Great engineering feats:

Lanka's hydraulic marvels

The hydraulic expertise of our forefathers is something we Sri Lankans can definitely rave about. The mighty irrigation systems prevalent in the country even today in the form of the many ancient tanks,canals and reservoirs are a testimony to their skills.It is believed by many a historian that these ancient tank builders were endowed with remarkable expertise to control large bodies of water which led to the building of massive reservoirs other civilizations could not have even dreamt to undertake.

Polgolla

Randenigala

Bowathenna

To build such massive tanks our ancestors had to channel the water from rivers by damming the rivers or via canals.The historians attribute the progress made in this area by our ancestors to two important factors:an amazing in depth knowledge of trigonometry and a thorough grasp of hydraulic principles.

Their method of regulating the flow of water from these artificial lake reservoirs which are identified as tanks or wewas , is simply amazing. By the 3rd century B.C., our forefathers had invented the Bisokotuwa which is known as the valve pit today.It is in fact the ancient version of the present day sluice gates regulating the flow of water from reservoirs.

According to, H. Parker, an Irrigation Engineer who was in charge of restoring many irrigation tanks in late 1800s, Europeans started using the valve pits in their resoviors only in the mid 18th century. That is about 2100 years later. He has stated this in his book 'Ancient Ceylon.'

Many of you may have learned about the multitude of ancient tanks, canals and reservoirs that dot the country today built by the different kings who ruled our country.

These engineering marvels which baffles the world even today need to be restored and conserved.

Many of these great irrigation systems have been renovated and preserved while others have ended up as ruins.

Our engineering wizards had built many large-scale irrigation networks across the parched landscape of the country making use of the waters of the mighty Mahaweli river, its trbutaries and the numerous rivers that flowed down to the plains from the mountains of the wet zone,as early as the first century A.D .

Even after the collapse of the long monarchy,the irrigation network started by the ancient kings in the country continued to be maintained and improved .The construction of tanks and reservoirs damming major rivers is an ongoing process.It has always been the focus of successive governments as our country is an agriculture- based one,with irrigation playing a pivotal role in the livelihood of many.

The tanks, canals and reservoirs are the lifeline of the farming community of this country and while preserving the existing water bodies, steps have also been taken to construct many new irrigation projects to facilitate agricultural activities in the country.Under the Accelerated Mahaweli Development Programme, one of the largest projects undertaken in the country's modern history of irrigation several massive reservoirs were constructed by damming the Mahaweli River which is the longest river in the country.

Today as the first in the series on 'Great irrigation feats (ancient and modern),' we like to briefly describe some of these major projects which come under the AMDP and a few tanks constructed by our ancestors which have been developed and are presently operational.

Many of you may have even visited these famous reservoirs and tanks which are great engineering feats.We will bring you more information about the other important hydro reservoirs of more recent origin as well as the numerous tanks constructed by our ancient kings in our future issues.

Victoria Reservoir

It is an arch dam constructed under the Accelerated Mahaweli Development Pogramme (AMDP) which is located 130 miles(209 km) upstream of the Mahaweli River's mouth and four miles from Teldeniya.

It is the tallest dam in Sri Lanka and supports a 210 MW power station, the largest hydroelectric power station in the country.Its main purposes are irrigation and hydroelectric power production.

The dam creates the Victoria Reservoir, which has a surface area of 22.7 km2 (8.8 sq mi),The construction commenced on August 14, 1978.It was opened on April 12, 1985.The hydroelectric power station at Hakuruthale still remains the largest contributor to the national grid with an output of 210 mega watts.

Features of the dam

Catchment: 1,869 cu.m

Length and height: 520 m and 122 m

Capacity: 722 m.cu.m

Randenigala

Reservoir

It is another reservoir built under the AMDP and the largest among the Mahaweli reservoirs.The hydro power station generates 126 Mega Watts of electricity. In addition the reservoir manages Mahaweli water which is being released to Mahaweli C and Mahaweli B zones.

