Evaluation of the factors contributing to the flooding of the city of n'djamena, case of the 7th district: gis and remote sensing approach

The management of flooding in the city of N'Djamena in general and that of the 7thdistrict, using GIS software and remote sensing, requires a multi-criteria analysis based on four main factors which are rainfall (rainwater), soil permeability (pedology), relief (topography), slope and land use. The study carried out on these factors shows that flooding in the 7th arrondissement is exclusively of a pluvial nature with an annual rainfall total reaching 200 to 300 mm. The topography factor is unevenly distributed and therefore the altitudes oscillate from 295 to 304 m with an average of 294 m. The slope is weak and is in the order of 0.10 to 2.02% with an average of 1.6% and is oriented towards the north-west instead of the south of the commune to flow into the Chari River. The results observed according to the altitudes of the 7th arrondissement reveal that the bank of the Chari River is higher than the interior of the commune. The other determining factor that causes flooding in the commune is land use with a high level of urbanization that has increased from 13% (926.45 ha) to 77.5% (5471.61) in 2020, i.e., an increase of 64.5%. The exponential growth of the population and the anarchic urbanization leads to the occupation of lowlands and water runoff paths. The pedological factor is to be pointed out because the commune is built on a soil constituted of hydromorphic soils (clay-sandstone and black clay), which have a low permeability that does not favor the infiltration of water towards the water table and generates flooding.