When heavy rain falls in Ilorin, the first environmental problem that may come to mind is flooding. But water can damage the environment in another way that is different from flooding: erosion.
Flooding is mainly about the accumulation and movement of excess water over land. Erosion is about the detachment and removal of soil and other land materials by agents such as running water and wind. The two can occur during the same rainfall event, but they are not the same environmental disaster.
Erosion can gradually remove fertile topsoil from farmland, deepen channels, undermine roads and structures, and eventually create large gullies. In severe cases, land that was once useful for farming, transportation or settlement can become difficult or dangerous to use.
For Nigeria, preventing erosion requires more than waiting for visible gullies to appear. It requires understanding how rainfall, vegetation, soil, slope, land use and drainage interact.
What Exactly Is Erosion?
Erosion occurs when soil or other surface material is detached and transported from one location to another.
Water is one of the most important agents of erosion. During rainfall, water first strikes exposed soil. If vegetation or other ground cover does not protect the surface, the impact of raindrops can loosen soil particles.
When rainfall becomes runoff, the moving water can carry those particles away.
The process can begin almost unnoticed.
A small amount of soil may be removed from a farm or roadside after each rainfall. Over time, however, repeated removal can form small channels. These channels can become deeper and wider until they develop into gullies.
Research describes gully formation as a significant form of soil erosion and land degradation because gullies can expand rapidly and become difficult to control once established (Vanmaercke et al., 2021).
Erosion Is Not the Same as Flooding
This distinction is important, especially for environmental health and environmental sanitation.
During flooding, water may cover roads, houses, farms or other areas temporarily.
With erosion, the major concern is the loss and displacement of soil or land material.
For example, if heavy rainfall causes water to accumulate on a road, that is flooding. If concentrated runoff cuts into the roadside and gradually creates a deep channel, that is erosion.
The two can reinforce each other. Floodwater can carry soil away, while poorly managed runoff can accelerate erosion. However, treating every erosion problem simply as a flooding problem can result in the wrong intervention.
A drainage channel may move water away from a location but, if poorly designed, it can concentrate fast-moving runoff and cause erosion further downstream.
Erosion in Kwara State
Erosion is not limited to Nigeria’s southeastern states.
A 2026 study specifically assessed soil-erosion variability across Kwara State using the Revised Universal Soil Loss Equation (RUSLE), GIS and remote-sensing data. The researchers estimated that approximately 73.15% of the state fell within the low erosion-risk class, 23.04% within the medium-risk class and 3.81% within the high-risk class (Ipadeola et al., 2026).
The study also found greater susceptibility in areas associated with steeper slopes, sparse vegetation and intensive land use.
This is particularly useful for environmental management because it shows that erosion risk is not evenly distributed.
Some parts of Kwara are more vulnerable than others.
That means prevention can be targeted instead of waiting until erosion becomes severe.
What Causes Erosion?
Several factors can increase erosion.
Loss of vegetation
Vegetation protects soil. Plant roots help hold soil together, while leaves and other plant materials reduce the direct impact of rainfall.
When vegetation is removed for farming, construction, road development or other activities, exposed soil becomes more vulnerable.
Poor land management
Repeated cultivation without appropriate soil-conservation practices can weaken the land.
Agricultural activities conducted on slopes without adequate conservation measures can increase runoff and soil loss.
Poorly managed runoff
This is particularly important in towns.
When buildings, roads and paved surfaces prevent water from infiltrating the soil, runoff can become concentrated in drains and channels.
If those channels discharge water onto exposed soil without adequate protection, erosion can develop.
Construction
Construction activities can expose large areas of bare soil.
If temporary drainage and erosion-control measures are not provided, rainfall can wash loose construction material into roads, drains and nearby waterways.
Steep slopes
Gravity makes water move faster down steep terrain, increasing its ability to transport soil.
This is why erosion-control measures must consider the slope and not simply the amount of rainfall.
A Useful Nigerian Example
The problem of erosion is visible in many parts of Nigeria, particularly where intense rainfall interacts with exposed soil and unsuitable land management.
Research in Zaria provides another useful Nigerian example. Scientists documented destructive surface and gully erosion in an area of the Ahmadu Bello University campus and examined how afforestation could help protect the land. The erosion was significant enough to contribute to sedimentation of the Kubanni reservoir, an important water source for the university community (Kamaru et al., 2022).
The lesson is relevant to Kwara.
Erosion does not necessarily remain where it begins.
Soil removed from an upper slope can be transported into drainage channels, streams and reservoirs. This can create sedimentation problems downstream.
