Banking on dam safety in Sri Lanka13 August 2008
Sri Lanka’s dam network fulfils critical functions across the country but extensive maintenance requirements have now become a priority. Nihal Fernando explains the World Bank’s involvement in what is to become Sri Lanka’s largest dam safety programme to date
Dam construction for water harvesting, flood control and agriculture is an age-old tradition and practice in Sri Lanka. Ancient kings averse to wasting water built large dams, and evidence of this hydraulic civilisation is visible to this day.
Sri Lanka is a tropical island in the Indian Ocean lying to the southwest of the Bay of Bengal. The country’s rainfall pattern is influenced by both the monsoon winds of the Indian Ocean and the Bay of Bengal. With an average annual rainfall of 2500mm, Sri Lanka’s wet zone covers the central mountains region, the west and southwest areas of the country. The dry zone lies across the southeast, east and northern parts where the rainfall is between 1200-1900mm annually.
The dam network
Sri Lanka’s dam network comprises about 350 large and medium dams and over 12,000 small dams. Of the 350 dams, 80 are large structures according to ICOLD’s classification. These large dams can be further classified in the Sri Lankan context as ancient, recent and modern dams on the basis of their period of development.
Ancient dams are mostly earthfill but fell into disuse and subsequently became dysfunctional. They decayed as internal wars raged, epidemic diseases such as malaria wiped out settlements, and capitals shifted. The British who ruled the country between 1805-1948, and the Independent Government of Sri Lanka between 1948-60, saw the wisdom of the ancient dams and restored, rehabilitated and improved them.
Those that fall into the recent category are mostly earthen or composite earth/rockfill dams, constructed between 1938-85. They were mainly developed for hydro power, irrigation and flood control and were constructed at locations where there were no ancient dams.
Modern dams are mainly multi-purpose concrete gravity and arch dams and barrages, composite dams, and rock and earthfill dams. These were built using new dam design and construction technology. They were constructed between 1973-88 under the Accelerated Mahaweli Development Program, the largest river basin development programme ever implemented in Sri Lanka.
The other 12,000 dams are typically called village tanks which are small seasonal water harvesting storages that serve domestic, irrigation and environmental water needs of the rural people.
The current challenge
This dam network and the related hydraulic assets and infrastructure serve the critical irrigation, hydro power, domestic and industrial water supply needs of the country. They also provide flood control in the river basins, and sustain human settlements particularly in rural areas. Power generation, and production of Sri Lanka’s staple cereal rice, are heavily dependent on these regulated water resources. The dry zone, which covers nearly two-thirds of the country, is home to a large majority of rural poor people. Their livelihoods depend either fully or partially on irrigated agriculture which utilises about 85% of the developed water. The water from these dams is the lifeblood that sustains the rural dry zone.
There are no privately owned dams or an agency which is mandated and responsible for dam safety regulation. The large dams are owned and operated by four state agencies who report to four Cabinet Ministries, namely: the Irrigation Department; Mahaweli Authority of Sri Lanka; the Ceylon Electricity Board; the National Water Supply and Drainage Board.
The larger dams are now ageing and have various structural deficiencies and shortcomings in operation and monitoring facilities. A World Commission on Dams consultation was held in Sri Lanka in 1998 and highlighted the need to draw prompt attention to the safety of Sri Lankan dams. Following the recommendations made at this event, the World Bank supported the Government of Sri Lanka in carrying out a safety assessment of 32 large dams that showed signs of risk. The study confirmed the need for urgent action including structural improvements to protect the general public, as well as safeguarding the economic and environmental functions of these valuable assets. Technical and institutional capacity building in the country for efficient regulation, operation and maintenance of the dams was also a priority action recommended by the study.
The Annual Report of the Central Bank of Sri Lanka in 2004 highlighted dam safety issues as a priority area for public investment. An independent consultant carried out a national consultation in 2005 which generated useful recommendations to ensure public safety against potential dam failures.
The tsunami disaster
The devastating human tragedy caused by the tsunami disaster in Sri Lanka on 26 December 2004 further deepened the need and urgency for the country to protect the public from natural disasters, including dam failures. Consequently, for the first time in the history of Sri Lanka, a Ministry of Disaster Management was created, a national Disaster Management Centre (DMC) established and the Sri Lanka Disaster Management Act (No. 13 of 2005) was passed by Parliament.
