Opinion

Dams did exacerbate Kerala’s floods

SP Ravi / KJ Joy / Neha Bhadbhade | Updated on September 19, 2018 Published on September 19, 2018

Inviting disaster Flood cushioning is often compromised for more hydro-power generation and irrigation.   -  H Vibhu

The Central Water Commission report is wrong in denying a link between dam releases, reservoir levels and the floods

The recent Central Water Commission (CWC) report on Kerala’s floods in August unequivocally says that dams are not responsible for the flooding. According to the report, “The dams in Kerala neither added to the flood nor helped in reduction of flood, as most of the dams were already at FRL (full reservoir level) or very close to FRL on August 14, 2018, due to more than normal rainfall in June and July 2018.”

Citing this situation, the report seems to suggest constructing more storage dams across the Periyar, Pamba and Achenkovil rivers. However, merely creating more dam storage is not going to help, if management of water release is not in place. In fact, if dams had not been full before the heavy burst of rainfall, the impact could have been different.

Such findings come in the wake of increasing criticism about reservoir operations and management prior to and during the August 15-17 floods. The CWC seems to have brought out the report in a real hurry. Probably that’s why the report carries a picture of a flooded Srinagar on its cover!

What it says

A major part of the report has been dedicated to discussing reservoir operations during the floods. It provides analysis of eight projects in the Periyar, Pamba, Bharathapuzha, Chalakudy and Kabani basins. It compares “the estimated run-off volume generated” during the August 15-17 rains in sub-basins where severe flooding occurred “with the discharge records of CWC observation sites.”

The report has come up with a long list of 25 findings. Finding number 24 summarises all: “In a nutshell, it can be concluded that August 2018 flood in Kerala was due to severe storm occurrences during August 8-9 and 15-17. The storm of 15-17 resulted in heavy flooding in the Periyar, Pamba, Chalakudi and Bharatpuzha sub-basins of Kerala.”

The report recommends: review the ‘rule curve’ (that is, the storage or empty space to be maintained in a reservoir during different times of the year) of the reservoirs in Kerala to create a dynamic flood cushion for moderating floods; increase efficiency of flood discharge from Vembanad lake; explore the possibilities of creating storage reservoirs in Periyar, Pamba and Achenkovil basins for flood moderation and other multi-purpose uses;, and inspect the Poringalkuthu dam in Chalakudy basin, and review flood, spillway capacity.

Issues with the report

The report admits that the release from Malampuzha dam in Bharatapuzha was 13 mcm (million cubic meters) in excess to the inflow into the reservoir. However, the report considers this to be insignificant when compared to the total flow of 1,510 mcm at the CWC river gauging station at Kumbidi in the downstream of the river.

Even though there are four gauging stations on Bharathapuzha below Malampuzha dam, they have only looked at the lowest station that receives water from 5787 km2 catchment. It should be noted that the catchment of Malampuzha dam is only 145 km2. The argument that the excess discharge from an upstream dam that covers only 2.5 per cent of the catchment area is insignificant in comparison to the total river flow near the river mouth is a classic case of comparing the incomparable.

The report claims that the Idukki project in Periyar basin achieved flood moderation to the tune of 60 mcm over the August 15-17 flood period. However, unlike at Malampuzha, the CWC did not find it necessary to compare the volume of flood moderation at Idukki with the total run-off of 1,925 mcm at their gauging station at Neelaswaram in the lower reaches of the basin, though the flooding had severely affected the downstream.

The report admits that Idamalayar project in the same basin could not help in achieving flood moderation as it was full before the start of the heavy rainfall spell. The report is silent on releases from smaller projects across the basin. Neither did it analyse the data at Bhoothathankettu barrage that receives all the waters from upstream projects.

It mentions that the Banasurasagar reservoir across the Kabini River was at FRL since July 16. Still the report does not seem to attach any significance to it. In fact, this was the case with many reservoirs in the State, including Kakki in Pamba River and Kerala Sholayar and Poringalkuthu across Chalakudy River.

For Chalakudy River, the figures provided by CWC are substantially lower than those available from other sources. The rainfall at Tamil Nadu Sholayar and Kerala Sholayar on August 15 is shown as 170 mm and 160 mm, respectively, in the report against 410 mm and 350 mm, respectively, as per data with the dam authorities. The flood discharges from both Parambikulam and Kerala Sholayar reservoirs are substantially higher than shown in the report.

These dams had a combined peak discharge of more than 2,000 cumecs (cubic meter per second) post midnight of 15th. The flow rate at Poringalkuthu, including yield from it’s own catchment, is likely to have been around 3,500 cumecs. This resulted in the extremely dangerous situation of water over-topping the dam by more than two meters. The report’s claim that “even with the 75 per cent-filled reservoir conditions, the current flood could have not been mitigated as 1-day rainfall in majority of the area was more than 200 mm and severe rainfall continued for 3 to 4 days” cannot be accepted.

It needs to be noted that the area of inundation increases exponentially with the rise in flood level. Had there been about 25 per cent storage space, the peak discharge could have been reduced significantly.

Basin management

Operation of individual reservoirs needs to be seen within the overall context of basin planning for flood management. Demand for cumulative impact assessments (CIAs) is gaining ground in India. The CWC should have conducted CIAs in the worst affected Periyar, Pamba and Chalakudy basins having multiple reservoirs. The recommendation to review the rule curve for operation of reservoirs is a much-needed one. This is especially true in the context of climate change. Long term average — known as stationarity — is not going to work. A new rule curve for reservoir operation also needs to be backed up by an institutional mechanism that can take timely decisions.

The situation gets further complicated as most of the dams are multi-purpose. Flood cushioning is always compromised for more hydro-power generation and irrigation. At least four dams in Kerala are managed by Tamil Nadu. Apparently, the disaster management sub-committee could not respond in time in the case of Mullaperiyar dam.

The Supreme Court had to step in to reduce the water level. It is not advisable to leave such decisions to the Supreme Court. Ideally, democratically constituted river basin agencies (RBAs) are best suited to take such decisions. Good science, precautionary principle and a humanitarian approach should guide decision-making in the case of floods as it happened in Kerala.

The writers are part of the Forum for Policy Dialogue on Water Conflicts in India.

Published on September 19, 2018
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