We prepared an urgent, strategic, flood risk assessment to help the city of Ibadan in central Nigeria cope with regular, severe flooding.

The Challenge

Ibadan is prone to severe and frequent flash flooding and river flooding. With rapid urban growth, poorly designed drainage, complex river networks, no early warning, and very limited capability within the emergency services to respond, the citizens of Ibadan are in a very vulnerable position.

Our Solution

The World Bank asked us to carry out an urgent, strategic-level study of flood risk for Ibadan. We were tasked with developing a series of short, medium and long-term measures to help reduce flood risk to the city. Our study identified a desperate need for immediate repair of infrastructure damaged in recent floods. It highlighted a need for a range of further works including: the development of a flood forecasting and early flood warning system; and the need for a long-term Flood and Drainage Master Plan for the city.

 

This would ensure the future security and safety for the communities that currently suffer regular and damaging flooding. This Flood and Drainage Master Plan would then be integrated with the overall sustainability plan for the city.

As a fundamental part of the study, we developed a city-wide numerical flood model allowing simulation of a range of return periods and future scenarios. This helped quantify the level of current and future risk, and scientifically assess the benefit of a range of mitigation options.

The Outcomes

  • Identified and coordinated requirements for urgent repair work on a large dam and associated reservoir just upstream of the city.
  • Identified and designed priority works to be carried out on the many bridges and river crossings damaged during recent flood events.
  • Made recommendations for flood mitigation. These included a wide range of structural and non-structural capital schemes and investments for improved drainage and flood protection throughout the city. All were designed to be both sustainable and cost effective, ensuring ongoing environmental, social and economic benefits.
  • Recommended the design and implementation of a flood forecasting and warning system. This was coupled with planning, preparation and improved emergency response.
  • The project has enabled better decision making and reduced the cost of flood damage. It has also increased the recovery rate following floods and provided peace-of-mind and security to the citizens of Ibadan.

Ibadan suffers from heavy rainfall resulting in some level of flooding virtually every year.

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