Search

Tidal bores, defined by sudden upstream surges of tidal water in estuaries, exert significant hydrodynamic forces on riverbeds, leading to complex sedimentary responses. This study examines the dynamic response and liquefaction potential of riverbeds subjected to tidal bores in macro-tidal estuaries. An analytical model, developed using the generalized Biot theory and integral transform methods, evaluates the dynamic behavior of riverbed sediments. Key factors such as permeability, saturation, and sediment properties are analyzed for their influence on momentary liquefaction. The results indicate that fine sand reduces liquefaction risk by facilitating pore water discharge, while silt soil increases sediment instability. Additionally, the study reveals that pressure gradients induced by tidal bores can trigger momentary liquefaction, with the maximum liquefaction depth predicted based on horizontal pressure gradients being five times that predicted based on vertical pressure gradients. This research highlights the critical role of sediment characteristics in riverbed stability, providing a comprehensive understanding of the interactions between tidal bores and riverbed dynamics. The findings contribute to the development of predictive models and guidelines for managing the risks of tidal bore-induced liquefaction in coastal and estuarine environments. [ABSTRACT FROM AUTHOR]

Since the late 1960s, the Qiantang Estuary has been narrowed on a large scale, significantly changing the water-sediment dynamics, riverbed evolution and their interaction processes. However, the tidal bore in response to the high-intensity human activities is not fully understood. Based on the measured data of topography, tide and tidal bore, combined with the mathematical model of tidal bore, the effects of large-scale contracted river for regulation on tide, river bed and tidal bore of Qiantang Estuary were studied. The results show that the distribution of shoal and channel was basically stable after the river was narrowed. With the increase of the ratio of river flow to tidal current, roughly bounded by Yanguan, the lower part of the tidal bore reaches was silted, the upper part was scoured, and the sandbar was moved downstream. The high tidal level rose along the estuary, the tidal range increased near the place where the tidal bore occurred and the upper part of the tidal bore reaches from Zhakou to Cangqian reach, and decreased from Cangqian to Yanguan reach. As a result, the occurrence point of the tidal bore and the maximum tidal bore position move downstream, the viewing positions of the tidal bore are fixed, the tidal bore scenery is abundant and stable, the tide bore arrival time is stable, the amplitude of the tidal bore height decreases, and the tidal bore height decreases from Cangqian to Yanguan reach. In order to protect the tidal bore, it is necessary to maintain a large tidal range and appropriate water depth in the tidal bore reach, and it is not suitable to carry out large-scale reclamation. [ABSTRACT FROM AUTHOR]

Tidal flats provide crucial ecosystem services and coastal protection. Comprehending the evolution of tidal flats, influenced by tidal bores and runoff, is key to protecting these environments in the Qiantang Estuary′s tidal bore zones. Based on 151 observations of the Jianshan mudflat terrain, taken approximately every two days, the research explored the mudflat′s evolution. Utilizing water level, suspended sediment concentration, river discharge, and remote sensing data, the study further investigated the driving mechanisms behind this evolution. The results are as follows: ① The Jianshan mudflat maintained a dynamic equilibrium. In the observation area, the dry- season deposition rate was 0. 01 m / d, with the slope stabilizing at 1‰. During the flood season, the mudflat bank retreat rate reached 3 m / d, causing a retreat width of 113 m. After the flood season, the mudflat recovered at a rate of 0. 05 m / d. ② During the flood season, the intensity of tidal bores slightly increased. Flood events lead to a bifurcated river regime, directing the main sediment transport of tidal bores through the southern channel, thereby reducing sediment delivery to the tidal flats in the northern channel. ③ Qiantang River runoff was the key factor controlling seasonal erosion and deposition changes. The evolution rate of the tidal flats showed a multivariate linear relationship with river runoff, initial elevation, and tidal range. ④ Floods altered the river regime, reducing sediment supply to the tidal flats. Runoff and ebbing tides combined to cause bank erosion and retreat. However, when water erosion decreased and sediment transport by tidal bores and rising tides became dominant, the tidal flat rapidly recovered. [ABSTRACT FROM AUTHOR]

