Controlling flood in Mahanadi: Subalaya barrage can be permanent remedy!

Some parts of Mahanadi delta have been flooded after intense spells of rain. Even though the flood this year (August 2022) is of moderate intensity with the highest discharge of 12 lakh cusecs at Munduli, it does bring in misery to the affected people. But such a situation is always avoidable. 

In the past, Mahanadi floods had been much more severe. For example, in 2008, inflow at the head of the Delta was 15.81 lakh cusecs while in 1982, we had flood at the head of the Delta with discharge of 15.87 lakh cusecs. Management of the Hirakud Reservoir during the current flood appears to have been satisfactory. 

What we need to take note of is that the mighty River downstream of Hirakud remains in a free flow condition even though a big river, Tel, with sufficient monsoon discharge, adds to the water flow of the Mahanadi. The only existing infrastructure for flood moderation of the Mahanadi is the Hirakud Reservoir. But this has a modest live storage capacity of only 3.9 million acre ft against the flood volume of 20 million acre ft of a typical flood in the Mahanadi. Therefore, the huge population in the delta of the river continues to be vulnerable to the ravages of flood even after 65 years of the creation of the Hirakud reservoir. Of course, Chhattisgarh state, upstream of Hirakud, has come up with irrigation works which also have some moderating impact on the flood water inflow to Hirakud Reservoir and, in times of severe flood, could moderate the distress downstream. 

Inflow of the Mahanadi at the head of the delta at 8.70 lakh cusecs is considered as no distress flood as the river embankments downstream can carry this volume of water. In other words, we need to keep flood water inflow at Munduli at 8.70 lakh cusecs even after taking into account the inflow from River Tel. If such an arrangement could be made, flood in Mahanadi which has brought untold misery to the people of the Delta for hundreds of years, would be a thing of the past. But is such an arrangement possible? 

In 1964, a project proposal was designed for flood control, irrigation and power generation with a Dam at Tikarpara. The Project envisaged full utilization of available water of the river. The proposed Reservoir would have led to submersion of 1200 villages, three towns and extensive forest resource. Even though foundation stone for the project was laid by then Prime Minister Nehru, the project had to be abandoned. Thereafter, another project was designed in 1985 to have a Dam at Manibhadra. This proposal had kept intact the flood control and irrigation component of the Tikarpara Project but was to have a power generation capacity of only 960 MW. There would have been submersion of 273 villages, two towns and much less forest area. Foundation stone for the Project had been laid by the then Chief Minister but the project could not take off due to resistance of the people.

A satisfactory engineering solution to the flood-problem in the delta had not been found till 1999. Could there be a design that would not lead to submergence of any town, not lead to submergence of any village permanently and would not lead to submergence of forests? Fortunately for us, such a blueprint has been prepared in shape of Subalaya Barrage that would provide irrigation to 1,14,000 ha; hydro electric power during monsoon for 210 MW and protective embankment for 73 villages. The total development cost was estimated at Rs 1720 crore only; but needs updating. The project would tackle the entire flood problem permanently. It is designed to reduce the maximum flood peak of 17.4 lakh cusecs on the basis of 100 years probability, to only 8.7 lakh cusecs at the head of the Mahanadi delta. This would be possible through dynamic storage from the conservation level of 54.9 meter to the maximum level of 77 meters and back again to the conservation level within a period of six days and six hours (in case of a 100 year probability based maximum flood). In this situation, 73 villages would remain below the flood level for a maximum period of a little over six days protected by high embankment. Cuttack city remains below the high flood level for considerably longer periods almost every year behind the protective earthen embankments. 

Let us appreciate the gravity of the flood in the delta by looking at one part of the Mahanadi delta. This part is influenced by the Kuakhai River. This River divides into three Rivers, namely, Bhargavi, Daya and Kushabhadra. These three Rivers influence a very large area. The maximum combined carrying capacity of the three Rivers is only one lakh cusecs. When there is a normal flood peak of 9.60 lakh cusecs in the undivided Mahanadi at the head of the delta, the Kuakhai, takes a share of 1.30 lakh cusecs which is 30% in excess of the carrying capacity. This additional quantity spills through escape structures provided for the purpose. As a result, flood water flows into unprotected area resulting in water logging, crop damage and rendering large area unfit for cultivation. With Subalaya barrage in place, there would be a completely different situation. The three branches of the Kuakhai would get a maximum flood peak of much less than one lakh cusecs. Lateral spill of flood water would be a thing of the past. Further, passage of flood within the natural river channels for long periods of time would improve the hydraulic efficiency of the channels which would be helpful in removing the river mouth congestion. 

Mahanadi delta is the largest River delta in peninsular India and is home to about a third of the state’s population. After every major flood, government spends huge sum of money on relief and rehabilitation. Should such ad hoc response be accepted as the most humane way of tackling the flood issue in the Mahanadi delta or should the government perform its obligatory responsibility of distress removal? It is a paradox that the state government keeps seeking huge centre assistance for relief and rehabilitation for Mahanadi flood but would not take up the Subalaya project which would bring permanent remedy. 

(DISCLAIMER: This is an opinion piece. The views expressed are the author’s own and have nothing to do with OTV’s charter or views. OTV does not assume any responsibility or liability for the same. The author can be reached at lonewalker.1942@gmail.com)

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