Hydrodynamic Characteristics of Undular Tidal Bores in the Qiantang River Based on Field Observations

Understanding the undular tidal bores in the Qiantang River is essential for effective river management and maintenance.While breaking tidal bores have been studied extensively, reports on undular tidal bores in the Qiantang Riverremain limited. Furthermore, observed data on undular tidal bores fulfilling the requirements of short measurementtime intervals, and spring, medium, and neap tide coverage, and providing detailed data for the global vertical stratificationof flow velocity are quite limited. Based on field observations at Qige in the Qiantang estuary, we analyzedthe characteristics of undular tidal bores. The results showed that the flooding amplitude (a) of the first wave isalways larger than its ebbing amplitude (b). Moreover, the vertical distribution of the maximum flood velocity exhibitesthree shapes, influenced by the tidal range, while that of the maximum ebb velocity exhibites a single shape. Duringthe initial phase of the flood tide in the spring and medium tides, the upper water body experiences multiple oscillatingchanges along the flow direction, corresponding to the alternating process of the crest and trough of the tide levelupon the arrival of the tidal bore. The tidal range is a crucial parameter in tidal bore hydrodynamics. By establishingthe relationship between hydrodynamic parameters and tidal range, other hydrodynamic parameters, such as the tidalbore height, maximum flood depth–averaged velocity, maximum flood stratified velocity at the measurement points,and duration of the flood tide current, can be effectively predicted, thereby providing an important reference for rivermanagement and maintenance.

Tidal Bore Dynamics Around the Similar Right-Angle Shoreline in the Qiantang Estuary,China

Tidal bores are a unique hydrodynamic phenomenon during flood tide in the Qiantang Estuary.The tidal bore propagation around the similar right-angle shoreline is rarely documented in tidal estuaries.To investigate tidal bores around this shoreline,a hydrodynamic model combined with a theoretical method is employed to reveal the characteristics of the bore propagation.The theoretical solution of the tidal bore intensity is deduced to illustrate the relationship of the incident tidal bores and the back-flow bores during the propagation.The hydrodynamic model based on shallow water equation is employed to perform the simulation of tidal bores in the estuary.Model results with respect to the bore height and the propagation speed of tidal bores have a favourable agreement with field data.The tidal bore dynamics in the neighborhood of the similar right-angle shoreline are elucidated.The characteristics of tidal bores in terms of water surface,velocity,bore steepness and the intensity are illustrated and the back-flow bore is analyzed by numerical and theoretical methods around the similar right-angle shoreline.The height of the back-flow bore relative to the incident tidal bore ranges from 1.05 to 1.77.Model result reveals that the ambient water depth and the shape of the similar right-angle shoreline are contributed to the back-flow bore formation.

Flume Experiment Investigation on Propagation Characteristics of Tidal Bore in A Curved Channel

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 freesurface 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 freesurface 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.

Impact of and adaptation strategies for sea-level rise on Yangtze River Delta

The Yangtze River Delta characterized by a dense population and a rapidly developing economy is highly vulnerable to sea-level rise. The data from the China Oceanic Information Network and the Zhejiang Provincial Hydrology Bureau are used to analyze sea-level rise. The rate of sea-level rise in the delta was 2.4 mm per year in 1981-2015. The annual sea-level at Daishan, Dinghai, and Dongtou stations in the south wing of the delta were 4.3, 3.1, and 5 mm per year respectively over the same period. The 10-year averaged results at each station also indicate a perceptible trend of sea-level rise. Sea-level rise is contributed to a larger proportion of intensified erosion, ranging from 3% to 14% in the delta. Meanwhile, the 100-year return period of tidal level has decreased to the 50-year rank at Dongtou and Dinghai stations. Moreover, the arrival time of tidal bores at Yanguan is 4 min earlier under sea-level rise of 0.145 m than that of 0 m. The height of tidal bores and the velocities at the surface and bottom layers have an increase under sea-level rise. The maximum increases of high and low tide levels are 0.122 m and 0.016 m while the maximum increases of the velocities at the surface and bottom layers are 0.07 m s^- 1 and 0.05 m s ^-1, respectively. Sea-level rise will bring about the damage of seawall, thus the design standard of constructing seawalls should adopt a higher level to minimize the associated risks in the Yangtze River Delta and its south wing.

Dynamic Behavior of a New Hydraulic Steel Gate

A new style of hydraulic steel gate based on the principle of bionics is proposed in this paper. It has a fish-like shape and consists of right arches, invert arches, connection components and a face plate. It would be first applied in the project of Caoe River Sluice, used as both tidal barrage and flood gate. Compared with conventional hydraulic steel gate of beam grids, this new style of hydraulic steel gate can save up to 30%-50% of steel consumption. The dynamic behavior of the new gate under the impact load of tidal bore is investigated. The impact load of tidal bore is considered by a load spectrum obtained by field observation over a long period of time. Then a numerical analysis of the gate under the load spectrum is carried out by finite element method. The fluid-structure interaction is considered in the analysis. And a comparison between the response of the gate under the impact load and the response of the gate under the corresponding static load is conducted and indicates that the gate has a dynamic magnification factor of 1.2.

Experimental hydrodynamic study of the Qiantang River tidal bore

To study the hydrodynamics of tidal bore, a physical modeling study is carried out in a rectangular flume with considera- tions of the tidal bore heights, the propagation speeds, the tidal current velocities, the front steepness, and the bore shapes. After the validation with the field observations, the experimental results are analyzed, and it is shown that： （1） the greater initial ebb velocity or the larger initial water depth impedes the tidal bore propagation, （2） the maximum bore height appears at an initial ebb velocity in the range of 0.5 m/s-l.5 m/s. （3） when the Froude number exceeds 1.2, an undular bore appears, atter it exceeds 1.3, a breaking bore occurs, and after it exceeds 1.7, the bore is broken.

A preliminary study of the turbulence features of the tidal bore in the Qiantang River,China

In this paper, the turbulence characteristics of the tidal flow in the Qiantang River, China, the world-famous Qiantang bore, are studied. A detailed field observation at the Yanguan section of the Qiantang River was carried out during the spring tide in October 2010 with a continuous collection of high frequency turbulence data. The data analysis shows that the hydrodynamic processes are characterized by a strong tidal bore. Statistics of the turbulence such as the probability distributions of the turbulent components, the variance terms and the covariance terms are found consistent with those of previous studies of estuaries without the tidal bore. However, along the vertical profile, the distributions of all variables become more scattered downwards. The horizontal turbulence fluctuations are of a similar magnitude while the vertical turbulence has a fluctuation magnitffde about 1/3 of that of the horizontal turbulences. The fluctuation strengths and the Reynolds stresses are much larger than those of other estuaries when the bore arrives. The bottom shear stress varies periodically with the tides, less than 0.44 N/m2 during the ebb but is increased drastically at the bore arrival, with the maximum being 0.92 N/m2. A good linear relationship is found between the bottom shear stress and the bottom suspended sediment concentration.

Effect of dike line adjustment on the tidal bore in the Qiantang Estuary,China

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.