Hydrological control and distributed rainfall-runoff modeling of flood inflows from the Bt River to the Aghien Lagoon (Cte dIvoire) using the ATHYS software

Quantifying hydrological contributions from tributaries to lagoon systems represents a major challenge for understanding the functioning of coastal hydrosystems and for the sustainable management of water resources, particularly in tropical environments exposed to strong climatic and anthropogenic pressures.This study aims to assess flood contributions from the Bété River to Lagune Aghien, a strategic potential resource for the drinking water supply of Abidjan, through distributed rainfall-runoff modeling using the ATHYS model.The methodological approach relies on hydrometeorological time series, spatial data derived from a digital elevation model, and event-based modeling based on the SCS-Lag and Route coupling implemented in the MERCEDES module.Model performance was evaluated using the Nash-Sutcliffe efficiency, Root Mean Squared Error (RMSE), Mean Absolute Error (MAE), and Controlled Recognized Environmental Condition (CREC) criteria.Results indicate satisfactory calibration performance, with Nash coefficients ranging from 0.77 to 0.93 in 2016 and reaching 0.95 in 2019, while validation produced acceptable performance (Nash = 0.68).Analysis of the optimized parameters highlights a high catchment storage capacity (S = 500 to 600 mm), a limited contribution of delayed flow (w = 0.04 to 0.52), and transfer velocities ranging from 0.54 to 2.1 ms⁻¹.Simulated volumes, estimated at 2.91 ×10⁶ m³ in 2016 and 4.46 ×10⁶ m³ in 2019 (subject to confirmation after verification of exponents), confirm a significant hydrological contribution of the Bété River to the water balance of Aghien Lagoon.This study highlights the determining role of soil storage and transfer mechanisms in controlling the catchment hydrological response and provides a scientific basis for future developments integrating hydrology-hydrodynamics-salinity coupling for the integrated management of Aghien Lagoon.