Flood Hazard Mapping And Risk Management In Parts Of Lagos State

Project and Seminar Material for Environmental Science

Flood Hazard Mapping And Risk Management In Parts Of Lagos State


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


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 ofheavy rainfall, snow melt and/or dam break resulting in some of that water to escape out of itsnatural boundaries (Leinster, 2009). It is a natural event that occurs on the land surface whichcan affect people and the environment negatively or even positively. “Among all kinds ofnatural hazards of the world: flood is probably the most devastating, widespread and mostfrequent” (Sanyal, 2004 P.383). Flood vulnerability is defined as “probability of floodoccurrences and its potential consequences” (Alexander 2011, p.6). So, flood vulnerabilitymapping 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 reducethe likelihood of flood occurrence and also reduce the consequences of flood disaster when ithappen (Kaoje 2016).

Flood is the most common occurring natural disaster that affects humans and theirsurrounding environment (Leinster, 2009). This natural disaster is common in Nigeria, it has been occurring in almost every raining season. According to Nigerian National Emergency

Management Agency (NEMA), in 2012 alone about 1.3 million Nigerians have been displaced and 431 have died from various floods occurrences. In that same year 30 of 36

Nigeria’s states were affected by the floods (IRIN 2012). A lot of physical damages were recorded, including destruction of houses and farmlands. Economic life was halted, people displaced and some lost their lives. It is understood that flood is a hazard that can be avoided or minimize not only by building more dams or constructing more flood defence systems butalso by the use of modern technologies and appropriate urban planning that provide information on flood risk areas (Cinque, et al 2003). The GIS application have gained a wide acceptability as (Atkinson 2008) noted that based on the legal system in the USA, GIS is currently been seen in favourable light when the topic appears in litigation.

Alexander et al (2011) supported the argument that “mapping has become the keystone for flood riskmanagement and communication in representing spatial relationships between hazard andvulnerability and resulting risk”.
Devastating flood events in Nigeria can be dated back to 1963 in Ibadan city, when Ogunpa River was over-flown causing loss of lives and property; these hazardous events reoccurred in 1978, 1980 and 2011, with estimated damages and deaths of over 30 billion naira and 100 people respectively, thus making Ogunpa River nationally and internationally famous (Adegbola and Jolayemi, 2012; Agbola et al., 2012). Between 2011 and 2012 alone, Lagos state recorded at least 8 major floods with more than 30 people deaths and many damages to properties (Editor, 2012; Komolafe et al., 2014). The worst but recent of all the flood events that caused a huge devastation across the geopolitical zones in the country was the July, 2012 event. The flood (the worst since 40years), which occurred in at least 33 states out of the 36 states of the country as a result of a very heavy rainfalls that caused a lot of damages both to lives and properties (UNCHA, 2012). According to EM-DAT: International Disaster Database on Nigeria disaster, in 2012 alone, about 7,000, 867 lives were affected by the widely spread flood while 363 and $500,000 deaths and economic damages respectively were recorded (Guha-Sapir et al., 2013).

1.2 Statement of the Problem

It is argued that whilst this statement recognizes flooding situation in Nigeria and the relevance of flood data for flood risk reduction, it laments the dearth of flood data for the country and the peculiar challenges that arise from utilizing commercial flood modelling codes to simulate such data. Moreover, the fact that Nigeria is one of the most populated countries of the world with population size estimated at over 170 million people compounds the situation. The theory that future population growth will drive future flood risk highlights the importance of urgency in finding means of preparing human population in the country to adapt to floods. It will be a welcome development for Nigeria to implement flood modelling since within European Union framework, such a technique is operationalized towards flood hazard/risk mapping of the constituting States. Recent floods and consequences in Lagos State is becoming too frequent and threat to sustainable development in human settlements.

Despite the attention flooding received in many other studies, still the question: “what is the remedy to the recurrent flooding in Nigeria?” remains unanswered. The lack of flood data and other ancillary data which is a major setback towards containing the threats of flooding in the country were raised but not addressed.

It is against this background that this study aims at assessing the flood hazard mapping and risk management in parts of Lagos State.

1.3 Objectives of the Study

In pursuance of the purpose of this study, the researcher considers the following specific objectives:

  1. To investigate and summarize evidence of flooding in Lagos Stateand to critically review efforts towards addressing its threats in the state.
  2. To identify knowledge gaps relevant to the reduction of flood risk in Lagos State.
  3. To present flood risk management as a way-forward towards pro-active flood hazards in Nigeria.
  4. To make supported recommendations towards building flood resilient communities.

1.4 Research Hypotheses

  1. H0: the present flood disaster in Lagos State does not affect the residents from the urban region of the state.
    H1: the present flood disaster in Lagos State does affect the residents from the urban region of the state.
  2. H0: there is no evidence of heavy flood hazard in most cities in Lagos State.
    H2: there is an evidence of heavy flood hazard in most cities in Lagos State.

