Rainwater harvesting for agricultural and rural development has ben practiced in Sri Lanka since the pre-christian era. The evidence indicates that as far back as in the 450 B.C. series of small tanks have been constructed to store water during the period of its abundance so that it could be used during the water deficit periods. These tanks had been constructed in such a way to join one another from upstream to downstream so that the maximum utilization of rainwater is ensured. This arrangement is described as small tank cascade system. This tank eco-system is such that the reservoir is located in the lower landscape while the area above is covered by forest, the latter serving as the catchment. On either side of the reservoir are the homesteads and further away from the catchment and homesteads is the area which is used for chena or shifting cultivation. Just below the dam is command area where mainly paddy and rarely other food crops are cultivated under irrigation. In ancienttimes the entire agricultural systems had been governed according to a set of established norms aimed at optimum utilization of land and water resources. A tank itseif has several features in order to reduce siltation, lengthen the storage life of water and a system of natural purification of water. In addition to agricultural production benefits, the small tank cascade systems offer several other benefits such as fish, flood control, maintenance of water table, lengthening the period of water availability, soil conservation and reduction of siltation. The small tank cascade technology and the institutional landscape surrounding them have been time-tested for its adaptation to the local environment.
展开▼