Tidal bores inject large amounts of energy to the estuaries, and the variation of tidal bore is related to its energy distribution. In this study, the temporal and spatial changes of the tidal bore energy are investigated to demonstrate the propagation characteristics of tidal bores in the Qiantang River Estuary. Based on high frequency field data, the characteristics of the potential energy and the kinetic energy per unit area during the passage of tidal bores at Yanguan station is demonstrated. Numerical model employing shallow water equations is established to investigate the tidal bore energy along the estuary. Tidal level, tidal current and tidal bore during spring tides in September, 2019 are verified, and the tidal bore energy and its distribution characteristics along the sections from Ganpu to Wenjiayan are illustrated. The tidal bore energy is significantly decreased in the Daquekou reach but decreased relatively small in the reach from Qige to Wenjiayan. There is the maximum energy loss in the Jianshan reach. The tidal bore energy declines to 15% at Wenjiayan during the passage of the energetic breaking tidal bores, indicating tidal bore disappearance in the upstream reach. [ABSTRACT FROM AUTHOR]

Tidal bores, defined by sudden upstream surges of tidal water in estuaries, exert significant hydrodynamic forces on riverbeds, leading to complex sedimentary responses. This study examines the dynamic response and liquefaction potential of riverbeds subjected to tidal bores in macro-tidal estuaries. An analytical model, developed using the generalized Biot theory and integral transform methods, evaluates the dynamic behavior of riverbed sediments. Key factors such as permeability, saturation, and sediment properties are analyzed for their influence on momentary liquefaction. The results indicate that fine sand reduces liquefaction risk by facilitating pore water discharge, while silt soil increases sediment instability. Additionally, the study reveals that pressure gradients induced by tidal bores can trigger momentary liquefaction, with the maximum liquefaction depth predicted based on horizontal pressure gradients being five times that predicted based on vertical pressure gradients. This research highlights the critical role of sediment characteristics in riverbed stability, providing a comprehensive understanding of the interactions between tidal bores and riverbed dynamics. The findings contribute to the development of predictive models and guidelines for managing the risks of tidal bore-induced liquefaction in coastal and estuarine environments.

In natural free surface flows, sediment particles in the surface layer of a sediment bed are moved and entrained by the fluctuating hydrodynamic forces, such as lift and drag, exerted by the overlying flow. Accurate prediction of near-bed hydrodynamic forces in rapidly varied flows is vital for coastal sediment transport and morphodynamics. Directly measured hydrodynamic forces within the rapidly varied flows over rough bed layer have been limited by previous spatial averaging shear force studies. Therefore, the direct measurements were designed and adapted to estimate tidal bore forces, including longitudinal (drag) and vertical (lift) force on near-bed sediment particle. Specially designed experiments were conducted to measure the instantaneous forces using a highly sensitive force sensor assembled with a target sphere. A novel 1D-CNN model (i.e. SedimentNet) has been developed for the prediction of hydrodynamic forces and compared with existing machine learning models (i.e. Decision Tree (DT), Random Forest (RF), Multilayer Perceptron (MLP), Support Vector Regressor (SVR), XGBoost, k -Nearest Neighbour (k -NN)). The parameters affecting near-bed hydrodynamic forces are also analysed. In the context of machine learning, both conventional dataset split and fivefold cross-validation approaches were implemented. The results indicated that the proposed SedimentNet was able to achieve marginally better cross-validation performance (i.e. R 2 score of 0.77 for drag force, R 2 score of 0.96 for lift force) for the prediction of drag and lift forces. RF and XGBoost were the second best models with R 2 score of 0.73 and 0.95 for drag and lift force prediction, respectively. Results also showed the potential of machine learning models for the efficient prediction of complex hydrodynamic forces in a coastal environment. A use-case edge computing solution for the reported machine learning-based prediction of hydrodynamic forces has also been proposed and discussed to demonstrate the practical implementability of the presented research. [ABSTRACT FROM AUTHOR]

Based on field data of river discharge, tide, tidal bore, and riverbed topography, the characteristics of river discharge, the effect of river discharge on riverbed erosion and sedimentation, and the feedback effect of riverbed erosion and sedimentation on the tide and tidal bore in the Qiantang River are analyzed. The results show that the inter-annual and seasonal variation of river discharge in the Qiantang River is noticeable, while the seasonal distribution of river discharge tends to be uniform after the construction of Xin'anjiang Reservoir. River discharge has a major effect on the erosion and sedimentation in the reach from Zhakou to Yanguan. There are laws of riverbed erosion in wet seasons and years and sedimentation in dry seasons and years. Relations in the Zhakou to Yanguan reach among the riverbed volume after the flood season, the mean and maximum river discharge during the flood season, and riverbed volume before the flood season are established. With the riverbed erosion from Zhakou to Yanguan, the low tide level decreases and the tidal range is amplified, and thus, the tidal bore is enhanced. The relation among tidal range, river discharge, and riverbed volume, as well as the one between the tidal bore height and tidal range is established on the basis of the field data. Furthermore, the variation range of tidal bores after the flood season is analyzed in wet and dry years. The indirect effect of the Xin'anjiang Reservoir on the height of the tidal bore is predicted and the mean height of the tidal bore from Zhakou to Yanguan decreases by 0.1–0.2 m. [ABSTRACT FROM AUTHOR]

