Exceptional minor rainy season inducing flooding of the UNESCO World Heritage site of Grand-Bassam (Côte d'Ivoire)

Abstract

Abstract This work focuses on the time and space variability of the Comoé river’s flow in relation with the flooding in 2019 of the UNESCO World Heritage city of Grand Bassam (GB) in Côte d’Ivoire (CI). The rainfall, sea level, ocean swell and the Comoé river flow data have been used to conduct this work. This study showed that the Comoé river flow is higher in September-October. The maximum flow depends of the annual precipitation accumulated from the North to the South. During the rainy period, the flow at GB increases till to reach an absolute maximum during the minor rainy season in October. The event of October 2019 is an exceptional event due to strong minor rainy season compared to the others years. Besides this year, the minor rainy season was stronger than the major one. To solve the problem of flooding, opening the channel to rebuild the estuary linking the Comoé river to the sea appears as a solution. But precaution should be taken because of salinification and, during September-October strong swells and highest sea level are observed along the coast of GB. Besides, these strong swells are an opportunity for removing sediments from the mouth of the estuary one month before the critical month of October. Meanwhile using the water of the Comoé river for irrigation is an alternative solution. Observing the annual precipitation of a given year until the end of September could provide some information about the occurrence of flooding this year.