This study investigates the hydro-sedimentary and geochemical functioning of the Agnéby River, a tropical coastal basin in southern Côte d’Ivoire, based on the combined analysis of suspended sediments (TSS) and dissolved constituents (TDS) during the 2020 hydrological year. TSS concentrations and fluxes exhibit a strong dependence on river discharge, with sediment export largely controlled by flood events. More than 50% of the annual suspended sediment load is transferred within a short period, reflecting an impulsive transport regime typical of medium-sized tropical catchments. Water chemistry is dominated by bicarbonates and alkaline-earth cations, indicating a geochemical signature primarily governed by chemical weathering of basement rocks under humid tropical conditions. Seasonal variations in TDS reveal dilution effects during high-flow periods and enhanced water–rock interactions during low-flow conditions. The TSS/TDS ratios, ranging from 0.08 to 0.30, highlight a transition from weathering-dominated conditions during baseflow to a mixed regime increasingly influenced by mechanical erosion during floods. Comparison with larger Ivorian river basins, such as the Bandama and Comoé rivers, shows that the Agnéby River differs markedly by its rapid hydrological response and limited sediment storage capacity, whereas larger systems exhibit more progressive seasonal sediment transfer. These findings emphasize the significant contribution of small and medium tropical coastal rivers to sediment and solute fluxes toward lagoonal and coastal environments, with important implications for coastal sediment budgets and the sustainability of the blue economy.