Tidal bore is a special and intensive form of flow movement induced by tidal effect in estuary areas, which has complex characteristics of profile, propagation and flow velocity. Although it has been widely studied for the generation mechanism, propagation features and influencing factors, the curved channel will complicate the characteristics of tidal bore propagation, which need further investigation compared with straight channel. In this study, the flume experiments for both undular and breaking bores' propagation in curved channel are performed to measure the free-surface elevation and flow velocity by ultrasonic sensors and ADV respectively. The propagation characteristics, including tidal bore height, cross-section surface gradient, tidal bore propagation celerity, and flow velocity are obtained for both sides of the curved channel. And three bore intensities are set for each type of tidal bores. The free-surface gradients are consistently enlarged in high-curvature section for undular and breaking bores, but have distinct behaviors in low-curvature section. The spatial distributions of tidal bore propagation celerity and flow velocity are compared between concave and convex banks. This work will provide experimental reference for engineering design of beach and seawall protection, erosion reduction and siltation promotion in estuary areas with the existence of tidal bores. [ABSTRACT FROM AUTHOR]

The study establishes, with the aid of field measurements and numerical modeling, that the upper reach of the Hooghly estuary (India), though damped, registers an intense tidal bore. The lower estuary is amplified but does not show signs of bore formation. Limited quantitative studies are available on bores forming in damped estuaries. This study attempts to fill this gap using tidal gauge and velocity observations supplemented with simulation results obtained using the open-source numerical shallow-water solver TELEMAC 2D. New estimates of bore intensity in the Hooghly are presented confirming that the bore Froude number may reach 1.37 in the upper estuary for higher tidal ranges. The numerical model is used to gain further insights into the formation and evolution of the Hooghly bore. The model, despite using a vertically averaged velocity field, simulates tidal wave propagation and estimates of velocity magnitude during bore propagation with significant accuracy. The study demonstrates that the proposed model is an efficient and inexpensive tool for capturing the bore phenomenon and may be used to supplement field observations. Using the simulation results, key features of the Hooghly bore, such as the distance of the bore inception from the ocean mouth and the threshold tidal range for bore formation are investigated. The numerical simulations highlight the impact of riverbed asymmetry in bore appearances in natural estuaries. The analysis also reveals new information about bores in the Hooghly estuary, which may be useful for planning shipping and berthing operations in the port terminals along the river. A comparison with other estuaries witnessing tidal bores indicates that the Hooghly experiences a strong bore, despite the high dissipative forces owing to the rapid convergence of river width. [ABSTRACT FROM AUTHOR]

A total of ten different marine/brackish water fish species was recorded at Tribeni, a completely freshwater region located 212 km upstream from the sea in Hooghly estuary just after tidal bore, a natural high wave and high flow regime created during the spring tide around full moon/new moon days. A range of 85 - 179 km upstream shift of recorded marine fish species from their normal distribution range may be attributed to high turbulence, flow, and wave associated with bore tide as there is no sign of saltwater ingress in the Tribeni area as revealed through the analysis of associated environmental parameters. In addition to salinity, such extreme climatic events like tidal bore should also be considered to explain the fish species distribution in a tidal estuary. [ABSTRACT FROM AUTHOR]

Tidal bores are a natural phenomenon with high flow velocity and destructive potential. A spur dike is a widely used river regulation and embankment protection structure that minimizes erosion, promotes deposition, and protects riverbanks. However, the scouring mechanism around a spur dike under the action of a tidal bore is not fully understood, and accurately estimating the maximum scour depth has always been a challenge, limiting the construction and maintenance of spur dikes in estuarine and marine environments. This study analyzed the scouring characteristics around a spur dike induced by tidal bores via field observation and model experiments. The results show that the scours around a spur dike can be divided into dike head scour and upstream side scour. The scour depth is related to the geometric shape of the spur dike and its surrounding riverbed, hydrodynamic forces, and sediment characteristics. The least squares method obtained the fitting formulas for the depth of the scour at the dike head and upstream side. Overall, the present study indicates an agreement of the scouring characteristics around a spur dike between the field observations and laboratory experiment, and the fitting formulas can be effectively applied to engineering practices of a macro-tidal estuary. [ABSTRACT FROM AUTHOR]

