HYDROLOGICAL IMPLICATIONS OF WETLAND ENCROACHMENT ON LOCAL FLOOD REGULATION IN ABEOKUTA, OGUN STATE, NIGERIA
DOI:
https://doi.org/10/3303/jees.2026.0301/025Keywords:
Flood regulation, Geographic Information System, Hydrological modelling, Wetland encroachmentAbstract
Wetlands function as natural hydrological buffers, storing excess floodwaters and gradually releasing them to maintain hydrological balance, thereby playing a critical role in flood management. Anthropogenic flood buffering of wetlands in Abeokuta, Ogun State, has driven rapid urban growth, thereby reducing the city’s natural capacity to buffer floods. Despite the recurrent flooding, there remains a paucity of empirical studies that have quantitatively evaluated the hydrological effects of such encroachment. This study attempts to map the geographical scope of wetland loss and assess its impact on runoff and peak discharge using a combined geospatial and hydrological analysis. The geospatial design, based on a quantitative approach using remote sensing, GIS, and HEC-HMS modelling, was adopted. Landsat 7 TM (2015) and Landsat 8 ETM+ (2025) multispectral satellite images (spectral range of 0.45-2.35 µm and 30-meter resolution, respectively) were used in the study, and rainfall and discharge data were obtained from NiMet and the Ogun-Osun River Basin Authority. Land use analysis revealed that wetlands increased by 7% and water bodies decreased by 0.3%. The model had a high calibration, NSE = 0.77 and R2 = 0.81. Findings indicated that runoff and peak discharge increased by 19.8% and 22.4%, respectively, and the lag time decreased by 24.4%. These results indicate that the loss of wetlands increases the velocity of surface water runoff and amplifies flood peaks. The study recommends delineating the boundaries of protected wetlands within the Abeokuta master plan and integrating wetland variables in urban hydrological models to enhance sustainable flood control.
References
Adeleke, B. O. (2022). Need for emergency response to wetlands loss in Southwestern Nigeria: a review. Ghana Journal of Geography, 14(3), 90-114.
Adeyefa, A. O. (2023). Spatial and Temporal variations in Water Quality of River Ogun, Abeokuta, Ogun State, Nigeria. Journal of Science Research, 20(1).
Agonafir, C., Lakhankar, T., Khanbilvardi, R., Krakauer, N., Radell, D., & Devineni, N. (2023). A review of recent advances in urban flood research. Water Security, 19, 100141.
Echendu, A. J., Stewart, R. A., & Ogunbode, T. O. (2023). Urban expansion and flood risk in sub-Saharan African cities: Implications for sustainable planning. Environmental Science & Policy, 136, 101–112. https://doi.org/10.1016/j.envsci.2023.06.014
Eteh, D. R., Adediran, A., & Udoh, J. (2025). Assessing the impact of climate change on flood patterns in downstream Nigeria using machine-learning and geospatial techniques. Discover Geoscience, 3, Article 76. https://doi.org/10.1007/s44288-025-00178-7
Garba, S. I., Ebmeier, S. K., Bastin, J.-F., Mollicone, D., & Holden, J. (2025). Wetland fragmentation associated with large populations across Africa. Nature Communications, 16(1). https://doi.org/10.1038/s41467-025-59373-2
Hockaday, A. C., et al. (2024). Freshwater wetlands for flood control: How manipulating hydrology affects performance. Environmental Research Communications, 6(2), 025011. https://doi.org/10.1088/2515-7620/ad20b9
Idiege, D. A., Akise, O. G., Amadi, D. C. A., & Uruku, N. M. (2017). Effect of urbanization on wetland and biodiversity in the mangrove forest of Lagos State, Nigeria. FUW Trends in Science & Technology Journal, 2(2), 991–995. www.ftstjournal.com
Komolafe, A. A., Adegboyega, S. A., & Akinluyi, F. O. (2020). Modelling flood-prone areas and vulnerability of the Ogun River Basin using GIS and multicriteria analysis. Hydrological Sciences Journal, 65(8), 1359–1372. https://doi.org/10.1080/02626667.2020.1764960
Manandhar, B., Cui, S., Wang, L., & Shrestha, S. (2023). Urban flood hazard assessment and management: A global review. Land, 12(3), 627. https://doi.org/10.3390/land12030627
Maryland Department of the Environment. (2023). Wetland disturbance and hydrological impact. https://mde.maryland.gov/programs/water/wetlandsandwaterways/aboutwetlands/pages/disturbance.aspx
Moon, H., Kim, J. S., Chen, J., Yoon, S., & Moon, Y. (2024). Enhancing urban flood resilience through a hybrid approach combining a comprehensive flood prevention plan (CFPP) and green infrastructure (GI). SSRN. https://doi.org/10.2139/ssrn.4637795
Mumuni, A. S., Mensah, H., Asamoah, S., & Simpeh, E. K. (2025). A systematic review on the causes and effects of urbanization on wetlands in Sub-Saharan Africa. Urbanization, Sustainability and Society, 2(1), 153-177.
