Floods and droughts in Sri Lanka – a sustainable solution


Dr. Janaka Ratnasiri

Continued from yesterday

Kalu Ganga surplus water

Next to Mahaweli, Kalu Ganga discharges the highest amount of water to the sea. A power plant with capacity 70 MW has been built on one of its tributaries Kukule Ganga. Originally, the plan was to build a large reservoir there by constructing a high dam, with the view to taking water to the South-East along a canal referred to as the South-East Dry Zone (SEDZ) canal, comprising part tunnel and part open duct, and running along the 120 m contour. Since there had been public protests because of the large extent of land getting inundated including Kalawana Town and also due to environmental concerns being close to the UNESCO Heritage site Sinharaja Forest, the original proposal was dropped. Hence, only a small pond for operating the power plant as a run-of-the-river system was built at the site.

However, Eng. G.T. Dharmasena, a former Hydrologist in the Irrigation Department is of the opinion that this project should be revisited because it is the only option to supply water to the South-East (http://wedc.lboro.ac.uk/resources/conference/32/Dharmasena.pdf). Even though work is in progress to divert Uma Oya to augment the water supply in the South, recent studies show that the flow in Uma Oya is marginal and there is a doubt as to whether the intended benefits can be achieved. (DSWRP Project Component III; Initial Assessment Report - Mahaweli Basin). Perhaps, a smaller version of the originally planned Kukule reservoir may be undertaken to take surplus water from Kukule to the South-East.

In recent years, there had been an attempt to build a dam across Kalu Ganga at Meehitiya, a few kilometres upstream of Ratnapura town, supposedly for protecting the town and the surrounding low-lying areas from recurring floods. After carrying out a detailed survey of the area by a foreign firm of consultants, the project was abandoned partly because of protests by villages whose land was getting inundated and partly due to some other reason. The President in 2006 had said that he wanted Kalu Ganga diverted to Ruhuna thereby solving two problems in one attempt referring to the regular recurrence of floods in Ratnapura and the occurrence of severe droughts in the Hambantota District (Daily News of 13.03.2006). Eng. Dharmasena had responded to this statement a few days later saying that the elevation of the proposed reservoir, which was about 50 m, is too low for taking water to the South-East.

Alternative proposal for diversion of Kalu Ganga

The writer proposed an alternative scheme to take surplus water to the South-East in an article published by him in The Island of 11th and 13th of November, 2011 (available on http://www.island.lk/index.php?page_cat=article-details&page=article-details&code_title=38840 and http://www.island.lk/index.php?page_cat=article-details&page=article-details&code_title=39005). The scheme comprised building small reservoirs on two tributaries of Kalu Ganga which flowed into the proposed reservoir, viz. Rath Ganga and Bambarakotuwa Oya, at about 200 m elevation and another on Wey Ganga which joined the Kalu Ganga below the proposed reservoir. This tributary contributes significantly to flooding at Ratnapura, but the proposed reservoir was not designed to regulate its flow. The three reservoirs could then be linked by trans-valley tunnels and the water taken to a tributary of Walawe Ganga, from where the water could be fed to the proposed SEDZ canal for taking to the South-East. In the process, there is potential to develop a significant amount of electricity also. Copies of the proposal was sent to relevant authorities, though no response was received officially.

When the government decided to abandon the project, a public meeting was held at Malwala Temple to apprise the people in the area of the government’s decision with two cabinet ministers from the area attending. At this meeting, the write brought to the attention of the ministers his scheme, but one minister present said that there was no necessity to take Kalu Ganga waters to Hambantota as the Uma Oya would be diverted to the South. However, with the findings of the DSWRP study that the expected amount of water may not be available from Uma Oya, the government will have to re-think the need to divert water from the Kalu Ganga to the South-East.

Kelani Ganga diversion

On an average, Kelani Ganga discharges the highest quantity of water to the sea, after Kalu Ganga. There are several reservoirs built for the purpose of generating hydro power on the tributaries Maskeliya Oya and Kehelgamuwa Oya which form Kelani Ganga, but the diverted water returns to the river after turning the turbines. Kelani Ganga is fed by its two main tributaries Seethawaka Ganga and Gurugoda Oya, the former joining Kelani Ganga near Talduwa and the latter near Ruwanwella. Hence, if a large reservoir is to be built to store surplus water received in the Kelani Basin on days of heavy rain, it has to be located downstream from their confluence.

The river flows between two hills near Glencore Estate at Kudagama which will be an ideal location to build a dam to capture the water flowing from the two tributaries. However, the land upstream is rather flat to build a reservoir. In ancient times, storage tanks were built on flat land by having a dam built encircling a wide area, such as in the case of Giant Tank in Mannar District. Perhaps, we can learn from ancient technology. There has been a previous proposal to divert Kelani Ganga and Maha Oya waters by a trans-basin diversion to the NW Province, the objective of the diversion being partly minimizing flooding of the lower Kelani valley, and partly irrigation in NWP (DSWRP Water Sector Report). Apparently, a detailed study has been done in 1961 on the diversion of Kelani Ganga by a firm of foreign consultants, and the project should be revived in view of the anticipated worsening of the drought situation in the country.

Diversion of rivers in the South

According to a report appearing in a Sunday Weekly on 22.06.2014, the government has initiated studies to divert water from Gin Ganga and Nilwala Ganga in the South to the South-East. Both these river basins, receive an average rainfall of 3,000 mm annually, and much of this water goes to the sea except for supplying water for municipal areas. In the present proposal, reservoirs will be built across Gin Ganga and Nilwala Ganga and after inter-linking them by trans-basin tunnels and canals, water will be taken to the South-East Dry Zone. The reservoir at Gin Ganga is expected to operate a power plant with capacity 49 MW. The diversion is expected to cost Rs. 73 billion.

Environmental and social impacts

Every developmental activity causes some degree of environmental and social problems. Building of reservoirs inundates fertile land, affects the biodiversity and river-side ecosystem and causes emission of methane due to submergence of vegetation which contributes to global warming. People will lose their homeland and compelled to resettle in new land. They will lose their traditional occupations and livelihoods and children will have to look for new schools. It is therefore important that the authorities look into all these aspects right from the conceptual stage in order to minimize these adverse impacts. Affected people need to be adequately compensated without causing any hassle to them in receiving compensation.


Studies show that in the future, severe droughts are likely to occur with more severity and frequency in Sri Lanka due to anticipated climate change. The government will therefore have to give the highest priority to implement measures that would give relief to people in drought-prone areas when droughts occur and water becomes scares. These projects will also reduce the occurrence of floods in river basins. In the foregoing, several possibilities to make availability of water more equitable than at present across the country have been suggested. Transferring of surplus water received in wet areas to dry areas is the only sustainable solution to this recurring problem. In some of these projects, preliminary studies have already been undertaken. These adaptation measures need to be reviewed and detailed studies should be undertaken. Under the UNFCCC, funding mechanisms are available for developing countries to undertake adaptation measures, and these funds as well as funds available under bilateral programmes for such activities should be sought.


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