Storage, release of water in dams should be reviewed: CWC report on Kerala floods

It is essential to review the rule curves of all the reservoirs in Kerala and it must be formulated for both conservation and operations during the flood, stated a fresh report released on Tuesday by the Central Water Commission’s (CWC) Hydrology South Directorate on the floods in Kerala.

The rule curve is the compilation of operating criteria, guidelines and specifications that govern the storage and release functions of a reservoir. It may also be referred to as operating rules, flood control diagram or water control schedule.

In general, it indicates limiting rates of reservoir releases required or allowed during various seasons of the year to meet all functional objectives of the project.

According to the CWC report, the rule curve should be reviewed particularly for the reservoirs having the live storage capacity of more than 200 million cubic metre (MCM) to create some dynamic flood cushion for moderating the floods of lower return periods particularly in the early period of monsoon.

The report adds that for efficient discharge of flood runoff from Vembanad lake, the approach channels to Thottappally spillway and the passage of the Thaneermukkom barrage should be widened, taking into consideration the lake hydrology, ecology, saline water intrusion, etc based on scientific and engineering inputs.

“And in basins like Periyar, Pamba and Achenkovil basins, Kerala should explore the possibilities of creating suitable storage reservoirs, wherever feasible, for flood moderation and other multipurpose uses,” the report says.

The report also adds that the Poringalkuthu dam should be inspected by Dam Safety Regulatory Panel and design flood, spillway capacity of Poringalkuthu dam must be reviewed.

The CWC report reveals that Kerala experienced an abnormally high rainfall from 1 June 2018 to 19 August 2018. “This resulted in severe flooding in 13 out of 14 districts in the State,” the report says.

As per the data of the Indian Meteorological Department, Kerala received 2346.6 mm of rainfall from 1 June 2018 to 19 August 2018, in contrast with an expected 1649.5 mm of rainfall.

This rainfall was about 42 per cent above the normal. Further, the rainfall over Kerala during June, July and 1st to 19th of August was 15 per cent, 18 per cent and 164 per cent respectively, above normal.

As per analysis carried out by CWC, the rainfall between August 15 to August 17 – with the eye of storm being near Peermade between Pamba and Periyar sub-basins – was almost of the same intensity as that of the rainfall in Devikulam, Kerala between July 16 to July 18, 1924.

After analysis, it has been found that the dams in Kerala neither added to the flood nor helped in reduction of floodwaters, as most of the dams were already at Full Reservoir Level (FRL) or very close to FRL on 14 August 2018, following higher than normal rainfall in the months of June to July 2018.

“It may be noted that, had the reservoir been a few feet below FRL, the flooding conditions would have not changed much, as the severe storm continued for three days and even for four days at majority of the places, and in any case, it would have been necessary to release from the reservoirs after 1st day of the extreme rainfall,” the report says.

The report adds that the release from reservoirs had only minor role in flood augmentation as released volume from the reservoirs were almost like inflow volumes.

“In fact, Idukki reservoir absorbed a flood volume of about 60 MCM during 15-17, August 2018. Even, with the 75 percent-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,” the report adds.

Around 400 people have lost their lives in the flood and thousands were displaced.

On Tuesday, the Chief Minister tweeted that the distribution of flood relief kits has been completed.

“The financial assistance given to victims, a sum of ₹10,000, has been transferred to 4,95,000 beneficiaries out of a total of 6,05,555 eligible persons,” the tweet read.