Malwathu Oya (called Aruvi Aru at the lower reaches) has a total length of 162 km and is the second longest river basin in Sri Lanka. It originates at Ritigala and Inamaluwa Hills (766 m and 383 m above MSL respectively) in the North Central Province and flows to the sea at Arrippu in Mannar district. About 70% of the upper catchment of Malwathu Oya is located in the Anuradhapura District while the lower catchment is located in Vavuniya and Mannar Districts.
There are two ancient reservoirs in the lower reach of the Malwathu Oya basin, namely Giant’s tank and Akattimurippu tank which has irrigable areas of 9,895 ha and 2521 ha respectively and operates with cropping intensities of 1.08 and 1.0 respectively. These two tanks are augmented through the ancient Tekkam anicut constructed across Malwathu Oya at a location about 36 km upstream from the sea mouth. As the storage capacities of both tanks are not sufficient to provide irrigation water for the full extent during a season, continuous diversions from Tekkam Anicut are required, especially during the late stages of the cultivation.
During the Yala season cultivation is not possible under both tanks as there is insufficient flow in Malwathu Oya. During the rainy season, a large quantity of water flows over the Tekkam anicut causing floods in the lower reaches of Malwathu Oya, especially in the Musali, Nanattan and Manthai West Divisional Secretary Divisions. Therefore, people living in the irrigable areas of Giant’s tank and Akattimurippu tank suffer due to drought during the dry season and floods during the wet season.
If the water overflow at Tekkam Anicut during the wet season can be retained and released during the dry season, the agricultural productivity of the two tanks could be improved tremendously. Further, this would reduce the flood risk in the Mannar District considerably. Therefore, it has been proposed to establish a reservoir referred to as Lower Malwathu Oya in the lower reaches of Malwathu Oya (In Bogoda Village) to retain the peak flow taking place during the rainy season.
Technical Details
| Description | Data |
| Gross Storage | 209 MCM |
| Area of Reservoir at FSL | 4422 Ha |
| Full Supply Level | 54.11 m msl |
| High Flood Level | 55.05 m msl |
| Bund Top Level | 58.52 m msl |
| Bund Top Width | 6 m |
| Bund Length | 3.59 km |
| Afflux | 1.24m (4.1ft) |
| Free Board without Afflux | 3.18 m (10.4 ft) |
| Maximum Height | 22.22 m (72.9 ft) |
| Type of Dam | Homogeneous Earth Fill |
Beneficiary Area
- Provide irrigation facilities to 1052 ha of new irrigable lands (Paddy & OFC), and 12,420 ha of existing cultivable lands under Giants Tank and Akathimurruppu tank
- 12 MCM of water to meet annual domestic water demand of Vavuniya, Mannar and Anuradhapura districts.
- Annual electricity of 4.68 GWh will be generated through the project which will be added to the National grid
- Resettlement of affected people.
- Development of tourism industry.
- Development of Thanthirimale under new town planning project.
- Flood mitigation in Vavuniya&Mannar districts.
- Introducing Solar power Projects.
- Lift irrigation project.
- New job opportunities during the project period.
- Development of fisheries & aquatic resources.
- Reforestation.
- Improving Forests / Wildlife Reserves while enhancing the movement of wild animals.
- Improvement of internal road network
- Strengthened Agrarian Services activities & institutional developments.
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