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Field visit to project of
Moragahakanda reservoir
On 1st April 2016
Visited Staff members and students of civil engineering department of
Sir John Kotelawala Defence University
Created by: D.S.ARACHCHIGE (ENG/13/023)
Content
1. History of the reservoir
2. Over view of the project
3. Benefits of the project
4. Construction techniques
5. Conclusion
1. History of the project
Mahaweli master plan is the biggest water resource management project ever
initiated in Sri Lanka, which is earmarked 365,000 ha land for development of
agriculture in dry zone of Sri Lanka. Master plan had series of reservoir,
hydroelectricity plant and develop irrigation channels to facilitate land development in
agriculture, electricity demand, fishery etc… In 1979 established Mahaweli Authority
to implement Mahaweli development programme by an Act in the parliament.
Under Mahaweli master plan project several large reservoir were built. Those
are Randenigal, Rantabe, Victoria, Kotmele, polgolla and Bowatanne. Ongoing
projects are Moragahkanda and Kalu gaga reservoir, Kivul reservoir etc…
Execution of Project I of Phase I was commenced in 1970 and scheduled for
completion in 1978. 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 Mahaweli Master Plan in divided into 12 viable Projects, which can be
undertaken simultaneously and completed in 5 to 6 years, provided the necessary
resources are available. The Government is committed to provide the social infra –
structure requirements such as health, education, transport facilities in addition to
agricultural inputs to achieve maximum production.
2. Over view of Project
Moragahakanda Irrigation project was inaugurated in January 2007, which is
one of the largest irrigation projects in the country six times larger than Parakkarma
Samudraya in Polonnaruwa. Moragahakana reservoir built across Amban Gaga and
which is a major component in Mahaweli development project. Project value was Rs.
61,321.7 Million second to Victoria reservoir. Currently project was completed up to
60%.
The dam is located across the Amban Ganga about 30 miles above the river
mouth, and about ¾ mile upstream of the existing Elahera anicut and about 10 miles
below the Bowatenna a reservoir. The dam site is accessible from Colombo, about
110 miles along existing macadamized roads and 20 miles from Dambulla, which is
the nearest town. The dam is situated near the tenth mile of the Naula- Pallegama
road, the nearest railway stations are Kekirawa.
The completion of the Moragahakanda reservoir project will contribute
towards increasing agricultural productivity in the island from 165 per cent to 185 per
cent and its total output value would be US $ 17 million. It is also expected to save
US $ 2.2 million locally by supplying water to households and for industrial purposes
Following are general information of the project.
Contract value - 252,302,221 US$
Contract period - From 2012.07.25 to 2016.7.25(208 weeks)
Contractor - M/s Sinohydro Corporation Limited
Funding agency - China Development Bank Corporation.
Client - Ministry of irrigation and water resource Management
Implementing agency - Mahaweli Authority of Sri Lanka
Dam operator - CEB
Morgahakanda reservoir has three dams, which are Main Dam-Rock filled with
core, Saddle dam1 Roller compacted concrete (RCC) and Saddle dam 2
Homogeneous earth fill of total length 5.070ft. The concrete gravity dam 56.5m. at
height and 375m. along the crest and crest width 8m, will be constructed across the
river channel. The left bank saddle will be closed by a rock-fill dam 63m maximum
height and 465m along the crest and crest width 6m. The smaller depression on the
extreme left bank will have an earth dam 21.5m maximum height and 275m long and
7m width crest.
The spillway is designed to deal with a flood of 0.1℅ frequently of occurrence,
having a peak discharge of 176,000 cusecs. This will be routed to a maximum 87,000
cusecs, with an afflux of 8.5ft. above the normal water surface elevation. The spillway
will be equipped with three radial gates 65ft. wide by 15ft. height.
The reservoir will have a gross capacity of 692 thousand ac. ft. an active storage
of 470 thousand ac.ft. and an annual regulated flow of 1,103 thousand ac. ft. which
includes the Mahaweli waters diverted at Polgolla. When the Kotmale reservoir is
constructed and commissioned, the annual regulated flow of the Moragahakanda
reservoir will increase by 293 thousand ac.ft. to 1,396 thousand ac.ft.
The hydro – electric station at the base of the concrete dam will be furnished
with 4 generators of 10MW capacity each. The firm power production is estimated at
17.2 MW and the firm power output at 149 million KWH per year.
3. Benefits of the project
Development of Moragahakanda reservoir many beneficial adds to Sri lank
directly and indirectly. Mainly facilitate to cultivate 5000 ha new land in North-
central and provide sufficient water supply for agriculture. Mahaweli River to the sea
will be restricted 60% of total drawn off.
Water from both, the Moragahakanda and Kalu Ganga reservoirs, will be
primarily used to support agricultural needs to an area of at least 81,422 ha (814.2
km2). This will increase rice production by 81% or 109,000 t (240,000,000 lb),
amounting to an estimated monetary benefit of US$1.67 million, annually.