Therefore, erosion control is also connected to water-resource management.
How Can Erosion Be Prevented?
The best approach is to prevent soil from becoming exposed and to control the movement of runoff.
Planting and protecting vegetation
Trees, grasses and other vegetation can provide valuable protection.
Plant roots help stabilize soil, while vegetation slows runoff and reduces the energy available to transport soil particles.
However, simply planting trees is not enough. The appropriate vegetation must be established and maintained according to the local soil, climate and land-use conditions.
Contour farming
On sloping agricultural land, cultivation along the natural contours of the land can reduce the speed at which water moves downhill.
This allows more water to infiltrate rather than rapidly flowing downslope.
Terracing
Where slopes are sufficiently steep, terraces can break a long slope into smaller sections and reduce runoff velocity.
This approach has been used in many parts of the world and can be adapted to appropriate Nigerian agricultural settings.
Check dams and gully control
Where gullies have already developed, small check dams and other structures can slow water and encourage sediment deposition.
Research on gully restoration has shown that check dams can help reduce channel-bed slope and promote conditions favourable to vegetation recovery (Vanmaercke et al., 2021).
The exact structure, however, must be designed according to the size and behaviour of the gully.
Proper drainage design
Urban drainage should not simply move water as quickly as possible.
It should move water safely.
Where drainage outlets discharge concentrated water onto bare soil, protective measures such as energy-dissipation structures, vegetation or appropriate lining may be required.
This is an area where environmental sanitation technology and civil engineering overlap.
Technology Can Help Identify Erosion Risk
Modern technology gives environmental professionals better tools for preventing erosion.
GIS can combine information about rainfall, slope, vegetation, soil type and land use to identify vulnerable areas.
Remote sensing can monitor changes in vegetation and land cover over time.
The recent Kwara study demonstrates how RUSLE, GIS and satellite-based vegetation information can be combined to map erosion susceptibility across a large area (Ipadeola et al., 2026).
This means authorities do not necessarily have to wait for residents to report a massive gully.
High-risk locations can be identified earlier and conservation measures prioritized.
What Can Ilorin Do?
For Ilorin, erosion prevention should form part of urban development planning.
Construction sites should manage exposed soil and runoff. Drainage outlets should be designed to prevent destructive discharge. Vegetation should be preserved where possible, especially around vulnerable slopes and drainage corridors.
Residents can also contribute by avoiding activities that expose or weaken soil unnecessarily.
Where erosion has already started, reporting it early is important.
A small erosion channel is much easier and cheaper to control than a large gully that has already removed several metres of soil.
This is one reason environmental monitoring matters.
My Environmental Health Perspective
My training in Environmental Health Science has taught me to look beyond the immediate appearance of an environmental problem.
A gully beside a road may initially look like a civil-engineering problem. But it can affect much more than the road.
It can create hazards for pedestrians, affect access to homes and farms, carry sediment into waterways and damage surrounding land.
This is where environmental health connects with land management.
The late Professor Henry Sawyer was among the lecturers who contributed to my academic foundation, and my Environmental Health Science training has continually reinforced the importance of prevention rather than waiting until environmental hazards become emergencies.
Conclusion
Erosion is an environmental disaster that can develop slowly but cause long-lasting damage.
Unlike flooding, which is primarily concerned with water temporarily covering land, erosion involves the progressive removal and transport of soil and land materials.
Kwara State’s recent erosion-risk assessment demonstrates that vulnerability varies across the state, with slope, vegetation and land use influencing areas of greater susceptibility (Ipadeola et al., 2026).
For Ilorin and other Nigerian communities, prevention should involve vegetation protection, appropriate land-use planning, erosion-conscious drainage design, agricultural conservation practices, early identification of vulnerable areas and the use of GIS and remote sensing.
The important lesson is simple:
Do not wait until a small channel becomes a massive gully.
Erosion is much easier to prevent than to repair.
References
Ipadeola, O. A., Adeniyi, F. E., Olatunde, G., Yusuf, A., Babalola, A., & Gbadamosi, A. A. (2026). Spatial assessment of soil erosion variability in Kwara State, Nigeria using RUSLE and GIS. Environmental Technology and Science Journal, 17(1), 208–216.
Kamaru, A. A., et al. (2022). Afforestation of Transformed Savanna and Resulting Land Cover Change: A Case Study of Zaria (Nigeria). Sustainability, 14(3), 1160.
Vanmaercke, M., et al. (2021). Measuring, modelling and managing gully erosion at large scales: A state of the art. Earth-Science Reviews, 218, 103637.
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