Dams in distress
Close look at the structural limitations
Amid accusations that the Kerala floods were a man-made disaster, it is important to take a of the State’s river basins and other issues such as topography, water and power needs, and extreme event predictions.
KERALA experienced its worst floods in recent history during the third week of August 2018. It was similar to the one that occurred in 1924, known as the “Great Deluge of 99”, the figure “99” denoting the year 1099 as per the Malayalam calendar. In the latest instance, extreme flooding affected 13 of Kerala’s 14 districts. The State has 1,564 villages, and just about half of them, 774 to be precise, were inundated. Out of a population of about 3.48 crore, more than 54 lakh people—or one sixth of the population—were affected by this deluge.
According to the India Meteorological Department (IMD), Kerala received 2,346.6 millimetres of rainfall between June 1 (traditionally the date of onset of the monsoon in Kerala) and August 19. This is 42 per cent above the normal rainfall of 1,649.5 mm. Further, the rainfall over Kerala during June, July and between August 1 and 9 was 15 per cent, 18 per cent and 164 per cent above normal, respectively.
But this comparison will not suffice to understand why this extreme precipitation created the kind of flooding Kerala witnessed during August 15-17. We must understand how “heavy rainfall”, “very heavy rainfall” and “extreme rainfall” events test, in varying degrees, the resilience of Kerala’s reservoirs, river channels, riverbanks, backwater lakes and the exit mechanisms that discharge the freshet, or flood from rivers, to the sea and lead to different flooding intensities.
There was heavy rainfall between July 15 and 20, which inundated the Kuttanad region, an area very susceptible to flooding whenever the Vembanad lake and the rivers draining into it get such heavy rainfall. During August 8-9, very heavy rainfall occurred at several places in the State. On August 9, rainfall of 398 mm, 305 mm, 255 mm and 214 mm was recorded at Nilambur in Malappuram district, Mananthavady in Wayanad district, Peermade in Idukki district, and Palakkad in Palakkad district, respectively, as per IMD data. This heavy storm resulted in severe flooding at several places in the Malabar areas, especially Nilambur in Malappuram district and Malampuzha in Palakkad district during August 8-10. This heavy spell was then followed by an extreme rainfall event, which started on August 14 and continued up to August 19. The peak of this event was observed between August 15 and 17.
Most of the reservoir systems of Kerala swelled during the first heavy spell during the third week of July, and the water level in several major reservoirs rose above 90 per cent of their storage capacity. But the heavy rainfall and extreme rainfall event in the August 8-19 period forced the authorities to open the spillways of most of the reservoirs in order to release the excess water, safeguard those structures and ensure public safety.
These spillway releases triggered a heated debate over whether the recent deluge was a man-made disaster caused by the discharges from the dams. Sweeping statements were made by responsible persons alleging that the dam managers were to be blamed for it, on the basis of inferences drawn without analysing the hard data or examining the structural limitations of the river basins.
What we must look at first is whether this year’s event is a replica of the one in 1924, and second, whether the spillway releases from