The elements of tank cascade systems in a nutshell
Representation of a typical tank-irrigated landscape and its ecological segments in the Dry Zone of Sri LankaTank bund (Wekanda): an earthen bund constructed to stop the runoff during the rainy season and so to collect the water for irrigation. The tank bund is the heart of the irrigated landscape. Tank (Wewa): stores the water and is the dominant feature of the landscape. Agriculture, livelihood and regular social behaviour are intensely affiliated to the village tank. Sluice (Horowwa): uses a movable gate to control the outflow of water from the tank via canals and is integrated into the tank bund. Drainage (Kiul Ela): the natural valley system and its streams prior to the tank construction, existence based on the flow accumulation and erosion. Tree belt (Gasgommana): a natural vegetation strip in the upstream area of the tank that helps to reduce evaporation by acting as a wind barrier and helps to conserve the biodiversity of the tank environment. Large tree species such as Kumbuk (Terminalia arjuna) and Maila (Bauhinia racemose) are common in this segment. Stream (Ela): leads runoff water into the tank from the upstream headwater areas. Old-field (Purana wela): this is the command area of the tank, an originally paddy-cultivated field located in the valley bottoms downstream of the earth bund; it is associated with the ancient tank and the service tenants’ lands. Originally, the villagers owned this area communally as it is best supplied with irrigation water. Acre field or leased fields (Akkara wela): newly cultivated fields laid out after the British colonial irrigation and agricultural reforms. Private ownership is common. Supply of irrigated water is less favourable than in the old fields. Slash and burn/chena cultivation fields (hen): fields with rain-fed agriculture that are located along the divide of the valley that hosts the tank. Interceptor (Kattakaduwa): this area is located immediately downstream of the tank bund; it is densely vegetated with high species diversity. Its main purpose is to prevent salt from entering the downstream paddy fields. Furthermore, it acts as a wind barrier. Temple: located in a focal position. Farmers organize main activities among themselves on this monastery land. Hamlet (Gangoda): a village located downstream of the tank close to the paddy fields.