Urbanization increases runoff potential by 14% in Abeokuta

Why It Matters

Understanding the direct impact of urban expansion on hydrological systems is crucial for sustainable urban planning and infrastructure design. Designers and engineers must account for these changes to mitigate flood hazards and manage water resources effectively.

Key Finding

Urban expansion in Abeokuta led to a significant increase in impervious surfaces, resulting in a 14% rise in urban area, a higher potential for runoff, and increased annual and peak discharge volumes, with runoff patterns mirroring urban development.

Key Findings

• Urban areas in selected catchments increased by 14% between 2000 and 2018.
• Average SCN-CN increased from 76.9 to 79.9, indicating higher runoff potential.
• Annual discharge depth increased from 891.84mm to 956.9mm.
• Peak discharge increased from 161.9 m³/s to 196.2 m³/s.
• Runoff patterns spatially correlate with the distribution of built-up areas.

Research Evidence

Aim: To quantify the impact of urban growth on surface runoff in flood-prone settlements by analyzing changes in land use and their effect on the Soil Conservation Service Curve Number (SCN-CN).

Method: Mixed-methods approach combining Geographic Information System (GIS) and hydrological modeling.

Procedure: The study utilized Shuttle Radar Topography Mission Digital Elevation Model (SRTM DEM) for SCN-CN derivation and Landsat satellite imagery from 2000 and 2018 to assess land cover changes. These data were analyzed using the Hydrologic Engineering Centre’s Hydrologic Modelling System (HEC-HMS) and ArcGIS to determine changes in average runoff, annual discharge depth, and peak discharge.

Context: Urban hydrology and land use change analysis in Abeokuta, Nigeria.

Design Principle

Urban development must be designed to manage and mitigate increased surface runoff through permeable surfaces and effective drainage systems.

How to Apply

When designing urban infrastructure or planning new developments, use GIS and hydrological models to predict the impact of land cover changes on runoff and incorporate appropriate mitigation strategies.

Limitations

The study suggests the need for higher-resolution datasets for more precise analysis and recommends further investigation into the implementation of sustainable urban policies.

Student Guide (IB Design Technology)

Simple Explanation: When cities grow and more concrete and buildings replace natural ground, water can't soak in as easily, leading to more surface runoff and a higher chance of flooding.

Why This Matters: This research highlights how design decisions in urban areas directly affect natural water systems, emphasizing the responsibility of designers to manage environmental consequences like increased flooding.

Critical Thinking: How might the specific types of urban development (e.g., residential vs. industrial) differentially impact runoff characteristics, and how could design interventions mitigate these varied impacts?

IA-Ready Paragraph: Research by Ologunorisa et al. (2023) demonstrates that urban expansion significantly increases surface runoff potential. Their study in Abeokuta found a 14% increase in urban land cover led to higher SCN-CN values and increased annual and peak discharge, highlighting the direct hydrological consequences of urbanization that designers must address.

Project Tips

• When investigating environmental impacts, clearly define the scope of your study area and the specific land-use changes you will analyze.
• Ensure your chosen modeling tools are appropriate for the scale and complexity of the environmental system you are studying.

How to Use in IA

• Reference this study when discussing the environmental impact of urbanization on hydrological processes in your design project, particularly if your project involves urban development or infrastructure.

Examiner Tips

• Demonstrate an understanding of how land-use changes, such as urbanization, directly influence environmental factors like water runoff and potential flooding.

Independent Variable: Urban land cover percentage, time (years).

Dependent Variable: Average runoff (SCN-CN), annual discharge depth, peak discharge.

Controlled Variables: Topography (DEM), rainfall patterns (implied by model inputs).

Strengths

• Utilizes established hydrological modeling techniques (SCN-CN, HEC-HMS).
• Combines remote sensing data with hydrological analysis for a comprehensive view.

Critical Questions

• To what extent can the observed runoff changes be attributed solely to urban growth versus other environmental factors like climate change?
• What are the socio-economic implications of increased runoff and potential flooding for the affected communities?

Extended Essay Application

• An Extended Essay could explore the effectiveness of different green infrastructure designs in mitigating the increased runoff identified in urbanizing areas like Abeokuta.

Source

An Evaluation of the Impact of Urban Growth on Runoff in Abeokuta, Southwestern Nigeria · Journal of the Geographical Association of Tanzania · 2023 · 10.56279/jgat.v43i2.274