| Uma Oya Hydropower Complex | |
| Name Official: | Uma Oya Multipurpose Development Project |
| Location Map: | Sri Lanka |
| Location Map Size: | 340px |
| Coordinates: | PD: DD: |
| Country: | Sri Lanka |
| Location: | Uva Province |
| Purpose: | Irrigation and Power |
| Status: | Operational |
| Construction Began: | April 2008 |
| Opening: | April 2024 |
| Builder: | FARAB |
| Dam Type: | Gravity dams |
| Dam Crosses: | PD: Dalgolla Oya DD: Mathatilla Oya |
| Dam Height Foundation: | PD: 45m (148feet) DD: 50m (160feet) |
| Dam Length: | PD: 175m (574feet) DD: 165m (541feet) |
| Dam Volume: | PD: 50000m2 DD: 70000m2 |
| Spillway Count: | PD: 3 DD: 3 |
| Spillway Type: | Chute spillways |
| Spillway Capacity: | PD: 2828m3/s DD: 2161m3/s |
| Res Capacity Total: | PR: 634826m2 DR: 970135m2 |
| Plant Name: | Uma Oya Power Station |
| Plant Operator: | Ceylon Electricity Board |
| Plant Type: | C |
| Plant Turbines: | 2 × 60 MW |
| Plant Capacity: | 120 MW |
| Plant Annual Gen: | 231 GWh |
The Uma Oya Hydropower Complex (also internally called Uma Oya Multipurpose Development Project or UOMDP) is an irrigation and hydroelectric complex in the Badulla District of Sri Lanka. Early assessments of the project date back to 1989, when the first studies was conducted by the country's Central Engineering and Consultancy Bureau. The complex involves building a dam across Dalgolla Oya, and channelling water over a 3975m (13,041feet) tunnel to Mathatilla Oya, both of which are tributaries of the Uma Oya. At Mathatilla Oya, another dam is constructed to channel 145000000m2 of water per annum, via a 15290m (50,160feet) headrace tunnel to the Uma Oya Power Station, where water then discharged to the Alikota Aru via a 3335m (10,942feet) tailrace tunnel.[1] [2]
The construction of the complex was inaugurated in April 2008 by former President Mahinda Rajapaksa and President Mahmoud Ahmadinejad.[3] The total project cost is estimated to be approximately (approximately), 85% of which is provided by the Government of Iran.[4]
The project was officially inaugurated by the President of Iran Dr. Ebrahim Raisi and President of Sri Lanka Ranil Wickremasinghe on the 24th of April 2024.[5]
In 2008 Sri Lankan government began the project with Iranian funding and the foundation stone for the project without obtaining Environmental Clearance for the project. Environmental Impact Assessment (EIA) Report of the Uma Oya Project was prepared by the University of Sri Jayawardhanapura and was submitted in November 2010. During the 30 working days the EIA was open to the public for review and comments Central Environmental Authority received many letters from environmental organizations who called the EIA inadequate. However despite the objections CEA gave clearance for the project.[6] [7]
Dalgolla Oya is impounded by the roller-compacted concrete Puhulpola Dam (PD), which is a gravity dam measuring 175m (574feet) and 45m (148feet) in length and height, respectively. The damming of this river creates the Puhulpola Reservoir (PR), which has a gross storage of 634826m2. The dam has a volume of approximately 50000m2, and consists of three chute spillways, allowing a combined discharge of up to 2828m3/s.
Water from the Puhulpola Reservoir is channelled to the Dyraaba Dam's reservoir via a 3975m (13,041feet) horse-shoe shaped free-flow conveyance tunnel, measuring 4.11NaN1 and 3.951NaN1 in width and height respectively, and with a discharge capacity of 15m3/h. Construction of the tunnel was completed on .[8] To build the tunnel, a drill-and-blast excavation method was used to displace approximately 55000m2 of earth.[9]
With a concrete volume of more than 70000m2, the Dyraaba Dam (DD) measures 165m (541feet), 50m (160feet), and 6m (20feet), in length, height, and crest width, respectively. It is constructed 986m (3,235feet) above mean sea level (MSL), and can withstand an estimated flood level of 995m (3,264feet) MSL. Just like the Puhulpola Dam, the Dyraaba Dam consists of three chute spillways, allowing a combined discharge of up to 2161m3/s.
The dam creates the Dyraaba Reservoir (DR) which has a gross storage of 970135m2 and active storage of 600000m2. Water from the reservoir is channelled through a 15290m (50,160feet) long circular pressurised-flow headrace tunnel measuring 4.252NaN2 in diameter, which has a discharge capacity of 19.5m3/h. To build the tunnel, a 180m (590feet) long TBM was used to displace approximately 222000m2 of earth.
The two pelton turbine generators of are fed via a 600m (2,000feet) vertical pressure shaft, after passing through the long tailrace tunnel. 68000m2 of earth was cleared to create the underground Uma Oya Power Station cavern. The power station will generate up to per year.[10]
The 5000m2 switchyard premises is built at 504m (1,654feet) above MSL. Power from the switchyard is delivered over 21.5km (13.4miles) of double-circuit 132KV transmission line, consisting of more than 70 transmission towers, to the Badulla Substation.
The annual discharge of approximately 145000000m2 of water from the power station is distributed out via a 3335m (10,942feet) cross-basin tailrace tunnel for agriculture use on 15km2 or existing land and 45km2 of new lands, including irrigation of 14 separate tanks.