The Uma Oya Multipurpose Development Project was designed to transfer approximately 147 million cubic meters (Mm³) of water to the adjacent basin (Kirindi Oya) for the irrigation of 5,000 hectares of agricultural land and the generation of 290 GWh of hydropower annually through two 60-MW generating units. The project was designed by Mahab Ghodss Consulting Engineering Company in association with AFRY (Switzerland), while construction supervision services were carried out by Mahab Ghodss. The project comprises the construction of two Roller-Compacted Concrete (RCC) dams, namely Puhulpola Dam and Dyraaba Dam, with heights of 35 m and 50 m, respectively. The reservoirs of these dams are interconnected through a 3.7 km transfer tunnel. The scheme also includes an underground hydropower plant with an installed capacity of 120 MW, connected to the Dyraaba Reservoir through a 15.5 km tunnel and a 618 m deep vertical shaft.
The engineering consultancy services contract was signed between Farab International Company and Mahab Ghodss Consulting Engineering Company on March 6, 2010. The original contract period was 60 months. The scope of engineering services, including the review of previous studies and development of project layout, feasibility and basic design studies, detailed design of all project components, preparation of construction drawings, construction supervision, and management of the associated ancillary works.
The Wey Oya Project is located in Sri Lanka, approximately 200 km east of Colombo, within the Uva Province.
Project Feature: The Wey Oya Project is recognized as one of Sri Lanka’s landmark dam engineering projects, particularly in the design and application of modern construction techniques tailored to the region’s challenging topographical and hydrological conditions. The key components of the project include Roller-Compacted Concrete (RCC) dams, a 120 MW underground powerhouse, and a 618 m deep vertical shaft recognized as one of the world’s deepest hydropower shafts.
The Puhulpola Reservoir is connected to the Dyraaba Reservoir through an interconnecting tunnel approximately 3.7 km long and 4.5 m in diameter. The tunnel transfers water from the Puhulpola Reservoir to the Dyraaba Reservoir with a maximum discharge capacity of 15 m³/s.
Water is conveyed from the Dyraaba Reservoir to the underground powerhouse through a 15.5 km headrace tunnel and a 618 m deep pressure shaft.
The pressure shaft has:
The Uma Oya Hydropower Plant consists of two 60 MW generating units, providing a total installed capacity of 120 MW.
The powerhouse cavern is located underground and has approximate dimensions of:
The generating units are equipped with vertical-axis Pelton turbines.
The discharged water is conveyed downstream through a 3.6 km tailrace tunnel operating under free-flow conditions.