1.5 Significance of the Study

The study of this nature is so relevance to the entire residence in the study area, the general public and town planners. Professionally the findings of this study will be of immense support to land surveyors in Lagos State. Specifically this study will be valuable to environmental agencies like Nigeria Metrological Agency (NIMET), National Emergency Management Agency (NEMA) and Nigerian Ministry of Environment to provide strategic management aimed at improving ways to reduce or mitigate flood disasters in Nigeria. Academically, this research will add knowledge to the students from estate management, also it will serve as a source material for future research by providing insights on related areas that a researcher can thus build on.

1.6 Scope and Limitations of the Study

This study centres on the devastating unprecedented flood disaster ravaged many states in Nigeria, especially Lagos State.

In the cause of the study, the researcher encounters some limitations which limited the scope of the study;

Time constraint:

The researcher will simultaneously engage in this study with other academic work. This consequently will cut down on the time devoted for the research work.

Inadequate Materials:

Scarcity of material is also another hindrance. The researcher finds it difficult to long hands in several required material which could contribute immensely to the success of this research work.

Financial Constraint:

Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet, questionnaire and interview).

1.7 Definition of Terms


This is collapse of series of social function of a nation which causes the loss of human lives, materials, economy and environmental components.


This is the accumulation of abnormal large volume of water which has refused to flow away, causing damage to the environment, human, aquatic lives, and properties.

Flood Hazard:

Flood hazard mapping is an exercise to define those coastal areas which are at risk of flooding under extreme conditions. As such, its primary objective is to reduce the impact of coastal flooding. However, mapping of erosion risk areas may serve to achieve erosion risk reduction.


Risk is the potential of gaining or losing something of value. Values (such as physical health, social status, emotional well-being, or financial wealth) can be gained or lost when taking risk resulting from a given action or inaction, foreseen or unforeseen. Risk can also be defined as the intentional interaction with uncertainty. Uncertainty is a potential, unpredictable, and uncontrollable outcome; risk is a consequence of action taken in spite of uncertainty.

Risk Management:

Risk management is the identification, assessment, and prioritization of risks (defined in ISO 31000 as the effect of uncertainty on objectives) followed by coordinated and economical application of resources to minimize, monitor, and control the probability and/or impact of unfortunate eventsor to maximize the realization of opportunities. Risk management’s objective is to assure uncertainty does not deflect the endeavor from the business goals.

Lagos State:

Lagos, sometimes referred to as Lagos State to distinguish it from Lagos Metropolitan Area, is a state located in the southwestern geopolitical zone of Nigeria.

1.8 The Study Area

Lagos state (3°E, 6°N) is the largest metropolitan area in West Africa, and the second in Africa, after Cairo but has a highest population growth rate in the continent (UN, 2008). It was founded in 1472 a fishing and farming settlement around its natural break for the approximated 2,500km-long West African creeks and lagoons parallel to the Atlantic coastline. It was the administrative headquarters of Nigeria and remains the commercial and socio-political nerve centre of the country (Odumosu, 1999; Ojo and Omotayo, 1988). The climate is tropical with high temperature all the year round and torrential rains between April and November. Lagos is a coastal metropolis with altitude of about 10m above sea level. It slips into the Atlantic Ocean at a low gradient. The geomorphology is dominated by coastal plain sands, barrier beaches and cutoff channels of coastal rivers and fringing lagoons. The population is estimated at about 10 million in 2007 and 24 million in 2020 (Agbola and Agunbiade, 2007). About two-thirds of the residents live in high population density- low income slum neighborhoods (Morakinyo et al, 2012). The slums originate from chaotic developments of unplanned squatter settlements, pressures generated by inadequacy of shelter delivery system for rising urban population and demand for land by teeming rural immigrants for their urban needs. They lack basic urban social services such as hospitals, schools, electricity andpotable water (Nwanna, 2012). The few spaces available are heaped by refuse. Living rooms are substandard and congested, sometimes without kitchen. Morakinyo et al (2012) estimated about 8.7 persons per room. Lagos slums are vulnerable to floods in view of their geographical characteristics and resilience by the residents. Drains and roads are provided and maintained poorly. Some property developers and residents are also noted for disregard to landuse regulations and controls which retard smooth flow of runoffs from torrential rains and water released for safety reasons by dams upstream Ogun, the main river draining the metropolis. The floods build up gradually from sluggish runoff from torrential rains, ocean/lagoon backwash and discharges by upstream dams on the existing rivers as occasioned by safety consideration. Incidences of flood disasters in recent times are perennial particularly in wet months. The months are a period that residents around floodplain and shoreline communities look forward to with no enthusiasm because of the high flood risks (Ayoade and Akintola, 1980; Ologunnorisa, 1999). Yet residents are unwilling to relocate because of properties and rents are cheaper. Six of the twenty local government areas of Lagos State are covered comparatively.

