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Could Sri Lanka get irrigation boost from ancient reservoirs?

Inland fishermen working in the Kala Weva, a massive 18sqkm water tank built 400 BC Sri Lanka's North Central Province Amantha Perera/IRIN
Inland fishermen working in the Kala Weva, a massive 18sqkm water tank built 400 BC Sri Lanka's North Central Province (July 2013)

One way Sri Lanka can better manage its water resources in the face of changing monsoon patterns is through centuries-old water reservoirs, experts say.

Experts at the Colombo-based International Water Management Institute (IWMI) say one way to ease fluctuating rice harvests (due to increasingly erratic monsoon seasons) is to use thousands of ancient small irrigation reservoirs spread out in the Northern, North Central, Eastern, North Western and Southern provinces.

“Tanks [reservoirs] can store water and so are buffers against irregular rainfall supplies,” said Herath Manthrithilake, the head of the institute’s Sri Lanka Development Initiative.

The reservoirs were built between 300 and 400 BC to provide nearby villages with water for agriculture and other needs. They became less important with the introduction of rain-fed cash crops by European colonizers in the 1500s and have been largely untouched since the 1970s with the development of large irrigation and hydropower schemes.

The tanks were constructed by excavating earth and building a large wall around the hole. Most tanks have filled up with sediment, others are hidden by overgrown shrubs or belong to dilapidated networks connecting them to the fields. There is no current estimate, but in 2004 the then government estimated that it would cost some US$20 million at the 2004 exchange rate ($15 million now) to make the tanks functional.

For Werrakoddi Archchilage Premadasa, a 33-year-old farmer from Tanamalvila town in southeastern Uva Province, the tank near his farm is the main source of water for cultivation. “Now the problem is half of the tank is overgrown and it’s also filled with sand… If we can get it to store to its maximum capacity, I don’t think we will have issues with water for cultivation.”

IWMI research has shown that reservoirs can also divert flood waters to the old tanks built on low-lying land, helping to minimize flood damage.

Manthrithilake said a major renovation of thousands of such reservoirs (estimated by researchers to number some 12,000) should be launched if they are to be used effectively. Some 1,000 tanks were repaired in 2004, with no additional repairs planned since then.

“Managing the water resources will be crucial. The monsoon, our main source of water, is changing, forcing us to change the way we use our water resources,” Waduwatte Lekamlage Sumapthipala, formerly the head of the Climate Change Unit at the Ministry of Environment and currently a government adviser, told IRIN.

Weather predictions

A recent World Bank report warned the island’s dry regions are likely to experience less rain while wet zones are at risk of even more deluges.

“The seasonal distribution of precipitation is expected to become amplified, with a decrease of up to 30 percent during the dry season and a 30 percent increase during the wet season,” the report predicted.

Late 2012 and early 2013 floods affected more than one million people nationwide, while a 2012 drought hit an estimated 1.3 million residents.

A survey of flood-affected communities conducted by the Sri Lanka government and the World Food Programme in January this year found 75 percent of the 557,000 people surveyed were either severely food insecure or borderline food insecure.

Of those surveyed, some 33 percent said their main income was through agriculture.

Fluctuating rice production

Rice production has been at the mercy of increasingly unpredictable monsoons in the past three years. In 2011, large harvest losses, around 20 percent of the main harvest, were recorded due to floods.

But the harvest recovered to an extent in mid-2011 when rain-fed irrigation helped to produce a higher-than-average secondary harvest (the country has two harvests annually).

During 2012’s drought the second annual rice harvest fell by up to 10 percent.

However according to the latest country assessments by the UN Food and Agriculture Organization, the rice harvest is expected to recover this year, and is likely to be above four million tons for the first time since 2009.

“The problem is the prices keep going up and down when the harvest falls and picks up. When we don’t have means to keep prices steady, we should look at keeping the harvest steady,” said Liyana Pathirana Rupasena, the deputy director of research at the governmental Hector Kobbekaduwa Agrarian Training and Research Institute (HARTI).

His concern is that poorer communities will cut back on calories or go for rice varieties that are cheaper but less nutritious during price hikes.

Rupasena said despite predicted harvest increases, rice prices are still higher than in 2011 and 2012. 

Hydropower problems

In addition to destabilizing rice production, water management problems have hit the country’s energy supply. Sri Lanka typically generates around 40 percent of its electricity using hydro generation.

During August 2012 when the drought was at its worst, hydro-generation barely reached 15 percent; the remaining power was generated through costly thermal sources, which forced the country to spend heavily on oil imports, according to the state.

The 2012 oil import bill for thermal power was around US$2 billion, around a tenth of what Colombo spent on imports for the entire year.

Heavy rains in 2013 have once again boosted hydro-generation to nearly 80 percent.

According to Tilak Siyambalapitiya, an energy expert based in Colombo, energy authorities should keep a close watch on the monsoon and emerging climate trends. He said pre-ordering oil stocks to face a potential loss in hydro capacity could save millions in foreign exchange fees.

“Right now the capacity of the reservoirs is totally dependent on the rainfall. There is hardly anything done to manage the water effectively once it’s in the reservoirs,” he said, referring to the reservoirs’ lack of maintenance.

The hope is that the pre-historic tanks can help ease demand for water from the nine main power-generating reservoirs, which farmers currently draw from for cultivation.


This article was produced by IRIN News while it was part of the United Nations Office for the Coordination of Humanitarian Affairs. Please send queries on copyright or liability to the UN. For more information: https://shop.un.org/rights-permissions

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