Episodic peaks in fluvial sediment flux as drivers of tropical delta morphodynamics[

According to their morphology, the deltas located at the eastern margin of the Gulf of Urabá, including the Mulatos River Delta, seem to be wave-dominated; however, after high or extreme river sediment fluxes shift to temporary river-dominated morphologies. Those events generate instantaneous flux accumulations of enough material at a sufficient rate to overcome the net alongshore sediment transport capacity, which in the long term seems to result in the analyzed deltas progradation.

We analyze the river deltas of the Urabá coast in the southern Caribbean Coast of Colombia (Northwestern South America), to elucidate the role of fluvial pulsatility (i.e., episodic peaks in fluvial sediment flux) in delta morphodynamics, we explored sediment flux balances by extending the classical long-term approach to a daily approach.

To calculate sediment flux balances, we retrieve hydrologic and wave data. Discharge and fluvial sediment flux toward the deltas apex was obtained from IDEAM gauging stations. For all the rivers, we used the gauges located closer to the coast. Using WAVEWATCH III, we retrieve the wave climate record for the computational nodes closer to the deltas of interest, located outside and inside of the Gulf.

There is a marked influence of highly discharge events in the east Gulf of Urabá rivers hydrology, which despite their geographical location and the monomodal precipitation, can even show erratic extreme high discharges of up to two orders of magnitude respect to the mean discharge and even four with respect to the minimum discharge values.

The observed morphology from Planet's recent satellite imagery (2016 – 2025) shows that, after high flood events, the deltas morphology could be altered into temporary morphologies that enhance alongshore sediment transport seeking to recover morphodynamic equilibrium, increasing the flanks angles and even forming temporary additional mouths.

The rivers of NW South America along the Gulf of Urabá eastern margin evidence monsoonal variability as supported by discharge variability metrics, which decisively influence delta morphodynamics.