From the Field An ancient water management system in Sri Lanka is being revived - here’s why


Originating nearly 2000 years ago, the primary service of Village Tank Cascade Systems has been the storage of rainfall to enable year-round paddy cultivation. However, there’s much more to this complex landscape than meets the eye.

This is the first of a series of blogs that will explore what Sri Lanka is doing to restore Village Tank Cascade Systems to their full potential, as reported by the Alliance’s Healthy Landscapes Project.  

Several centuries ago, as populations expanded into the dry zone of Sri Lanka, efficient water storage became a high priority. Most rivers and streams found in the country’s dry zone are seasonal, emerging only during the monsoon season with their flow dependent on the amount of rainfall received. The resourcefulness of ancient communities led to the creation of Village Tank Cascade Systems (VTCS) or Ellangawa (made up of the Sinhalese words ‘ellan’, meaning hanging and ‘gawa’, meaning one after the other). 

VTCS consist of an intricate network of small to very large tanks (or reservoirs) connected through a series of canals. The tanks, which store water from seasonal streams, each have a specific purpose. For example, the village tank, which all other tanks in the system drain into, is used for irrigation, as well as other community activities, while the ‘water hole’ is constructed for the trapping and deposition of silt. When fully functional and well managed, the tanks provide villages in the area with a year-round water supply, thus helping the surrounding landscape and communities to thrive.   

While these ancient irrigation systems still function as a crucial element in supplying water for agriculture, they have other significant functions. 

1. Village Tank Cascade Systems harbour rich biodiversity

Cascade landscapes are home to a variety of wildlife including wild elephants, egrets and crocodiles. They are also home to dragonflies, which are not only indicators of clean and fresh water, but also help control the mosquito population, thereby reducing the risk of spreading malaria and dengue fever. The varied surrounding landscapes support high levels of globally significant agrobiodiversity and agroecological practices- in fact, it is believed that much of the genetic diversity of rice in Sri Lanka (recorded at more than 2,000 land races!) is found in these cascade landscapes.  


Mr. Somapala, a farmer in the Nachchaduwa VTCS, inspects his green gram cultivation which he planted as an inter-seasonal crop for the first time. Credit: Sampath Thennakoon, Provincial Department of Agriculture.

2. They can help moderate extreme weather events and mitigate climate change 

Globally, climate change is expected to worsen the frequency, intensity, and impacts of extreme weather events. Cascade landscapes can help moderate the effects of such extreme weather events (e.g., floods and droughts) by capturing runoff and storing storm water in numerous tanks.  

Tank ecosystems and surrounding home gardens also contribute to carbon sequestration- the process of reducing the amount of carbon dioxide in the atmosphere by storing it in plants and soil and slowing global warming. 


Part of the Thumbikulama tank in Palugaswewa. Credit: Thejana Bandara, PMU, HLP.

3. They promote overall health and well-being

The cascade landscape’s lush greenery, serene setting and cool microclimate make it an ideal environment to spend time in to relax and recharge. Additionally, as tanks are common and regular meeting places for villagers, they help connect the local community, potentially reducing loneliness and providing peer support when needed. Plants with medicinal properties and other health benefits are also present in VTCS, such as butterfly pea and hibiscus. The flowers of both plants can be brewed into teas and are rich sources of antioxidants. 


Butterfly pea and hibiscus flowers are abundant in tank villages and are used to make Nil katarodu & Pokuru wada - antioxidant-rich drinks. Credit: Wasantha Kaluarachchi, Provincial Department of Agriculture.

4. They can improve nutrition for all

Historically, cascade landscapes have been the site of multiple and diverse food production systems that produce cereals, vegetables, fruits, nuts and fish- ensuring a healthy, balanced and diverse diet for the community. The tanks are also an important source of hydration, providing safe water for drinking and cooking. Unfortunately, today, cascade landscape communities are believed to be consuming nutritionally inadequate diets, especially low in calories and deficient in almost all micronutrients.  

The Healthy Landscapes: Managing Agricultural Landscapes in Socio-ecologically Sensitive Areas to Promote Food Security, Well-being and Ecosystem Health (or Healthy Landscapes project in short) aims to improve the nutrition, health and overall being of cascade communities, while also strengthening the restoration and sustainable management of VTCS, for the enhanced provision of ecosystem services and protection of biodiversity. 


A woman feeds her granddaughter Poshana Pittu, a nutritious dish made of germinated green gram. Credit: Wasantha Kaluarachchi

The Global Environment Facility (GEF), the world’s largest public funder of international environmental projects, is supporting the Healthy Landscapes project led by Sri Lanka through the Ministry of Environment as the Lead National Agency. The Alliance of Bioversity International and CIAT is coordinating the project with implementation support from the United Nations Environment Programme (UNEP).