Integrated risk assessment of dams required to prevent human-made disasters: Experts

The recent floods in the Mahanadi basin in Odisha have brought to the fore, the faulty management of dams, which were built to mitigate floods and not be the cause of them.

Operators of the Hirakud reservoir in Odisha were told to open 40 barrage gates August 18, 2022, when the level of water in the dam was nearly filled to the brim.

Most of the Mahanadi river catchment, where the Hirakud dam is located, is in Chhattisgarh. Adequate intimation from Chhattisgarh dam authorities on the amount of water that would come gushing out was not given, authorities in Odisha had told DTE previously.

India has 5,745 large dams according to the National Register of Large Dams, 2019, prepared by the Central Water Commission. Some 5,334 of them are operational and the remaining 411 are under construction.

Also, 227 large dams are older than a century and 18 per cent are more than 50 years old.

The recent lack of communication between Chhattisgarh and Odisha dam operators is common among states that share dams across the country and has always been a longstanding issue when it comes to flood mitigation.

On August 8, the Union Ministry of Jal Shakti (water resources) reiterated in a press release that it has given directions to state governments under the Disaster Management Act, 2005, to give adjacent state authorities adequate prior warning before releasing water from reservoir or dams.

Tamil Nadu Chief Minister MK Stalin recently wrote to Kerala Chief Minister Pinarayi Vijayan, assuring him that officials of his state managing the water flows to the contentious Mullaperiyar dam, located in the Idukki district of Kerala, have been instructed to maintain communication with officers in Kerala.

Most importantly, the aforementioned press release by the Jal Shakti ministry admitted that “data on flooding caused due to faulty operations of reservoirs is not maintained centrally.”

A 2021 paper on dam safety in India by the National Institute of Public Finance and Policy recommended that the Union Ministry of Environment, Forest and Climate Change (MoEF&CC) should establish an integrated database.

The database should have information from dam failure analyses of cleared projects and other essential information on static dams from the Indian Space Research Organisation’s Water Resources Information System.

The paper cited the example of the United States web-based integrated risk management tool called Dam Sector Analysis Tool. The tool was developed using variables from dam failure models and decision support systems, which enables the software to project downstream risks in the case of a dam failure. 

‘Not legally binding’

A risk failure has to be mandatorily conducted while doing Environmental Impactment Assessments of potential dams.

But there is no standardisation of how the failure is analysed and reported, according to the paper by Devendra Damle, a former researcher at the National Institute of Public Finance and Policy.

He said in the paper:

While the CWC has developed some guidelines on this, they are not legally binding. MoEF&CC, therefore, needs to institute legally binding standards for conducting and reporting dam failure analysis.

While dam failure analysis was mandatory for environmental clearance, it was unclear how many projects actually complied with this requirement, he added.

“Existing dams, where no new engineering activity is planned, are not required to conduct dam failure analysis. Dam failure analysis needs to be a regular activity for all large dams. The methodology should be further refined to use the latest data from routine inspections and surveillance,” Damle stated.

He recommended using inundation maps as part of the failure analysis to aid local officials in charge of mitigation.

Sanjay Srivastava, chief of disaster risk reduction at the United Nation’s Economic and Social Commission for Asia and the Pacific told Down To Earth:

Water infrastructure (dam) is built for 50-100 years of life cycle. The risk analysis is often done with past climate data, with about 20-30 years old flood / drought datasets, which are no more indicative of future risk scenarios especially in view of the changing climate.

Most of the dams in the past were built on traditional construction and hydraulic design and were not risk- informed. Civil engineering and climate science need to be coupled for resilient water infrastructure, Srivastava noted.

“Inundation modelling simulates potential risk scenarios, which can precisely determine a dam’s safety parameters. Inundation modelling is however data-intensive. A combination of simulation modelling and historical inundation mapping is good strategy,” Srivastava said.

It requires close contour surface data, digital elevation models, land use / land cover maps and high resolution climate model to create inundation scenarios precisely which could inform the design and safety features of the dams / water infrastructure, he added.

 Dams that oveflowed in the recent past

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