Studies on the variability in ocean wave climate provide engineers and policy makers with information to plan, develop, and control coastal and offshore activities. Ocean waves bear climatic imprints through which the global climate system can be better understood. Using the recently updated ERA5 dataset, this study evaluated the spatiotemporal distribution and variability in significant wave height (SWH) in the Eastern Tropical Atlantic (ETA). The short-term trends and rates of change were obtained using the Mann–Kendall trend test and the Theil–Sen slope estimator, respectively, and decadal trends were assessed using wavelet transformation. Significant, positive monthly and yearly trends and a prevailing decadal trend were observed across the domain. Observed trends suggest that stronger waves are getting closer to the coast and are modulated by the Southern and Northern Atlantic mid-latitude storm fields. These observations have implications for the increasing coastal erosion rates on the eastern coast of the Tropical Atlantic.

Debris flows tend to erode sediment from or deposit sediment on the bed, which changes their volume and, thus, in turn, affects their rheological properties. However, previous modeling studies on debris flows mostly ignore sediment erosion/deposition. Here, three models are presented: a debris model without bed deformation, which is similar to traditional models in that it does not consider sediment erosion/deposition but uses the Herschel–Bulkley formulation to describe the non-Newtonian nature; a debris model with bed deformation, which is better improved than the traditional model in that it considers sediment erosion/deposition; and a turbidity current model, which is further simplified from the debris model with bed deformation by ignoring the non-Newtonian nature. These models, formulated in the same modeling framework, are solved by a shock-capturing finite volume method. These models were firstly validated against three laboratory experiments, which indicated that the debris models with and without bed deformation with reasonably well-specified parameters can give satisfactory agreements with the measurements, whereas the turbidity current model overestimated the experimental result due to its lack of yield stress and dynamic viscosity. Moreover, a hypothetical field application was used to explain the difference between a turbidity current and debris flows with and without bed deformation. It was shown that debris flows and turbidity currents are capable of impacting the bed significantly. However, turbidity currents have thinner tails, less shear stress, and form horizontal deposits on the bed, while debris flows have a thicker tail, high shear stress, and form vertical deposits on the bed. Finally, sensitivity analyses were carried out to study the impact of sediment size, bed slope, concentration, and porosity on the deformation of the bed after debris flow where they all showed a positive correlation.

The deposits of subaqueous dunes are a fundamental building block of verticallystacked alluvium in river to tidal settings and are responsible for producing the largest component of frictional resistance to flow via form roughness. Thus, dunes have attracted considerable attention amongst researchers for decades since they are found in virtually all environments (headland rivers to abyssal plains) and grain sizes (coarse silts to gravels) along the source-to-sink sediment transport pathway. Of these environments, dunes produced by rivers (unidirectional flows) are the most widely studied with respect to their morphologic dynamics and their scaling of height and wavelength to flow depth, whilst our understanding of these same characteristics within bidirectional (tidal) and combined-flow (currents with a unidirectional and oscillatory component) is quite limited. This knowledge gap is addressed herein by evaluating a set of multibeam echo sounding (MBES) surveys of the main channel of the Lower Columbia River (LCR), WA/OR, USA, within its downstream most hydraulic regime, which is dominated by bidirectional tidal-flows and/or combined-flows consisting of a tidal component and a shorter period (oceanic to intrabasinally derived) wind-wave component. Specifically, variations in dune geometric parameters (e.g., height, wavelength, roundness, symmetry, dimensionality, stoss- and lee- angle, and ratio of stoss- to lee- angles) and scaling of height and wavelength to flow depth are systematically quantified within the main channel (0- 32m depth) and are linked to depth transitions in formative current styles. These findings provide insight into the morphologic differences (i.e., form roughness) between dunes generated within non-uniform and unsteady flow conditions and those from more uniform and steady flows, whilst further adding to our understanding of the scaling of height and wavelength to depth within such dynamic flows. Preliminary results show that dunes remain asymmetric at all depths and possess lee-angles ≤ 15°, their roundness is maximized at both the shallowest and deepest depths, and present river-tidal scaling relations overpredict their heights and wavelengths, which suggests that new relations are needed to better understand the dunes of tidal and combined-flow settings.