A Flood Forecasting Model for the Mahanadi River in Odisha

What is the problem?
The Mahanadi River Basin is one of 12 major river basins in India, and in terms of its catchment area only the Ganga, Godavari and Krishna River Basins are larger. The Mahanadi delta region is the most prone to flooding of all river basins in India, because of the large catchment area but inadequate carrying capacity of its river channels. The main aim of building the Hirakud Dam in 1953 was to provide flood relief through storage of excess water in flood years. Prior to the Dam, Odisha witnessed 8 severe floods every 10 years; post-Hirakud this figure has been reduced to over 3. The dam provides good protection for floods of lesser magnitude.
However, Hirakud was not designed for the kind of rainfall that the catchment area now receives due to changing rainfall patterns through climate change. Its carrying capacity is inadequate, and this is now exacerbated by a growing siltation problem. High volume flood discharges of a magnitude that its designers considered would arise only once in 1,000 years have been recorded 10 times since the construction of the dam. Frequent floods are a regular occurrence, and climate change poses a growing risk.
The current system of flood forecasting allows a maximum of 8 hours lead time in times of heavy rains, which is not sufficient to allow a full response, such as evacuation. This has led to heavy loss of lives and livelihoods over recent decades, with serious floods in 2003, 2008, 2011 and 2013, and many smaller ones between.
Over 10 million rural people live in the delta area, where levels of population density are high, a large proportion are poor, and there are extreme levels of vulnerability. The proportion of people living below the poverty line in Odisha is high. Nearly three quarters of Odisha’s population depends on climate-sensitive natural resource-based livelihoods, centred around agriculture, forestry and fisheries. Earning a livelihood from agriculture a precarious business.

What is ACT doing about it?
ACT was requested by the Department of Water Resources, Government of Odisha to design and develop a new hydrology model that now takes climate change into full consideration. It includes a huge range of detailed geophysical information, builds in localized weather forecasting, and can predict with a much higher degree of accuracy and much longer reaction times how the catchment area and downstream river flows will react in times of heavy monsoon rainfall. The maximum flood forewarning previously was 8 hours, insufficient for adequate action that could be taken to completely avoid fatalities of human and livestock. Passing information to relevant authorities used to be a lengthy and tedious process.
Effective flood forecasts need to provide flood warnings 48 to 72 hours ahead, and this is what the new system aims to do. This intervention responds to the need for an early warning system (EWS) that will allow the highly vulnerable communities living in affected downstream areas to take precautionary measures, and possibly evacuate in a timely manner when serious flooding occurs.

How does government benefit?

This activity is intended to provide a better decision support system for government to use in managing and minimising flood damage. The work conducted is the first step in provision of a better forecasting and early warning system. Early warning is a major element of disaster risk reduction, and early response can often prevent a hazard from turning into a human disaster by preventing loss of life and reducing the economic and physical impacts to lives, livelihoods and property. This forecasting system is being set up to avoid or reduce the impact of flood hazards, and as such will significantly increase resilience.
Owing to cumbersome processes and ways of working, governments often find it difficult to respond to short-term priorities, and do not have the financial flexibility to take on the high quality technical support that they need. In this instance, ACT was able to supply just such inputs, and this has enabled the government to develop an EWS designed specifically for local conditions. This is a high-profile issue in Odisha where mortality and loss of livelihoods from flooding is an all-too-common disaster..How do the poor and vulnerable benefit?
This work will have an extraordinarily positive impact on resilience and on the lives and livelihoods of hundreds of thousands of very poor people in the predominantly agricultural delta area. Life there is precarious, and heavy loss of life has occurred in previous serious floods. When combined with other response activities, the EWS will permit people to evacuate to safe places during these kinds of events. This is likely to provide a hugely increased sense of domestic safety and security. Leading from this should emerge a growing confidence in secured livelihoods, with an increased likelihood of investment of human, financial and physical livelihood assets. What happens next?
The flood forecasting model has been tested under field conditions, but there remains some further calibration and fine-tuning to be done. There is further modelling work to be done also for flood inundation, which addresses how flood water moves within the delta. Once the models are fully prepared, they will be installed in their assigned locations. Capacity building of government officers will take place to ensure that they are fully prepared and able to run the system unassisted.

The ACT consultants will continue to support government to fully develop and install the models. This will include demonstrating and validating them, building capacity, and providing further handholding support to the government as it moves into full implementation.

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