Outstanding Features

About 40% of the annual rice production in Sri Lanka originates from the dry-zone, where the rainfall is concentrated in a rainy season of 3 months. For a sustained water supply the majority of farmlands depend on ancient irrigation systems that evolved in response to this climatology, during the period from 300 BC to 1200 AD. The intricate irrigation systems consist of a large number of interconnected reservoirs (weva or tanks). Thanks to the chain-like structure in the organization of small tanks, water from upstream tanks is successively stored in those downstream. These small cascades are linked to large reservoirs and giant feeder canals to form extremely complex large irrigation systems.

Each tank system in a cascade has a small reservation catchment, the reservoir, a strip of trees downstream of the reservoir that act as a wind breaking barrier, paddy fields, and the village. The reservation of the next tank of the cascade starts immediately below the paddy fields of the upper tank. The system of tanks, paddy fields and canals are so much integrated and interwoven with the natural environment, it is difficult to identify tank systems as man made structures.

One of the intriguing features of the tank systems is their sheer density: There are about 30,000 tanks which have been built in the land area of about 40,000 km2 of the dry zone, resulting in nearly a tank for every square kilometre. This large density of tanks and their long-term existence (more than 1000 years in many cases) makes them an important component in the environment and ecosystems of the region. Most of these tanks are found in the Kurunegala (32 %) and Anuradhapura (23%) districts. About 330,000 farm families live in these tank-villages, cultivating about 148,000 ha of irrigable lands.

Traditional communities had made every attempt to conserve soil, water, and natural habitat. Food security was one of the in-built aspects of their culture. There are two rice cultivation seasons: “maha” (October –March) and “yala” (April – September).

Use of groundwater for agriculture was never practiced which assured the water security. An adequate dead storage was maintained in tanks to be utilized during dry period for all purposes and had been the only source of water for cattle and wild animals. There was a broad diversity in flora and fauna around the tank, and the availability of tank water during dry periods assured their survival.

Each and every component was considered an essential element of the ecosystem. Attention was paid not only on macro-land uses such as paddy land, settlement area, chena lands, tank bed etc. but also on micro-land uses such as goda wala (upstream sediment trap), iswetiya (upstream conservation bund), gasgommana (upstream wind barrier), perahana (upstream grass strip to filter the sedimen), kattakaduwa (downstream wind barrier), tisbambe (land strip around the hamlet for protection), kiul-ela (common drain of the irrigated lowland) etc.

Sharing resources equally and the equity of ownership were the most striking features of their culture, which led to build up a peaceful and sustainable rural society.

Most importantly the independence provided through the ancient tanks to each village has paved the way for a unique decentralized social system in Sri Lanka, where farmers had the highest social rank.

It is reasonable to assume that the social system organized around the village tanks in ancient Sri Lanka was significantly different from the feudalism in medieval Europe and elsewhere in the world. Study of the history of Sri Lanka does not reveal evidence that a centralized bureaucracy ever even existed to run the country's irrigation works. The necessary maintenance work was organized by the villagers themselves: there was never a centralized bureaucracy to direct such work or to ensure that it was carried out. Until the colonial government instated irrigation department in 1860s in fact, the management of village tanks completely remained on the hands of the locals. The development of tank irrigation systems was a crucial element in the social organization and cultural traditions in the dry-zone. Numerous villages in the dry-zone are having names synonymous with the name of the village tank.

In addition to cultural and religious factors, historians increasingly see a contribution from the very decentralized and independent nature of the village tanks system towards the freedom of thinking in Sri Lanka.

Goods and Services Provided

The primary service provided by the tanks was storage of rainfall that comes in 3 months to enable year long rice growing with two seasonal crops. In addition to irrigation water, the tanks provided a number of services. They made the microclimate pleasant and cool, enabled agro-biodiversity. These systems also constitute one of the richest sources of wetland biodiversity in the country. The tanks, moreover, served as the common bathing place and meeting point for the village .

Threats and Challenges

During the last few decades rain-fed shifting (Chena) cultivation in catchment areas of village tanks and new colonization programmes under major irrigation schemes have collectively made a drastic reduction in the dry zone forest cover. Disappearance of floral and faunal communities, loss of fertile lands, destruction of the village ecosystem and increased severity of droughts are the most distinct consequences. The most heavily affected areas are the ingenious tank-village ecosystems and the communities living there.

The poor knowledge on the function of the system had lead to either ignorance or unplanned disruption of the ancient tank systems during the large-scale irrigation development projects during the 20th century. The modern development has not been able to capture the harmony between local and regional hydrological characteristics that the older small cascades tank systems and ancient large reservoirs could capture so admirably. For example the modern ancient Jayaganga feeder canal is entirely dependent on its feeder reservoir as it shuts off the valley drainage by its high embankments. The ancient feeder canal, in contrast, having one embankment open to catch the runoff and following the contour lines had a very low velocity and minimum loss of command area.

Another major threat is the role abandoned ancient tanks in the dry-zone play as breeding media for malaria vectors. The restoration, use and proper maintenance of village tanks is, therefore, also of great importance to the reduction of the malaria epidemic.

Policy and Development Relevance

Sri Lanka's per capita rice consumption is about 150 kg/ year, out of which only less than 10% is imported. Hence, a stable rice production remains an important requirement for sustainable development and alleviation of poverty and hunger in the country. Additionally, each effort in securing reliable water supplies is extremely important to reduce the widespread poverty in the rural agricultural areas in the dry zone. Towards this goal, the conservation and reconstruction of the ancient irrigation works in Sri Lanka are a crucial component. The government of Sri Lanka launched a project to rehabilitate 1000 village tanks during the year 2004. It is a great challenge, as well as a national priority, to search for, un-cover and combine whatever knowledge that has remained with isolated individuals to document this great heritage and to inform future generations.

The sustainable development challenges lie in understanding the human and social needs and meeting them through the co-existence with nature. In this context, reviving the ancient irrigation system in modern day social context by expanding their services to accommodate current societal needs while designing norms and procedures for community based management of these systems, to be sustainable eco-systems, would be a worthy endeavour that identifies closely with the objectives of GIAHS.

Global Importance

The lessons and experiences from these systems can be very useful in the quest of various development alternatives, especially for eco-development pursuits in dry zones of the world.