Deduru Oya

Deduru Oya (Sinhala: දැදුරු ඔය; Tamil: தெதரு ஆறு) is a river in northwest Sri Lanka. It originates from the eastern border of the Central Province, flows across Kurunegala and Puttalam districts and enters into the Indian Ocean at Chilaw (Somaratne et al., 2003). The river is 115 km long and mainly comprises 8 tributaries (Somaratne et al., 2003; Wickramaarachchi, 2004). They include Ratwila Ela, Kospothu Oya, and Dik Oya in the upper basin; Maguru Oya, Hakwatuna Oya, and Kimbulwana Oya in the middle basin; and Kolamuna Oya, Thalagala Ela in the lower basin (Mishra et al., 2017).

The river flows through all three climatic regions in which 94% of the area falls into the intermediate zone while 5% and 1% of the area belongs to the wet and dry zones, respectively (Jayasena et al., 2008). The Deduru Oya Reservoir was built across this river about 300 m upstream of the existing Ridi Bendi Ella anicut in 2014 under the Deduru Oya Project by the Ministry of Irrigation.

History

The ancient name used in Pali chronicles to identify the Deduru Oya river was Jajjara-nadi (Nicholas, 1963). Parakramabahu I (reigned: 1153-1186 A.D.), in developing the resources of his principality of Dakkhinadesa, harnessed the waters of Jajjara-nadi by damming the river at three points; Kotthabaddha, Sukaranijjhara, and Doradattika (Nicholas, 1963).

River basin

The Deduru Oya river basin extending in an area of about 2,616 km² is the 4th largest basin among the named 103 major river basins in Sri Lanka (Jayasena et al., 2008; Lakmali et al., 2015). 97% of the basin’s area is covered by the North Western Province (Kurunegala and Puttalam districts) and 3% by the Central Province [(Kandy and Matale districts) Wickramaarachchi, 2004]. The basin contains a number of small and large reservoirs, mostly rain-fed, used for irrigating paddy cultivation.