Effect of Urbanization on Stormwater Runoff and Flooding

1.1 Introduction

Urbanization is defined as the process by which rural areas transform into urban centers through population growth, infrastructural development, and expansion of built environments (United Nations, 2019). It is widely acknowledged as a critical driver of social and economic development, yet it is also associated with numerous environmental challenges (Douglas et al., 2016). Stormwater runoff refers to the excess water from rainfall or snowmelt that flows over the land surface rather than infiltrating into the soil. In natural conditions, much of the precipitation is absorbed by vegetation and soil, recharging groundwater systems. However, in urban areas, where impervious surfaces dominate, stormwater runoff is greatly increased, overwhelming drainage systems and leading to urban flooding (Akinbile & Olatunji, 2017).

As a prelude to other parts of this study, this chapter will discuss the background upon which this study was initiated, the statement of problems that led to this study, the Aim and Objectives of the study. Others are Significance of the study, Scope of work, Research hypothesis and questions, Limitation of the study and Definition of terms.

1.2 Background of the Study

Urbanization has emerged as a dominant global trend, significantly influencing environmental processes and posing challenges for sustainable urban management. According to United Nations (2019), urbanization is the progressive increase in the proportion of a population residing in urban areas, often resulting in profound changes in land use, infrastructure, and environmental conditions. While urbanization drives economic growth and modernization, it also creates environmental stresses, particularly through its impact on hydrological systems. The transformation of natural landscapes into built-up areas reduces infiltration and increases stormwater runoff, leading to urban flooding (United Nations, 2019).

Douglas et al. (2016) reported that urban flooding is one of the most visible consequences of rapid and unplanned urbanization, especially in developing countries where infrastructural development is inadequate. They emphasized that impervious surfaces such as roads, pavements, and rooftops prevent natural percolation of water, thereby accelerating runoff and overwhelming drainage systems. Akinbile and Olatunji (2017) asserted that stormwater runoff has become a major environmental concern in Nigerian cities, where poorly planned urban growth coincides with inadequate drainage infrastructure and weak institutional frameworks.

In the Nigerian context, flooding has become a recurring disaster with devastating socio-economic impacts. Olanrewaju and Adebimpe (2019) stated that Ilorin, the capital of Kwara State, is increasingly prone to flood hazards due to rapid urban growth, poor drainage facilities, and indiscriminate waste disposal that often clogs drainage systems. They further affirmed that the vulnerability of residents is heightened by settlement patterns, as many low-income households reside in flood-prone areas without adequate protective infrastructure. Similarly, Adeleye et al. (2020) contended that urban poverty interacts with environmental hazards, making the urban poor more exposed and less resilient to flood risks.

Climate variability also plays a critical role in worsening the problem. Adelekan (2016) affirmed that the increasing frequency of intense rainfall events in West Africa, linked to climate change, has aggravated flooding in many urban centers. Ogunbode (2021) reported that the interplay of human-induced land use changes, inadequate planning, and climatic variability creates a scenario in which cities like Ilorin are highly vulnerable to recurrent flooding. The inadequacy of urban planning regulations and weak enforcement mechanisms further exacerbate the risks, as floodplains and drainage channels are often encroached upon by residential and commercial developments. This study is set against the backdrop of the growing concern over the effects of urbanization on stormwater runoff and flooding in Ilorin, Kwara State.

1.3 Statement of Problems

Investigation revealed that urbanization is one of the most pressing drivers of environmental change, and its effect on stormwater runoff and flooding is increasingly evident in rapidly growing cities. As natural land surfaces are replaced with impervious materials such as asphalt, concrete, and rooftops, the infiltration capacity of the soil is drastically reduced (Adelekan, 2016). In Ilorin, unplanned urban growth is becoming a major factor that is worsening flood vulnerability, with residential, commercial, and industrial developments encroaching on natural drainage paths.

The situation is further compounded by inadequate drainage infrastructure, which is often poorly designed, or blocked by waste. The inability of the existing stormwater systems to cope with the increased runoff is resulting in frequent flash floods, property damage, traffic disruption, and threats to human life (Olanrewaju & Adebimpe, 2019).

On the other hand, population pressure and the rising demand for housing are pushing many residents to settle in flood-prone areas, thereby increasing their exposure to disaster risks. The urban poor are particularly vulnerable as they often lack the resources to adapt or relocate, making flooding not just an environmental concern but also a social and economic challenge (Adeleye et al., 2020). It is against this backdrop that this study seeks to analyze how urbanization influences stormwater runoff and flooding in Ilorin, Kwara State in Ilorin, Kwara State.

