AN ASSESSMENT OF HEAVY RAINFALL AS A DETERMINANT FLOODING IN LAGOS STATE(A FOCUS ON 2024)

CHAPTER ONE

INTRODUCTION

Background of the Study

The issue of flooding in Lagos State has become a persistent and progressively severe challenge, greatly impacting the lives and means of subsistence of its residents. Heavy rainfall is a major element that worsens the city's vulnerability to floods, along with other contributing variables. A flood is the result of an excessive amount of water gathering and rising to a level that causes it to overflow into territory that is typically not flooded (Mukhopadhyay, 2018). Flooding can occur when a river overflows due to extended periods of seasonal rainfall, heavy rainstorms, melting snow, dam failures, the buildup of rainwater in low-lying areas with a high water table, or insufficient storm drainage. Floods may also result from the encroachment of seawater into coastal areas during cyclonic or tidal surges (Handmer, Penning-Rowsell, and Tapsell, 2018). 

According to Askew (2019), floods are responsible for around one third of fatalities, injuries, and damages caused by natural disasters. The occurrence of flooding in different regions of Nigeria has resulted in the displacement of numerous individuals from their residences, the destruction of enterprises, the contamination of water supplies, and an elevated susceptibility to infections (Jeb and Aggarwal, 2018). 

Floods in Nigeria have been happening for a long time, as documented by several researchers. The recent instances of flooding in Nigeria, including the Sokoto flood in 2010, Ibadan flood in 2011, Lagos flood in 2011, and widespread flooding across the country in 2012, have demonstrated that flooding is a significant environmental issue in Nigeria. 

Floods in Nigeria can be categorised into three primary types: coastal flooding, river flooding, and urban flooding. An analysis of these various types of floods has revealed that no singular reason can be exclusively attributed as the sole cause for each type of flood. However, it is worth noting that certain factors, such as heavy rainfall, can contribute to the occurrence of all types of floods. According to the Federal Ministry of Environment (FME) (2020), Lagos experiences a higher frequency of floods compared to other areas in Nigeria (Nkwunonwo et al, 2024). However, the earliest documented occurrence of flooding in Lagos dates back to 1947, when the city was only a small coastal community, as reported by the Daily Times in that year. Over time, there has been a change in the frequency of flood episodes, with a noticeable increase (Odunuga 2018). Starting from the 1960s, Lagos has experienced a growing vulnerability to several forms of flooding. However, pluvial flooding has been responsible for the majority of the significant flood incidents in Lagos (Olajuyigbe et al., 2019). The frequency and severity of flooding in Lagos have intensified since the year 2000, as indicated by the increased occurrence of floods during the rainy seasons. This increase is attributed to heavy rainfall and storm surges, affecting both the mainland and coastal areas of the city. The impacts of flooding have become more frequent, with floods now occurring more than once a year. This information is supported by studies conducted by Nkwunonwo et al. (2018) and Adelekan (2018). 

There has been notable instances of floods in recent times. The 2020 flood in Ikorodu, a region in Lagos that is prone to flooding, had significant consequences when water was intentionally discharged from the Oyan Dam into the Ogun River to keep it from overflowing. However, this water ended up flooding the area instead. In July 2021, a total of 25 individuals lost their lives and more than 5000 individuals were forced to leave their residences due to a continuous downpour lasting 17 hours, resulting in a rainfall of 230mm. This amount of rainfall is often seen over the course of an entire month (IFRC, 2018). In 2011, flooding in Lagos caused the Nigerian industry to suffer financial losses of around NGN30 billion (USD200 million). However, this estimate does not include the expenses incurred for property damage and uninsured items. Additionally, in June 2022, a torrential downpour of 200mm led to an intense flood, causing significant disruption and ultimately in the unfortunate loss of 7 lives (Adelekan, 2016)

In contrast, according to a report from Vanguard (2024), Lagos can be quickly overwhelmed by a few hours of modest rainfall. The intense rainfall on the Wednesday 3rd  of July before last caused significant flooding in various areas of the city-state. The most astounding instances occurred in affluent neighbourhoods such as Lekki, Marina, portions of Surulere, Isolo, Magodo, and others. The heavy rainfall inundated and destroyed thousands of automobiles and flooded residences, workplaces, and stores. The Lagoon directly expanded into the inland areas of Lekki Phases I and II. 

Moreover, the causes of this significant flooding can be attributed to the insufficient efforts of both the government and the state's citizens in preventing regular rainfall from escalating into catastrophic events. The persistent practice of obstructing the sewers with waste instead of appropriately disposing of it in containers for removal persists. Individuals continue to construct buildings on drainage systems. The predicted outcome of this negligent obstruction of water's passage is persistently perpetuated by individuals. Regrettably, similar to other regions in the nation, the governmental bodies in Lagos State responsible for enforcing applicable laws are inadequate for the job. Against this backdrop, a survey will be conducted in order to assess heavy rainfall as a determinant of flooding in Lagos state.