A tidal bore is known for its abrupt change in water flow with a complex and violent leading front. The powerful tidal bore can quickly move up the sloped beach and overtop the seawall, leading to significant damages along the coast. In the past, many coastal seawalls were constructed to shield the coastal regions from the destructive power of tidal bores. The typhoon-induced shear force and pressure imbalance can significantly affect the tidal bore height and its propagation speed. Therefore, it is important to evaluate how strong winds impact the hydrodynamic transformation and overtopping of tidal bore at the seawalls. However, there are few research on this topic. To address the limitations of previous research, this study applies a high-resolution two-phase flow solver to numerically examine how strong winds impacts the overtopping characteristics of tidal bore at coastal seawalls. The effects of main factors, including wind speed, tidal bore height, water depth, and beach slope, are thoroughly examined. Research findings indicate that the presence of wind can cause notable changes in the hydrodynamic evolution and overtopping characteristics of both undular tidal bore and weak breaking tidal bores, whereas its impact on the overtopping characteristics of breaking tidal bore is relatively limited. Simultaneously, the presence of wind can significantly increase the intensities of the undular tidal bore and weak breaking tidal bore at the seawall. The high nonlinear behavior of the breaking tidal bore at the seawall is demonstrated by its impactful intensity when influenced by wind. It is hoped that the present study will enhance knowledge on the hydrodynamic overtopping characteristics of tidal bores in harsh weather conditions. • Hydrodynamic overtopping processes of different types of tidal bores at the seawall under the wind have been numerically investigated by applying a high-resolution two-phase flow solver. • Influences of major factors, such as wind speed, tidal bore height, initial water depth, and beach slope are investigated in detail. • Research results reveal that the wind can noticeably reshape the hydrodynamic evolution and overtopping characteristics of the undular tidal bore and weak breaking tidal bore, except the breaking tidal bore. [ABSTRACT FROM AUTHOR]

Tidal bores are a natural phenomenon with high flow velocity and destructive potential. A spur dike is a widely used river regulation and embankment protection structure that minimizes erosion, promotes deposition, and protects riverbanks. However, the scouring mechanism around a spur dike under the action of a tidal bore is not fully understood, and accurately estimating the maximum scour depth has always been a challenge, limiting the construction and maintenance of spur dikes in estuarine and marine environments. This study analyzed the scouring characteristics around a spur dike induced by tidal bores via field observation and model experiments. The results show that the scours around a spur dike can be divided into dike head scour and upstream side scour. The scour depth is related to the geometric shape of the spur dike and its surrounding riverbed, hydrodynamic forces, and sediment characteristics. The least squares method obtained the fitting formulas for the depth of the scour at the dike head and upstream side. Overall, the present study indicates an agreement of the scouring characteristics around a spur dike between the field observations and laboratory experiment, and the fitting formulas can be effectively applied to engineering practices of a macro-tidal estuary.

Tidal bores are sudden discontinuities in water depth, and can be classified as undular and breaking bores when tidal waves propagate upstream in a river mouth and on beaches. The impact of different types of bores on sediment transport is not clear; hence, specially designed experiments were conducted to clarify the mechanism of sediment initiation. Here, a laser Doppler anemometer, a force sensor, and ultrasonic displacement meters accompanied by video recordings were used to investigate simultaneously the incipient motion of sediment under tidal bores. No sediment motion was observed during the initial steady flows. It was observed that only a few particles changed their initial position during the undular bore; however, a group of particles were seen moving upstream during the breaking bore. The inception of sediment motion was closely related to the passage of the breaking roller, that is, the forces that caused the inception of particle motion were not only due to velocity but also to the sudden discontinuity in free water surface. According to the experimental results, the upward vertical force due to swelling in free water surface before the roller toe was the main force in destabilizing the particles. Later, a large upstream longitudinal force was found to be the dominant cause promoting upstream particle motion during the breaking roller passage. Furthermore, phases of both horizontal and vertical forces play an important role in tidal bore propagation. It is interesting to note that by using the measured force, the observed phenomenon can be well explained by the Shield threshold criterion. Key Points: Simultaneous measurements of sediment incipient motion, horizontal and vertical velocity, and force componentsVisual observation demonstrates that no pebbles moved during an undular bore and rolling, sliding and short hops had occurred beneath the breaking boreUpward vertical force was the main destabilizing parameter and horizontal force promoted the upstream particle motion beneath breaking bore [ABSTRACT FROM AUTHOR]