1.4 Aim and Objectives of the Study

The aim of this study is to analyze how urbanization influences stormwater runoff and flooding in Ilorin, Kwara State. The specific objectives of this study include:

1. To assess the adequacy of existing drainage infrastructure in managing stormwater runoff.
2. To investigate the impact of land use changes on the frequency and intensity of flooding.
3. To examine the relationship between urban growth and stormwater runoff in Ilorin.
4. To identify socio-economic consequences of flooding on residents of Ilorin.
5. To recommend strategies for sustainable urban planning and flood management in Ilorin.

1.5 Research Questions

Based on the stated objectives, the study will address the following research questions:

• What is the relationship between urban growth and stormwater runoff in Ilorin?
• How have land use changes influenced the frequency and intensity of flooding in Ilorin?
• To what extent is the existing drainage infrastructure adequate for managing stormwater runoff?
• What are the socio-economic consequences of flooding on residents of Ilorin?
• What strategies can be adopted for sustainable urban planning and flood management in Ilorin?

1.6 Significance of the Study

It is believed that at the completion of the study, the findings will assist urban planners and policymakers in making informed decisions that will reduce flood risks. The study will also will be significant in developing strategies that will integrate sustainable drainage systems into urban planning and ensure resilient city growth in Nigeria.

Furthermore, the research study will benefit residents of Ilorin by providing knowledge that will empower communities to adopt practices that will reduce their vulnerability to floods, such as improved waste disposal methods and avoidance of illegal settlement along waterways.

Lastly, academic institutions will also benefit, as the study will add to the existing body of knowledge on urbanization, hydrology, and disaster risk management, serving as a reference for future research.

1.7 Research Hypotheses

In order to pursue the objective of this study, the following generalized statements have been designed to guide and aids in obtaining the result for the experiment to be conducted. For this work, the null hypothesis will be represented with H0 while the alternative hypothesis will be represented with hypothesis H1.

• H₀1: There is no significant relationship between urban growth and stormwater runoff in Ilorin.
• H₀2: Land use changes significantly increase the frequency and intensity of flooding in Ilorin.
• H₀3: The existing drainage infrastructure in Ilorin is inadequate to manage stormwater runoff effectively.

1.8 Scope of the Study

The scope of this research is focused on the Effect of Urbanization on Stormwater Runoff and Flooding using Ilorin, Kwara State as a case study.

1.9 Limitations of the Study

A study of this nature is bound to experience certain problems as such the constraints imposed on the research include:

1. Time Constraints: A study of this nature needs relatively long time during which information for accurate or at least near accurate inference could be drawn. The period of the study was short, time posed as constraints to the research.
2. Financial Constraints: The research would have extended the survey to other area at the empirical level, but limitation as included cost of transportation to the source of material and the cost of time setting of the already completed work.
3. Lack of Cooperation: Many of the respondents are usually aggressive on issue that border cooperation among the respondents border.
4. Response Bias: The study will involve surveys and interviews with cooperative managers and members. Response bias may occur if respondents provide socially desirable answers or if there is reluctance to disclose negative financial information due to privacy concerns or fear of repercussions.

1.10 Definition of Terms

Urbanization:

Urbanization is the process by which rural settlements transform into urban areas through population growth, infrastructural development, and expansion of built environments (United Nations, 2019).

Stormwater Runoff:

Stormwater runoff is the portion of rainfall or surface water flow that does not infiltrate into the ground but flows over land surfaces and into drainage systems (Akinbile & Olatunji, 2017).

Flooding:

Flooding is the overflow of water that submerges land which is normally dry, often caused by excessive rainfall, poor drainage, or overflow of rivers (Smith & Ward, 1998).

Drainage Infrastructure:

Drainage infrastructure refers to the system of channels, pipes, and constructed facilities designed to collect and convey stormwater safely away from urban areas (Olanrewaju & Adebimpe, 2019).

Land Use Change:

Land use change is the alteration of natural land cover for human purposes such as housing, industrial development, or agriculture, often linked to environmental consequences like flooding (Douglas et al., 2016).

Climate Variability:

Climate variability is the fluctuation in climate patterns, including rainfall intensity and frequency, which influences stormwater management and flooding risks (Adelekan, 2016).