Climate Change

As heavy rains lash, dam outflows too increase in Karnataka

Mismanagement by dam officials leave state staring at worrying scenario

By Shagun
Published: Thursday 06 August 2020

Heavy rainfall, along with full reservoir levels and overflowing rivers, has resulted in a worrying scenario for Karnataka, which is again staring at a flood-like situation.

The situation is precarious because heavy showers in several districts have coincided with the release of water from dams as many reservoirs in the Krishna and Cauvery basin are already full.

Four out of 10 dams monitored by the Karnataka State Natural Disaster Monitoring Centre (KSNDMC) in the two basins, are between 75-90 per cent full.

Harangi dam in Kodagu district, where the Cauvery has crossed the danger level and is rising further, has been 85 per cent full. The outflow from the dam has increased from just 50 cusecs from July 29 to 12,111 cusecs on August 6, 2020.

The storage on July 29 was 8.1 thousand million cubic feet (TMC). The dam authorities have been trying to reduce the storage after rainfall began, to accommodate more water. This should ideally have been done before.

The state level dam authorities do not often follow the rule curve properly and start releasing water only during rainfall, a Central Water Commission (CWC) official from the Bengaluru division, who did not wish to be identified, told Down To Earth.

“The CWC had already issued warnings and we are in touch with them constantly, asking them to gradually increase the outflow,” he said.

The rule curve — an international practice of dam operation — must be followed by dam management authorities, as any lapse may lead to dam-induced floods, of which there are several instances in India.

The rule curve mentions the measures to regulate when and how dams should be filled and emptied, thus ensuring that dams are full only towards the end of the monsoon, providing them a cushion during times of excess rain and curbing chances of floods in downstream areas.

The CWC had issued an advisory on August 2 for three dams in Karnataka:

  • Upper Tunga Project (Gajanur Dam), that was full up to 100 per cent of its capacity
  • Harangi Dam, that was 92 per cent full
  • Kabini Dam, that was 80 per cent full

The advisory had said there was a likelihood of rapid rise in rivers’ levels and a close watch had to be kept for increased inflows likely during the next three to four days in view of the heavy rainfall warning.

“Releases from any of these reservoirs may be done according to the rule curve and standard operating procedure. Information regarding releases may also be provided to all downstream areas in Karnataka as well as to lower riparian states,” it had said.

The commission again pointed out that the Harangi Dam in the Cauvery Basin in Kodagu district was filled up to 91 per cent of its full capacity in another advisory on August 5.

“Due to heavy rainfall in Kodagu district, the dam is expected to get increased inflows. Since very heavy to extreme rainfall has been forecasted to continue for another 4-5 days, proper precautions have to be taken and advance release of water may have to be resorted to in order to avoid panic discharges after dam attaining FRL (full reservoir level),” the advisory had said.

Similarly, the Kabini dam in Mysuru district was 84 per cent full on August 6. It received 37,462 cusecs of water on August 6, whereas the outflow in a single day has been 43,933 cusecs. It was 22,058 cusecs on August 5 and a flood alert was issued to people residing in low-lying areas.

The outflow from the dam to the Kapila river and canal increased substantially on August 5, after heavy rainfall.

The total outflow in the previous week — between July 29 and August 4 — when a forecast of heavy rainfall was already issued, had only been 16,484 cusecs. The storage position during that period, however, was somewhat similar.

On August 4, the storage in the reservoir was 16.64 TMC, around 85 per cent of its capacity. But the outflow from the dam was only 3,521 cusecs.

This was when the Central Water Commission (CWC) had already issued an advisory for three dams in Karnataka, including Kabini.

With rains battering the district, the outflow was increased suddenly the next day.

Malaprabha and Ghataprabha dams in Belagavi district, which was one of the worst-hit in the 2019 floods, were between 60-66 per cent full. Heavy rains have again created a flood-like situation in the district this year.

Himanshu Thakkar of New Delhi-based SANDRP (South Asia Network on Dams, Rivers and People) said the operations of the upper Krishna basin dams in Karnataka and Maharashtra were problematic.

“Maharashtra seems to have learned from last year’s crisis as the reservoirs there have a somewhat better cushion cover but Karnataka doesn’t seem to be interested,” he told Down To Earth.

“The situation is scary right now in Karnataka as rains are heavy in the upstream areas. Even after the CWC advisory, the dams were full. The rule curves for these dams are also not in the public domain. Hence, there is no way to know if they are following the standard operating procedure or not,” he said.

The situation in Maharashtra and Kerala is under control for now with respect to their reservoirs. Both states have a forecast of heavy to very heavy rainfall.

“There is increased inflow into the Idukki and Edamalayar dams. Since rainfall is expected to continue for 3-4 days, the inflows are likely to continue, depending on the intensity of rainfall. However, there is sufficient storage available in these dams,” the CWC said about Kerala.

In Maharashtra, major dams such as Koyna, Warna, and Doodhganga are 55 per cent, 70 per cent and 71 per cent full, the CWC said.

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