Randenigala Reservoir /Dam

The Randenigala Project, the fourth major multi-purpose project and the largest reservoir under the Accelerated Mahaweli Development Programme. Randenigala project is located about 26 km. below the Victoria Head works and 6 km. upstream of Minipe anicut from where the main Right Bank and Left Bank canals will divert the Mahaweli waters for irrigation. It is also the reservoir with the largest storage capacity having gross storage of 860 million cubic metres (697,000 acre ft.) at full supply level. The project is expected to generate about 525 GWh of electrical energy which amounts to 20% of the island’s present demand. It will serve as the most important base reservoir for water management in System ‘A’, ‘B’ and ‘C’.

Project Features

The project chiefly consists of the construction of a 94 m.(308 ft) high, 485 m.(1590 ft.) long Rock-fill dam across Mahaweli, created a reservoir of 860 million cu.m. (697,000 ac.ft.). The Power House on the Left bank immediately downstream of the dam has an installed capacity of 126 MW. A steel lined tunnel 6.2 m. dieameter, 270 m. long, convey water to the Power House to run the turbines. The triple gated chute spillway is 48 M. wide, about 232m. long and is capable of discharging the probable maximum flood of 8085 cumecs.

Finances

The total cost of these Headworks is approximately Rs. 4898 million of which Rs. 1207 million is the local component and Dautsche Marks 410 million is the foreign component in 1985. The Federal Republic of Germany first granted a loan for a value of about DM 240 million (Rs.2160 million) and has extended a loan to the value of DM 400 million on favourable terms for Randenigala Project. (Rs. 2,528,455 as at the balance sheet 2004) (Rs.’000)

Consultancy services

The consultants for the Project is Joint Venture Randenigala (JVR), a firms, Salzgitter Consult GmbH, Agrar-Und Hydro-technik GmbH and Electrowatt Engineering Services Ltd along with the Engineers of the Central Engineering Consultancy Bureau. (CECB)
Construction work commenced in 1982. The reservoir was impounded in March 1986, construction of the rockfill dam, spillway and power station were completed in 1986, according to schedule. The two turbine generator units were commissioned in August and September 1986.

Scope

A dam at Randenigala site with power station and other appurtenant structures together with a lower dam at Rantembe (immediately below the confluence of the Uma Oya with the Mahaweli ganga), and power station.

The Main Physical Components of the Project

The average annual rainfall within the Randenigala Project area ranges from 1250mm to 3000 mm.

The Randenigala Project basic parameters :

Dam type Rockfill with Claycore

Recervoir

(As at Projects & Programme 1988)

Catchment area - 2,330 sqKm
Gross storage capacity - 861 MCM
Live storage capacity - 558 MCM
Surface at retention level - 1350Ha

Main Dam

Dam Length - 485 m
Dam Height - 94.0 m
Crest elevation - 239.0 m MSL
Crest width - 10 m
Maximum base width - 303 m
 

Spill way

Maximum capacity - 8,100 m 3/ s
Number of gates - 3
Type of gates - Taintor
Hight of gate - 15.26 m
Width of gates - 16.70 m
Length of chute spillway - 232 m

Tunnel Bottom & Irrigation Outlet

Length - 5646 metres
Diameter of tunnel
Inside concrete lining - 6.2 metres
Depth of surge chamber - 116 meters
Generators & Turbines

Number of turbine & Generator - 2
Type of turbines - Francis
Setting of turbines - 148.50 m MSL
Installed capacity - 2 x 63 MW
Annual estimated energy
Generation firm - 428 GWh (one million units)
Secondary - 100 GWh