The Anuradhapura Kingdom - VIII

The Anuradhapura Kingdom - VIII

Contiued with part seven   here to go privious one

The first five centuries of the Christian era constitute the most creative and dynamic era in the history of irrigation activity in Sri Lanka. A variety of seemingly intractable technical and physical problems were confronted and overcome, and the skills acquired and experience gained in this period were a rich lode mined by future generations. In the first century AD, the main problem was that the water resources of the Kala and Malvatu oyas, dry zone rivers which dwindled to a mere trickle of water for much of the year if they did not dry up altogether over long stretches, were unequal to the demand for an abundant and dependable supply of water set off by population

Growth in a vigorous civilisation demanding an ever increasing agricultural surplus. This could only be ensured by the diversion of water from rivers like the Mahavali and others closer to the wet zone south of Anuradhapura. The most notable of the irrigation projects of this early period was the Ajahara canal which took the waters of the Ambanganga, a tributary of the Mahavali, to the Anuradhapura region. This canal, first mentioned in the Mahavamsa account of the reign of Vasabha,5 stretched about 30 miles from a weir across the Ambanganga. Its length was testimony to the maturity and competence of the irrigation engineers of ancient Sri Lanka. During the reign of Mahasena (274-301 AD), the Alahara canal became the main source of water supply for the Minneriya tank which he built, and which was by far the largest tank up to that time.

Mahasena is credited with the construction of sixteen tanks and canals, four of which are in the Anuradhapura area, and one in the Puttalam district. Three notable trends in the development of irrigation facilities during his reign were: a resolute endeavour to harness the waters of the Mahavali and the Ambanganga, the most important project being the massive Minneriya tank; the improvement of facilities for water conservation in the north western part of the island; and the attempt to develop the south western part of the dry zone on the periphery of the wet zone. Together they accelerated agricultural development in the vicinity of Anuradhapura, and opened up new areas for cultivation in the east and southwest. All the major irrigation projects initiated by him were achieved by a prodigious investment of labour resources on an unprecedented scale, and they reflect, too, a notable advance in irrigation technology in the island.

A thriving civilisation dependent on irrigation for its sustenance has an insatiable demand for water, and the search for a dependable and permanent supply of water is a never ending one. Breakdowns caused either by some structural fault or by depletion of water supply in periods of drought were inevitable, with the result that not every unit or link in this chain of interconnected tanks and channels was working at peak efficiency (or for that matter working at all) at any given phase of the island's history in these centuries. Quite apart from essential repairs and maintenance, renewal was vitally important, as too were extensions of this irrigation network. Major initiatives in irrigation activity called for a tremendous burst of energy, and these were not very frequent. Most rulers were content with keeping the tanks and channels which formed the country's stock of irrigation works functioning at a reasonable level of efficiency.

The reign of Dhatusena (455-73) matched, if it did not surpass, the achievements of Mahasena and Vasabha in the extension of the island's irrigation network. He is said to have added to the irrigation works in the Mahavali region by building a dam across that river. But the main focus of attention in irrigation activity during his reign seems to have been the development of water resources in the western part of the dry zone. By far the most impressive achievement by this period is the construction of the Kalavava, which tapped the Kala Oya and helped to supplement the supply of water to Anuradhapura and the area round the city.

The Kalavava had an embankment 3.25 miles long and rising to a height of about 40 feet. Its bund was constructed of blocks of dressed granite morticed together to enable a very close fitting. Through a canal 50 miles in length the Jayaganga its waters augmented the supply in tanks at Anuradhapura and its environs such as Tissa, Nagara and Mahadaragatta, apart from irrigating an area of about 180 square miles. This canal was an amazing technological feat, for the gradient in the first 17 miles of its length was a mere 6 inches to a mile. There was also the Yodavava in the Mannar district, attributed to Dhatusena. It was formed by building an embankment about 7 miles long. Fed by a 17 mile canal from the Malvatu Oya, the Yodavava covered a vast area. It was a shallow reservoir, and its efficiency in water storage must have been severely affected by the heat and aridity of the region, but the topography of the area made it impossible to construct a tank with a greater depth without resorting to techniques of lift irrigation. Carefully laid out canals flowing at a low gradient distributed the water from the Yodavava to a multitude of village tanks around it. Together with the Panankulam this tank was a vitally important asset in an area Mannar which records some of the lowest rainfall in the island.

By the end of the fifth century two major irrigation complexes had been developed, one based on the Mahavali and its tributaries, and the other on the Malvatu Oya and Kala Oya. These were elaborated further in subsequent centuries. The two cities of Anuradhapura and Polonnaruva located here were vital centres of cultural activity and these contained the most impressive monuments of Sinhalese civilizations. Anuradhapura was much the larger of the two, and necessarily hence, for during the first ten centuries of the Christian era it was, with brief interludes, the capital of the island. There was a third core of Sinhalese civilisation in the dry zone of the south east in Rohana where the climate was more severe and the rainfall much less reliable.