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.