The Act established the National Council for Disaster Management, whose functions include protecting the public from potential dam failures. A national, public consultation on dam safety was carried out by an independent non-governmental organisation. It highlighted the potential public safety hazards posed by the dams and recommended immediate remedial actions.
In response to this national priority, the World Bank approved the Dam Safety and Water Resources Planning Project on 27 March 2008, to be implemented over a period of five years starting in 2008. The project aims to improve the operational efficiency of 80 dams and establish sustainable institutional arrangements for the safe management, operation and maintenance of major dams in the country. Special attention will be paid to the safety of 32 dams that have been categorised as high risk from this group. The project will also support:
• Upgrading and modernising the country’s hydro-meteorological data and information collection network.
• Institutional capacity building for efficient data and information collection and processing for disaster management, water resources development and water management.
• Preparing a national water use plan and updating the Mahaweli Water Resources Development Plan.
• Preparing a water resources development plan for the Mundeni Aru river basin.
• Preparing feasibility studies for priority water development options.
The total estimated cost of the project is US$71.66M of which US$53.14M is allocated for dam safety. The World Bank is committed to finance US$65.33M. The Government of Sri Lanka will contribute US$6.33M.
Addressing safety issues
Under the dam safety component, the project is designed to address major structural deficiencies and institutional shortcomings to ensure the safety of the dam projects. Typical safety issues commonly observed in the dams are:
• Erosion of upstream and downstream slopes due to the wave action of the water.
• Slope sloughing/slips, erosion of abutments, settlement and cracks along dam crests.
• Damage to the outlet and intake structures.
• Cracks in concrete spillways and outlet gates.
In the case of concrete gravity dams, the common issues are:
• Malfunctioning of dam monitoring instruments due to ageing and a lack of maintenance, plus the need for replacement and repairs.
• Repairing and replacing spillway and outlet gates and gate hoisting mechanisms.
Apart from these major deficiencies, almost all the old large dams and some modern dams lack basic safety facilities, such as monitoring and deformation measuring instruments, functioning communication and lighting systems, all-weather access roads and emergency power supply equipment.
Some reservoirs have also experienced excessive sedimentation and reservoir rim deformation and do not have basic up to date engineering and operational information, such as updated reservoir elevation-capacity curves.
The first part of the project will focus on the Randenigala dam where initial reports show rising of the core and cracking in the spillway control room. Randenigala, a modern rockfill dam constructed in the 1980s, will now be fully investigated to determine the necessary remedial action.
There are safety issues with earthen dams too. There are concerns at Kalawewa dam about ancient sluice sections and seepage through rubble masonry works. Maussakelle hydro power dam has issues with deferred maintenance, non-functioning drainage, saddle dam earth embankment maintenance, plus concerns about stability. Rajangana dam has damaged rip-rap for embankment protection, and problems with gate operations and maintenance, and downstream seepage in several sections. Nachchaduwa dam has many safety issues including spillway inadequacy, operational problems with outlet gates, collapsed embankment slopes in many sections, leakage through the dam body and sand boils at the downstream toe. All of these need to be addressed promptly.
Future dam safety assurance
The project aims to help strengthen and underpin a systematic and sustainable management programme for safe dam operation. Strengthening the dam safety agencies will be key but other institutions can also potentially play important dam safety roles, such as the Sri Lanka National Committee on Large Dams.
Elements critical to this institutional strengthening include the development of a uniform code of practice and mandatory dam safety inspection practices. Other important considerations will be:
• Setting up dedicated dam safety units within each dam owning organisation.
• Establishing dam safety regulations.
• Institutionalising a sustainable dam safety, operation and maintenance funding mechanism and arrangement.
• Assessing the skill and capacity building of the technical and operational staff.
It is crucial that inter-agency and sustainable institutional arrangements for dam safety are implemented in Sri Lanka. These will not only ensure that optimum use is made of water harvesting, but will also guarantee the safety of the surrounding human settlements and public and private assets.
Nihal Fernando is a senior rural development specialist at the World Bank’s Agriculture and Rural Development Department in Bangladesh. Email: [email protected]
|The breach of Kantalai dam|
One fairly recent example of dam failure is the breach of Kantalai dam in the Eastern Province of Sri Lanka in January 1986. The disaster killed 127 people, affected 10,864 residents, destroyed 1200 houses and substantially damaged agriculture, commercial and public infrastructure and private assets.