The Maduru Oya project, a component of the Mahaweli Development Scheme, is located in the basin of the Maduru Oya, which lies to the east and is separate from that of the Mahaweli Ganga itself. The first major project taken up for construction under the Accelerated Programme of Mahaweli Development was the Maduru Oya Project.
The Maduru Oya has its source in the Uva hills east of Bibile at an elevation of 274 m. (900 ft.) above sea level. It flows north-eastwards covering a distance of about 136 km. (80 mls.) and disgorges into the Vandaloos bay near Kalkudah on the east coast. Apart from the Northern plains, the flat littoral to the east of the Mahaweli, drained by the Maduru Oya and other streams rising in the Uva hills received the attention of our tank building kings. This is attested to by major works lying in disuse on the Maduru Oya basin itself.

The Maduru Oya basin situated in thick jungle, adjoins the Mahaweli basin on the eastern side and has an area of 453 sq. kms. (175 sq.miles). The Maduru Oya project envisage the construction of a 43 metres high and 1090 metres long rock fill dam across the Maduru Oya to create a reservoir of 478 million cubic metres (379,000 ac.ft.) capacity, enabling the downstream development of system B. The reservoir will be augmented by Mahaweli flows diverted from the now Minipe anicut. Three 2.4 MW turbines will be installed at the sluices for generation of hydro-power, at a later date.

The construction work was ceremonially inaugurated on this Project on August 14, 1978 with financial assistance of the Canadian Government and inaugurated in 1982.

System B project covers 114,650ha of gross area and fall within the 3 administrative districts of Polonnaruwa (about 65% of area), Batticaloa (30%), and Amparai (5%). This system is divided into the Left bank and the Right bank. About 75,000ha of land fall within the left bank, and the rest is within the right bank. The downstream development of system B left bank commenced in 1981 with assistance of the United States of Agency for Development (SFD) and Organization of Petroleum Exporting Countries (OPEC). The Zones 1 and 5 were the first to be taken up for development, covering about 32,6000ha of gross extent and providing settlement development for 9,381 farm families. In 1985, zones 2 and 3, covering about 24,000ha of gross area with settlement capacity of 6,700 farm families were taken up for development. Zone 4A which covers about 18,000ha with a settlement capacity of 4,500 farm families was taken up in 1987. The development of System B right bank has been suspended due to security reason.

The construction of the Left bank main canal and its branches was carried out with the USAID assistance in 1982-1986.

Historical Background

Ancient Bund:

Many centuries ago an earthen dam had been constructed at the very site chosen for the new dam. The remains of the massive ancient embankment on the right bank of the river about 23 metres (75.4 ft.) high and pitched with round stones along the upstream slope to break the ripple action indicate the magnitude of the reservoir constructed by our forefathers.
A matted forest canopy hid the breached earthen embankment on the very spot that foreign and local engineering experts chose to straddle the river.
These experts had the use of intricate surveys, sophisticated instruments, rainfall and river data to make their calculations, obviously the ancient Sri Lankan engineers were also backed by a knowledge of exact sciences without which such a technological achievement would not have been possible thousands of years ago.

Ancient Sluice:

The Maduru Oya project has attracted a great deal of attention after construction workers discovered an interesting sluice structure in the old earthen dam. Measures have been taken to preserve this structure in situ as an artifact of Sri Lanka's hydraulic civilization.

A technical review committee appointed by the Canadian International Development Agency (CIDA) in a special report to Mr. Gamini Dissanyake said:

" The upstream portion of the sluice is a masterpiece of construction. Twin conduits with corbelled arches approximately 2.5 m. apart pass through the bund. At the downstream and a carved terracotta relief depositing between the two arches. The dancing figures have been mutilated and the marks of the chisel used can be clearly seen on the carved relief.

" Major irrigation works and water control structures have been constructed throughout the civilized world since the 4th Millennium BC. These works include earth and rock dams, spillways, canals, dykes and embankments - the same structures that modern day engineers design for the same purposes. Some of the structures were advanced in engineering concept, major in scale, and in view of the lack of sophisticated machinery for construction, Herculean in execution. "The sluiceway and old bund at Maduru Oya rank in the forefront of these works. Several unique features of this structure testify to the sophisticated level of engineering practiced by the ancients. These include: "conduits were designed for low velocity conditions with upstream gate control.

The Main Physical Components of the Project

The average rainfall within the Maduru Oya project area = 1700 mm.
Catchment area - 453.0 Km 2 (175 sqr. Miles)
Full Supply Level (FSL) - EL 96.0 m
Gross Storage up to FSL - 596.6 x 10 6 m 3 (483,470 acre ft.)
Dead Storage - 111.6 x 10 6 m 3 (90,350 acre ft.)
Live Storage Capacity - 485.0 x 10 6 m 3 (393,000 acre ft)


Main Dam

Dam Crest Length - 1009 m
Dam Height - 45 m (max.)
Rock fill - 1,800,000 m 3
Filler Material - 250,000 m 3
Core Material - 435,000 m 3
Surface water area - 6280Ha
Left Bank Saddle Dam
Length - 600 m
Height - 20 m (max.)
Right Bank Saddle Dam
Length - 70 m
Height - 15 m (max.)

Spill way

Type - Un Gated Ogee Spillway
Design discharge Capacity - 1610 m 3
Link Tunnel - 5740 m long with an effective diameter of 5m.
(Sources Maduru Oya Reservoir Project : final report ; part A; scope and management of project, August 1984)


Head works

Dam and Reservoir - gross storage 555 10 6 m 3
Link tunnel from Mahaweli - capacity - 34 m3/s
Share (with System C) of the Minipe right Bank Trans Basin Canal in the Mahaweli Valley.

Main and Branch Canal

Systems - 248 km
Left Bank Canal - capacity/at head works 56.2m3 /s
Right Bank Canal - capacity at head works 32.5 m 3/s
Tertiary systems, drainage, land levelling, etc
Homesteads and settlements

Non irrigation infrastructure.
Physical Features

The Southern part of the project area, occupied by that portion of the Maduru oya basin which drains to the proposed reservoir, is separated from the Mahaweli Ganga valley by a north-south line of hills of height up to about 670 m above sea level. These hills are Precambrian in origin, in common with the underlying formations throughout the project area. The link tunnel planned to divert water from the Mahaweli Ganga into the Maduru Oya reservoir will penetrate this line of hills. A spur from the Northern end of this range transverses the Maduru Oya valley in a generally southeasterly direction. The gap thorough which the Maduru oya flows in its northerly course forms the site of the proposed dam. At this point the river is about 67 above sea level.
The irrigation area lies along either side of the Maduru Oya downstream from the Maduru Oya dam site. It is bounded on the southwest by the Hungamala Ela and System C, on the northwest by the floodplain of the Mahaweli Ganga, on the north by System A, on the east by the lagoon lying inland from the Bay of Benagal, and on the southeast by the Meeyankolla Ela.