A review on Diyakaliya in Yodha Ela. A unique structure of the canal irrigation system of ancient Sri Lanka

Long extending canals, distributing water for vast areas are one of the ancient irrigation structures of Sri Lanka. Normally, in terms of functionality, these canals are of four types. One; supply of water for paddy fields located at the destination point of the canal. Second; supply of water for small tanks located alone the canal which ultimately feed paddy fields. Third; canals that distribute water for the entire downstream area enabling people to use free water or water diverted by temporally earth dams or Amuna (anicuit). Other types of canals were made to provide water to tanks located alone its way as well as to its destination reservoir. Yoda ela, the longest and marvellous canal built by our ancient irrigation engineers belongs to the latter category. It starts from a large reservoir called Kalawewa being passed about 54 km to its destination reservoir Tisawewa located in Anuradapura ancient city. Yoda ela is mostly famous for its engineering aspect of carrying a large volume of water maintaining the same flowing capacity for a distance of 17 mile even though higher amount being provided for surroundings agricultural lands. On the other hand, Yoda ela has been constructed mostly in higher elevated sites in the downstream opposite to contours. The research explored that actually Yoda ela is not only a canal of water carrying, but also a water source freely flown on the ground can be denoted as a flown tank. At some places even today this is evident. In addition, archaeological investigation confirmed hundreds of small village tanks had been directly fed by the canal. Research exploded in addition to tanks, many other unusual structures had been there. One of them is Diyakaliya that differs from tanks. The main concern was given to study these ancient structures focusing attention on their engineering, hydrological and water management aspects and the functionality. Present paper as an outcome of that research, first discusses structural layout of the Diyakaliya from engineering point of view and then highlights its functionality from a hydrological engineering and environmental perspectives. Research was basically undertaken with field investigation together with topographical map interpretation. By the present as Yoda ela canal has been damaged and subject to modify under the Mahaweli Development project undertaken in 1970s. Thus ruins and limited remnants of the canal were the focal point of concern of this research. A number of Archaeological excavations were done at that sites. Opinions of old persons in the area were also used to understand the ancient layout of the Diyakaliya and its functionality. Research explored that ancient Diyakaliya is a means of intensifying water flowing capacity of the canal. Furthermore it worked as an instrument of water purifying, sediment and flood controlling of the canal itself and the surrounding. It is also evident that these structures have played a considerable role in the canal based water management systems. Therefore Diyakaliya is an unique feature that our attention should be further focused.