Hydraulic Civilization

Encyclopaedia Britannica describes the early Sinhalese civilisation as hydraulic, meaning that it was based on storing water and using it for the regular cultivation of wet fields. Its home was the dry zone, mainly the northern and eastern parts of the island. A proposal prepared by Sri Lanka's Ministry of Agriculture with the FAO defines the dry zone as land with a mean annual rainfall of less than 1,750 mm and a distinct dry season from May to September.

Water therefore had to be held back for the dry months. The answer was the reservoir, called a wewa in Sinhalese and a tank in English. Britannica records that the early settlers grew rice and began with simple schemes for damming rivers, and that small reservoirs fed by seasonal streams later became a feature of nearly every village.

An FAO study of Sri Lanka's reservoirs states that the earliest construction that can be identified with certainty is the Abhayawewa at Anuradhapura, built by King Pandukabhaya in about 300 BC. It is now known as the Basawakkulama wewa.

The same study singles out one device, whose Sinhala name means queen's enclosure. It is the equivalent of a valve pit, which regulates the outward flow of water from a reservoir, and the study dates its invention by Sinhala irrigation engineers to more than 2,200 years ago. The Mahaweli Authority of Sri Lanka adds that the ancient sluice could control the release of water up to a head of 30 feet, or 10 metres. Where the water stood higher, builders repeated the sluices at different levels so that each one worked within that limit.

As royal power grew, kings took up large schemes. Britannica dates these from about the 1st century CE, in the reign of King Vasabha, when perennial rivers were blocked with earthen dams and water was carried by canal to distant fields. King Mahasena, in the 3rd century, is credited with the Minneriya tank and its feeder canals. The FAO study records that King Dhatusena dammed the Kala Oya in 459 AD, and that by the 8th century water was being transferred from one river basin to another.

The work reached its peak under Parakramabahu I, who reigned from 1153 to 1186. He is reputed to have built or restored 165 dams, 3,910 canals, 163 major tanks and 2,376 minor tanks. The Parakrama Samudra, or Sea of Parakrama, at Polonnaruwa dates from the 12th century and is a reservoir of 2,262 hectares at full supply level.

Alongside the royal works ran a village system. The FAO describes the cascaded tank-village system, known locally as ellangawa, as a connected series of small tanks set one after another along a seasonal stream. Each tank is formed by an earthen dam across the valley. Surplus water from a higher tank spills into the one below, and a sluice releases water to the paddy fields. A cascade is made up of about four to ten tanks.

Each tank has managed land around it, including a natural tree strip (gas gommana), an upstream meadow (perahana), a soil ridge (potawetiya) and a strip that intercepts seepage (kattakaduwa). Farmers plant in two seasons that follow the rains: maha, the major season, and yala, the minor one. The FAO states that the system evolved over nearly two millennia.

The Mahaweli Authority records a setback in the 11th century, when Chola invaders damaged irrigation works and the capital moved from Anuradhapura to Polonnaruwa, and a fall in the 13th century. Britannica relates that as the capital and population drifted to the south-west, the network of managers who had maintained the works disappeared. Many large reservoirs were breached, and smaller tanks fed by them lost their supply.

Repair came much later. The FAO study places most of the rehabilitation under British rule in the 19th and early 20th centuries, and says that almost all the major ancient works have now been rehabilitated. The cascaded tank-village system has been an FAO Globally Important Agricultural Heritage System since 2017. The FAO notes that farmers there still grow traditional rice varieties such as Suwandel and Kaluheenati, and that the uplands produce other cereals, vegetables, spices and oil crops.