Urban Erosion in the City of Mataméye: Vulnerability, Damages, and Control Strategies
Abstract
Urban gully erosion represents a growing environmental hazard in rapidly expanding Sahelian cities, where intense rainfall events interact with fragile soil conditions, topography, and unplanned urban development. This study assesses the vulnerability of Mataméye (Niger) to gully erosion resulting from the combined influence of climatic, physical, and anthropogenic factors, and evaluates its environmental and socio-economic impacts while critically examining existing local management strategies. The methodology integrates field observations, morphometric measurements of gullies, spatial analyses, and hydrometeorological data between 1998 and 2021. Field investigations identified seven active gullies concentrated in the most vulnerable urban neighborhoods, with lengths ranging from 17 to 120 m and widths exceeding 10 m. In 2019, four major occurred with an estimated total soil loss of 3,540.7 m³, whereas the number of gullies increased from four to seven, with volumes ranging from 60 to 1,800 m³, indicating rapid expansion driven by repeated extreme rainfall events, which produced simultaneous formation of three distinct gully types within the same area, namely the R5 gully (characterized by aggressive and intense erosion), the R6 channel (representing passive gully erosion), and the R7 gully (defined by aggressive vertical incision). This variability highlights the heterogeneity of soil erodibility within the study area. The geometric properties of the measured gully channels were mathematically estimated based on an idealized parabolic gully geometry. The predictions consistently underestimated the observed values, indicating scale bias. The Standardized Precipitation Index (SPI) indicated that the 12-year period preceding the measurements was characterized by extreme drought conditions, followed by the last five years of excessive rainfalls, being closely associated with gully erosion processes and the lack of vegetation cover. The rainfall events converted the watershed to 5th order stream gully network.The Modified Fournier Index (MFI) ranges from 158.6 to 167, indicating very high to extreme erosivity, while the erosivity factor (R) varies between 8,500 and 9,500 MJ mm ha⁻¹ h⁻¹ yr⁻¹, promoting runoff concentration and the rapid development of gullies. The results indicate that erosion intensity is strongly amplified by anthropogenic factors, notably unpaved roads, lack of drainage infrastructure, and progressive occupation of natural flow paths. Local mitigation measures (infilling and the use of sandbags) remain temporary and largely ineffective, highlighting the absence of an integrated approach and the urgent need for coordinated watershed-scale strategies.
Keywords
Mataméye City, urban erosion, gully erosion, management strategies, vulnerability
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