Based on 2022 and 2023 hydrometric data and
satellite images (Sentinel 2022, SPOT 2010), this study aims to present the
Nokoué Lake and its channels’ re-cent hydromorphological characteristics. Integrating
flow, tributary morphology, and topography data determined specific power
values along the axes studied. The values obtained range from 2.69 to 12.92
W/m2 for Ouémé River and 2.46 to 10.99 W/m2 for S？ River. The
resulting water erosion on banks and bottoms is of linear, areolar, or gully
and claw types. Lake bathymetry varies from -0.5 to -2.6 m (low flow period)
and -1 to -4 m; in the Ouémé, S？, and Totchè rivers, it varies from -5 m to -7
m, reaching -10 m at the Cotonou channel entrance (flood period). Bathymetric
profiles reveal varied “U”, “V” and “Intermediate” bottom morphologies,
influenced by erosion/sedimentation processes and human activities. The flow
facies identified are lentic in the northern tributaries and lotic in the
Cotonou and Totchè canals. Spatial analysis identified nine (09) thematic classes.
In 2022, the surface area of the water body has increased from 274 km2 at low water
to 280 km2 at high water, whereas in 2010 (a recent year of exceptional flooding),
the surface area was 270 km2 at low water and 277 km2 at high water. Significant
changes in land use are observed between 2010 and 2022. The floodplain area decreased
slightly, from 421 km2 in 2010 (year of exceptional flooding) to 419 km2 in 2022.
The evolution of land use shows a progressive expansion of the urban environment
to the detriment of the natural environment. In the medium to long term, this trend
could threaten the hydromorphological balance and even the existence of this important
lagoon ecosystem.
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