Book excerpt: This report on small tank cascade systems is based on a study conducted on seven tank cascades of the Walawe river basin, one of the three main river basins in the Ruhuna benchmark basins selected by the International Water Management Institute (IWMI) for its benchmark basin study.The overall objective of this study is to document the situation of small tank cascade systems in the basin, paying special attention to their evolution under agro-ecological, socio-economic and institutional changes on an unprecedented scale in the country after the introduction of open market economic policies in the 1970s, and thereby to contribute to the existing knowledge on small tank cascades, a key feature of water resources in the Dry zone regions2 of Sri Lanka since time immemorial.