Unlike 2018, the storage levels of dams and reservoirs were maintained better this year, using a concept called “Upper Rule Level”
Unlike 2018, the storage levels of dams and reservoirs were maintained better this year, using a concept called “Upper Rule Level”
Climate change is a clear and present danger globally and Kerala is no exception. The State’s monsoon pattern is shifting, with rainfall peaking in August instead of July in recent years. In 2018 and 2022, rainfall levels in August exceeded that of June and July on many days. However, there was minimal loss of lives and relatively much lesser flood damage compared to 2018 in the State. While it is true that the intensity of rainfall was relatively lower in 2022, the introduction of new dam management concepts, relying on global weather models apart from IMD predictions and improved communication with downstream flood measurement stations helped keep the reservoir levels in check and prevented river water from breaching the banks
August anomaly
In both 2018 and 2022, Kerala recorded copious amounts of rainfall on many days of August, exceeding the levels seen in June and July. This is a shift in the State’s rainfall pattern, as August, in general, receives lower rainfall, as suggested by the Long Period Average (LPA) which declines in August after June and July
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Higher August inflows
In 2018 and 2022, due to heavy August rainfall, the inflow of water to reservoirs also increased. In 2018, the inflows in August did not exceed the June-July levels. However, in 2022 it did. This shows that in 2022, a higher share of rainfall in August fell in the catchment area of the reservoirs, a crucial factor in flood management
Stark difference in storage
The key difference between 2018 and 2022 was that, despite similar patterns of rainfall and comparable inflows, the storage levels of most dams and reservoirs stayed below the 90% mark in August this year. In 2018 however, the storage levels of most dams abruptly reached 100% in mid-August, leading to a catastrophe
Suppressed spills
If storage levels peak, the spills — excess water deliberately released from reservoirs — will rise. Unlike planned discharges, spills are not meant for specific utilisation such as irrigation. As storage levels of most dams remained below the 100% mark in 2022, the spills were sporadic unlike in 2018. This proved to be the crucial difference
Crossing the limit
As per the Central Water Commission, levels in 13 of the 44 flood monitoring stations across Kerala recorded an Extreme Flood Situation in 2018. The table on the right lists the name of the rivers and the measuring stations where the Extreme Flood Situation was recorded in 2018. Such a situation arises when a river exceeds the previously set Highest Flood Level (HFL) in that station in its history. In other words, in 2018, 13 stations recorded record-level of floods. In 2022, none of the 44 flood measuring stations witnessed an Extreme Flood Situation
“Relied on global models this time”
While Kerala’s monsoon rainfall patterns remained similar in 2018 and 2022, the State manage to keep flood damage relatively lower this year. James Wilson, who heads Kerala State Electricity Board Limited’s Reservoir Monitoring Cell explains why
Usually, in Kerala, rainfall levels are higher in June-July and reduce sharply by August. However, in 2018 and 2022, August rainfall exceeded the Long Period Average by many times…
What you observed is correct. We are witnessing a shift. If you look at the history of extreme events, it was mostly in mid-July, then shifted to late-July and now happens in August. Not only extreme rainfall events, even normal rainfall events have shifted and most of the peaks are now in August
Did this impact the style of dam management?
Yes. We tried to bring a new concept in Kerala flood management called “Upper Rule Level (URL)”. Rule levels make a dynamic flood cushion in the reservoir below the “Full Reservoir Level (FRL)”. As per this scheme, a reservoir is only allowed to reach its full capacity by the end of both monsoons. As the monsoon progresses, we keep increasing the URL in small steps. We operate the reservoir in such a fashion that water level will never cross the URL. But, during a heavy spell, if it crosses, we will bring it below the URL in a couple of days by discharging the excess water slowly. For instance, in 2022 in Idukki, during the first flood in August, the water level increased above URL but we immediately brought it back by spilling it for a couple of days. When the river was in spate, we accommodated the heavy inflow of water in the reservoir in the dynamic flood cushion and released the excess when the river was depleting.
Were there any other crucial factors that played a vital role in mitigating the floods in 2022?
One of the biggest hurdles we are facing is the inconsistencies with weather prediction. For example, this time, IMD told us that, you (Kerala) are going to have a normal (rainfall) in June, you are going to have a (rainfall) deficit in July and August. Also, they said that other parts of India are going to have a surplus or above normal rainfall, while Kerala is going to drop below normal rainfall. But that did not happen. In 2018, we were depending mostly on IMD predictions. This time, we decided to look at various forecasts from global agencies in the European Union, U.S., Australia, Germany and France. The global models said that we are going to have some heavy rainfall events in mid-July and in the second half of July as well. So we decided to increase our power generation this time and keep the levels at check. This strategy proved crucial.
We also observed that in 2018, at least 13 river flood monitoring stations in Kerala breached the Highest Flood Level, while in 2022, none did so. Was this the result of a conscious effort?
After 2018, we created emergency action plans. We created scenarios like, for example, what will happen if we discharge 5,000 cumecs of water from Idukki, which areas will be submerged. We also improved our communication systems. As we mostly operate from forest areas, mobile networks are poor. This time we were in constant contact with the Central Water Commission. Every hour, we got feedback on the river water levels. So I was taking a call, based on that information. I knew that, if I release water from the dam at this time, it will reach this flood measurement point downstream, at a particular time. I will get feedback from the engineers from this measurement point downstream, every one hour. In this way, now things are under my control. If the river at the downstream point is rising at a faster rate, I will throttle the release. On the other hand, if the river is receding, I can send maximum water.
So, would you call the 2022 dam management as a success?
See, there is a thin line between success and failure when it comes to dam management. If based on IMD warnings I discharge large amounts of water, anticipating very heavy inflows, that itself will create flooding in the downstream. On the other hand, if it was a false alarm, and if it does not rain, after I took a decision to discharge a lot of water, then also I’ll be accused of taking a wrong call. However, if I don’t discharge and it indeed rains like predicted and there is a flood, they will ask why I did not listen to IMD. So all this aside, I take my calls putting safety of the public first.
Interview by Sonikka Loganathan and Vignesh Radhakrishnan
Data scraped by Pratap Vardhan who runs statsofindia.in
Source: Kerala State Load despatch Center
Listen to Podcast “Data and dams: How Kerala cracked flood management” for the full interview
Also read: Data | An unusually wet October fills up reservoirs in Kerala
