As climate change makes extreme rainfall events more frequent in the Mahanadi River basin in Odisha and Chhattisgarh, there is urgent need to better manage the river and its dams
Extreme precipitation events are the new normal in India. Of the recent disasters related to such extremes, the Kerala deluge haunts the national memory the most. The World Meteorological Organisation (WMO), in its latest State of Global Climate report, noted that among the extreme weather events in 2018, the Kerala floods caused the maximum number of casualties globally.
As the debate is yet to settle whether extreme rainfall or faulty management of dams were to blame for the Kerala floods, in the eastern state of Odisha, the Hirakud dam — arguably Asia’s longest earthen dam and blamed for many floods – is up for another challenge: extreme precipitation events.
Last monsoon, fortunately enough, a disaster was averted due to sheer luck. Fortunately, the date of massive rainfall and that of dam’s floodwater release missed each other by a few days. The debate over extreme precipitation events and urban flooding currently centres more around large cities, but smaller cities adjacent to dams need to be seriously watched and preparations for building their resilience to such extreme events need to be built. This case tells us why.
On July 27 last year, Manju Seth, a lady in her mid-forties, was busy gathering all that remained in the riverbed where she had a small hut just a week ago near Kachheri Chhak Ghat of Mahanadi River in Sambalpur. The district administration on July 20 had forced her and 13 other families dwelling in the place to evacuate their dwellings because Hirakud dam was to release the first lot of floodwaters on July 24.
Manju was reluctant and so were all the other families. They had been asked by the district administration to stay on the riverbed just about a year ago, when they were displaced from a slum on the river bank to give way to a bridge being built across the Mahanadi. “We had been living here at the Kachheri Chhak for more than 50 years, and when they decided to build a bridge they just asked us to vacate. Where would we go?” asked Manju, who works as a maid, sweeping homes, cleaning utensils and washing clothes for some well-off families of the city.
Ironically, the district administration had supplied electricity to this new habitation a few months ago, knowing very well that a riverbed cannot be a permanent settlement. “We were not sure about the rains and water this time, as for the last 3-4 years the water level had not touched this side of the river bed where we built our houses,” she said. This time, the rainfall was scary for Manju and for the whole district.
While the district administration had not yet fully realised the dangers of an extremely heavy rainfall that was making its way to the city, it kept persuading Manju and others to vacate the place and shift to a flood shelter. “They were evacuated because the dam was to release first lot of floodwaters on July 24. What surprised us was that on July 21 and 22, just after they were asked to shift to a flood shelter in Chhanrpur Jharapali village on the other side of the river, the city received unprecedented rainfall, something that has not seen since 1982,” said Jagdish Mishra, a local social activist.
On July 21, when heavy rainfall lashed most parts of the state and the government’s attention was concentrated on the state’s capital city of Bhubaneswar, Sambalpur, just downstream of Hirakud, was drowning as well. Burla, the city on the other end of Hirakud dam, received as high as 622 mm of rainfall in a day, breaking a 36-year-old record of the district. See: Act now to spur urban climate resilience
It was almost 41% of the entire year’s rainfall. More than half of the city was engulfed in water. Reports of the administration said that this rainfall affected at least 125,000 people and damaged more than 700 homes. Around 2,500 people were provided shelter in 22 relief camps and at least one person died.
The Hirakud reservoir was swelling that day as more than 100,000 cusec of water was entering into the reservoir for incessant rains upstream in Chhattisgarh that borders Odisha in the north. For four days prior to the Odisha rains, the dam was being filled with more water from the upstream state. On July 20, at night at around 9 pm, the water level had crossed 608.62 feet. The dam, which has been failing in controlling floods, runs into safety risks at such levels of water.
In 1982, Sambalpur had received 582 mm rainfall that had engulfed almost two thirds of the city under floodwaters. The city had never seen such a flood before. One of the main roads of the city, that runs parallel to Mahanadi River, breached because a major drain carrying both backwater of the Hirakud reservoir and rainwater forced its way to the river.
