Local scour around submerged square piles is very common in offshore and coastal engineering and can result in pile failure. In the study reported here, because the flow intensity (the ratio of the depth-averaged velocity to the threshold velocity for sediment particle motion) is one of the most important factors affecting the maximum scour depth in local scour, its effects on local scour around a submerged square pile were studied under clear-water scour conditions. A series of experimental tests with flow intensity in the range of 0.39–1.04 was conducted in steady current, and the flow intensity was classified as weak, transitional, or high according to the pattern of the scour hole upstream of the pile and the sand dunes downstream. The characteristics of sediment scour and deposition for temporal sediment bed elevation along a pile side and the temporal maximum scour depth were found to vary greatly among the three flow intensity conditions. An exponential function, which fitted the experimental data well, was used to fit how the maximum scour depth evolved, and the coefficients of timescale and scour depth proportion in the initial and development scouring stages were obtained at different values of the flow intensity.

Foundation scour is the erosion of sediments around pile foundations by wave and current in offshore wind energy. This phenomenon destabilizes foundations and poses a threat to pile safety. Therefore, scour protection becomes a crucial challenge in offshore wind projects. This paper reviews and synthesizes recent publications and patented technologies related to scour protection. Considering the primary engineering concerns, the paper proposes design principles for effective scour protection schemes to standardize evaluation criteria. These principles prioritize efficacy, independence, and cost-efficiency, enabling the analysis of scour protection scheme applicability. In addition, this paper summarizes and describes common protection schemes in the literature. The effectiveness of their protection is analyzed and summarized, and their economic and performance independence is evaluated. This paper categorizes flow-altering scour protection schemes found in the literature. Based on a comprehensive understanding of the mechanisms and engineering requirements of scour protection, the paper proposes a focus on determining the erosion reduction rate curve ($Ep-U/U_c$ curve) as a key criterion for evaluating the effectiveness of protection schemes under varying flow velocities and the erosion reduction rate of scour protection schemes under extreme conditions. The study highlights the necessity of establishing a comprehensive design evaluation methodology, which is crucial for addressing the significant challenges related to scour encountered in offshore wind power projects.

Ocean surface waves exposed to extreme weather conditions, such as tropical cyclones (TCs), are critical environmental forces acting on the coastal and offshore structures. Therefore, it is necessary to investigate the applicability of the third-generation wave model WAVEWATCH III for simulated waves in the China Seas, where TCs are frequent. This study compares different packages of wind input and wave dissipation (ST1, ST2, ST3, ST4, and ST6) during five TCs with significant wave heights (SWHs) and wave spectra in the Yellow Sea, East China Sea, and South China Sea. The results show that ST6 performs best in the simulation of the SWHs, presenting the only positive deviation, with a normalized mean bias of 1.76%. ST2 systematically underestimates the large SWHs due to insufficient wind input from the spectra. However, the suitability of the packages varies in different sea conditions. ST6 is preferred in extreme wave simulations during TCs, ST4 performs best under the weak influence of TCs, and ST2 has the best performance in calm sea conditions.

The dynamic coastal environment is characterized by complex and variable interactions, often reflected in shoreline changes. This study analyzes shoreline changes in the estuarine area of Rizhao from 1985 to 2020 based on remote sensing images from Landsat 5 and Landsat 8. The largest shoreline changes were attributed to large-scale harbor construction, while relatively natural shorelines showed minor fluctuation. Due to the complex dynamics at the estuaries, shorelines on both sides of the estuaries were extracted and analyzed using the Digital Shoreline Analysis System (DSAS) in ArcGIS. Results indicate the southern shoreline experienced minor fluctuations, with a Linear Regression Rate (LRR) ranging from -2.27 m/y to 1.87 m/y. In contrast, the northern shoreline exhibited more significant fluctuations, with an LRR ranging from -7.62 m/y to 13.54 m/y, likely due to more intense dynamics near the cape and Muguan Island. Intra-annual seasonal shoreline was found to be more pronounced than inter-annual variations. Correlation analysis between the Net Shoreline Movement (NSM) and dynamic factor intensities across seasons revealed the highest correlation with runoff volume. Typhoon passages were observed to cause shoreline erosion, while sediment-laden runoff partially mitigated this erosion.

Estuarine sediment transport is driven by the combined action of a multitude of influencing factors, including astronomical tides, waves dynamics, and river discharges. This study focuses on the effects of wave forces on sediment transport patterns in micro-tidal estuaries near Wanbao Beach, China. Numerical simulations are carried out using Delft3D. Modeling scenarios are configured using different wave characteristics, spanning from typical waves to those with a return period of 50 years. Results show that waves have a positive effect on landward sediment transport, resulting a larger active range of sediment. By comparing the spatial geomorphic variations under varying wave conditions, we find that modifications in significant wave height (Hs) primarily impact the position of erosion and deposition zones, whereas alterations in spectral peak period (Tp) predominantly influence the magnitude of these changes. The finding is further demonstrated by a comparison of residual currents under different wave intensities. Analysis of sediment transport rates in different transects indicates that the sediment transport rate is highest at the mouth transects and lowest at the alongshore transects. Moreover, variations in sediment transport rates exhibit distinctive patterns between the two outlet transects, even when subjected to identical wave conditions. The disparities are attributed to differences in runoff and the topographical features in proximity to the estuaries. Additionally, we find the sediment transport rate becomes insensitive to the variations in Hs when Hs is larger than a threshold value. The threshold decreases with increasing Tp.