Green History of Sri Lanka

Sri Lanka has well developed ancient hydraulic civilization in the dry zone dating back to pre-Christian times. Legendary story of civilization in ancient Ceylon begins when the island was inhabited by people of original tribes Yakka, Raksha and Naga. They were gradually developed systems of  sedentary agriculture based on irrigation. Folklore said that the Yakkas built some ancient irrigation tanks. Some believe that the multi-headed cobra symbol often discovered at the sites of ancient irrigation structures and other water works, was the insignia of a Naga line of royalty well versed in hydraulic engineering.

The early Vijayan settlers probably harnessed the skills of local inhabitants to construct irrigation works.The early hydraulic societies thrived on small irrigation systems with unique assemblages of land uses and agricultural attributes (Leach, 1959). Possibly these systems evolved from early rain-fed shifting agriculture into small-scale irrigation that, in turn, led to major systems. The sedentary way of life facilitated by this hydraulic base led to land tenure, property inheritance, and social organizations that persisted for centuries.

The land and water use system that developed over centuries to satisfy these requirements has been described as a "cascading system". Organization of small tanks into a cascading sequence within micro-catchments allowed greater efficiencies in water use. Drainage from the paddy fields in the upper part of the cascade flowed into a downstream tank for reuse in the paddy fields below. 

The system fully expressed the well known dictum by the King Parakramabahu (AD 1153) that 

"not a single drop of water received from rain should be allowed to escape into the sea without being utilized for human benefit."

The land use associated with tank cascades demonstrated a profound knowledge of resource management in a challenging environment essentially transformed from natural ecosystems into agro-ecosystems. Integrated land and water resources management in ancient times is reflected in the zonation of land use within the micro catchments. 

• The tanks and the paddy fields occupied the valleys where Low-Humic-Gley soils with poor drainage had limited use other than for bunded paddy cultivation. 
• Ridge summits, often strewn with rock outcrops and inselbergs, were converted into works of art and places of worship and spiritual retreat. 

The influence of Buddhism led to the establishment of sanctuaries early in history and the enduring protection of wildlife unusual in many parts of the world.

As Brohier (1934) noted, “tank" would appear to be synonymous with "village," implying that each agricultural settlement had a tank and paddy field below it.

As Needham noted,

“already in the first century AC, they understood the principle of the oblique weir.... The height of dam spillways were adjusted by removable pillar sluices were well understood, ... the inside surfaces of reservoir abutments were faced with 'ripple bands'... which acted as wave-breaking groynes ... The most striking invention was the intake-towers or valve towers (bisokotiiwa)." 

They developed the knowledge to construct long canals with extremely low gradients, such as the Jaya Ganga, which carried water from Kalawewa to the city tanks of Anuradhapura along a canal 87 kilometers long. The 'yoda ela', which had a gradient of less than 10 cm per kilometer

within its first 27 kilometers, continued to maintain itself as a natural stream. Some of the major ancient tanks, such as Yodawewa in Mannar district, were constructed to feed a large number of small tanks .

The establishment of forests and construction of ponds, reservoirs and irrigation systems were considered great meritorious acts in accordance with popular Buddhism, the faith of the leaders and the large majority of the people. Sri Lanka's history is full of achievements of kings who contributed to the development of water resources.

An indigenous expertise developed over the centuries which appears to have been called upon by other countries of South Asia.

The ancient hydraulic civilization of the Dry Zone disappeared after the twelfth century. Climatic change, malaria, depletion of soil fertility, foreign invasions and famine are some of the reasons cited. The breakdown of the efficient irrigation management system may have resulted' from annihilation of the kulinas — the Dry Zone nobility who possessed irrigation expertise — by invading South Indian forces (Paranavitana, 1960).