Written sources such as the Mahavasma, the chronicle of Sri Lanka, give evidence that the larger wewa systems were constructed and directed by various kings beginning from 300 BCE onwards (Jayasena & Selker 2004, Panabokke et al. 2002). They were implemented and managed under the stewardship of the kings. The Bassawakkulama tank in Anuradhapura (107 ha reservoir surface) was built around 300 BCE and is assumed to be the earliest large irrigation reservoir (Brohier 1934). All other ancient major irrigation works in Sri Lanka were most likely constructed later, namely in the period from 300 BCE to 1200 CE (Chandrajith et al. 2008). During the historical period of Anuradhapura, the number of major tanks steadily grew, reaching its peak in the hinterland of Anuradhapura in the period between 8th – 10th century CE (Gilliland et al. 2013). Contemporary thousands of small tank cascade systems were designed, built and governed by the village communities (Panabokke et al. 2002). According to missing historical records it is still unclear when the construction of these small irrigation systems began. It is widely assumed that the construction of the tank cascade systems developed out of the operation of rain-fed agriculture (DeSilva 2000, Panabokke 2010). Dahdouh-Guebas (2005) estimates that more than 30,000 human-made tanks were built all over Sri Lanka in historical times. Two thirds of these were tank cascade systems (Zubair 2005). At present, more than 10,000 of these ancient wewas are still in use (Dahdouh-Guebas 2005, DeSilva 2000), belonging to approximately 3,500 tank cascade systems (Murray 2004).

In 993 CE Anuradhapura was destroyed by conquerors invading from South India (Domrös 1976) and the tank cascade systems around Anuradhapura fell into disuse (Gilliland et al. 2013). These conquerors founded their new capital 80 km south east of Anuradhapura in Polonnaruwa. Here, King Parakramabahu, who reigned in the 12th century CE, was famous for his tank-building activities. It is documented that he had built around 2500 major and minor tanks as well as more than 4000 canals (Kenyon et al. 2004). The construction and service of the large wewa systems was carried out by a small number of professional engineers and administrators (Kenyon et al. 2004).

In the north-central region of Sri Lanka, especially after the 13th century CE, numerous major wewa systems fell into disrepair and were abandoned because of wars and epidemics (Zubair 2005). Under the British colonial administration in the 19th century, several of the major ancient irrigation works were restored. After the first World War, restoration programs also included numerous tank cascade systems, resulting in a “stabilization of the small tank irrigated agriculture'' within the dry zone of Sri Lanka (Panabokke et al. 2002).


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