The reservoirs would also create a source of inland fishing, generating
approximately 4,700 t (10,400,000 lb) or the monetary equivalent of US$1.67 million,
annually.
It also expected to provide domestic Water supply with the reservoir of the
Moragahakanda and the Kalu Ganga Dam, an increase of 64,000,000 m3 (2.3×109 cu
ft) of potable and industrial water supply could be ensured by 2032, to regions
including Matale, Anuradhapura, Trincomalee, and Polonnaruwa.
Water from the Moragahakanda Reservoir will be used to power the 25-
megawatt Moragahakanda Hydroelectric Power Station, also currently under
construction. The substitution of this hydropower with traditional fossil fuel power
generation is estimated to save up to US$ 2.49 billion annually. Construction of the
power station costs US$382 million, with an IRRof 22%.
Transportation network is improved. Koombiyangahaela to Moragahakanda
relocation road which is 13.5km is in progress with carpet laying. The 24.1km length
new road from Moragahakanda up to Thorapitiya Wellewela via Guruwela new
settlement area with 77 culverts and 10 bridges was constructed, and road paving to
be done. Construction of new hamlet and market roads and improvement to the
existing roads facilitate project activities.
Development of Guruwela and New Laggala new towns are on progress.
Construction works of post offices, health care centers, administrative buildings,
schools were completed. Guruwela police station construction is in progress while
police staff quarters were completed.
Families who are living in Kaluganga Dam construction site were resettled
about 05km away from their original homes at Guruwela resettlement area and
compensations too were already paid. The families affected under Moragahakanda
reservoir were provided new lands at Thorapitiya resettlement area. Kaudulla LB
canal extension development area- Medirigiriya – Bisopura is also in progress.
The project has paid special attention to minimize the impact on environment.
The following activities are currently being implemented as stipulated as in
Environmental Effect Assessment (EIA) Report.
Reforestation of about 1365 ha in the immediate catchment of Amban
Ganga Basin
Demarcation of 100m buffer zone around Moragahakanda reservoir and
reforestation of 650ha inside this buffer zone.
Establishment of an elephant corridor between Giritale – Minneriya
nature reserve and Wasgamuwa National park. Habitat enrichment in the
above areas.
Rehabilitation of tanks in adjacent nature reserves and eradication of
invasive plants.
Establishment of electric elephant fence around the resettlement area
Introduction of new farming technology and capacity building of newly settled
farmers are very important for successful resettlement process. In order to achieve this
project has established a 27 ha Model farm at Guruwela resettlement area. The farm
plays a vital role in farmer training, supplying of planting materials for the new
settlers, introduction of organic farming and to illustrate agriculture potential in the
area.
4. Construction techniques
Before going to construct the dam detail design procedures are conducted. In the
19th
century dam were designed by considering rule of thumb with little concern for
the principle of mechanics of the material. And these small gravity dams based on
elastic analysis is sufficient. But when designing large gravity dam sophisticated
methods such as finite element methods will be used. Mainly, hydrological data
necessary when establishing required capacity of the reservoir and freeboard
elevation.
Stability of the gravity dam and forces acting on the dam can be representing in
following figure. Forces are horizontally hydrostatic force due to water body and
hydrostatic force due to earthquake and vertically weight of dam and uplift force.
Effective force on the base will be vectorial resultant of the forces.
A gravity dam may be fail sliding along the horizontal plane, by rotation about
the toe, or by failure of the material. Failure will be occurred in any section or
foundation plane of the dam. When exceeds the net horizontal force than resisting
shear force in the dam sliding or shear failure will be occurred. Overturning and
excessive compressive stress can be avoided by selecting proper cross section.
Geologic structure and the engineering conditions at the Moragahakanda dam
site are of considerable diversity and complexity. Loosely fragmented sediments are
found everywhere on the surface, to depths of as much as 34ft. and are notable for
their high water permeability. Underlying these are metamorphic rocks [quartzitic and
quartz – biotitic. Gneisses and granulites] forming an anticline with the axis. Results
of exploratory drilling indicated two fault zones [45 -95 feet] represented by highly
weathered broken and highly fractured gneisses, Granulities, Quartzites and karstic
cavernous limestone. These rocks are generally characterized by specific water
absorption of more than50 gallons per minute, under pressures of 100 1b, per sq. inch
Partly to slightly weathered and fractured rock occur at depths of 8 – 46 feet in the
fault zone [60 – 100 feet from the ground surface]; thickness of deposit varies
between 3 – 8 and 20 – 35 feet respectively. Ultimate strength of these rocks ranges
from 5,500 – 8,500 to 14,000 – 21,000 1b/m2. The fractures will require careful
washing and grouting.
Before construction work starts streamflow must be diverted. And cofferdam
will be constructed by providing safe working area during flood situation. Cofferdam
are temporary structure which exclude the water from the construction site. Coffer
dams are low cost but practically should be water tight. When we visiting time main
rock-fill dam and concrete gravity dam under construction, we observed that
cofferdam built at main rock-fill dam.