1.2 Statement of the Problem

Annually, during the rainy season in Nigeria, numerous states are submerged by flooding, spanning from the northern to the southern regions. This results in a wide range of conditions, varying in severity, with some posing significant health risks. According to the World Health Organisation (2019), the rainy season commences in the southern region and poses a possible concern for a duration exceeding 200 days. 

During the year 2018, floods impacted around 1.9 million individuals in 12 different states of Nigeria. Over 500,000 individuals were forced to leave their residences. The occurrence of intense precipitation is not a fresh occurrence for the residents of Lagos state, since they have been residing in locations susceptible to flooding for generations. Similar to many urban regions in developing countries, Lagos state has undergone rapid population increase, resulting in significant changes in land use activities. Specifically, changes in land use directly affect the size and characteristics of floods (Civco, Hurd, Wilson, Song, & Zhang, 2019). 

In Lagos, flash flooding poses a significant issue since it erodes the road surfaces, rendering them nearly impossible to traverse. This frequently leads to unnecessary traffic congestion, which greatly detracts from the enjoyment of driving. Flash flooding, mostly caused by the unique geography of Lagos, is a significant element contributing to the regular damage of roads in the city. Hence, it is in the light of these that the study seeks to assess heavy rainfall as a determinant of flooding in Lagos state.

 1.3  Objectives of the Study

The main purpose of this study is to assess heavy rainfall as a determinant of flooding in Lagos state. Specifically, the study will;

Determine the extent to which heavy rainfall contributes to flooding in Lagos state.

Evaluate the adequacy of drainage systems designed to manage heavy rainfall and reduce flood risk.

Assess the various causes of flooding in Lagos state.

Proffer flood management measures to migrate flooding in Lagos state.

1.4  Research Questions

The following questions have been prepared for the study:

What is the extent to which heavy rainfall contributes to flooding in Lagos State?

How adequate are the drainage systems designed to manage heavy rainfall and reduce flood risk in Lagos State?

What are the various causes of flooding in Lagos State?

What are the flood management measures to migrate flooding in Lagos state?

1.5 Research Hypotheses

H0: Heavy rainfall does not significantly contribute to flooding in Lagos State.

Ha: Heavy rainfall significantly contributes to flooding in Lagos State.

1.6 Significance of the Study

The findings will enable urban planners to design urban development plans and infrastructure projects that are more resistant to floods. Possible solutions may include the implementation of improved drainage infrastructure, flood control methods, and land-use policies aimed at reducing the vulnerability of Lagos Island to future floods.This includes enhanced drainage infrastructure, flood prevention measures, and land-use rules designed to decrease the susceptibility of Lagos Island to future flood occurrences. 

Additionally, officials at the local, state, and federal levels will utilise the data to formulate and implement precise legislation and regulations that address the fundamental elements that contribute to flooding in Lagos Island.

Furthermore, future scholars will utilise it as a comprehensive analysis of existing literature. Consequently, future students interested in researching this field will be able to utilise this work as existing material that can be critically evaluated. Undoubtedly, the study's findings provide a significant contribution to the existing academic knowledge on how heavy rainfall influences floods in Lagos state.

1.6 Scope of the study   

The scope of this study is boarded on heavy rainfall as a determinant of flooding in Lagos state. Empirically, this study will determine the extent to which heavy rainfall contributes to flooding, evaluate the adequacy of drainage systems designed to manage heavy rainfall and reduce flood risk, assess the various causes of flooding and proffer flood management measures to migrate flooding in Lagos state.

Geographically, the study will be delimited to residents of  Ikorodu, Lagos state.

1.7 Limitation of the study

In the course of carrying out this study, the researcher experienced some constraints, which included time constraints, financial constraints, language barriers, and the attitude of the respondents. In addition, there was the element of researcher bias. Here, the researcher possessed some biases that may have been reflected in the way the data was collected, the type of people interviewed or sampled, and how the data gathered was interpreted thereafter. The potential for all this to influence the findings and conclusions could not be downplayed. More so, the findings of this study are limited to the sample population in the study area, hence they may not be suitable for use in comparison to other schools, local governments, states, and other countries in the world.

 1.9 Definition of Terms

Flood: An overflow of water that submerges land which is usually dry. Floods can occur due to various reasons including heavy rain, rivers overflowing, dam breakages

Rainfall: The amount of rain that falls over a certain period in a specific area.

Drainage: A natural or artificial removal of surface and sub-surface water from an area.

---

---