A tidal bore is a water discontinuity at the leading edge of a flood tide wave in estuaries with a large tidal range and funneling topography. New measurements were done in the Garonne River tidal bore on 14–15 November 2016, at a site previously investigated between 2010 and 2015. The data focused on long, continuous, high-frequency records of instantaneous velocity and suspended sediment concentration (SSC) estimate for several hours during the late ebb, tidal bore passage and flood tide. The bore passage drastically modified the flow field, with very intense turbulent and sediment mixing. This was evidenced with large and rapid fluctuations of both velocity and Reynolds stress, as well as large SSCs during the flood tide. Granulometry data indicated larger grain sizes of suspended sediment in water samples compared to sediment bed material, with a broader distribution, shortly after the tidal bore. The tidal bore induced a sudden suspended sediment flux reversal and a large increase in suspended sediment flux magnitude. The time-variations of turbulent velocity and suspended sediment properties indicated large fluctuations throughout the entire data set. The ratio of integral time scales of SSC to velocity in the x-direction was on average T E,SSC /T E,x ~ 0.16 during the late ebb tide, compared to T E,SSC /T E,x ~ 0.09 during the late flood tide. The results imply different time scales between turbulent velocities and suspended sediment concentrations. [ABSTRACT FROM AUTHOR]

Quantitative real-time observations of a tidal bore in a macro-tidal estuary are difficult and dangerous, particularly in large estuaries. Mathematical and numerical models have been used to predict tidal bore advances; however, to date, there have been no validations of large-scale flow patterns. A marine radar can provide valuable real-time information on tidal bore propagation. In this paper, a template matching method using a cross-correlation algorithm was explored to estimate the evolution and celerity of a tidal bore with medium resolution marine radar images. The Qiantang River tidal bore was recorded at two different geographical locations. Characteristic flow patterns were derived and analysed, including temporal changes over a relatively large-scale area. The experimental results showed that the radar-derived celerity and calculated height of the tidal bore were consistent with visual observations in this estuarine zone. Image 1 • Quantitative real-time observations of a tidal bore in a macro-tidal estuary. • Cross-correlation between successive radar images yield instantaneous bore celerity. • Both magnitude and direction of the bore celerity are derived. • Radar-derived results are validated by visual observations. [ABSTRACT FROM AUTHOR]

Abstract 2D numerical simulations of tidal bores were obtained using the OpenFOAM CFD software to solve the Navier–Stokes equations by means of the Finite Volume Method by applying a LES turbulence model. The trajectories of non-cohesive sediment particles beneath tidal bores were estimated using a tracker method. Using the fourth order Runge–Kutta scheme, the tracker method solves the Maxey and Riley equations, which requires the knowledge of the velocity field at time t. From 2D numerical simulations of tidal bores, we proposed a classification of tidal bores with respect to the Froude number Fr (or r the ratio of water depths). For a Froude number 1 < F r < 1.43 (1 < r < 1.57), the tidal bore is undular. For a Froude number 1.43 < F r < 1.57 (1.57 < r < 1.75), the tidal bore is partially breaking, which is similar to the transitional tidal bore defined by Furgerot (2014). And for a Froude number F r > 1.57 (r > 1.75), the tidal bore is totally breaking. The numerical results of trajectories of non-cohesive sediment particles are similar to the type of trajectories given by the analytical model proposed by Chen et al. (2012) with some modifications to take into account the effects of gravity, elevation, and attenuation. The parameters of modified Chen's model, β 1 , β 2 and β 3 , are linearly proportional to the Froude number Fr. This is because the level of turbulence for undular tidal bores is low. The flow induced by an undular tidal bore is not complex. This physical phenomenon is quasi linear. The parameter β 1 , related to the front celerity of the undular tidal bore, decreases when the Froude number Fr increases. The parameter β 2 , related to the elevation, increases when the Froude number Fr increases. And the parameter β 3 , related to the attenuation of the secondary waves, increases when the Froude number Fr increases. [ABSTRACT FROM AUTHOR]

In this study, a three-dimensional model is developed to investigate sediment transport under tidal bores in the Qiantang estuary. The sediment transport is modelled by the advection and diffusion equation, and the exchange of sediment between the riverbed and the flow is determined by a net flux. A new formula of sediment carrying capacity based on recent field data is used and the settling velocity is resolved with an empirical formula accounting for the flocculation of fine sediment. Skill assessment is employed to show the model performance and relatively high predictive skills are demonstrated. The significant rise of sediment concentration under tidal bores is accurately reproduced. Sediment concentration with the arrival of tidal bores increases more than 10 times, and the depth-varying characteristic of suspended sediment is captured. It is concluded that the amount of sediment transport under tidal bores amplifies an order of magnitude, and the reverse sediment transport pattern is documented. [ABSTRACT FROM AUTHOR]