Moragahakanda reservoir consist three dams, from them earth dam was
completed. Earth dam are constructed commonly rolled fill method. The stability of
an embankment dam is enhanced if the downstream portion can be maintained free
from seepage. Internal drains are therefore put within the dam. See figure, leaving the
'dry' compacted fill as support. The section A-A represents the filter, drainage, filter
divisions. The Consolidation achieved by using heavier equipment such as sheep-foot
roller or pneumatic tried rollers. After completion of earth dam soon as possible
grasses are planted to stop the erosion.
Rock-fill dam have characteristics midway between earth and gravity dam and
rocks serve major structural element of the dam. There are two types of rock fill
dams: the impervious face and impervious earth core. Moragahakanda used
impervious earth core dam to control the seepage, following figure shows cross
section of the dam.
In the impervious earth core type of rock fill dam an impervious core is placed
near the center of the embankment. It is important that the core be separated from the
rock fill by a transition zone of fine graded material.
After constructing the cofferdam, critical needs supervision of the constructing
of the clay core. The rock under the construction of the clay core is first grouted by
the cement paste which the cement grout is pressured through the rock cracks. It
prevents the water to leak through the rock. Before this process is done surfing must
be done to make sure that the pressured grouting part is not coming to the surface
along the rock cracks to immerge in the other part of the rock surface. Surfing process
provides a barrier to the grouting to prevent the leaking of the grouting at the rock
surface.
Saddle dam 2 was Roller compacted concrete (RCC) gravity dam situated in
the middle of other two dams. This concrete gravity dam consist the spillage, radial
sluice gate, power housing unit and gallery.
Construction process of the saddle dam 1 done by using roller compacted
concrete first time in Sri Lanka. And roller compacted concrete which has the slump
0. It is just like the solid paste which has less liquid proportion. It is mainly
transported to the site by the trucks. In this saddle dam construction, the roller
compacted concrete is places in to 15 layers. In the placing of the one layer it lay up
to 6 m and it should me immediately consolidated. Before it sets the concrete the
other layer should lay on that. If it is taken considerable amount of time to lay the
other concrete layer the cement mortar should applied before the roller compacted
concrete is applied.
When concrete set, a great deal with temperature rise of RCC concrete and as
concrete cools, it shrink and crack may develop. To avoid cracks occur, special low
cement may be used. In addition, the material which go into pouring site befor its cool
normally concrete mix temperature should keep around 10 to 25 celceius.
Occasionally future cooling process achieved by near cooling plant which is
expensive. Following figure shows cross section of RCC gravity dam. Inside gravity
dam in the gallery cement grouting are processed in high pressure injector.
Main layer of the concrete gravity dam are shown in the figure. from that The
shear key and the curtain grouting was provided to the saddle dam. The main purpose
of the curtain grouting is to prevent the seepage occurring from the reservoir side. It is
mainly build up to 40m depth from the base of the saddle dam. Shear key place an
important role in the dam construction which is govern the slope stability in the dam.
Constructing of a shear key provides the considerable failure length which avoid the
shear failure in the dam. Inside the dam, the tunnel was constructed for the inspection
purposes and to install the grouting in to the rock.
Curtain grouting is the construction of a curtain or barrier of grout by drilling
and grouting a linear sequence of holes. Its purpose is to reduce permeability. It may
cross a valley as a vertical or an inclined seepage cut-off under a dam; it may be
circular around a shaft or other deep excavation; or it may be nearly horizontal to
form an umbrella of grout over an underground installation. A grout curtain may be
made up of a single row of holes, or it may be composed of two or more parallel rows.
Shotcrete treament also important which applied near the dam to prevent
seepage from exsisting abutment. Which is inject or compressed air forces mortar or
concrete through a hose and nozzle onto a surface at a high velocity. Materials used in
the shotcrete process are generally the same as those used for conventional concrete-
Portland cement, lightweight aggregate, water, and admixtures.
Material requirement of the project is about excavation in foundation earth
1,030,000 cu.yd, excavation in foundation rock 698,000 cu.yd, quantity of concrete
552,000 cu.yd, quantity of rock-fill 975,000 cu.yd, quantity of earth fill 1,120,000
cu.yd, quantity of cement 91,500 cu.yd and quantity of steel 750 Tons.
5. Conclusion
Visting Moragahakanda development project as undergraduatee was
effectively gathered techinical knowledge and construction process. Initial project
introduction was helpful to understand about Master plan, current developments of
master plan, resettelement programme under Mahaweli Authority, benefits after
development and technical informations.
Going to the site, we observed two dams of main rock fill dam and saddle dam
1 RCC gravity dam. At the site there was site engineer explained strucutral features
and construction activities. Newly I have learned about gravity dam,earth dam, Rock
fill dam, grouting curtain, shear box or key, shotcrete and cofferdam to control flood.