The impact of tidal oscillations on groundwater in coastal reclamation land demonstrates the complex hydrodynamic interaction between seawater and coastal hydrological aquifer systems. The tidal action not only affects the temporal variability of groundwater levels but also exerts a significant influence on the groundwater gradients of salinity within the subsurface aquifers. This study takes the Songmu Area as an example to investigate this ocean–groundwater interaction. Songmu Area is located on a peninsula with coastal land reclamation in Dalian, China. Field campaigns were conducted in this area to measure the tidal action and groundwater parameters in a coastal reclaimed area at artificial backfill layers with pressure and salinity sensors, where the tidal signal can influence groundwater levels and salinity up to a one-kilometer range of inland. Tidal changes in the surface of the sea can be broken down into a number of simple, regular harmonic vibrations, each of which is called a tidal split. The tide and groundwater data were extracted using an enhanced harmonic analysis method. The fluctuations of groundwater levels and salinity were decomposed in response to the periodic tidal oscillation. Various constituents of tide attenuation in the coastal groundwater system were investigated. Our research shows that there is an exponential reduction in the fluctuating amplitude of groundwater levels and the groundwater salinity as distance further inland from the coast. The constituents of tide M₂ (the period is 12.42 h of semi-diurnal tides, S₂ (the period is 12.00 h of semi-diurnal tides), K₁ (the period is 23.93 h of full-diurnal tides), and O₁ (the period is 25.82 h of full-diurnal tides) behave differently for the tidal wave propagation and salinity variability in the coastal aquifer of reclaimed land. Among those constituents, M₂ and S₂ exhibit a higher degree of attenuation compared with K₁ and O₁. Understanding the relationship between groundwater levels and tidal fluctuations in coastal backfill areas is crucial for effective groundwater management strategies and mitigating the adverse impacts of seawater intrusion. This study can serve as a good understanding for assessing the impacts of various mitigation strategies.

A fixed dual cylindrical oscillating water column (OWC) acting as a breakwater-type wave energy converter (WEC) is proposed to harvest the wave energy effectively for shallow offshore sites. An analytical model is developed to investigate the hydrodynamic characteristics and the energy capture capacity of the cylindrical OWC device in severe waves. Based on the linear potential flow theory, the analytical solutions of the velocity potential in diffraction mode are solved by matching the Eigen-function expansion technique, and the continuous conditions of the velocity potential and fluid velocity between the computational sub-domains are involved in solving the problem for determining a solution. The proposed model is verified against the published data. The effects of the wave height, the angle of chamber clapboard and the radius of the inner and outer cylindrical column on the energy conversion efficiency are investigated in this paper. To improve the energy conversion performance and obtain a faster prediction for structural optimization of the cylindrical OWC, the geometrical parameters are further discussed in the analytical model. The results indicate that the geometrical parameters of the chamber have significant effects on the wave energy absorption efficiency. It is found that the effective frequency bandwidth of the dual cylindrical column can be broadened by improving the angle of the chamber clapboard and the inner–outer cylinder diameter ratio.

Multiple submerged breakwaters (MSBWs) are commonly used coastal protection structures due to their specific advantages over the emerged ones. Rip currents, as the inevitable natural hazard in the gaps of these constructions, are investigated numerically in the present study. A fully nonlinear mild-slope equation (NMSE) model possessing both fully nonlinear and fully dispersive properties is validated and adopted in the simulations. With four monochromatic wave conditions of different wave heights, periods and incidences representing low-energy, typical, storm and oblique waves tested, the flow patterns and the low-frequency oscillations of the rip currents are studied. For the convenience of risk assessment, the rip risk level is divided into three degrees according to the maximum rip flow speed. The effects of the configurations of the MSBWs on the rip current system as well as the rip risk level are examined, considering different breakwater widths, heights, forms, gap widths and gap numbers. Simulation results suggest that the cross-shore configurations of MSBWs influence the rip risk level by inducing different wave energy dissipations but the longshore configurations of MSBWs by changing flow field patterns.

Cigarette butts, often discarded as litter, are considered a common form of waste, containing a variety of pollutants within this hazardous residue. This study, which was designed to assess the environmental release of certain metals from cigarette butts, investigates a variety of scenarios under varying climatic conditions. Thus, in order to assess the level of metal contamination, samples of cigarette butts were collected in urban areas from seven popular brands in China, smoked artificially, and examined through graphite furnace atomic absorption (GF-AAS). The findings indicated mean concentrations of 1.77 for Cr, 2.88 for Ni, 12.93 for Cu, 24.25 for Zn, and 1.77 µg/g for Pb in the case of newly smoked butts. The emission of each of the metals increases to 8–10% when cigarette butts remain in the environment for an extended period of time. Furthermore, rainfall can accelerate metal leaching, reaching values of 18–20% compared to the controlled scenario. The worst-case scenario releases 2129.31 kg/year of metals into the environment, while the best-case scenario sees a lower release of 844.97 kg/year. The data reflect variations in metal emissions across different scenarios. There was also a strong correlation between cigarette butts in public spaces and cities. This research highlights the need to educate smokers and increase urban maintenance efficiency to reduce this litter and the metals it leaches into the environment.

Typhoon storm surge disasters are one of the main restrictive factors of sustainable development in coastal areas. They are one of several important tasks in disaster prevention and reduction in coastal areas and require reasonable and accurate calculations of wave height in typhoon-affected sea areas to predict and resist typhoon storm surge disasters. In this paper, the design wave height estimation method based on the stochastic process and the principle of maximum entropy are theoretically advanced, and it can provide a new idea as well as a new method for the estimation of the return level for marine environmental elements under the influence of extreme weather. The model uses a family of random variables to reflect the influence of a typhoon on wave height at different times and then displays the statistical characteristics of wave height in time and space. At the same time, under the constraints of the given observations, the maximum uncertainty of the unobtainable data is maintained. The new model covers the compound extreme value distribution model that has been widely used and overcomes the subjective interference of the artificially selected distribution function—to a certain extent. Taking the typhoon wave height data of Naozhou Observatory as an example, this paper analyzes the probability of typhoon occurrence frequency at different times and the characteristics of typhoon intensity in different time periods. We then calculate the wave height return level and compare it with traditional calculation models. The calculation results show that the new model takes into account the time factor and the interaction between adjacent time periods. Furthermore, it reduces the subjective human interference, so the calculated results of the typhoon’s influence on wave height return level are more stable and accurate.

The accurate determination of cross-shore longshore current profiles in the surf zone is essentially important in understanding of coastal physical processes and modelling of longshore sediment transport. In this study, a comprehensive laboratory study was undertaken to directly measure longshore current profiles over plane beaches with two mild slopes, 1:40 and 1:100, in a wave basin 55 m long, 34 m wide, and 0.7 m deep. Different wave conditions with an incidence angle of 30° were generated by piston-type wave makers consisting of 70 individual paddles, and two arrays of 29 Acoustic Doppler Velocimeters (ADVs) were used to measure longshore currents in the surf zone. Based on the experimental data collected in this study, three types of cross-shore longshore current profiles were found on the two plane beaches under different testing wave conditions, namely quasi-Rayleigh, quasi-Gaussian, and M-shape profiles. The quasi-Rayleigh profile was found on the beach slope of 1:40, and the other two types were found on the beach slope of 1:100. Analytical formulae were proposed to describe these profiles and agreed well with the laboratory data. The fluctuations of longshore currents observed in this study were attributed to their shear instabilities based on linear instability analysis. The results of the linear instability analysis and the spectra of measured velocities also showed that the three types of velocity profiles led to different instability characteristics.