Polgolla
Reservoir/Dam
The water resources of the Mahaweli Ganga Basin and its
utilization for agricultural and power development, as well as for
other uses had been studied over a period of four years and a Master
Plan was prepared accordingly. The Master Plan provided for a step
wise implementation of the Mahaweli Ganga development consisting of
15 multipurpose projects;
04 trans-basin diversion canals; and several power stations, having
a total installed capacity of 960 MW over a period of 30 years.
The first
project, Polgolla Diversion Complex consisting of a diversion dam
built across the Mahaweli Ganga at Polgolla for diverting the waters
of the river to the Dry Zone through five miles long an under-ground
tunnel connecting Mahaweli to the Sudu Ganga, and Hydro-electric
power station of 40 MW. An extent of approximately 140 hectares (350
acres) of land had been acquired for this complex.
Historical
Background
The Master
Plan
A UNDP/FAO
team with Sri Lankan counterparts carried out a survey of the
Irrigation and Hydro-Power potential of the Mahaweli Ganga and the
adjoining river basins during the four year period 1965-1968 and
formulated a Master Plan for the development of the available
resources. The Master Plan is described in the three volumes on
“Mahaweli Ganga Irrigation and Hydro-Power Survey” FAO, Rome in
1969.
The plan
envisages the development under irrigation of 900,000 acres of land
and generation of 2,037 million kilowatt hours of hydro electric
energy from an installed capacity of 507 megawatts. The capital cost
estimated in 1968 was Rs. 5,583 million, excluding cost of
activities resulting directly from the project, but having their own
economic justification, estimated at Rs. 1,120 million. In view of
the large magnitude of the work and investment involved, the Master
Plan was divided into three phases for purposes of implementation.
Phase I of the
Master Plan for which feasibility studies have been prepared by the
UNDP/FAO team has been sub-divided into three projects. The sub
division of Phases II and III was left to a later stage when
execution of the projects is taken up for consideration. Each of the
projects in Phase I, and Phases II and III were individually
evaluated and found to be economically viable. Each project can be
constructed in a period of 4 to 6 years. The entire master Plan was
phased for stepwise implantation over a time period of 30 years.
Implementation:
Execution of
Project I of Phase I was commenced in 1970 and completed in 1977. It
comprises of a barrage across the Mahaweli Ganga at Polgolla to
divert a maximum of 2,000 cusecs through a 5 mile long pressure
tunnel to a power plant of 40 MW installed capacity situated in the
adjacent Amban Ganga basin. The tail race water flows down a
tributary of the Amban Ganga into a reservoir at Bowatenna formed by
a concrete dam across the river, which diverts part of the flows
into the adjacent Kala Oya basin, through a 4 Mile long tunnel and a
Tran basin canal into Kalawewa and Kandalama reservoirs. The rest of
the diverted water along with the natural flow of the Amban Ganga is
sent down the river to be diverted at the existing Elahera and
Angamedilla diversion weirs into existing conveyance canals. The
total extent of land benefited by Project I is 132,000 acres of
existing fields and 91,000 acres of new lands.
The discharged
of 1,300 cusecs is sent farther down the Amban Ganga and diverted at
the Elahera anicut through Elahera – Minneriya- Kantalai-Yoda Ela
canal to Minneriya, and from there to Kaudulla and Kantalai tanks,
which supply water to system D-1. The Mahaweli System ‘G’ is
irrigated directly from this canal.
The remaining
700 cusecs is transferred through the Polgolla-Kala Oya canal (P K)
to Kalawewa and Kandalama tanks, from which 70 percent of System ‘H’
is irrigated.
The Main
Physical Components of the Project
Polgolla Head
works
General
Description:
Dam type - Concrete Barrage
Dam Height - 14.6 m
Length - 144 m
Gross Storage - 4.1 mcm
Live Storage - 2.1 mcm
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