By Dr Chandima Ariyarathna
Dr Chandima Ariyarathna
Not even a drop of rain water must be allowed to flow into the ocean without being made useful.
Indigenous knowledge stems from human observations and interactions with nature, and it teaches communities the skills they need to manage natural resources for survival. In Sri Lanka, traditional knowledge systems emphasize sustainable stewardship, equitable sharing, and conservation of nature for future generations – and has built communities’ capacity to develop the knowledge and technologies they need to address their day-to-day challenges.
The management of water resources is of fundamental importance to agricultural sustainability in any civilization. Climatic conditions in Sri Lanka, a tropical island which receives rain from two monsoon seasons, have given rise to the manmade ‘Tank Cascade Systems (TCSs)’ (referred to as Elangawa in Sinhalese) – an ancient system designed to recycle and reuse rainwater through a network of small to large scale tanks and canals. These tanks are referred to as Wewa.
Across Sri Lanka, there are over 7,600 ancient Wewa which remain operational, and which represent essential water management systems for agriculture in the dry zones of the country. The earliest of these is the Basavakkulama tank in the World Heritage city of Anuradhapura, which was built in 300 BC and is still operational today.
The functionality and design of village tanks provide fascinating insights into ancient wisdoms around common resource stewardship and sustainable development. A typical TCS consists of four main zones (Figure 1): a tank bund and tank bed; irrigation channels and paddy fields; protected forest in the catchment; and a high elevation household area. Stone liners on the embankment protect against erosion from waves, and there are dedicated places for different human activities such as bathing and the collection of drinking water. The main village tank, or Maha Wewa, stores and provides water for irrigation purposes and wider community activities.
Each part of this seamlessly integrated system serves a separate function which reinforces and protects the entire system. If we look closer, cascades of other tanks drain into the village tank, providing a constant supply of good quality water.
The Kulu Wewa, or forest tank, is constructed in the upper catchment to capture rainwater that eventually drains into the village tank through seepage. Kulu Wewa also provides water for wild animals, thereby preventing them from trespassing into the village in search of water and food.
Meanwhile, Kayan Wewa is used to trap sediment and control salinity, while Olagam Wewa is used as a source of water for seasonal cultivation, and Goda Wala is constructed to prevent siltation and sedimentation of the main village tank by trapping and deposition of silt. Finally, Ihala Wewa stores water used for paddy cultivation and other community activities.
Evidently, this ancient system of resource management and distribution has proven incredibly resourceful. The forest cover, for example, increases the groundwater table through infiltration and gradual release of water to the tank during dry seasons. The forest cover is also used for the sustainable extraction of non-timber forest products, including medicinal herbs or edible plants. Meanwhile, an upstream, naturally-grown belt of vegetation consisting of large trees and climbers above the tank bed – serves as a wind barrier for the system, while minimizing evaporation from the tank by lowering water temperature.
Notably, the roots of large trees also create breeding grounds and living places for fish and other aquatic species. Upstream meadows, soil ridges, and water holes filter out the sediment flowing from upstream, and downstream drainage filters water draining into the paddy tract. In addition, the native plant species Pandanus kaida is grown along the bund to strengthen its stability, and the villagers often use parts of this species as food, fuel wood, medicine, timber, fencing materials, or as raw materials for cottage industries.
The wisdoms of ancient knowledge
TCS were the back-bone of the Sri Lankan hydraulic civilization. The associated ancient wisdom translates into knowledge and technology for rainwater harvesting, retention of soil moisture and groundwater, prevention of soil erosion and siltation control while ensuring the maintenance of ecological balance in the system.
TCS also provided the basis for eco-friendly and sustainable agricultural practices and farming systems such as Bethma – a method of paddy farming practiced during droughts, whereby farmers agree to share available water on a fair basis.
The genius of the TCS system lies in its ability to maintain natural ecological balance and skillfully harness nature for human use. They have also fostered embedded and highly efficient social systems within each village – systems which rest upon shared responsibilities, social equity, community leadership, and responsible resource stewardship.
Knowledge frameworks associated with TCS have given rise to a holistic understanding of the local ecosystems and helped communities find optimal development solutions. Indeed, TCS have been used for over 2,000 years by local communities and continue to be used for a variety of water demands, even amidst climatic fluctuations or lack of management during periods of socio-economic instability.
Such ancient wisdoms must not only be respected and preserved – but also brought to the fore and integrated with our contemporary understandings of climate change to co-produce solutions for efficient water usage, the enhancement of food production, and the mitigation of the impact of recurrent droughts, seasonal flooding, and land degradation. Academic researchers have a vital role to play bridging gaps between various knowledge systems – which can go a long way to support meaningful collaborations on issues related to climate change adaptation, natural disaster preparedness, biodiversity management, and sustainable development at large.