The Victoria Dam

The Victoria Dam is located across the Mahaweli ganga immediately upstream of the Victoria falls rapids at about 130 miles from the river mouth. The site is about 72 aerial miles east of Colombo. 4 miles from Teldeniya. There is a good road from Colombo to Teldeniya distance about 84 miles. The present access from Teldeniya to the site is along the jungle track 4 miles long. The nearest railway station is Kandy.

Construction work was ceremonially inaugurated on this Project by President Jayawardana on August 14, 1978. It was ceremonially commissioned on April 12th 1985.

Main contractors for the Dam and Tunnel were the Joint British Venture, Balfour Beatty Nuttal and the Power Station was contracted to Costan International.

Victoria dam is the highest dam in Sri Lanka and has the largest Power Station in the country. It consists of a double curvature arch dam of maximum height 122m (400ft), a circular concrete-lined tunnel of 6 meters diameter (19.7ft) leading to 3 Francis turbines, each of 70 MW capacity and generating 780 GIGA Watt hours, housed in a reinforced concrete power station 52 m (170ft) long and 30m (98ft) wide. The dam which is located between the Hulu ganga confluence and the Mahaweli ganga rapids called “Victoria Falls” measures 507m (1663ft) along the crest. The catchment area at this dam site is 1869 sq km(730sq miles) and the gross capacity of the reservoir is 728 M cu.m.(500,800 acre feet) at a full supply level of 438 m(1437 ft). there is a 21 meter (69ft.)diameter concrete-lined chamber to protect the tunnel from surge, effects.

Eight radial gates 12.5 meters (41 ft)wide and 6.5meters (21 ft) high are provided for the dam so designed as to open automatically when pre-determined water levels are reached. The design of these radial gates which require power only for closing, won an award for innovation in Civil Engineering from the Institute of Civil engineering (UK) for the consultants who designed them. The effective width of the over spill is 100 meters (328ft) and allows a maximum discharge capacity of 8,200 cu.m.per second (289,542 cusecs) under a head of 11 meters (36 ft). Two low level sluices are provided in the dam for drawing down the reservoir at initial filling or any subsequent time and also to pass silt which may accumulate immediately above the dam.

The Consultants for the civil engineering works are Sir Alexander Gibb and Partners of U.K. and for the electro-mechanical part, M/s

Basic Features

The catchment area of the river above the dam site is 730 sq.miles. up stream of this site, the Polgolla dam for the diversion of a maximum flow of 2,000 cusecs has been constructed and is in operation. Detailed investigations and feasibility studies for the construction of a dam acroos the Kotmale Oya. A major upper right bank tributary of the Mahaweli Ganga are being prepared and are in its final stages of completion.
The drainage area of the reservoir is situated in the central hills ranging up to about 8,000 ft.
The long term mean annual runoff at the dam site is 2,430 thousand acre feet of which 1.100 thousand ax.ft is presently being diverted at Polgolla.

Dam and Reservoir

The dam is located in the deep valley of the Mahaweli ganga just above the Victoria Falls rapids. The engineering geologic conditions of the dam site are favourable. The foundation will be of hard slightly fractured granulated gneiss deposited at depths 8 to 17 ft in fragmented and weathered rock. The shape of the valley and the geologic conditions are favourable for the construction of an arch will have a maximum height of 338 feet and the length along the crest will be 1400ft. the middle part of the dam from the spillway, which will be furnished with 4 radial gates 50 ft. wide and 30 ft. high. The spillway will reduce flood peak of 0.1% frequency of 225,000 cusecs to 175,000 cusecs with a flood lift of 7 ft. above the normal water surface elevation of 1410 MSL.

The gross capacity of the reservoir is 415 thousand ac.ft the active capacity 390 thousand ac.ft. which will have an annual regulated discharge of 926 thousand ac.ft. for irrigation releases. During ‘shut down’ period and for emergency use an under sluice of size 7x7’ having a discharge capacity of about 1200 cusecs, will be provided.

Historical Background

The Victoria project is located in an area of great scenic beauty, congenial climate and of historic importance. The valley inundated below the Polgolla barrage is considered by geographers as a ”a misfit valley” due to the precipitous nature in relation to the large volume of water carried by the river. The climate in the Victoria is broadly similar to that of Kandy, but the rainfall is less and it is considered an area which has a climate between the dry and wet zone types.

The area affected by the project has played a very significant role in the religious, cultural and historical development of Sri Lanka. The evidence of early human settlement is shown from the Brahmi inscriptions found at the ancient temples at Goawatte and Bambaragala, which date back to the first century B.C. During the 15th century an area which is covered with water has played a very significant role in the politics of the time, particularly in view of the fact that some of the decisive battles have been fought against the foreign invading armies in this area. There were palaces of Sinhalese Kings situated in this area, and even today many of the inhabitants of this area perform various rituals connected with the temple of the Sacred Tooth relic of Lord Buddha in Kandy.

The Main Physical Components of the Project

The average rainfall within the Victoria project area ……… mm.
(Victoria project consists of a high concrete arch dam, a four mile long tunnel and power station)
Reservoir

Full supply level - 438 m.
Gross storage capacity - 722 million m3
Surface water area - 2270 Ha

Main Dam :Double Curvation Arch Dam

Dam Crest Length - 520 m
Dam Height (above foundation) - 122 m (max.)
Crest Roadway level - 442.5 metres MSL
Minimum thickness - 6 m
Maximum thickness - 25 m

Tunnel

Length - 5646 metres
Diameter of tunnel
(inside concrete lining - 6.2 metres)
Depth of surge chamber - 116 meters
Power Station :
Turbines

Type - Francis
Design (net head) - 190 meters
Speed of rotation - 333 revs/mm
Generators

Type - Semi umbrella
Generating voltage - 12.5 kv
Energy production capability - 686 GWH/ year (firm)
Energy production capability - 284 GWH/ year (initial)
(Sources Projects and Programme 1989)