Sri Lanka’s well-recognized village tank cascade techniques, historical irrigation buildings that interconnect small tanks for rainwater-reliant cultivation, are a outstanding adaptation and mitigation technique practiced on the island for coping with excessive weather conditions.Some of the tank cascade techniques are more likely to have been constructed round 500 BCE and proceed to operate sustainably, although not at full capability; consultants are calling for his or her restoration with excessive care to make sure optimum performance.Recognized as a globally vital agricultural heritage system by the U.N. Food and Agriculture Organization (FAO), most of those tanks are actually uncared for and below strain from the altering local weather, land use, inhabitants and agricultural intensification, regardless of their worth as a novel local weather adaptation plan.Sri Lanka’s dry zone has greater than 14,000 small historical village tanks with many nonetheless in fine condition, supporting 246,000 hectares (608,000 acres) of paddy cultivation, about 39% of the whole irrigable space, however poor upkeep has rendered many others dysfunctional.
ANURADHAPURA, Sri Lanka — Current local weather fashions forewarn that Sri Lanka’s dry zone is more likely to turn out to be drier attributable to local weather change, leading to water shortages for agriculture. A rustic that has twice been ranked among the many high 10 international locations within the local weather threat index, Sri Lanka intends to revive its village tank cascade techniques, a uncared for however extremely environment friendly collection of historical irrigation techniques as a part of its local weather adaptation technique.
A tank cascade system is a hydrologically interconnected collection of tanks organized inside micro-catchments within the dry zone panorama. The water launched to paddy fields from one tank flows to the following, successfully sharing water from the highest to the underside and feeding many paddy lands. Each part in a cascade system adopts a selected practical objective that may be defined in fashionable science though they had been designed centuries in the past, based on analysis.
A graphical illustration of the tank cascade system. Image courtesy of IUCN Sri Lanka.
“Restoring the tank cascade system has a wider implication from the perspective of local weather change because the system has proved its resilience to excessive climate occasions,” mentioned P.B. Dharmasena, former analysis officer on the Department of Agriculture and a specialist in soil and water administration.
The system can soak up shocks of pure disasters resembling floods, which could be managed by storing water, and drought influence, by lowering water loss from tanks by absorption within the surrounding surroundings. The cascaded tank-village system additionally contributes to environment friendly water administration with water from one tank flowing to a different, by a community of tanks and streams, Dharmasena informed Mongabay.
These potentialities will likely be helpful as an adaptation technique, as Sri Lanka faces the results of local weather change. There is now renewed curiosity in restoring these tank techniques by the National Climate Adaptation Strategy. The restoration can also be listed within the nation’s Nationally Determined Contributions (NDC) to the U.N. conference on local weather change, making Dharmasena hopeful of those historical techniques receiving their due recognition.
A small human-made tank within the North Central province, contributing to enhanced aesthetic enchantment of the dry zone panorama. Image courtesy of the Ministry of Irrigation.
Scientific restoration is vital
“There is a science behind the performance of a tank cascade system, and restoration must be executed with nice care,” mentioned C.M. Madduma Bandara, emeritus professor of the University of Peradeniya who first described the tank cascade techniques by his 1985 analysis.
Madduma Bandara supplies an instance of a neighborhood authorities authority as soon as repairing a tank within the North Central province. The tank was broken throughout the next wet season and the native physique repaired it as soon as once more, nevertheless it was no use, as the next wet season introduced the identical outcomes. Perplexed authorities consulted Madduma Bandara for recommendation, and it was really helpful to revive tanks positioned within the close by wilderness.
Restoration of the tanks in a cascade system must be executed consistent with the science behind the hydrology of the system. Image courtesy of IUCN Sri Lanka.
A cascade system additionally has tanks known as kulu wew, or forest tanks, normally positioned within the higher catchment wilderness across the village, which may successfully retain extra water throughout wet seasons. “As these tanks are restored, the primary tank is ready to stay intact and turn out to be efficient,” Madduma Bandara informed Mongabay, emphasizing the necessity to think about the tank cascade system in its entirety.
