HYDERABAD: A technical study by the Indian Institute of Technology, Hyderabad, (IIT-H) has clearly indicated that the impact of the Polavaram dam in Andhra Pradesh on surface water levels in Bhadrachalam town in the event of Godavari floods is as small as two-centimetre increase.
The study, ‘Backwater Effect Due to Polavaram Dam Project under Different Return Periods,” carried out by research scholars C.R. Amarnath and T. Shashidhar, was funded by the Telangana state government.
The findings of the study were in sharp contrast with the claims of transport minister Puvvada Ajay that the Polavaram dam backwaters had a severe impact on Bhadrachalam town, the inundation of which in the recent floods was more because of high water levels at the cofferdam in Andhra Pradesh.
Ajay also kicked up an inter-state political controversy demanding that the seven mandals in erstwhile Khammam district which were transferred to Andhra Pradesh should be given back to Telangana state.
According to the study, given the discharge of 36 lakh cusecs, the highest level of flood recorded in the history of the Godavari, the water level in Bhadrachalam in steady state condition after constructing the Polavaram dam would be 57.02 metres against 57 metres without the dam.
Similarly, if the discharge went up to 50 lakh cusecs, which the Polavaram dam was re-designed to withstand, the water level in Bhadrachalam would be 61.79 metres post completion of Polavaram dam against 61.77 metres without the dam.
The study pointed out that the water levels in Bhadrachalam in unsteady conditions would be 59.84 metres if the dam gates kept closed even after the discharge level reached 36 lakh cusecs. The study said the level would be 59.52 metres if there was no dam which in other words the increase in water level the dam might be forcing, that too with all gates closed, will be 20 cm.
“The question of closing gates at 36 lakh cusecs discharge will not arise at all for the simple reason that the very safety of the dam will be in danger,” a senior irrigation official admitted.
Another irrigation expert who played a crucial role in the Polavaram dam, on condition of anonymity, said inundation of Bhadrachalam was a regular phenomenon during floods even before the cofferdam was built in AP.
The backwater effect would be felt when the discharge levels cross 10 lakh cusecs. Once the discharge level is high in the upstream, the dam will be depleted to that extent and will be refilled with the receding floodwaters. “The dam will never be kept at full reservoir level in case of floods,” he said, adding that the backwater effect on Bhadrachalam was also due to congestion of the river cross section at Papikondalu.
The IIT-H study gave utmost importance to the maintenance of dam gates, the failure of which it warned, would endanger Bhadrachalam and surrounding areas.
“Regular and periodic maintenance of the gates of the Polavaram dam is a must for the safety of upstream areas. Dam gates should be well operated, keeping in mind the inflows and submergence that would be caused by improper closing/opening of the gate walls,” the study pointed out. It also stressed the need for construction of levees and dredging of riverbeds to reduce the water surface elevation.
…
