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This experimental study investigates the effect of surface waves that are superimposed on a unidirectional current around a bridge pier in a gravel bed, which employs particle image velocimetry (PIV). A comprehensive examination of various flow characteristics, which include the intermittency factor (IF), turbulent kinetic energy (TKE), and vorticity analysis, is conducted to elucidate the variations around the pier with respect to the Keulegan–Carpenter (KC) number. The findings reveal a correlation between the KC number and the flow dynamics in combined conditions: specifically, due to combined wave–flow conditions, escalation in the frequency of vortices near the pier and the increment in turbulent strength, in terms of the TKE. Of note, this augmentation in turbulent strength is associated with an increase in the KC number. At a low KC number, the maximum scour depth occurred downstream near the pier, which shifted to upstream with an increase in the KC number. In addition, the results could be utilized for the development and validation of numerical models, which accurately estimate the local scour under combined flow conditions. [ABSTRACT FROM AUTHOR]

Desalination plants employing feed water sourced from saline groundwater (SGW) are a feasible approach to tackle freshwater scarcity and seawater intrusion (SWI). Available studies lacked comprehensive analysis quantifying the impact of pumping from a coastal aquifer, on changes in solute transport mechanism. This study investigates the impact of different rates of SGW pumping on the solute transport in a coastal aquifer. A regional-scale model resembling the Upper Floridan aquifer was modelled using SEAWAT to quantify SWI variables. The study found that the length of intrusion of toe (Ltoe), width of mixing zone (WMZ) and residual salt mass (RSM) varied with dispersivity values. The ratio of saltwater to freshwater influx was unaffected by dispersivity values. Significant decrease in the toe-length occurred when the pumping rate was highest and the dispersivity was lowest. The WMZ was found to be the most sensitive SWI variable towards varying dispersivity, with 65% difference for higher pumping rates. The mid-bottom region was experiencing substantial modifications, leading to an inclined response at increased pumping rates, which suggested that the diluting process was primarily taking place in the bottom portion. This study gives insight into saline wedge movement in a coastal aquifer system which will benefit in the design of SGW well system for desalination plants. [ABSTRACT FROM AUTHOR]

This study investigates the local scour around the cylindrical pier mounted on a gravel bed for a low coarseness ratio (d/d50), which is defined as the ratio of pier diameter d to the median particle size (d50) of the bed material. An experimental study was conducted in a flume with varying pier diameters and flow conditions. The effect of flow depth on the scour was observed for a limiting condition, i.e. the ratio of flow depth (h) to the pier diameter (d) is less than 4.33. The critical limit of h/d for affecting the scour depth for the gravel bed was found to be three times more than that of the sand bed. From the experimental results, an empirical relationship is proposed based on the dimensional analysis for the estimation of scour depth for a low coarseness range (d/d50 < 25). The proposed relationship estimates the scour depth with an error of less than ±15%, within the acceptable limit. Furthermore, it is also performing well for the coarseness ratio up to 100 with an error within the range of ± 30%. The results from this study can be useful for scour prediction and for the design of a bridge pier in a gravel bed with a low range of coarseness value. [ABSTRACT FROM AUTHOR]

The present study illustrates an experimental investigation of flow hydrodynamics in the vicinity of a submerged circular pier across various submergence levels under only current and wave–current combined flow conditions. The instantaneous velocity data are collected using particle image velocimetry for three distinct frequencies of waves to determine the influence of wave superimposition on the current-induced turbulence parameters. The distribution of phase averaged turbulence quantities, such as mean velocities, Reynolds shear stress, turbulent kinetic energy, flow patterns, and vorticity analysis by Q-criterion, are presented. The results provide insight into the impacts of wave frequency and submergence ratio on the formation of horseshoe vortices, trailing vortex, and reverse flow zones. From the results it is observed that a decrease in the submergence level of the structure causes the formation of strong horseshoe vortices and reverse flow zones in the absence of waves. Also, an increase in wave frequency intensifies the turbulence kinetic energy at the upstream of the pier and eddy generation behind the pier. The present findings highlight the effects of pier submergence and wave characteristics, such as frequency, wave height, and wave period, on flow patterns and turbulent flow characteristics and aid in the design of marine structures. Furthermore, experimental data serve as a valuable resource for validating theoretical or mathematical models related to combined wave–current environments. [ABSTRACT FROM AUTHOR]

The objective of this study was to explore the higher-order turbulence statistics of flow and turbulent length scales around a complex pier (CP) and compare the results with those for a simple pier (SP). The velocity data were recorded in a laboratory flume using particle image velocimetry (PIV). The PIV data were analysed to estimate the velocity fluctuations of third order, turbulence production and dissipation rates, turbulent length scales and the contributions of burst–sweep events to the total Reynolds shear stress around the piers mounted on a rigid flat surface. The skewness and advection coefficients indicated a more asymmetric distribution of velocity fluctuations for the SP than for the CP. Ejection and sweep events illustrated the dominance of similar strengths for an extended period, downstream of the piers. The upstream turbulent kinetic energy production was similar for both piers, while the upstream dissipation rate was higher for the CP. The length scales were greater at the upstream for the case of the SP while, downstream, they were greater for the CP. The findings of this work demonstrate the importance of a pile cap in restricting downward-moving flow by showing a lower magnitude of scour-inducing turbulence parameters for the CP as compared with the SP. [ABSTRACT FROM AUTHOR]