for the year 1969. Table II - Tide Levels, Datums, etc., at Standard Ports..." shown to me by the Ports Authority Librarian. Nor does it find "honourable mention" in the Tide Tables. Was there another kind of marker on that island? Had I been misled, or had I misunderstood the Survey Dept. Officer in Galle? The latter seemed the more likely.

I combed through W.T.Jayasinghe’s monograph "Kachchativu and the Maritime Boundary of Sri Lanka" and stumbled on to a possible explanation: one made up of several bits of information scattered in the book. If my reasoning is correct, there is a marker, set up by GTS, but it had nothing to do with Tides or sea levels. It was a trignometrical station ("Trig. Station") set to link the Ceylon Surveys with the Indian GTS. Let me put all this together:

In 1908 the first survey of that island was done by Mr. Ingles of the Survey Dept. and H.C.Cottle, Govt. Printer, joined the party. In his Report Cottle says that, in "The eastern corner of the island, opposite which we anchored, is a miniature headland of coral stone and on this Mr. Ingles found the remains of a trignometrical station evidently erected when the Indian Government surveyed the coast line of the Island for the Marine survey". In 1876, two trig. stations each, had been erected at Kachchativu and Delft by India, for the survey, and at the expense of Ceylon. They had been maintained by the Ceylon Survey Dept. and reports submitted to India till 1910 or so when they were closed down. While this information, which I have put together, is correct has yet to be confirmed, it would appear that my informant at Galle had been referring to this Trig. Station.

It was in an Indian publication that I found the story. Clemens R.Markham, in his "A Memoir on the Indian Surveys" (1878) says:

"The revision of the southern portion of the Great Arc was completed in 1874…. Major Branfill then proceeded to reconnoiter the Gulf of Mannar with a view to connect the triangulation of India and Ceylon. He selected an island called Kachi-tiva , halfway between Rameswar and the island of Nediven-tiva, on which a base was measured between two stations about a mile apart. From this base the positions of the next two stations on Nediven-tiva erected by the Ceylon Government were fixed, and Colonel Fryers, R.E., the Superintendent of the Ceylon Survey will complete the connection. In 1874 the Ramnad Longitudinal Series was commenced to extend along the parallel of 9 ¼ degrees Eastwards from the Great Arc to Rameswar, with a view to the connexion between the triangulations of India and Ceylon …. In 1876 Major Branfill completed the Ceylon connecting triangulation; and on 9th. May 1876, made over his charge to Captain W.M.Campbell, R.E." pp127-8,

Kachchativu is a scrap of bare, uninhabited land a little more than a square mile in extent, which I remember from a single visit in 1973. A trig.station on such exposed terrain would have been marked by a large cairn of rocks, or a concrete pillar, standing upright over a brass plug fixed in concrete. By the time Cottle made his Report (1908) there was only the remains of one and probably nothing remains now. There is, I believe, a WGS-84 benchmark on that island now, which serves the purpose.

Sea levels,

It is apparent that the benchmarks referred to by my informant in Galle were Trig. Stations connected to the land survey and in no way connected to the Tides, as those in Colombo, Galle and Trincomalee were. The above quotation from Markham also shows that the triangulation of Ceylon for land survey had begun independently of the GTS. In "Notes on the Base Lines of the Ceylon Triangulation," by J.E. Jackson, Empire Survey Review, Vol. 3, 1929, pp. 129–130), and later quoted by Clifford J. Mugnier, C.P., C.M.S. the following appears:

"The Triangulation of Sri Lanka commenced in 1857 with the measurement of a base (one side of a triangle) in Negombo on the West Coast (latitude 7º 10') and at Batticaloa on the East Coast (latitude 7º 40'). Both bases are in low, flat country; and brick towers up to 70 feet high had to be built over the terminals to enable observations to be taken to surrounding points. The bases were measured in 1857 and 1859 respectively for the Topographical Survey. The Negombo base was measured with a 100-foot heavy iron chain along the … The Batticaloa base was measured with the same chain laid on planks and trestles…. "

Thus the land survey of Sri Lanka had commenced in 1857, and the link with GTS, via Kachchativu and Delft had been finalized in 1876, 19 years later. This reference also speaks of brick towers of 70 ft. high erected for the survey. There are pictures of such towers in India, but in Sri Lanka I could only find one: an old Dutch Tower which had been used as a Survey Tower for the Negombo-Kandawala baseline, but which had collapsed a few years back. It had stood on Baseline Road, Katana, a suburb of Negombo. This would have marked one end of the baseline: "Kandawala is a geodetic datum first defined in 1930-01-01 and… it references the Everest 1830 (1937 adjustment) ellipsoid and the Greenwich prime meridian". So "Kandawala" here is not the one in Ratmalana. And Mt. Everest? Alas! the datum is not named after the mountain. Both the datum and the mountain are named after a man! Despite the mountain already being called ‘Chomolungma’ by the Tibetans and ‘Sagarmatha’ by the Nepalese, the British decided, in 1856, to name it after Colonel George Everest, head of the survey (although he was always rather embarrassed by the honour). The reasoning was so deliciously colonial:

"The mountain has no name intelligible to civilized men and Colonel Waugh has therefore ventured to denominate it ‘Mount Everest’ after a former surveyor-general."

Back to Kachchativu and Sovereignty. W.T.Jayasinha’s book describes the history of this vexed question and how it was solved. Among the many documents produced by Sri Lanka in support of our claim were letters pertaining to the trig.stations on Kachchativu and Delft islands. In all of them, the Govt. of (British) India had worked on the basis that the islands were part of (British) Ceylon, and the cost of building the stations were borne by Ceylon. Of course there were other documents and arguments produced in favour of our claim, but the trig. Stations on the islands had done their bit!

My informant in Galle, over 25 years ago was right and, as I do not even have a name for him, I would like to thank him publicly for his insights.

Thank you, Sir!


Interestingly, there was another island that Ceylon annexed, but in the interests of safe navigation. Under existing law this rocky outcrop was outside our territorial waters. Since it was deemed necessary to build a lighthouse there it was decided to annex it: there being, of course, no counter-claimants. To quote from "The Ceylon Manual for the Year 1910":

"A proclamation was issued on August 3rd., 1891 publishing letters patent passed under

the Great Seal of the United Kingdom for the Annexation of the

Great Basses Rock and the Little Basses Rock to the Island of Ceylon"

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