Monitoring by satellite imagery of the dynamics of the banks of the Logone, between the Maga reservoir and Lake Tchad

Abstract

Endorheic watercourse which contributes more than 90% to water supplies of Lake Chad and natural border between Cameroon and Chad, the Logone-Chari system has often been studied in terms of variability of the hydrological regime and of the risks associated with floods in the neighboring plain. The evolution of the riverbanks, which involves important socio-economic and strategic stakes, has until now been little documented. The objective of this study is to contribute to the assessment and characterization of the dynamics of the eastern banks, part of the Cameroonian territory. The methodology combines discretization of the active band on multi-chronic Landsat images, field observations and surveys and analysis of data in a GIS. The results indicate that advances and setbacks follow one another over time, due to variations in hydrological parameters and the diversity of the alluvial material. In 30 years, variations range between -200 (decline of the banks) and 171 meters (fattening of the banks) in the section of the Chari in the north of Kousseri, against -121 and 125 meters in the section of Logone in the South. For the same period, there is a territorial gain of almost 853.32 ha, representing the differential between fattening (1,397.1 ha) and decline (543.78 ha). However, this evolution is not linear. It is done in jerks, during the seasonal cycles, following processes interrupted by negative feedbacks. The sinuous or braided areas are the most exposed. Although shoreline erosion is essential to dissipate the energy of water, protective measures should be considered where the safety of property and persons is threatened. The integrated management of the Logone plain should take into account the necessity to preserve a minimal space of freedom around the banks, in order to allow the water to retain its potential for lateral and longitudinal adjustment.