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

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