The tidal bore of the Garonne River (France) was investigated on 29 August, 31 August and 27 October 2015, during which instantaneous velocity measurements were performed continuously at high-frequency (200 Hz). The tidal bore occurrence had a marked effect on the flow field and turbulent Reynolds stress data, indicating large shear stresses, together with large and rapid fluctuations, during the bore passage and the early flood tide. Like many natural process flows, the tidal bore flow motion was dominated by coherent structure activities and turbulent events, with significant impact on the natural systems including in terms of sediment processes. Herein a new turbulent event analysis was developed for the highly-unsteady rapidly-varied tidal bore flow. The analysis was based upon basic concepts, in which turbulent bursting events were defined in terms of the instantaneous relative turbulent flux, and the method was extended to the rapidly-varied, highly-unsteady tidal bore motion. The turbulent event data showed relatively close results for most fluxes during the tidal bores. The event duration showed some tidal trend, with longer turbulent events immediately after the tidal bore passage, occurring simultaneously with major sediment erosion processes. The field data set and analyses suggested that a turbulent event analysis may be applicable to highly-unsteady rapidly-varied flows, providing quantitative details into the turbulent bursts that are responsible for major mixing and sedimentary processes. [ABSTRACT FROM AUTHOR]

A tidal bore is a positive wave traveling upstream along the estuary of a river, generated by a relatively rapid rise of the tide, often enhanced by the funneling shape of the estuary. The swell produced by the tide grows and its front steepens as the flooding tide advances inland, promoting the formation of a sharp front wave, that is, the tidal bore. Because of the many mechanisms and conditions involved in the process, it is difficult to formulate an effective criterion to predict the bore formation. In this preliminary analysis, aimed at bringing out the main processes and parameters that control tidal bore formation, the degrees of freedom of the problem are largely reduced by considering a rectangular channel of constant width with uniform flow, forced downstream by rising the water level at a constant rate. The framework used in this study is extremely simple, yet the problem is still complex, and the solution is far from being trivial. From the results of numerical simulations, three distinctive behaviors emerged related to conditions in which a tidal bore forms, a tidal bore does not form, and a weak bore forms; the latter has a weakly steep front and after the bore formed it rapidly vanishes. Based on these behaviors, some criteria to predict the bore formation are proposed and discussed. The more effective criterion, suitably rearranged, is checked against data from real estuaries, and the predictions are found to compare favorably with the available data. Key Points: The formation of tidal bores is investigated numerically within a schematic frameworkA phenomenological analysis revealed the occurrence of nontrivial distinctive behaviorsThe proposed criterion to predict tidal bore occurrence performs favorably also for real estuaries [ABSTRACT FROM AUTHOR]

ABSTRACT Ni X.; Huang S.; Feng W., and Yao W., 2018. Numerical simulation of tidal bores using SPH method. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 951–956. Coconut Creek (Florida), ISSN 0749-0208. A tidal bore is a natural hydraulic phenomenon normally formed in funnel-shaped estuaries with large tidal ranges. Water levels and flow velocities change rapidly in both magnitude and direction when a tidal bore arrives. These strongly nonlinear water body movements have significant influences on scouring and deposition processes along the riverbed and produce hydrodynamic impacts on piers and dikes. In this paper, a mesh-free numerical method known as the smoothed particle hydrodynamics (SPH) method is used to implement a numerical model capable of handling complex free-surface flows and solve the Navier-Stokes equations with a large-eddy simulation. A tidal bore generation scheme suited for a mesh-free numerical method is also proposed based on the SPH open boundary technique. Various types of tidal bores, including undular bores, weakly breaking bores and breaking bores, are simulated and validated with measured data. The numerical results represent the evolutionary processes and hydrodynamic characteristics of tidal bores ranging from weak to strong intensities. The generation and evolution of dipole substructures in breaking tidal bores are also discussed. By studying the bed shear stresses and depth-averaged vorticities of the tidal bores, it can be concluded that the sediment incipience intensity grows nonlinearly in the second order with an increase in the tidal bore intensity, while the sediment transportation intensity grows linearly. [ABSTRACT FROM AUTHOR]

