Analyses des sous-systèmes d’inondation dans la Commune Urbaine d’Antananarivo, Partie Centrale Madagascar

RANAIVOSON Heriniaina Angelo, RATRIMO Voahangy, RAZAFIMBELO Marie Rachel

Abstract


Flooding in the Urban Municipality of Antananarivo (CUA) results from complex interactions between precipitation, rapid urbanization, lithological characteristics, and drainage infrastructure. This study aims to analyze these sub-systems. The adopted methodology follows a multi-dimensional and integrated approach, combining remote sensing, hydrological analysis, geotechnical assessments, and hydraulic modeling. The Enhanced Normalized Difference Impervious Surface Index (ENDISI) and the Modified Normalized Difference Water Index (MNDWI) were used to quantify and map impervious surface expansion and stormwater accumulation areas, respectively, using Sentinel-2 and Landsat imagery processed with machine learning algorithms (Digital Earth Africa) in Python. The geotechnical study of soil samples from boreholes distributed across different zones revealed that superficial formations are predominantly clayey and silty, with an average thickness of 2 to 3 meters, limiting infiltration and increasing surface runoff. Based on the imperviousness index, the average runoff coefficient was estimated at 0.442, which underestimates actual flow rates. Hydraulic analysis revealed runoff values between 0.5 and 0.7, mainly due to drainage network saturation and sediment accumulation in collectors (evacuation channels, retention basins, etc.). Despite this, theoretical drainage capacities of major infrastructures should be sufficient to handle moderate rainfall events (30 m³/s for the Andriantany Canal, 20 m³/s for the C3 Canal, and 15 m³/s for the GR Canal).

Keywords


urban flooding; runoff; drainage network; urbanization; lithology; precipitation; system

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DOI: http://dx.doi.org/10.52155/ijpsat.v49.2.7037

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