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FLOOD HAZARD MAPPING AND RISK MANAGEMENT IN PARTS OF LAGOS STATE

ABSTRACT

The prevalence of flooding within Nigeria which has been generally attributed to climate change and poor urban planning is an issue of critical importance within the context of national development. Over the period 1985 to 2014, flooding in Nigeria has affected more than 11 million lives with a total of 1100 deaths and property damage exceeding US$17 billion. Although more frequent floods are recorded in Niger, Adamawa, Oyo, Kano and Jigawa states possibly due to the influence of rivers Niger, Benue, Ogun and Hadeja, Lagos state seems to have experienced most of the floods in the country. With rapid population growth and urbanization in the country the risk of flooding to human lives and properties assumes critical dimensions. Critically, poor awareness of the hazard is a major impasse towards its management. This creates a significant gap in the knowledge of how to improve on the current efforts towards addressing the challenges of flooding in Nigeria. Since attempts to tackle the hazard appear to be limited, the present study is driven by the need to identify those limitations in the flood management efforts in Lagos State.

CHAPTER ONE

INTRODUCTION

1.1      BACKGROUND OF THE STUDY

The rate of flooding occurrence in recent times has been unprecedented. With 70 million people globally exposed to flooding every year, and more than 800 million living in flood prone areas, climate change with more frequent and severe rainfall events, sea level rise, rapid population growth and urbanization, the rate of development on floodplains, the level of awareness of flood risk and the ineffectiveness of efforts towards tackling flooding in many places are factors of concern within the global context.

Flood hazard is one the most devastating and frequently occurring natural hazards in the world. Impacts of flood disaster on the society and its effect on sustainable development are overwhelming in recent years. The increasing climate change, accompanied with excessive rainfalls and its devastating consequences remain indelible in the lives of many people and the environment. Over the years and in almost every part of the world, excessive rainfalls due to climate change have resulted in flooding, which has claimed lives and properties. These unpalatable experiences have placed many countries, on hold in their struggle for development. As the world’s population increase at an alarming rate with increase in infrastructural development on the rise, more lives and properties are becoming vulnerable to the risk of flood hazards whenever extreme events occur (Dutta et al., 2013; Herath and Wang, 2009; James and Hall, 1986). The devastating effects are recorded in terms of mortality and economic risk by both national and international agencies. Although research claims that the mortality rate is reducing globally due to the established early warning systems in some countries (mostly the developed), but in some localities, especially in the developing and under developed countries, those living in the coastal areas, increasing deaths are witnessed because of their level of exposures and vulnerability. In Nigeria, flood accounts for the highest occurring natural hazards, with great consequences on the life and property (Aderogba, 2012).

Flood is an overflow of water that covered the land surfaces that are normally dry. This includes overflow from water bodies like river, lake, sea and also overflow as a result of heavy rainfall, snow melt and/or dam break resulting in some of that water to escape out of its natural boundaries (Leinster, 2009). It is a natural event that occurs on the land surface which can affect people and the environment negatively or even positively. “Among all kinds of natural hazards of the world: flood is probably the most devastating, widespread and most frequent” (Sanyal, 2004 P.383). Flood vulnerability is defined as “probability of flood occurrences and its potential consequences” (Alexander 2011, p.6). So, flood vulnerability mapping is the presentation or representation of areas that are at risk of flood events on maps.

Flood vulnerability mapping is very important for an appropriate urban planning to reduce the likelihood of flood occurrence and also reduce the consequences of flood disaster when it happen (Kaoje 2016).