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Humps and fears

Print edition : Jul 07, 2001

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The building of the three-metre-high humps on the Sardar Sarovar dam causes a controversy as it raises the dam's height to 93 metres from the stipulated 90 metres.

THE Gujarat government has completed building three-metre-high humps on the Sardar Sarovar dam and has thus raised the dam's effective height to 93 metres. The State government's action followed the clearance given by the Narmada Control Authority (NCA). The NCA decided to permit construction of the humps after obtaining legal opinion from the Attorney-General of India, Soli Sorabjee. However, activists of the Narmada Bachao Andolan (NBA) have protested against the measure and have alleged that it violated the Supreme Court's majority judgment in the Sardar Sarovar Project (SSP) case delivered on October 18, 2000.

The Sardar Sarovar dam is an all-concrete one and has 62 monolithic sections, 30 of which form the spillway and the rest the non-overflow portion. The spillway, which allows flow of water over it during floods, is designed for streamlined flow and for dissipating the kinetic energy of the flowing water in a stilling basin. This shape will emerge when the dam's height goes beyond 110 metres.

At the present height of 90 m, when there are floods water flows over the incomplete portion of the spillway and falls in the form of a jet, hitting its downstream portion and the stilling basin. The falling water causes considerable damage to the spillway and the stilling basin, particularly during high floods. In order to streamline the flow of water over the incomplete spillway, a hump is constructed at the edge of the dam's top so that the flow follows the final spillway profile and water falls into the stilling basin.

In 1995, when the construction of the dam was stayed, the Supreme Court permitted the building of humps to ensure the safety of the dam. In 1998, when the court permitted the raising of the dam's height from 80 m to 85 m, it also permitted the construction of three-metre-high humps over and above the sanctioned height of 85 m.

In its October 2000 judgment, the Supreme Court permitted further construction, up to a height of 90 m. It also directed that for any further construction on the dam, the clearance of the NCA's sub-groups on resettlement and rehabilitation (R&R) and environment would be required. These sub-groups were to give such permission only after consulting the grievance redressal authorities in Gujarat, Maharashtra and Madhya Pradesh, and confirming that the conditions stipulated in the Narmada Water Disputes Tribunal Award were met.

Later the NBA, which had filed a petition against the construction of the dam, filed an application in the Supreme Court seeking clarifications on the majority judgment. When this was taken up on November 23, 2000, senior counsel for the Union of India, Ashok Desai and Solicitor-General and senior counsel for Gujarat, Harish Salve, stated that even if humps were constructed, the effective height of the dam was not to be raised beyond 90 m for the purpose of submergence. They also said that it will be done only after further construction was permitted according to the conditions laid down in the judgment. Accepting the stand of the Central and Gujarat governments, the court disposed of the NBA's application.

Later, in an order on March 29, 2001, the Supreme Court also dismissed an NBA petition that sought a review of its October judgment. The project authorities then raised the height of the spillway sections of the dam uniformly to 90 m.

The R&R and environment sub-groups have not given permission to raise the height beyond 90 m or to construct humps above that height. Apparently, they have not done so because, they are not convinced that all people evacuated for the construction of up to 90 m have been rehabilitated and the necessary environmental protection measures have been implemented.

Apparently, Attorney-General Soli Sorabjee advised the NCA that if the construction of the humps did not raise the water level or the level of submergence, then it need not be construed as the raising of the dam's height. Since the effective height for the purpose of submergence would, according to technical opinion, remain at 90 m, Sorabjee advised that the construction of the humps need not follow the procedure laid down in the directions of the majority judgment.

Sardar Sarovar Narmada Nigam Limited has claimed that humps designed as per hydraulic geometry, while preventing the jet fall of water, also allow the easy overflow of flood waters. With streamlined flow conditions created by humps, the high flood water line, with or without the humps, remains at the same level and does not result in any additional submergence, Nigam officials said.

THE Nigam's view is based on the Dam Safety Panel's observation on this hydraulic phenomenon. The panel found that the introduction of a three-metre-high hump of the suggested shape and geometry over El (elevation level) 90 m of a truncated spillway has the advantage of containing the afflux for a 100-year frequency flood at the same level as without the hump but with a significant relative improvement in the flow conditions along the downstream glacis of the spillway dam and the stilling basin, as observed by the panel at the Central Water and Power Research Station.

The panel said: "This would indeed be an added benefit from the R&R angle as it knocks off the mistaken notion that by constructing a three-metre-high hump the reservoir level under high flood conditions would also rise by three metres and would therefore be unacceptable for the present stage of R&R."

"If during monsoon submergence increases, as could happen once in 100 years, there is a contingency plan in place to meet such a threat," said a Nigam official. The implication is that even if the humps are not built, the authorities have to be prepared for floods during a good monsoon. The official argument is that it is not the humps that lead to flooding and submergence.

At the last NCA meeting held in New Delhi in May, the Madhya Pradesh government disagreed with the plan to build humps and pointed out that it should have been planned by the Gujarat government while raising the height from 85 m to 90 m. Madhya Pradesh referred to the Central Water Commission's (CWC) letter dated April 17, 2001, which stated that the provision of three-metre-high humps would result in a higher temporary reservoir level during floods. Although the Maharashtra government agreed to the construction of humps to ensure the safety of the dam, it asked the NCA to consider the necessity of humps in the future.

However, the CWC has explained the temporary rise in water level and said that owing to the construction of humps, the co-efficient of discharge increases from 1.475 to 1.85, enabling a higher discharge to pass over the hump while maintaining the same afflux level at the dam for a once in-100-years flood (the maximum discharge of river water expected, on the basis of the discharge during the last 100 years).

The Secretary, Union Ministry of Social Justice and Empowerment, and the representative of the Ministry of Environment and Forests felt that prima facie the submergence would increase owing to the construction of humps as the permanent submergence level would rise to 93 m. Both felt that, following past practice, a height of 95 m instead of 93 m should be considered for the purpose of R&R.

However, the NBA activists have challenged the CWC's explanation. "When thousands of people are in the 90 m submergence zone, mere fine-tuning on the basis of the once in-hundred-years flood levels is another tragic consequence of mere mathematical jugglery," said an NBA activist. However, the Nigam officials say that all Project- Affected Families living in areas that might be only under temporary submergence during floods with rare severity (when the water level would reach a peak of about 112 m for a few hours or a few days and then recede) have been already resettled.

It may well be that the humps are required to mitigate damage downstream. But it appears that the Gujarat government did not anticipate the necessity of humps when it gave an undertaking to the Supreme Court that the dam's effective height including the humps would not go beyond 90 m until it got the clearance from the NCA's sub-groups. If the humps would not increase the submergence level, why was this fact not revealed to the Supreme Court when it disposed of the NBA's application seeking a clarification on its majority judgment, and again when it dismissed its review petition later? Had the court known this, it would have allowed construction of the dam only up to 87 m, thus leaving scope for building the three-metre hump. Moreover, the NCA would have been spared the embarrassment of having had to ignore the views of its own sub-groups while giving the clearance to the Gujarat government to build the humps.

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