Recently, there have been reports from communities in Lagos concerning flood incidents and rising flood waters affecting their homes and livelihoods. It was said that the reasons for these floods is that Lagos is sinking. There is also the issue of the rising sea level attributed to global warming. This sinking is called land subsidence, a situation where the surface of the earth settles gradually or sinks suddenly due to removal of subsurface earth materials. This occurrence is usually expected when there is a withdrawal of massive amounts of groundwater from specific kinds of rocks, like fine-grained sediments.
According to a research by the University of Lagos and a thesis with the title, “Evaluation of Induced Seismicity and Liquefaction Potential of Coastal Sands Using Integrated Method in Part of Lagos Wetlands,” land subsidence is a threat to majority of Lagos’ inhabitants. The lead investigator of Earth Signature Research Group, Department of Geosciences, University of Lagos, Prof. Lukmon Adeoti, stated that there are evidential facts that there is an increasing subsidence rate in many Nigerian cities.
Subsidence of land is happening faster than sea level is rising.
The research was conducted with reference to a published study in 2022 by three US scientists — Peo-Chin Wu, Meng Wei and Steven DiHondt — who were students of the Graduate School of Oceanography, University of Rhode Island, USA. During the research, the subsidence rater of 99 coastal cities in countries around the world between 2015 and 2020 was measured. The satellite data of the research revealed that sea level is rising slower than land is subsiding in many coastal countries across the world.
In the report, there was an identification of 5 × 10 km in the center of Lagos as having a subsidence faster than 2 mm/yr. Recommendations in the report suggested expansion of monitoring and policy interventions for reduction of subsidence rates and minimization of the consequences. There was also a suggestion that Permanent Global Navigation Satellite System (GNSS) stations could see to provision of accurate measurements of coastal subsidence (mm/yr) but have limitations in their spatial coverage and resolution.
There is a threat to the community and exposure to danger.
It was said that Interferometric Synthetic Aperture Radar (InSAR) is capable of providing larger spatial resolution with effective accuracy (a few mm/yr). InSAR data is responsible for showing that a massive portion of the Lagos coastal area is subsiding faster than sea level is rising but there is no publicly accessible GNSS data for any visibly subsiding locations in the same region. There is a tendency that actual subsidence rates may be higher than estimated from InSAR data in cities with unavailable openly accessible GNSS data, given that there is subsidence in the reference area.
Speaking on this issue, the professor of Applied Geophysics, Prof. Adeoti, appealed to the media to assist in the campaign for sensitizing the public in safeguarding the surface of the earth from increased land subsidence. Without tackling this situation efficiently, the community is threatened and exposed to danger. He added that before human activities like building, water sourcing and others are conducted, it is important that Geotechnical and Geophysical Methods are implemented in testing the earth sub-surface’s soil and determining the type of foundation to be set.
Improper incineration should be replaced with recycling.
Prof. Ife Adewunmi, Civil Engineer and Professor of Water Resources and Environmental Engineering, added that Lagos is not the only sinking coastal region in Nigeria. This is because coastal cities like Bayelsa and Ayetoro Ondo State have parts of them sinking too. Prof. Adewunmi encouraged every Nigerian to make efforts to enable reduction of environmental pollution caused by anthropogenic activities. Improper incineration that involves open burning of refuse is an harmful practice that contributes to pollution and should be curbed; recycling be adopted instead.