On the mechanisms controlling near-coast circulation in the southern Colombian Pacific at tidal, seasonal, and interannual time scales

Abstract

This research analyzed the near-coastal circulation along 300 km in the southern Colombian Pacific, a meso-tidal region formed by Tumaco Bay and the Mira River Delta. The interaction between tidal dynamics and the Mira River plume stratification and dispersion is not well known. Moreover, the combined effects of tide and density gradients on the circulation patterns in Tumaco Bay have rarely been studied. The region was investigated using the Delft3D hydrodynamic model, calibrated and validated using field data. The results show that Tumaco Bay is ebb-dominated, and the tide and bottom shape are the dominant forces in the circulation patterns inside the bay. The weak horizontal density gradient induced by Mira River did not show a substantial effect on the circulation of the bay. Near the mouth of the Mira Delta, the water column was predominantly partially mixed, but stratification changed within the tidal cycle, presenting tidal straining along the minor axis of the plume. This may generate strongly stratified conditions in the water column during flood periods. Although tidal straining is very common along the major axis of tide-dominated estuaries, it is not as common in coastal river plumes. The analyzed system provides additional evidence about this phenomenon in a tropical delta. • Hydrodynamics of Mira River and Tumaco Bay as an integrated system is studied for the first time using 3D modelling. • Tumaco Bay is ebb-dominated, and the bottom shape dominates the circulation patterns. • Tidal straining is observed along the minor axis of the Mira River plume. • Cross-shore tidal straining in the plume of tropical rivers has been barely reported previously.