Most of the people affected by CKDU are from the dry zone
There are no reports indicating that the CKDU prevailed and significant death tall occurred during history in these regions.
According to history, people in the area used to get potable water from the tanks. Therefore we argue that the adverse changes that took place to the ecosystem of the tank cascade system and new commercial practices of agriculture of dry and intermediate zone of the country have also become reasons for the spreading of CKDU.
WHAT IS TANK CASCADE SYSTEM?
In order to overcome the limited water availability during May to September period, the ancient Sinhalese developed their own water management system now known as the
Tank Cascade System. “A tank cascade
is a connected series of tanks organized within a meso-catchment of the dry zone landscape, storing, conveying and utilizing water from an ephemeral rivulet” (Madduma Bandara,
1985). “This system has been recognized as a Globally Important Agricultural Heritage Systems” (GIAHS) by the FAO in 2018.
The watershed boundary of the meso-catchment, the individual micro-catchment boundaries of the small tanks, the main central valley, side valleys, and axis of the main valley, component small tanks, and the irrigated rice lands are the main elements of a cascade.
Fig 04. Indicates the components of a village
tank and their relative positions in the small tank village in Sri Lanka (adapted from Tennakoon, 2015)
Wewa is the main element of tank cascade system and Wewa refers to an artificial lake for storing water on the surface of the ground, which has been constructed by local people at a geographically suitable location using their indigenous skills mostly during ancient times.
Ancient people used to get drinking water from a separate place called Diyamankada of the tank where they planted Kumbuk trees. Kumbuk tree is believed to purify and cool the water, and believed to have an ability to reclaim saline and alkali soils and reduce soil erosion on banks.
Even when the water quantity is less in the tank, villagers were used to getting the water to a clay pot, filtered using a piece of cloth and add
Ingini seeds to purify the water. According to studies, Ingini seeds have the capability of settling down the clay and other suspended matter in the water and softening it. However, after the introduction of groundwater wells to the dry zone in the 1950s, people used groundwater as a source of drinking water.
Components of Wewa and their roles in managing the water pollutants
Wewa consists of some bio-engineering structures in order to conserve the soil, control water flow and purifying water. Schematic representation of components of the small tank is shown in figure 04. Proper functioning of these components, the earthen dam (We-kanda), sluice gates (Sorrowwa), spillways (Pita Wana), valve pit (Bissokotuwa), iswetiya (upstream conservation bund), gasgommana (upstream wind barrier made of tree plantations), kattakaduwa (downstream wind barrier, located in between the sluice and paddy), tisbamme (land strip around the hamlet for protection), thaulla (upper peripheral gentle sloping land) and wew ismaththa (closer catchment) ensure the better quality, quantity and sustainability of the water for the wewa. At present, all these components may not be present in all small tanks in a cascade system.
WEW ISMATHTHA (CLOSER CATCHMENT)
There was essentially an upstream land area dedicated to the tank from which water drained to the tank (closer catchment) through Wew thaulla.
The extent of this area depended on the water area of the tank and this area was maintained as a forest in the past.