These forest tanks can filter particles and silt. They additionally present water to wild animals, and the supply of forest tanks helps cut back the variety of wild animals from reaching village tanks and ending up raiding crops or worse — attacking individuals and their properties. “Sadly, there are situations that these forest tanks are additionally used for irrigation as demand for paddy lands will increase,” Madduma Bandara mentioned.
The historical system has many fascinating parts, such because the naturally rising tree belt on either side of the uppermost areas of every tank often called gasgommana, which acts as a windshield and is ready to reduce off the dry wind and cut back water evaporation, mentioned Shamen Vidanage, IUCN’s nation consultant.
Another thick stripe of vegetation positioned between the tank bund and the paddy fields is named Kattakaduwa, or interceptor. It has salt absorption capability attributable to having a water gap known as yathuru wala, which permits the discount of salinity and purification of the water that flows to the fields.
Aerial view of a tank in Kappirigama. Image courtesy of IUCN Sri Lanka.
Hydraulic know-how at its greatest
Previous makes an attempt have been there to revive the tank cascade system by ecological enhancements, largely undertaken by the Sri Lankan workplace of the International Union of Conservation of Nature (IUCN). A research revealed in Dec. 2022 additionally reveals the worth of the ecosystem providers offered by these tanks as they harbor a range of many wildlife.
As this method doesn’t have a single identify, consultants have coined the identify Ellangava, with ellan which means hanging and gava which means subsequent to at least one one other.
Following a proposal submitted by Dharmasena and his group, the tank cascade system has been named a globally vital agriculture heritage system as designated by the U.N. Food and Agriculture Organization (FAO).
The area people serving to the restoration of a tank cascade system as a mannequin venture in Kappirigama. Image courtesy of IUCN Sri Lanka.
Meanwhile, the 2022 analysis has highlighted how the paddy fields and human settlements round tank cascades have expanded lately, whereas forest areas have shrunk dramatically, disturbing the right performance of the tank cascades. Researchers studied the Mahakanumulla tanks system in Anuradhapura district within the island’s North Central province, the place the runoff coefficient has modified from 0.29 to 0.45 indicating excessive outflow from the system along with much less water retention.
According to Madduma Bandara, a patch of forest is present in each village, often called ‘gam kele’. These vital forest patches have been decreased considerably owing to human encroachment, primarily for functions of agriculture. Wrong land use patterns are impacting the small tanks as they expertise extra sedimentation and elevated tank siltation.
It is estimated that Sri Lanka’s dry zone is dotted with greater than 14,000 small historical village tanks and lots of are nonetheless in fine condition, supporting 246,000 hectares (608,000 acres), making up about 39% of the whole irrigable space.
However, most of those techniques have fallen into disuse attributable to poor upkeep. Experts have known as for his or her fast restoration as a part of the island’s local weather change preparedness and demand that such restoration additionally must be undertaken with utmost care to make sure individuals can profit from them.
De L.W. Samarasinha, G. G., Munaweera, T. P., A. Shantha, W. H., C.S. Bandara, M. A., & N.M. Dias, M. P. (2020). Assessing vulnerability to local weather change: A research on farmer communities within the dry zone of Sri Lanka. Hector Kobbekaduwa Agrarian Research and Training Institute.
National adaptation plan for local weather change impacts in Sri Lanka 2016 – 2025. (2016). Ministry of Mahaweli Development and Environment Sri Lanka.
Madduma Bandara, C. M. (1985). Catchment ecosystems and village TankCascades within the dry zone of Sri Lanka a time-tested system of land and water useful resource administration. The GeoJournal Library, 99-113. doi:10.1007/978-94-009-5458-8_11
Wickramasinghe, M.R.C.P., Dayawansa, N.D.Okay., Jayasiri, M.M.J.G.C.N., De Silva, R.P., (2023). A research on exterior pressures of an historical irrigation cascade system in Sri Lanka. Agricultural Systems 205 (2023) 103593.
Banner picture of a village tank with paddy fields cultivated with its water, courtesy of IUCN Sri Lanka.