EXCLUSIVE| Odisha Flash Flood Threat: CWC Forecasts Heavy Reservoir Inflow Surge from Balimela, Kolab to Hirakud As Deep Depression Near Coast

Bhubaneswar: With multimodal ensemble betting on how the Low Pressure Area post intensifying into a powerful deep depression will knock at the South Odisha – North Andhra Pradesh Coast by September 23 morning, it seems South Odisha is entering a potentially critical phase, with a flood threat building even as the region braces for heavy rainfall from the approaching deep depression.

The immediate trigger is striking: the Indravati reservoir has opened one of its seven gates for the first time in seven years, with Gate No. 6 lifted by 0.5 metre to release water. The administration has simultaneously warned residents in low-lying areas, citing the prospect of heavy rainfall in the coming days.

But the more consequential warning lies in the latest flood-forecast projections.

The CWC flood forecast inputs for September 20–27 point to sharp inflow surges in South Odisha's major reservoir systems around September 24–25, precisely when the deep depression is expected to bring its strongest rainfall impact over south Odisha and adjoining north Andhra Pradesh.

The forecast indicates that the Balimela and Upper Kolab reservoirs could face sudden, high-volume inflow surges, raising the possibility of rapid water releases and short-duration flooding downstream.

This makes today's Indravati gate opening more than an isolated reservoir-management decision. It comes at a time when the wider southern Odisha water system is already being placed under pressure by the anticipated rainfall.

Why today's Indravati opening matters

The Indravati reservoir has seven gates, but Gate No. 6 has now been opened by 0.5 metre to release water.

The significance is not simply the quantity of water being released today. The timing matters.

The administration's warning for low-lying areas comes as rainfall associated with the approaching system is expected to intensify. The flood-forecast projections simultaneously indicate that the larger reservoir network of southern Odisha could experience substantial inflow increases in the next few days.

In other words, the first visible reservoir response has begun even before the forecast peak in inflows arrives.

The CWC forecast graphs examined for September 20–27 show the most pronounced short-duration signals over the Balimela and Upper Kolab systems around September 24–25.

That timing is important because the projected rainfall and reservoir response overlap with the period when the deep depression is expected to move inland across south Odisha/north Andhra Pradesh.

South Odisha's two reservoir systems flash the biggest immediate warning

The flood forecast separates South Odisha's immediate hydrological risk from the slower-building Mahanadi problem.

Reservoir / River	Forecast signal	Expected peak	What it means
Balimela / Sileru	Sharp inflow surge around Sept 24–25	~1,900 m³/sec	Rapid reservoir pressure and potential emergency releases
Upper Kolab / Kolab	Sharp inflow surge around Sept 24–25	~1,550 m³/sec	Potentially rapid downstream water-level rise
Hirakud / Mahanadi	Sustained, escalating inflow	>9,200 m³/sec by Sept 27	Longer-duration downstream flood and drainage pressure
Gunupur / Vamsadhara	Relatively modest rise	~82.1 m	Remains below 83 m warning level
Purusottampur / Rushikulya	Moderate rise	~12.9 m	Remains well below 15.835 m warning level

The Balimela projection is particularly important. The forecast shows its inflow climbing sharply to around 1,900 cubic metres per second, while Upper Kolab is projected to reach around 1,550 cubic metres per second. Both surges are associated with the intense rainfall projected immediately beforehand.

This is the classic setup in which rainfall itself is only one component of the flood threat.

When intense rain falls over reservoir catchments already receiving substantial inflow, reservoir operations become an additional variable. Water has to be managed upstream, while communities downstream have to contend with both rainfall runoff and possible releases.

The flash-flood window: September 24–25

The forecast identifies September 24–25 as the critical period for South Odisha's reservoir inflow response.

The operational scenario outlined in the forecast is that Balimela and Upper Kolab, both carrying currently closed gates in the assessment, could see sudden inflows exceeding their immediate buffering capacity. The projected response is therefore a potentially rapid opening of gates to manage the incoming volume.

That creates a distinctly different risk from a conventional river flood that builds gradually over several days.

A sharp rainfall burst + steep catchment runoff + rapidly rising reservoir inflow + subsequent controlled releases can produce sudden flooding in low-lying areas.

The forecast specifically flags the possibility of rapid, short-duration flooding in low-lying village areas of Malkangiri and Koraput if the projected inflow surge materialises.

Therefore, the present warning should not be interpreted as a forecast that every part of South Odisha will be inundated.

Rather, the concern is localised flash flooding and rapid water accumulation, particularly around vulnerable downstream stretches and low-lying settlements, if rainfall and reservoir inflows evolve close to the projected scenario.

A crucial distinction: river gauges are not yet showing a widespread flood

The current river-level projections provide an important counterpoint.

At Gunupur on the Vamsadhara, the river is projected to rise from around 80.8 metres to approximately 82.1 metres, while the warning level is 83 metres.

At Purusottampur on the Rushikulya, the projected peak is around 12.9 metres, against a warning level of 15.835 metres.

Both therefore remain below their respective warning thresholds in the forecast period.

This distinction matters.

The present warning is being driven primarily by the projected reservoir inflow behaviour, not by an already-established major river flood at these downstream gauges.

That is why the Indravati development assumes significance. The administration has already begun reservoir-level water management even though some major downstream gauges remain below warning levels.

The bigger South Odisha equation

The forecast essentially divides Odisha's hydrological risk into two different phases.

Phase one is South Odisha's rapid-response threat.

Balimela and Upper Kolab could experience their strongest inflow surges around September 24–25. Their response will depend heavily on how much rain actually falls over their catchments and how quickly that water reaches the reservoirs.

Phase two is the Mahanadi's slower but potentially much larger downstream pressure.

Hirakud is already carrying a severe escalating risk, with the reservoir at 629.95 feet against an FRL of 630 feet and 99.64% live storage in the assessment. The projected inflow is then shown climbing beyond 9,200 m³/sec by September 27.

That is a different problem from the sudden South Odisha flash-flood threat.

The southern reservoirs could face sharp, concentrated inflow spikes. Hirakud represents a sustained volume-management problem.

Why the next 72–120 hours matter

The most important message from the flood forecast is therefore not that South Odisha is already under a major flood.

It is that the hydrological system is entering the period in which a major change can occur quickly.

The forecast projects Balimela and Upper Kolab inflows to surge around September 24–25, while the deep depression's rainfall is expected to affect the same broad region. The Indravati reservoir has already begun releasing water and authorities have warned low-lying residents.

Taken together, these developments create a heightened watch window for Malkangiri, Koraput and other vulnerable southern pockets, particularly where heavy rainfall coincides with rapid reservoir inflow and downstream releases.

The flood risk, however, remains dependent on the actual rainfall distribution and the evolution of reservoir inflows. The available forecast itself shows that Vamsadhara and Rushikulya gauges are not projected to cross their warning levels, underscoring that the threat is not uniform across South Odisha.

For now, the evidence points to a heightened flash-flood watch rather than a declaration of a widespread flood emergency. But if the September 24–25 rainfall and reservoir inflow projections verify, low-lying areas downstream of the southern reservoir systems could face rapid water-level changes with comparatively little lead time.

South Odisha, therefore, is not waiting for the flood to arrive.

Its reservoir system is already beginning to prepare for the water that the forecast says could arrive next. 
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