A major tsunami-like event, locally known as ‘marrobbio’, impacted the southwestern coast of Sicily on 25-26 June 2014. The event was part of a chain of hazardous episodes in the Mediterranean and Black seas during the last week of June 2014 resulting from an anomalous atmospheric system (“tumultuous atmosphere”) propagating eastward over the region. The synoptic patterns and vertical structure of the atmosphere over Sicily at the time of the event indicate that atmospheric wave ducting was responsible for the generation of tsunamigenic air pressure disturbances that produced especially high sea level responses (“meteotsunamis”) at certain sites along the Sicilian coast. The strongest sea level oscillations were observed at Mazara del Vallo, where a 1-m meteotsunami bore, propagating upstream in the Mazaro River, was generated. The combined effects of external resonance (Proudman resonance on the western Sicilian shelf) and internal resonant conditions (bathymetric and topographic characteristics of specific sites) were found to be the key factors that caused the meteotsunami (marrobbio phenomenon) on the coast of Sicily and the meteobore at Mazara del Vallo. [ABSTRACT FROM AUTHOR]

In a natural estuary, a tidal bore may progress on a small sloping bed from the downstream to the upstream. In this study, a simple analytical solution for tidal bore formed in a small slope channel was developed using the finite control volume analysis. New unsteady experiments were conducted to verify the theoretical model. The model predictions generally agree with the observations. A general relation is obtained for the conjugate depth ratio as a function of the Froude number and the channel slope from the experimental data. The results indicate that the conjugate depth ratio increases with an increasing Froude number as well as with a decrease in channel slope. On a negative slope, the Froude number increases as the bore propagates along the channel, and decreases for a positive slope. The theoretically based model is accurate and simple to estimate the celerity of the tidal bore progressing along a small slope channel. [ABSTRACT FROM AUTHOR]

The factors that govern the distribution and transformation of tidal waves in the macrotidal estuary of the Mezen River have been considered, including tide range in the mouth section, water discharge in the river's lower reaches, estuary shape, and bed resistance coefficient. Data on variations of water discharge over period 1920-2008 are given. The parameters of estuary channel narrowing in horizontal and vertical sections have been considered. The effect of narrowing and bed hydraulic friction on tide wave amplitude has been evaluated. Froude number values for the tidal estuary suggest that tidal bore can form at the Mezen mouth. The conditions of the propagation of tidal waves to the mouths of different rivers and tidal bore formation in them are considered. [ABSTRACT FROM AUTHOR]

Due to accelerated anthropogenic activity, a significant amount of pollutants has been directly or indirectly discharged into coastal estuaries of Kampar. Nutrient pollution along the river to the estuary that adversely affects coastal and estuary ecosystem mainly originates from inland such as industrial effluent, household, and agricultural waste as well as a naturally derived pollutant from biogeochemical cycle, which is controlled by the propagation of undular bore (Bono). The purpose of this study is to determine the environmental impact of distribution of nutrients caused by the mechanism of Bono. This research employed a purposive quantitative method, the concentration of dissolved phosphate, nitrate, nitrite and ammonia was analyzed using a spectrophotometer, tidal data retrieval was measured for 30 days' near the estuarine area, while, current flow was measured for 24 hours' measurement. Phosphate concentrations ranged from 0.02-0.1 mg.L-1, nitrate concentrations ranged from 0.76-5.73 mg.L-1, ammonia concentrations ranged from 0.2-0.41 mg.L-1, nitrate concentrations ranged from 0.001-0.03 mg.L-1. The tidal type is mixed tide prevailing semidiurnal with tidal range reach 4.2 m during spring tide condition. At the time of Bono propagate, drastically enhance the surface elevation and directly increase the drift of velocity with the flow direction from estuary into the river upstream, that mechanism affects the nutrient distribution in Kampar river. [ABSTRACT FROM AUTHOR]

In this paper, the effect of the dike line adjustment on the Qiantang Tidal Bore (QTB) is studied by physcial experiments. A lab-scale physical model of the Qiantang Estuary is built and the tidal bore is generated. With this model, the formation and pro-pagation processes of the tidal bore are simulated with or without the dike line adjustment. It is shown that the adjusted dike line changes the direction of the reflected tidal bore. The height of the tidal bore increases in the upstream region where the dike line is contracted. In the tested bent and forking regimes, the bore height at the upstream station is increased by 0.10 m and 0.04 m, respectively. Furthermore, the crossing bore still exists near the Daquekou station and the location slightly moves by about 3 km to the downstream region. [ABSTRACT FROM AUTHOR]

