Assessing sediment connectivity and the beneficial use of dredged material as a nature-based solution in the Mallorquín coastal wetland

This study evaluates the hydro-sedimentological dynamics of the Mallorquín Wetland, a coastal wetland in northern Colombia affected by erosion, hydraulic disconnection, and shoreline instability. The aim was to assess sediment connectivity between the Magdalena River mouth and the Mallorquín littoral cell, and to test whether alternative placement locations for maintenance-dredged material could reconnect that sediment with the active coastal system. The methodology combined field measurements, multitemporal shoreline analysis, and Delft3D hydrodynamic–morphodynamic modelling, including three dredged-material placement configurations. Results show severe erosion, with an average shoreline retreat rate of 16.29 m yr⁻¹ between 2015 and 2025 and a maximum cumulative retreat of 239.18 m in the most affected sectors, while the formation and growth of a littoral spit since 2019 have modified coastal hydrodynamics, attenuated wave energy, and promoted local sediment accumulation. This morphological change coincides with the documented dredging record, but it is not attributed causally to dredging, because the relative contribution of each sediment source was not quantified. The placement experiments indicate that the redistribution of the material depends strongly on the placement location, and that sites within the hydrodynamically active zone west of Bocas de Ceniza retain a connection with the littoral transport system that the present offshore disposal area does not. Under the current operation the morphological benefit is therefore incidental; converting it into an intentional sediment-based nature-based solution requires placement location and depth to be treated as design variables, supported by sediment-compatibility analysis, source-partitioned sediment budgets, and repeated topo-bathymetric monitoring.