1.9 Organization of the Study

This research work is organized in five chapters, for easy understanding, as follows

  1. Chapter one is concern with the introduction, which consist of the (overview, of the study), statement of problem, objectives of the study, research question, significance or the study, research methodology, definition of terms and historical background of the study.
  2. Chapter two highlight the theoretical framework on which the study is based, thus the review of related literature.
  3. Chapter three deals on the research design and methodology adopted in the study.
  4. Chapter four concentrate on the data collection and analysis and presentation of finding.
  5. Chapter five gives summary, conclusion, and recommendations made of the study.

Chapter Five

Summary Conclusion and Recommendation

5.1 Introduction

It is pertinent to note that this research was aimed at examining the impacts of flood disaster and the measures to manage it adverse effects and risk, thus the topic “flood hazard mapping and risk management in parts of Lagos State”.

In the preceding chapter, the relevant data collected for this study were presented, critically analyzed and appropriate interpretation given. In this chapter, certain recommendations made which in the opinion of the researcher will be of benefits in addressing the challenges associated with flood and natural disasters in Nigeria.

5.2 Summary

Flooding in Nigeria is generally linked to poor urban planning and climate change (Adeloye & Rustum 2011, Action Aid 2006, Cline 2007, BNRCC 2008). The impacts have been severe and every part of the country’s life stream is affected with significant economic losses (mainly through destruction of farmlands, social and developmental infrastructure) and economic disruption (most notably in oil exploration in the Niger delta, traffic congestion in many cities in Nigeria, disruption in telecommunication and power supply) (Ogunbodede & Sunmola 2014, Ologunorisa 2005, Fadairo & Ganiyu 2010). In 2012, the country experienced the worst flooding in more than 40 years as a result of heavy storms that lasted many days. The incidence affected 32 states with 24 considered severely affected (NEMA 2013). The floods lasted from July to October that year and affected 7.7 million people with more than 2 million others reckoned as internally displaced (IDPs). More than 5000 people were physically injured along with over 5900 houses which were destroyed.

From the review of various literatures in this study, it is clear that the impacts of flooding in Nigeria continue to trigger concerns for food security, vulnerability of local communities within the country, humanitarian needs and services, primary health delivery, environmental management, solid waste management, urban development, professionalism in journalism practice and the dynamism or lethargy of Nigerian democracy and political system (Clement 2012, Adelekan 2010, OCHA 2012, Uzochukwu et al. 2014, Ochuko 2014, Obeta 2014, Douglas et al. 2008). Whilst investigating these factors vis-à-vis flood risk mitigation in Nigeria is vital, key features of flooding which influence its level of impacts in the country include flood water depth, inundation extent and duration of inundation. Respectively, flood width, height, annual frequency and duration in Nigeria can measure over 700m, 11m 10and 25 days respectively (Aderogba 2012).

5.3 Conclusion

Critical issues relating to widespread flooding in Nigeria have been explored with view to charting a more proactive solution towards addressing the challenge within the country. Over the period 1985 to 2014, the effects of flooding on people, properties and economic activities have been arguably overwhelming. Whilst virtually all states in Nigeria have experienced the hazard, more frequent floods are experienced in Lagos, 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 and this has been associated to poor urban planning and climate change with more frequent and intense rainfall. Present efforts at tackling flooding in Nigeria appear to be limited and have been grossly criticized as ad-hoc, poorly coordinated and not in line with globally acknowledged ‘best practices’ in flood risk reduction. Whilst such practices do not seem to be governed by the idea of ‘living with floods and not fighting them’, which dominates in flood risk reduction literature and many international and regional flood management policies such as the European Union Flood Directive, flood modelling approaches are evidently lacking. Given the relevance of flood risk/hazard mapping within the framework of flood risk reduction, the specific roles of flood modelling are presented. Basically, it is shown that flood modelling simulates flood hazard data (flood water depth, extent, and duration as well as flow velocity) for flood risk/hazard mapping. However, the dearth of these data among other factor constrains efforts at tackling flooding in Nigeria. Although ground survey and remote sensing approaches can be applied to acquire these data, limitations inherent in these approaches undermine their applications in Nigeria.

Finally, the results and information generated from this study have demonstrated that it is possible to effectively produce flood hazard maps at various levels (low, moderate and high vulnerability levels) as well make predictions as regards flooding in the study area.

5.4 Recommendations

Based on the findings of this study, it is recommended that;

  1. The quality of data, maps produced as well as the modelling process carried out will be of great importance in the proper handling and management of flooding in Lagos State.
  2. This project may be adopted and used as a source for planning and management in the study area and indeed in other administrative capacities.
  3. The development of good policy and proper planning with the results obtained from this study will go a long way in reducing flooding occurrences as well as help in the control and management of such occurrences in the study area.
  4. Proper data provision, updating and management for such studies should be carried out. This will ease the execution of such studies more frequently, thereby providing up to date information at various times. v. Proper flood warning systems should be put in place for the study area for flood monitoring processes.

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