Preserving Tank Cascade Systems to build Agroecological Landscape Resilience in the Dry Zone of Sri Lanka  (Special article on
International Mother Earth Day)

Sri Lanka’s tank cascade systems promote an important traditional water management strategy that has been used for centuries to build agricultural resilience in the dry zone. These are a series of small reservoirs or tanks that are interconnected through canals, designed to capture and store rainwater during the wet season and provide irrigation water during the dry season and a part of Sri Lanka’s hydraulic civilization. These systems interconnect small human-made reservoirs which capture seasonal rainwater for agriculture, household, and environmental purposes and are considered the lifeblood of communities in the Dry Zone of Sri Lanka. Tank cascade systems have helped to address drought and flood mitigation historically. They help to build agricultural resilience in the dry zone, those are:

Sustainable water supply: tank cascade systems provide a sustainable water supply for irrigation, particularly during the dry season when rainfall is limited. This can help to reduce crop losses due to water stress and increase agricultural productivity.

Drought mitigation: tank cascade systems can also help to mitigate the impact of droughts by storing water during the wet season and releasing it during the dry season. This can help to ensure that crops have access to water during periods of prolonged drought.

Increased crop diversity: tank cascade systems can support increased crop diversity by providing water for a range of crops, including paddy, vegetables, fruits, and spices. This can help to reduce the risk of crop failure due to pests or diseases and provide a more varied and nutritious diet for local communities.

Improved soil fertility: tank cascade systems can also improve soil fertility through the deposition of sediment and nutrients in the tanks and canals. The use of organic fertilizers and other CSA practices can further enhance soil fertility, leading to increased crop yields.

Cultural heritage preservation: tank cascade systems are an important part of Sri Lanka’s cultural heritage and have been maintained and improved over centuries by local communities. The preservation and promotion of these systems can help to maintain cultural traditions and support sustainable livelihoods for rural communities.

Tank cascade systems are remarkable and one of the most efficient water management systems in the world. In ancient times, these systems functioned sustainably, in harmony with the environment, and were maintained by the communities that benefitted from them.

The CSIAP initially planned to develop 122 cascades in 11 districts in Sri Lanka. For that, the CSIAP has already completed the Participatory Rural Appraisal (PRA) at the tank level, hydrological assessments including the water balance study, engineering survey, and prepared Hotspot Area Agriculture Development Plans (HSAADPs) based on the 47 agrarian service centre divisions covering 256 GN divisions in 11 districts and 06 provinces. With the reduction of project funds during the country’s economic crisis, CSIAP is able to develop nearly 60 cascades only with available funds. The following table explains the ongoing tank rehabilitation and cascade development in climatically vulnerable hotspot areas in Sri Lanka.

The Cascade development is not a simple intervention. As I already mentioned, the intervention is interrelated with multiple sectors, multi-disciplinary subjects, and multi-stakeholders. Therefore, CSIAP is be careful when taking the steps to develop the cascades in climatically vulnerable hotspot areas. According to the community’s point of view, the rehabilitation of tanks and the cascade developments are related to the livelihood of the people, the balance of ecosystems including biodiversity, and the prevention of disasters etc. People from the community say that “when you touch the tank or cascade for the rehabilitation intervention, you must think that you are touching the heart of the community in the village. Tanks and cascade are not a physical infrastructure, those are feeling of the community”.

As I already mentioned, CSIAP started the tank rehabilitation and the cascade development interventions by doing multiple studies, surveys, and screening to ensure that no harm to the ecosystem and the community in the climatically vulnerable hotspot area. To avoid and prevent the impacts and the risks, CSIAP conducted the PRA, hydrological assessments, engineering survey, HSAADP, PIR, and environmental and social screening for the cascades and the tanks in the climatically vulnerable hotspot areas. The cascade development is an integrated intervention. Therefore, CSIAP ensured that tank rehabilitation and cascade development works are done without harm to the ecosystem and the community.

CSIAP is rehabilitating and developing the different types of tanks in a cascade with different functions (forest tanks, tanks for water purification/ silt trapping, tanks for seasonal cultivation with no permanent settlements, and village tanks). A village tank consists of many components, each serving a specific purpose to maintain the integrity and hydrological connectivity of the system. With the absence of this integrity, the small tank cascade systems fail to deliver the ecosystem services and socio-cultural benefits such as the provision of water for irrigation and other domestic uses, water purification, groundwater recharge, flood management, erosion control, provision of food, medicines, raw materials, recreational benefits, cultural and spiritual bonding, habitats for wildlife, and carbon sequestration.

The components of a village tank are a stream (seasonal stream), a filter (a strip of grass and reeds on the periphery of the water body that acts as a filter to trap silt), a water hole (an upstream sediment trap), a windbreak of trees (an area planted with large trees that act as a windbreak to minimize evaporation from the surface of the tank), soil ridge (an upstream bund to manage soil erosion and sedimentation), and interceptor (the stretch between the tank bund and paddy fields). This acts as a downstream wind barrier, reduces tank seepage, and prevents sodium, magnesium, and iron from entering the paddy land, paddy field, and drainage.

We can say that pocket of biodiversity can be identified in the tank cascade system. Or we can say that tank cascade systems are rich in biodiversity. Tank ecosystems create a mild microclimate that supports a variety of flora and fauna that otherwise would not have inhabited the climatically vulnerable hotspot areas. The long-term sustainability of tank cascades depends on the holistic understanding of socio-ecological aspects and requires a multidisciplinary and multi-stakeholder approach. In this way, CSIAP is establishing the Cascade Management Committees (CMCs) with the relevant stakeholders in climatically vulnerable hotspot areas in Sri Lanka. 

It is most important to point out that, the CSIAP always ensures the long-term knowledge management and transparency of investments in tank management to ensure community ownership. Also, the project is promoting community-centred tank rehabilitation. We identified that more cost-effective compared to third-party contracting.

The CSIAP has conducted sufficient cascade-wise technical studies required before rehabilitation work. Cascades-based approaches are helping sustainable agroecological landscapes, cascade-based climate adaptation, and cascade-based disaster risk reduction. In this project, we implemented a cascade-based approach for tank rehabilitation and cascade development, while blending the scientific results with traditional indigenous knowledge and practices. We successfully brought back the community lead maintenance and management of tanks, without losing the vital contribution made by the stakeholder agencies. The achievements of the project will be highly significant. Key lessons learned from the CSIAP can be used about cascades in climatically vulnerable hotspot areas on how to empower communities with the means and knowledge to embrace their heritage and environment and become self-sufficient.

Article Written By: Sharmila Thirhiharan, Gender Development Officer,
Project Management Unit, Climate Smart Irrigated Agriculture Project
Photographs by Deputy Project Director's Office (Southern)

Posted by CSIAP Sri Lanka Read full article Published Date : 2023-04-26