A tidal bore is a hydrodynamic shock, propagating upstream as the tidal flow turns to rising, with macro-tidal conditions in a funnel shaped system with shallow waters. The tidal bore of the Garonne River was extensively investigated in the Arcins channel between 2010 and 2013, typically over one to two days. In 2015, new field measurements were repeated systematically at the same site on 29 August-1 September 2015 and on 27 October 2015. The nature of the observations was comprehensive, encompassing hydrodynamics and turbulence, as well as sediment properties and transport. The tidal bore occurrence had a marked effect on the velocity and suspended sediment field, including a rapid flow deceleration and flow reversal during the bore passage, with very large suspended sediment concentrations (SSCs) during the passage of the tidal bore front and early flood tide, as well as very large suspended sediment flux during the very early flood tide. The suspended sediment concentration (SSC) data indicated a gradual increase in initial mean SSC estimate prior to the bore from 29 August to 1 September 2015. A comparison between suspended sediment flux data showed very significant suspended sediment flux on the first day of tidal bore occurrence, with a decreasing magnitude over the next three days. The data suggested a two-stage bed scour process: at each tidal bore event, surface erosion occurred initially, in the form of stripping; the first stage was followed by delayed mass erosion, occurring about 5–15 min after the tidal bore. [ABSTRACT FROM AUTHOR]

Tidal bores are believed to induce significant sediment transport in macrotidal estuaries. However, due to high turbulence and very large suspended sediment concentration (SSC), the measurement of sediment transport induced by a tidal bore is actually a technical challenge. Consequently, very few quantitative data have been published so far. This paper presents SSC measurements performed in the Sée River estuary (Mont-Saint-Michel Bay, northwestern France) during the tidal bore passage with direct and indirect (optical) methods. Both methods are calibrated in laboratory in order to verify the consistency of measurements, to calculate the uncertainties, and to correct the raw data. The SSC measurements coupled with ADCP velocity data are used to calculate the instantaneous sediment transport ( q s ) associated with the tidal bore passage (up to 40 kg/m 2 /s). [ABSTRACT FROM AUTHOR]

Over the last decade there has been an increasing interest in tidal bore dynamics. However most studies have been focused on small-scale bore processes. The present paper describes the first quantitative study, at the estuary scale, of the conditions for tidal bore formation in convergent alluvial estuaries. When freshwater discharge and large-scale spatial variations of the estuary water depth can be neglected, tide propagation in such estuaries is controlled by three main dimensionless parameters: the nonlinearity parameter ε 0 , the convergence ratio δ 0 and the friction parameter ϕ 0 . In this paper we explore this dimensionless parameter space, in terms of tidal bore occurrence, from a database of 21 estuaries (8 tidal-bore estuaries and 13 non tidal-bore estuaries). The field data point out that tidal bores occur for convergence ratios close to the critical convergence δ c . A new proposed definition of the friction parameter highlights a clear separation on the parameter plane ( ϕ 0 , ε 0 ) between tidal-bore estuaries and non tidal-bore estuaries. More specifically, we have established that tidal bores occur in convergent estuaries when the nonlinearity parameter is greater than a critical value, ε c , which is an increasing function of the friction parameter ϕ 0 . This result has been confirmed by numerical simulations of the two-dimensional Saint Venant equations. The real-estuary observations and the numerical simulations also show that, contrary to what is generally assumed, tide amplification is not a necessary condition for tidal bore formation. The effect of freshwater discharge on tidal bore occurrence has been analyzed from the database acquired during three long-term campaigns carried out on the Gironde/Garonne estuary. We have shown that in the upper estuary the tidal bore intensity is mainly governed by the local dimensionless tide amplitude ε. The bore intensity is an increasing function of ε and this relationship does not depend on freshwater discharge. However, freshwater discharge damps the tidal wave during its propagation and thus reduces ε and consequently limits the tidal bore development in the estuary. To take into account this process in the tidal-bore scaling analysis, it is necessary to introduce a fourth external parameter, the dimensionless river discharge Q 0 . [ABSTRACT FROM AUTHOR]

Laboratory experiments are reported where the analogue of a tidal bore is generated with a centimeter-scale local tidal range in a water channel. A discussion of the hydraulic regimes allows to set the experimental conditions to observe the bore. Temporal measurements of the free surface deformation with an acoustic sensor display an analogue of the tidal asymmetry met in nature between the ebb and the flood. Spatial measurements of the free surface deformation are performed with a laser sheet which delineates the interface thanks to the fluorescent re-emission of fluoresceine diluted in water. Afterwards, a parameter space is provided for the observation of a mini-bore with different hydrodynamical regimes (undular, undular–breaking, breaking) by showing the influence of the analogue local tidal range on the shape of the tidal wave. Finally, flow visualizations reveal the inner structure of the velocity profile of the mini-bore in the undular–breaking regime characterized by flow reversals. [ABSTRACT FROM AUTHOR]