Insights into Hydrodynamic Controls on Sediment Grain Size Variability in Tropical Tidal Flats of Calabar and Great Kwa Rivers, Nigeria

Abstract

This study investigates the hydrodynamic influences shaping sediment grain size distributions in tidal flats along the Calabar and Great Kwa Rivers in Southeast Nigeria. Utilizing extensive tidal current velocity measurements and sediment grain size analyses from supratidal, intertidal, and subtidal zones, we reveal distinct patterns of sediment sorting and transport driven by ebb-dominant tidal flows coupled with fluvial inputs. Calabar River flats showed predominantly medium to coarse sediments in Adiabo, and very fine to silty sediments in Marina (Iyata) tidal flat. In the Great Kwa River, extensive muddy sands dominated the Idundu flat, while the Atu flat showed medium to coarse sands. Results demonstrate that sediment grain size variability is strongly governed by spatial and temporal fluctuations in flow velocity and energy regimes, resulting in characteristic depositional facies that differ significantly between the two river systems. These findings advance the understanding of sedimentological processes in tropical tidal flats and provide a baseline for predicting responses to environmental change in similar systems.