Features of the dam

Catchment:550 sq.m

Length and height:485 m and 91 m

Capacity:860 million cu.m

Rantambe

Reservoir

Rantambe Reservoir is the smallest reservoir made across the Mahaweli River.It receives water from Randenigala, released after generating of hydroelectricity and also from Uma Oya.

The concrete dam structure is located three km down stream from Randenigala.

Features of the dam

Catchment area :1095 sq.mi

Length and height of dam:420 m

and 41.5 m

Capacity: 22 million cu.m

Polgolla Diversion

As the initiative of the Mahaweli Master Plan and the key point of diversion of the Mahaweli River to Rajarata. it is of great significance.Diversion comprises of a concrete dam constructed across the Mahaweli River which is 146m. in length and 15.4 m. in height.

It has 10 floodgates which can be open when needed which directs water down the river.

Features of the

Polgolla Diversion

Catchment:738 Sq. Km.

Length and height: 143.86 m

and 14.8 m

Capacity:4.1 million cu.m

Kotmale Reservoir

The Kothmale Reservoir was also built under the AMDP by damming Kotmale oya, and is the highest in alttitude among Mahaweli reservoirs.Hydro-electricity generation, flood control, stabilising the water diverted at Polgolla are some of the main objectives of this reservoir project which included the first ever underground power station built in Sri Lanka.

Features of the dam

Catchment:561 Sq. Km.

Length and height: 600 m and 87 m

Capacity at FSL::174 million cu.m

Bowathenna Reservoir

A reservoir constructed under the Mahaweli Master Plan. Part of the Bowathenna dam was constructed with concrete and the other part was earth-filled.

It specially serves the complexity of Mahaweli water management by following ways: 1. Gathers water from the Mahaweli river and Amban Ganga( river)2. Channels water through the irrigation tunnel to Lenadora.3. Channels water for hydro-power generation through the power generation tunnel.4. Directs water down stream through main gates when necessary.

Features of the dam

Catchment area:382 Sq.km

Length and height:327m and 30m

Capacity:56.02 million cu.m

Facts and pix: Internet

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Why are dams constructed?

Sri Lanka which has a over 500 year old history in the construction of dams has about 12,000 small ancient dams, 320 large ancient dams and thousands of man-made lakes in the lowlands while in the Northern province alone there are over 10,000 reservoirs.

These dams have been built to fulfill all or some of the following purposes

* For agricultural development

* Supply of water for the domestic and industrial sector

* Flood prevention

* For hydro power generation

* To facilitate industrialization

Due to the many advantages of dams and the services rendered by them many large-scale projects to construct dams were undertaken in many parts of the world.

However as the construction of such dams , leads to the displacement of thousands of people, a special non-governmentalinternational commission to monitor the construction of dams, especially large-scale ones was founded in 1928 with its central office in Paris, France.

Comprising 90 member national committees which have a total membership of about 10,000 individuals the International Commission on Large Dams, or ICOLD, is dedicated to the sharing of professional information and knowledge of the design, construction, maintenance, and impact of large dams. Then in 1997 the World Commission on Dams (WCD) was set up following the growing opposition to the construction of large dams worldwide. It was a body initiated by the World Bank and the World Conservation Union (ICUN).It was given the mandate to not only review the development of such large dams but also to develop guidelines that were acceptable internationally for the planning, construction and design of these dams.

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Fact File:-

* There about 30,000 tanks in Sri Lanka of which the majority was built from 3rd century BC to 12th century.

* Ancient irrigation systems of Sri Lanka comprise a large number of village tanks which are known as wewas in local language, gigantic reservoirs and a intrinsic network of water canals which connect these tanks while supplying water to farming land.

* Abhaya Wewa is recorded to be the first large tank to be built in the country in 3rd century BC

.* H. Parker, in his book Ancient Ceylon states that the BisoKotuwa or valve pit, is believed to have been developed by ancient tank builders of our country as early as the 3rd century BC. About 2100 years before the Europeans began to use them in the construction of reservoirs .

* The dams built by our ancestors had broad bases which were able to withstand very heavy pressures, and the outlets for the discharge of water had been installed at suitable points in the embankment.

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