The Problem

The city of Ibadan in central Nigeria is prone to severe and frequent flooding in the forms of 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 left in a vulnerable position.

The Solution

The World Bank commissioned Ambiental 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 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 Plan would then be integrated with the overall sustainability plan for the city.

As a fundamental part of the study, Ambiental 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 Outcome

As a result of the scoping study, Ambiental:

• Identified and co-ordinated 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 regarding flood mitigation through a wide range of structural and non-structural capital schemes and investments for improved drainage and flood protection throughout the city. These 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, coupled with planning, preparation and improved emergency response.

The project has, ultimately, enabled better decision making, reduced the cost of flood damage, increased the recovery rate following floods and provided peace-of-mind and security to the citizens of Ibadan.