The city’s planning took a major shift after that. Strengthening embankments became a priority along with strong sluice gates on these drains at points they join the river. Sambalpur is on the bank of Mahanadi River, just about 10 km downstream the Hirakud dam, built in 50s. The region is now prone to increased number and intensity of extreme precipitation events, partly due to climate change.
Boon or bane?
“The Hirakud dam that was built to control floods in the delta districts of the river 300-400 km downstream has not only been unsuccessful in doing that but also has increased the floods in the upstream districts such as Sambalpur, where flood was not known earlier,” said Arttabandhu Mishra, a retired teacher from the Sambalpur University who has studied the Hirakud dam extensively.
This dam, spreading over 746 sq. km — almost half of the size of Delhi — is the only major dam project and flood control system on the 858 km long Mahanadi River, India’s sixth largest river, that drains an area of around 141,600 sq. km. The two major riparian states — Chhattisgarh and Odisha — have locked horns over the sharing of water of this river and the conflict centres around reducing flow of water from the upper state (Chhattisgarh) due to construction of a number of dams and barrages.
A major area of the conflict that does not make news is the potential of increased flood disasters due to increased number of dams and barrages being built upstream of Hirakud. Even though Odisha has raised this point during a Chief Ministerial level meeting held on the conflict, both the states have not chalked out any joint mechanism to streamline and strengthen coordinated flood management strategies.
Civil society organisations such as the Water Initiatives Odisha (WIO) have been consistently raising concerns about the failed flood management in the Hirakud, alleging that the so-called rule curve that is followed in managing the inflow and outflow of floodwaters during the monsoon has drastically failed in factoring issues such as developments upstream that changes the flood flow, and climate change that increases rainfall variability. The Comptroller and Auditor General has also rapped the state government for failures in flood management due to similar reasons.
The heavy downpour that happened in July cannot be ignored any further as a stray event. Studies point to dangerous trends that grip the river basin already. Mahanadi is already facing increased high floods and researchers attribute this to climate change. A study by researchers from Indian Institute of Technology, Kharagpur, published in the Journal of Hydrology concludes, on the basis of their analysis pertaining to post-Hirakud dam construction period, that the recent incidences of high floods in the Mahanadi basin is due to an increase in extreme rainfall in the middle reaches of the basin. It means the extreme rainfall received at Sambalpur in July this year is a new normal and threat.
“The summer monsoon is very important for agrarian countries like us as it brings 80% of the rainfall and that’s going to be impacted due to increased extreme precipitation events,” Sandeep Pattnaik of IIT Bhubaneswar said. Pattnaik is co-author of the research paper titled Ramifications of Atmospheric Humidity on Monsoon Depressions over the Indian Subcontinent that has been published in the Nature Scientific Reports.
“There has been a constant increase in extreme rainfall events over central India during 1950-2015 and it’s going to increase as the surface gets warmer,” he said. “We have studied four monsoon depressions, three of which are from the Bay of Bengal and have found out that the Mahanadi catchment area will experience increased extreme precipitation events.”
New approach needed
Manju survived the rainfall all because the river was still dry and Hirakud had not released any floodwater. Manju and others were demanding permanent rehabilitation and at a place close to the city. “I have three children and the elder girl is studying in class 10th. This is a critical year and we cannot manage her studies from a faraway place,” she said. Her struggle for rightful rehabilitation will continue, as will be the case of the millions who are displaced by disasters in the country, and live in dingy informal settlements.
The city of Sambalpur with its 335,000 people, and other places downstream, cannot be complacent any longer, knowing the fact that flood events due to extreme precipitation are going to grow and cities like Sambalpur will be at the receiving end. There is an urgent need to integrate city planning with climate change induced calamities. We just can’t leave it to luck, as there is no guarantee we can avoid days of extreme precipitation coinciding with those of floodwater release from the dam.
“There are various lacunae in our current data generation methods. We don’t have high-density surface observation systems. The existing weather stations are too less and their recordings can miss the complete picture,” Pattnaik said. “While high-density weather observation stations are needed starting from catchment areas to the delta, a proper cooperation and coordination between both the states is also vital.