Channel-scale tidal currents from vessel-mounted ADCP in three navigation channels of the Colombian Pacific: phase-dependent vertical structure and its dissociation from stratification

Tidal currents in port access channels are usually characterized from single bottom-mounted moorings, yet in bathymetrically heterogeneous channels the vertical structure and asymmetry of the flow can vary along the channel, and vessel-mounted surveys remain underused as a channel-scale alternative. Here we characterize the tidal currents of the navigation channels of Tumaco, Buenaventura, and Málaga bays (Colombian Pacific) from vessel-mounted ADCP surveys carried out between 2020 and 2024 (1.48 million profiles, 18.9 million binned observations), CTD profiles with concurrent CTD–ADCP pairs, and a month-long moored record in the Tumaco channel; all vertical-structure metrics are computed in a bottom-following normalized coordinate that avoids the composition bias arising when profiles of different total depth are pooled into absolute-depth bins. The median profile is surface-intensified in the three channels and in both tidal phases, but the phase contrast differs sharply: the lower-third to upper-third speed ratio is phase-independent in the Tumaco channel (Rflood/Rebb = 1.00) and markedly phase-dependent in Buenaventura (1.38) and Málaga (1.45), with ebb shear exceeding flood shear by a factor of 1.77 in both. The bulk velocity distributions of the three channels are ebb-dominant (median ebb-to-flood ratios of 1.18, 1.10, and 1.23), robust to the diurnal sampling imbalance of the surveys. The Buenaventura channel is partially mixed (ηs = 0.328, φ = 61 J m-3, median gradient Richardson number 1.7) whereas the Málaga and Tumaco channels are well mixed (ηs = 0.098 and 0.011), and the freshwater flow ratio computed from measured water-surface areas, tidal prisms, and modelled river discharges reproduces that ordering (0.0052, 0.0187, and 0.0063). The moored record yields a description of its channel qualitatively consistent with the survey-based one. Two channels with opposite mixing regimes therefore display nearly identical vertical phase asymmetry, so stratification alone cannot account for the contrast, pointing to an additional contribution from channel geometry and friction; the balance between freshwater delivery and tidal exchange is instead the plausible driver of the stratification contrast itself. A conclusive test of single-point representativeness would require concurrent moored and vessel observations, which these records do not provide.