Hirakud Inflow Nears FRL on Aug 19: Will Odisha See a Redux of the July Floods? | Special Report

Bhubaneswar: The steep rise in inflow to the Hirakud Reservoir is expected to reach the Full Reservoir Level (FRL) by the evening of August 19. How will the heavy inflow to the Hirakud Reservoir – when seen through the prism of the 17 gates opened so far – pan out downstream in the Mahanadi system?

According to the latest data available from the Odisha Water Resources Department and the Central Water Commission (CWC), the inflow into the Hirakud Dam is expected to peak during the evening hours of August 19. However, the same hydrological forecast suggests a major shift thereafter.

This surge in inflow has prompted the reservoir authorities to increase discharges, opening 17 gates as of this noon. With the inflow peaking close to the FRL today and expected to stay elevated until tomorrow, the moot question is: will the dam authorities open more gates in the near future?

A glance at the CWC data suggests a key change in the trajectory of the inflow. The hydrological advisory shows that the peak upstream pulse will subside by around August 19 or 20, with inflow expected to fall sharply over the next two days and drop below 4,000 cubic metres per second. Consequently, the present gate configuration should soon be sufficient to handle the incoming water

Why August Turned Different From July

The present Mahanadi situation is strikingly different from the flood episode at the end of July.

The July flood was the product of a rare hydrological coincidence. A powerful deep depression moved across Odisha at the end of July, producing exceptionally heavy rainfall not just over the upper Mahanadi catchment but also across downstream and coastal Odisha.

At the same time, Hirakud had to release a massive volume of water, with 22 gates opened during the peak phase. The downstream catchments were already saturated because of intense local rainfall. The Tel, Kusabhadra, Daya and Devi systems had little spare carrying capacity, meaning the Hirakud discharge eventually met an already swollen downstream river network.

That synchronisation was the real reason the July flood became severe. The Naraj gauge crossed its danger level and touched 26.61 metres as upstream discharge collided with heavy downstream runoff.

August, so far, has produced a very different hydraulic setting.

While Hirakud has received a substantial inflow pulse, the lower Mahanadi catchment has largely remained dry or recorded negligible rainfall. Cuttack, Naraj, Mundali and Pipili, for instance, recorded 0 mm rainfall in the last 24 hrs.

That has left the downstream channels with considerably greater absorption capacity. Consequently, even the high discharge from Hirakud can move through the river system without producing the same kind of hydraulic bottleneck seen in late July.

Peak Inflow, But No Repeat Of The July Flood

The August 19 inflow surge nevertheless remains significant.

At noon on August 19, Hirakud was receiving 3,79,761 cusecs against a controlled outflow of 2,80,343 cusecs. But the forecast indicates that this was the crest of the current flood wave rather than the beginning of another sustained spell.

The advisory's simulated inflow curve shows the water pulse falling steeply after the August 19 forecast point. The inflow is expected to decline below 4,000 cubic metres per second during the following two days.

This changes the gate equation.

At the peak, engineers had to respond to a temporary mismatch between inflow and discharge. But once inflow falls rapidly, the existing gates can discharge water faster than it is entering the reservoir. The forecast therefore indicates that no further opening of gates should be necessary.

Naraj Has Enough Headroom

The downstream picture also offers reassurance.

Naraj is currently around 23.84 metres and is forecast to peak at approximately 24.85 metres on Aug 20. Even that projected peak remains below the 25.41-metre warning level and substantially below the 26.41-metre danger level.

However, there could still be minor inundation in low-lying pockets downstream, particularly in parts of Puri, Khordha and Jagatsinghpur. But that is fundamentally different from the widespread Mahanadi flooding witnessed when the July depression simultaneously filled both the upper and lower catchments.

The Bottom Line

The August Mahanadi flood pulse is therefore increasingly looking like a short-lived upstream surge rather than a repeat of the late-July flood.

July had the dangerous combination of heavy upper-catchment rain + massive Hirakud releases + saturated downstream catchments.

August has so far produced a sharp upstream inflow pulse + relatively dry downstream catchments + rapidly falling inflow.

That difference explains why Hirakud's August 19 peak is unlikely to translate into another major Mahanadi delta flood. The immediate pressure at the reservoir is expected to ease, and the latest forecast points towards stabilisation rather than another round of gate opening. 

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