Polavaram Dam- A Prescription for the Most Shocking National Economic Disaster?
– Prof T Shivaji Rao
A.P. state proposes to construct a few China-wall like embankments to protect several villages of Khammam District likely to be inundated due to floods due to construction of Polavaram dam. These structures will be 44 Km.long with a height of 189 feet, with a free board of 6 ft. above the level of 183.6 ft., the peak flood mark that touched during the 35 lakh cusecs flood of August 1986. The cost is estimated at Rs.307 crores. Such embankments failed to stop inundation of vast areas of the temple town of Bhadrachalam during the August 2006 floods of Godavari river. The Government insisted that polavaram Dam will be able to discharge a peak flood of 49 lakh cusecs .
But the AP State Government must realise that the Central Water Commission [CWC] has adopted a 1000-year return flood for spillway design for Sardar Sarovar project and 10,000-year return flood for the Tehri dam because Tehri dam failure is likely to cause the death of several lakhs of people in Rishikesh and Haridawar and other towns in gangetic belt in addition to large scale economic damages to crops and properties. The AP State Government stated that the 1986 kind floods occur once in 500 years while 49 lakh cusec floods occur once in 1000 years.
The basic mistake being committed by the AP state Government and the Central Government is their failure to consider that the probable maximum flood (PMF) shall not only be based on hydrological and technological considerations but also on the socio-economic and environmental considerations including major catastrophic dam failure hazards as per the modern methods followed for the design of the dam and the spillway in almost all the major countries of the world. Since India is also member of the international committee on large dams [ICOLD] it is the duty of the Central Water Commission to revise the design flood of 50 lakhs cusecs [cubic feet per second] as recently calculated by it in October 2006 for the Polavaram project to atleast 75 lakhs cusecs. This view is on the basis of the inflow flood of 1,70,000 cumecs [cubic meters per second] equivalent to about 60 lakhs cusecs as adopted by the eminent hydrological experts of the National Institute of Hydrology [NIH], Roorkee who conducted the dam break analysis operations in June 1999. Dam break analysis was done at the specific request of the Andhra Pradesh state Government for the purpose of preparing disaster management, risk analysis and environmental management programmes as per the conditions stipulated under the regulations of the environmental impact assessment report prepared as per rules of the Environmental Protection Act 1986.
Moreover, the Central Water Commission[CWC] while estimating the 1000-year return period flood for spillway design of the Sardar Sarovar Project had concluded that for the catchment area of 88,000 sq. km of Narmada River, the maximum flood was estimated at 87,000 cumecs and this means that the peak flood estimate comes to about one cumec [cubic meter per second] per sq.km area. Since Godavari catchment area is having similar characteristics and is also adjacent to Narmada catchment in terms of meteorological and topographical features, the probable Maximum Flood [PMF] at Polavaram under similar conditions has to be estimated at about 2 lakhs cumecs which is equivalent to about 75 lakhs cusecs.
.Surprisingly, if the water storage in Polavaram is transformed into an additional incremental flood in case of a dam failure, the additional reservoir -based flood comes to about 70,000 cumecs that is equivalent to about 25 lakhs cusecs. Consequently, the inflow design flood for Polavaram project must be taken as 100 lakh cusecs which is the actual magnitude of flood estimated by the eminent hydrological experts of the National Institute of Hydrology [NIH] in their report on dam break analysis for Polavaram project submitted to the AP State Government as already stated above. In view of the anticipated deaths of lakhs of people in the Gangetic belt due to a hypothetical failure of Tehri Dam, CWC has considered areturn flood of 10,000 years period amounting to15,540 Cumecs from a catchment area of 7,550 sq.km. Since Polavaram Dam is located in a more hazardous site with many highly vulnerable towns and cities, CWC must follow the international guidelines for the design of this major project and should not plan to wipe out of existence 45 lakhs of people in Godavari delta by resorting to the underdesigning of the spillway of Polavaram by using a very low value of 50 lakhs cusecs of probable maximum flood.
.Eminent irrigation Expert, Padmabhushan,Dr.K.L.Rao, a former Union Minister for Irrigation & Power, had already warned the A.P.state Government in April 1983 that since Polavaram dam spillway is highly underdesigned, the project is bound to fail and Godavari water cannot be expected to transferred into krishna river as anticipated under this project. If Polavaram project is designed as a barrage,it will be a safe project like the cotton barrage and if it is designed like a dam with storage of about 200 Thousand cubic feet [TMC] of water, this storage gets converted into huge flood of over 24 lakh cusecs, equivalent to peak flood of a river like Krishna and hence when the dam fails due to a maximum credible accident, the millions of people downstream of polavaram have not only bear the burden of the 1986 flood of 36 lakhs cusecs but also the Polavaram reservoir induced additional flood of 24 lakhs cusecs for which the existing river banks do not have the carrying capacity with the result that all the 50 lakhs of peple downstream in all cities, towns and villages in the godavari delta will face a watery grave.
That is why the Polavaram project cannot be taken up as a big storage dam but should be constructed only as a safe barrage as recommended by the former Eminent Technical Experts of both the Union Government and the Central Water Commission like Dr. A N Khosla [in 1953], Mr. Gulhati [in 1963] and Dr. K L Rao [in 1983] after making an honest and in-depth technical assessment of the optimal utilisation of Godavari and Krishna river waters at the request of the Government of India during the periods mentioned above.
Director, Centre for Environmental Studies, Gitam University,
Visakhapatnam-530 045 INDIA