A comprehensive multi-year field campaign, the North Passage Channel Measurements (NP-ChaM), was designed and executed to enhance our understanding of the hydrodynamics and sediment dynamics in the North Passage, the primary navigation channel of the Changjiang Estuary, China. The NP-ChaM campaign comprised eight observational sites and spanned 50 d, distributed over 4 years, including two dry seasons and two wet seasons. A series of tripod systems, equipped with multiple instruments, were deployed on the seabed to monitor near-bed physical processes reliably.

The resulting dataset comprises the following: (i) fluid motions, encompassing pressure, flow velocity and direction (at the bottom and throughout the entire water column), and wave patterns; (ii) near-bed environmental conditions, including temperature, salinity, and turbidity (at the bottom and across a near-bed 1-meter range); (iii) supplementary meteorological data sourced from credible providers; and (iv) preliminary results from post-processing, showcasing the practical application of the data, such as lateral flows and turbulent kinetic energy characterizations.

This dataset is especially valuable due to its extensive temporal and spatial coverage, as well as the high concentrations characterizing many of the observations (from several grams per liter to tens of grams per liter). Conducted annually from 2015 to 2018, the NP-ChaM campaign facilitated detailed observations of seasonal variations in environmental conditions and associated physical processes. The eight observational sites, positioned on either side of the deep channel, enable quantifications of channel–shoal exchanges, along-channel flow dynamics, and saltwater intrusion. This dataset is suitable for advancing our understanding of along-channel and cross-channel dynamics in a channel–shoal system and for calibrating numerical models. The dataset has undergone rigorous quality control to ensure reliability and accuracy.@en

Lateral flow significantly contributes to the near-bottom mass transport of salinity in a channel-shoal system. In this study, an integrated tripod system was deployed in the transition zone of a channel-shoal system of the Changjiang Estuary (CE), China, to observe the near-bottom physics with high temporal/spatial resolution, particularly focusing on the lateral-flow-induced mass transport. These in situ observations revealed a small-scale salinity fluctuation around low water slack during moderate and spring tidal conditions. A simultaneous strong lateral current was also observed, which was responsible for this small-scale fluctuation. A high-resolution unstructured-grid Finite-Volume Community Ocean Model has been applied for the CE to better understand the mechanism of this lateral flow and its impact on salinity transport. The model results indicate that a significant southward near-bed shoal-to-channel current is generated by the salinity-driven baroclinic pressure gradient. This lateral current affects the salinity transport pattern and the residual current in the cross-channel direction. Cross-channel residual current shows a two-layer structure in the vertical, especially in the intermediate tide when the lateral flow notably occurred. Both observation and model results indicate that near-bottom residual transport of water moved consistently southward (shoal to channel). Mechanisms for this intratidal salinity variation and its implications can be extended to other estuaries with similar channel-shoal features.

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