With the monsoon's first low-pressure area still lying over the northwest Bay of Bengal, the big forecast is in the next 36 hours (from the night of June 14) there will be very heavy rain in the Mahanadi river basin (both upstream and downstream). The heavy rain alert in the basin has put the water resources department officials in the State on their toes.
The Forecast
As per IMD, GFS and ECMWF, from the night of June 14 to the night of June 15, there is a forecast that the Mahanadi river basin (both upstream and downstream) will receive rainfall to the tune of 8mm to 45 mm per hour. The rainfall is predicted to be very heavy on June 15, when there is a forecast that the Raigarh (Chhattisgarh) basin of Mahanadi will record very heavy rainfall (20-40mm/hour).
The forecast further says that the Mahanadi downstream from Sambalpur up to Cuttack district will receive an average rainfall of over 30-40mm/hour on June 15-16.
Rain Impact On Mahanadi Basin
As per the data available with the State Water Resources Department, the current level of the Hirakud reservoir is around 600.7 ft. The current inflow to the dam is stated to be at 2300 cubic metre per second (cusecs), whereas the outflow has been over 13000 cusecs. The inflow will post a sharp rise on around June 15 and 16, following very heavy rain forecast at the upstream of Mahanadi river (Raigarh reservoir).
"There is no flood threat in the Mahanadi river basin, despite widespread rainfall in Odisha. Even as the monsoon will make its onset over Chhattisgarh on June 14-15, there is no looming flood threat in Mahanadi basin," informed water resources department official Jyotirmaya Rath.
Hirakud Rule Curve
The information provided by senior officials of the State Water Resources Department reveals that when the rule curve for Hirakud mandates the State government to maintain the reservoir level of 595 ft by July 1, the current level is over 600.7 ft. Significantly, the rule curve has mandated the water resources department to maintain the reservoir level of Hirakud Dam at 590 ft till August 1.
Though the current reservoir level is only over 5 ft more than the recommended level, a heavy inflow from upstream and heavy rains downstream may trigger a flood-like situation at some low lying villages along the Mahanadi downstream and its tributaries in the States, feel experts.
"As the current reservoir level is marginally higher than the mandated level of Rule curve, heavy rains in Chhattisgarh, especially at Mahanadi upstream, will see 4 times rise in inflow to Hirakud in coming days, and in order to maintain the reservoir level at around 590 ft till August, the outflow from the dam will witness a sharp rise in next 72 hours. Moreover, the rainfall along the downstream has also been around 24 - 75 per cent of the total June rainfall," informed a senior water resources department official.
However, the State Water Resources Department informed that there is very little chance of flood in the Mahanadi river basin.
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Any Flood Threat To Odisha?
Historically seen, the flood time in Odisha has been the months of July and August. The State has hardly witnessed any flood in the month of June. But the flood fears in the first low pressure is due to the State receiving 157 mm rainfall in May, up 122 per cent, thanks to cyclone Yaas.
For which, the data with State Water Resources Department hints at the need for constant monitoring of major river basins.
• As per the data, readings at the three gauge sites in the Mahanadi basin show that, though there has been no rising trend as of today, the levels are only 5-9 mt below the danger level.
• Since cyclone Yaas has triggered a flash flood in Budhabalanga, and water inflow in the basin has been more than normal, gauge readings tell a different tale.
• The water level is rising in the Brahmani river basin. Only 5-6 mt below the danger level.
• One gauge site of Budhabalanga basin post a rising trend.
• Though Vansadhara at Kashipur is just 2mt below the danger level and showing a rising trend, there is no forecast of heavy rain in south Odisha during the next 48 hours.