Hydrodynamic functioning of Nokoué Lake in the Oueme Delta in Benin

Rita Houngue, Abel Afouda

Friday 3 july 2015

14:15 - 14:30h at Africa (level 0)

Themes: (T) Managing deltas, (ST) Adaptive delta management

Parallel session: 16K. Managing deltas - Adaptive delta management

Urban flooding is a prominent issue, not only at a local scale but even more at the global level. In 2008, over half of the world's population was living in urban conglomerations, many of which are situated at locations where large river systems meet the ocean, called Deltas. Hence these megacities in delta areas are quite naturally exposed to flood events coming from either direction: inland or ocean (Talukdar, 2006). This research work which is about the hydrodynamic functioning of Nokoué Lake in the Oueme Delta in Benin in the problematic of the flood at Cotonou has been dedicated to the lake’s hydrodynamic according to the contributions of soft water caused by the Ouémé and Sô rivers ; the contributions of rain and sea water considering its contact with the Atlantic Ocean. In the same way it examined the influence of the anthrophic activities and climate change on the lake surface. We describe the hydrodynamic functioning using Saint Venant equations since we are in shallow water. Then, because of lack of data especially bathymetry, a deterministic approach has been used according to the periodicity of the water levels variations in the lake due to the tidal pressure. This approach allows us to write the sinusoidal equations of the lake dynamics during the low and the high waters. At the end of this research, we keep that the daily amplitude maximum is 0.2 m, the monthly one is 0.60 m and the yearly one is 1.5m. These sinusoidal equations are: - In low water: (m) - In rise water: (m) With , and Where is the water level in (m), _ is is the phase in (rad), is the time in (h), and are some variables in (m). These results will be verified later by hydrodynamic modeling using Mike 21 software.