FLOOD IN THE MAHANADI

Mahanadi delta is presently flooded. The devastating flood has brought in human suffering on a massive scale. Apart from loss of human lives, the fury of flood has caused widespread damage. As I write today ( September 23, 2008) about the flood, the worst seems to be over and the inflow at the head of the delta had reduced in the morning to only 7.83 lakh cusecs. 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. The flood this year was severe because the inflow at the head of the Delta this year has reached a level of 15.81 lakh cusecs. In 1982, we had a flood of about this magnitude when the inflow at the head of the Delta was slightly higher, at 15.87 lakh cusecs. Management of the Hirakud reservoir during the current flood appears to have been satisfactory. What added to this year’s problem was the contribution of the Tel River (downstream of Hirakud) of 13 lakh cusecs. The existing infrastructure for flood moderation of the Mahanadi is the Hirakud Reservoir which has a modest live storage capacity of 3.9 million acre feet against the flood volume of 20 million acre feet 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 fifty years of the creation of the Hirakud reservoir. In 1964, under the able guidance of Dr AN Khosla, the Governor of the state, the first competent project proposal was designed for flood control, irrigation and power generation with a Dam at Tikerpara. 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 the Prime Minister, Pandit Nehru, the project had to be abandoned mainly due to the inevitable massive submersion of human habitations. The extent of submersion could have been reduced by lowering the height of the dam. This would have reduced the hydro power generating capacity of 2000 MW substantially. Thereafter, another project was designed in 1985 to have a Dam at Manibhadra. This proposal had kept in tact the flood control and irrigation component of the Tikerpara 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 Chief Minister but the project could not take off due to resistance of the people who were to be affected. 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 by a team of dedicated engineers led by an Engineer of outstanding merit and vision, Shri Pravat Kumar Misra, a former Engineer-in Chief of Government of Orissa. The plan envisages a 724 meter long barrage from Puta Hill to Ranitala Hill; a 2400 meter long dam --20 meter high (average height)-- from Manibhadra hill to Subalaya hill and 2200 meter long dykes joining Subalaya hill with Puta hill and Ranital hill with Mitcalfpur hill; right head regulator to provide irrigation to the right side of the Subalaya barrage and protective embankment rings around 73 villages with road connections to higher levels ( Rs 640 crore). At a later phase there would be provision for power generation of 210 MW during monsoon but power generation of 14 MW during non monsoon period by making use of the release of power house release from the Hirakud dam( Rs630 crore). In the intermediate phase, the project would get the irrigation component to ensure irrigation to 140,000 hectares with provision for contributing about 1400 cusecs to the Rushikulya basin (Rs450 crore). All the three phases would cost about Rs 1720 crore only. This estimate may have to be revised now; but the figures have been mentioned to highlight the economic way by which the entire flood problem could be tackled permanently. The proposed Subalaya barrage 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. It may be mentioned here that 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 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, as per given geometry, 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 a 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. Every year crores of rupees are spent on flood protection. After every major flood government spends a big 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 the government should perform its obligatory responsibility of distress removal? It is ironic that the state government keeps demanding from the centre a huge amount of money for relief and rehabilitation when the state reels under the fury of flood and would not take up the Subalaya project which would bring permanent remedy. I am indeed thankful to Shri Pravat Kumar Misra, former Engineer-in-Chief of Government of Orissa for his help in preparing this article. ******************************