Dam safety has become a focal point of attention across India, where the World Bank is supporting an initiative to assist with rehabilitation, safety and project management.
India’s first recorded dam failure was caused by overtopping of the Tigra Dam in Madhya Pradesh in 1917. More than 60 years later, the country’s worst dam failure occurred in 1979 when overtopping also took place at the 24.7m high Machu-II Dam in Gujarat. A flood of 1400m3/sec inundated the designed spillway capacity of 6180m3/sec. Two sections of the dam’s earthen flanks were washed out and 2000 people were killed, with 12700 houses being destroyed.
To date 36 dam failures have been reported across India.
Indian dams are vital for ensuring water security and regulating floods during the rainy season. Indeed, they are becoming increasingly important with today’s changing climate and the strive towards long term resilience. There are more than 4900 large dams across the country, and while there are about 350 currently under construction, several thousand smaller dams are also in existence.
With an increasing numbers of ageing dams, dam safety is becoming an important consideration for India but there is heightened concern about the ability to address such issues. Many states are reported to have inadequate budgets for dam maintenance and repairs, while many dams have varied deficiencies and do not meet modern design standards – both structurally and hydrologically.
Dam Rehabilitation and Improvement Programme (DRIP)
In April 2012, the Indian Government’s Central Water Commission, with assistance from the World Bank, began the six-year, US$350M Dam Rehabilitation and Improvement Programme (DRIP). Its aim is to assist dam-owning agencies in rehabilitating selected dams, as well as to strengthen dam safety initiatives and project management skills.
A variety of issues are being addressed by DRIP and include:
- Hydrology – Many ageing Indian dams were constructed long before current hydrological practices were put in place – such as the Veeranam Reservoir which was built in the 9th century. Design flood reviews have been undertaken for all dams being considered under DRIP, and there are concerns about the dams’ hydrological safety. In 58% of cases the design floods have undergone substantial increased revisions and some of the existing spillways cannot cater for this. Furthermore, topical constraints mean that structural interventions to mitigate for enhanced flood estimates will not be viable, and so non-structural measures such as modifying dam operations need to be implemented.
- Dam safety – Investigations into structural safety have highlighted typical issues such as swelling, shrinkage and loss of strength in concrete and masonry; and earth and rockfill issues have centred on slope instability, settlement of material, internal erosion and piping, excessive seepage and vegetation in embankments. Reviews of hydro-mechanical equipment and dam instrumentation has highlighted deficiencies in gates and hoisting systems, and malfunctioning monitoring instruments. Seismic hazard mapping for Peninsular India has also been carried out, with consideration being given to covering the rest of the country.
- Sedimentation – Addressing sedimentation issues in reservoirs, particularly at hydropower dams in the northern Himalayan state of Uttarakhand and the southern state of Tamil Nadu, has become a serious issue. Severe sedimentation has occurred at Maneri Bhali Dam in Uttarakhand where the reservoir has already been silted up to the spillway crest level, causing extensive damage to equipment. DRIP has assisted in proposing mitigation measures such as traps for boulders and large sediments, regular sluicing and light dredging in the catchment area. Plans are also underway to publish guidelines on Assessing and Managing Reservoir Sedimentation to encourage best practices and management, monitoring and measurement at other DRIP dams and reservoirs throughout India.
- Dam Break Analysis – Currently there is limited capacity to perform Dam Break Analysyes, so these have been undertaken by DRIP. Inundation maps have been prepared which can be used for Emergency Actions Plans.
Other noticeable achievements under DRIP include efforts to strengthen institutional dam safety. These have encompassed the organisation of three national dam safety conferences; more than 65 national training programmes for more than 2350 delegates; plus two international study tours to the US and The Netherlands. Sixteen guidelines will also be published on various aspects of dam safety while more than 100 users have been trained and data has been uploaded for 220 DRIP dams using a web-based asset management software called Dam Health and Rehabilitation Monitoring Application (DHARMA). DHARMA will help to collect and manage information, bring stakeholders together and be a useful tool to assess dam health. In addition, lessons learnt from DRIP have contributed to the finalisation of a Dam Safety Bill which is working its way through Indian Parliament.
Another interesting perspective of DRIP’s work has been its involvement in a government initiative called Swachchata Pakhwada which aims to create greater awareness about cleanliness. Throughout March 2017 DRIP implementing agencies organised stakeholder awareness programmes to educate and create greater understanding of waterbodies – more specifically dam safety for downstream communities and procedures to be followed during an emergency associated with dams. Local college and school students were invited to a one-day awareness programme at nine different dam sites. Social and cultural events were also organised to drive home the message. Younger people were targeted in the hope that they wold return to share information with the rest of their community.
Key lessons appear to have been learnt about Indian dams during the DRIP experience to date. According to Manoj Kumar from the Central Water Commission:
- A lack of systematic assessment and monitoring, coupled with inadequate resources, is the primary cause of poor maintenance of dams and appurtenant works.
- Rehabilitation of old dams using the latest materials and technologies can enhance the life of a dam for many more decades.
- Well planned monitoring systems based on data collection and evaluation using modern instrumentation is the key to early detection of defects and ageing scenarios.
- State dam safety organisations need to be strengthened with more employees.
- Training, both in India and abroad, using up-to-date knowledge, is key to the development of competent dam safety systems.
The first phase of DRIP targeted 242 dams for rehabilitation across seven states, all of which are now in advanced stages of completion. Proposals for a second phase will focus on 400 large dams. Although scheduled as a six-year project, DRIP has been granted a two-year extension until June 2020.
For more information see the DRIP website www.damsafety.in
Dam Safety in India. DRIP presentation by Manoj Kumar, Deputy Director, Central Water Commission.
DRIP information Bulletin No.6. February 2017.