Olabode, A., Adeleke, E., & Samuel, O. (2025). Extreme climate conditions and loss of faunal biodiversity in the rainforest zone of Abeokuta, Ogun State, Nigeria. Sustainability and Biodiversity Conservation, 4(2), 1-22.
Oscar, A. L., Ikezam, W., & Brown, I. (2022). Exploring the nexus between urban growth trend and wetland loss in port harcourt municipality. Int J Hydro, 6(4), 102-106.
Nepal, D., Roth, K., & Alexander, L. (2024). Evaluation of wetland area effects on hydrology using SWAT modelling. Hydrological Processes, 38(7), e14921. https://doi.org/10.1002/hyp.14921
Popoola, L. (1990). Economics of alley cropping of marginal land in Ogun State, Nigeria (Doctoral dissertation, University of Ibadan, Nigeria). Department of Forest Resources Management.
PopulationStat. (2026). Abeokuta, Nigeria population. https://populationstat.com/nigeria/abeokuta
Prasanya, J., Kanmani, S., & Kumar, P. S. (2024). A review of the wetland’s restoration mechanisms and its economic and social benefits. Water Practice & Technology, 19(11). https://doi.org/10.2166/wpt.2024.241
Soaga, J. A., Shotuyo, A. L. A., Oduntan, O. O., & Fatoki, J. G. (2014). Economic analysis of bushmeat trade in Abeokuta, Ogun State. Journal of Agricultural Science and Environment, 14, 97–108. © FUNAAB.
Tonade, E. (2023). Assessment and mapping of the distribution of food and medicinal tree species in abeokuta metropolis, Ogun State, Nigeria. Ethiopian Journal of Environmental Studies & Management, 16(4).
United Nations Environment Programme (UNEP). (2025). Wetland fragmentation in Africa: Drivers, patterns, and hydrological implications. Nairobi: UNEP Publications. https://www.unep.org/resources
Wu, Y., Sun, J., Hu, B., Zhang, G., & Rousseau, A. N. (2023). Wetland-based solutions against extreme flood and severe drought: Efficiency evaluation of risk mitigation. Climate Risk Management, 40, 100505. https://doi.org/10.1016/j.crm.2023.100505
Yang, B., Yuan, X., Tang, F., & Liu, D. (2024). Small wetlands: Critical to flood management. Science, 386(6724), 859–859. https://doi.org/10.1126/science.ads2055
Zeng, X., Zhang, H., Zhou, B., Liang, X., Cui, L., Li, H., Qu, Y., & Luo, C. (2024). Hydrological dynamics and its impact on wetland ecological functions in the Sanjiang Plain, China. Ecological Indicators, 169(1), 112878. https://doi.org/10.1016/j.ecolind.2024.112878.
