Tidal Bore Research Articles

Turbulence and turbulent flux events in tidal bores: case study of the undular tidal bore of the Garonne River

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.

Nutrient Condition of Kampar Big River Estuary: Distribution of N and P Concentrations Drifted by Tidal Bore ”Bono”

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. Keywords: Bono, Fluid dynamics, Nutrient distribution, Tidal bore, Water quality

池大雅筆『銭塘観潮図屏風』の主題再考察 : 図様と文学的典拠を探る(第五十五回美学会全国大会発表要旨)

池大雅筆『銭塘観潮図屏風』の主題再考察 : 図様と文学的典拠を探る(第五十五回美学会全国大会発表要旨)

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.

High Frequency Field Measurements of an Undular Bore Using a 2D LiDAR Scanner

The secondary wave field associated with undular tidal bores (known as whelps) has been barely studied in field conditions: the wave field can be strongly non-hydrostatic, and the turbidity is generally high. In situ measurements based on pressure or acoustic signals can therefore be limited or inadequate. The intermittent nature of this process in the field and the complications encountered in the downscaling to laboratory conditions also render its study difficult. Here, we present a new methodology based on LiDAR technology to provide high spatial and temporal resolution measurements of the free surface of an undular tidal bore. A wave-by-wave analysis is performed on the whelps, and comparisons between LiDAR, acoustic and pressure-derived measurements are used to quantify the non-hydrostatic nature of this phenomenon. A correction based on linear wave theory applied on individual wave properties improves the results from the pressure transducer (Root mean square error, R M S E of 0 . 19 m against 0 . 38 m); however, more robust data is obtained from an upwards-looking acoustic sensor despite high turbidity during the passage of the whelps ( R M S E of 0 . 05 m). Finally, the LiDAR scanner provides the unique possibility to study the wave geometry: the distribution of measured wave height, period, celerity, steepness and wavelength are presented. It is found that the highest wave from the whelps can be steeper than the bore front, explaining why breaking events are sometimes observed in the secondary wave field of undular tidal bores.

Flow and turbulence structure in a hypertidal estuary with the world's biggest tidal bore

AbstractTurbulent and flow structure associated with breaking tidal bores are deliberately investigated on the basis of field measurements. High‐resolution velocity and hydrographic data are collected in the middle Qiantang Estuary by a vertical array of acoustic Doppler velocimeters and optical backscatter sensors, collaborated with a bottom‐mounted acoustic Doppler current profiler. Besides obvious variations in diurnal and spring‐neap tidal cycles, the estuarine dynamics is featured by extreme asymmetry in flood and ebb tides. The flood tide is abnormally accelerated to generate tidal bores at the first 10 min or more, with breaking or undular configurations at the front. The occurrence of peak flow velocity, turbulent kinetic energy (TKE), and TKE dissipation rate (ε) is definitely associated with breaking bores, with their values several times to 2 orders of magnitude larger than the corresponding secondary peak values during the maximum ebb flows. Flow and turbulence dynamics are significantly affected by the tidal‐bore Froude number. A sandwich ε structure is clear exhibited with the maximum value at the surface, secondary maximum near the bed, and the minimum at the intermediate. Dual TKE sources are indicated by an approximate local balance between shear production and dissipation near the bottom, and a top‐down TKE dissipation using the modified Froude scaling in the vertical water column. The highly elevated dissipation by breaking bores is comparable to that by intense breaking waves in the surf zone, and the former potentially penetrates the entire water column to produce extreme sediment‐resuspension events in combination with intense bottom shear stress.

Upstream Propagation of Surges and Bores: Free-Surface Observations

In a free-surface flow, a sudden increase in water depth induces a positive surge, also called compression wave or bore. Herein a physical study was conducted in relatively large-size rectangular channel with a smooth bed. The upstream propagation of breaking and undular bores were investigated with a broad range of Froude numbers Fri ranging from 1.1 to 2.3. Both instantaneous and ensemble-averaged free-surface measurements were performed nonintrusively. The observations showed the occurrence of undular bores for 1 < Fr1 1.2 to 1.3, breaking bores for Fr1 > 1.4 to 1.5, and breaking bores with secondary waves for 1.2-1.3 > Fr1 1.4-1.5. The propagation of a breaking bore was associated with an upward free-surface curvature immediately before the roller toe for Fri < 2, and an abrupt increase in free-surface elevation with the passage of the breaking roller. The propagation of undular bores was characterized by a smooth upward free-surface curvature, followed by a smooth first wave crest and a train of secondary quasi-periodic undulations. For all tidal bores, the passage of the bore front was always associated with large free-surface fluctuations, occurring slightly after the arrival of the front. During the generation process, the positive surge formed very rapidly and the surge celerity increased very rapidly, reaching maximum values excess of the fully-developed bore celerity. With increasing time, the surge decelerated and the bore propagated at an early constant celerity for (xgate —x)/xgate > 10.

Successive impact of tidal bores on sedimentary processes: Arcins channel, Garonne River

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.

Monitoring Tidal Bores using Acoustic Tomography System

Kawanisi, K.; Zhu, X.-H.; Fan, X., and Nistor, I., 2017. Monitoring tidal bores using acoustic tomography system.Continuous measurements of flow velocities and suspended sediments were carried out in the Qiantang River (China) with extreme tidal bore conditions. Fluvial and coastal acoustic tomography systems (FATS/CATS) were used in the field studies simultaneously with acoustic Doppler current profilers (ADCPs) and optical backscatter (OBS) equipment. A couple of broadband transducers were installed diagonally across the river around 90 km upstream of the mouth. The length of the sound transmission line was 3050 m. Cross-sectional averaged velocities (V) collected by FATS/CATS enabled the authors to estimate important characteristics of the tidal bores (bore height and celerity). The changes in V recorded during the upstream movement of the bore ranged from 1.35 to 1.76 ms−1. The height and celerity of the bore varied from 1.0 to 1.32 m and 7.59 to 8.29 ms−1, respectively. Since a point/vertical measurement cannot represent a river's cross section, the ADCP data for velocity and water level (pressure) near the riverbank underestimated the bore height by 22% and 16%, respectively. The maximum suspended sediment concentration (SSC) was observed to have occurred approximately 1 h after the bore's arrival; the time lag between the maximum SSC and the bore front is considerably larger than the time lags in previous works. In the case of larger bores, the section mean SSCs, which were deduced from the sound attenuation of FATS/CATS due to suspended sediment, appeared to be appropriate. The time history of the velocity, measured by ADCPs, during the passage of the bore deviated from the normal velocity profile, i.e. the velocity magnitude decreased with an increasing height above the bed for the relaxation time of a few minutes following the arrival of the bore.

Environmental Effect of Tidal Bore Propagation in Kampar River

The environmental effect of the tidal bore propagation in kampar river is investigated. Propagation of the tidal bore satisfy Korteweg and de Vries (KdV) equation where the environmental effect will be given as a perturbation term of the KdV equation. The environmental efects taken into considerations are river discharge and bottom sediment. The result show that a river discharge that flow opposite to wave motion will give the damping effect that is decreasing of the wave velocity and the amplitude. The bottom sediments will give the damping effect so that a fine bottom sediment would cause the waves propagte slower than coarse sediment.

New record of Carcharhinus leucas (Valenciennes, 1839) in an equatorial river system

Bull sharks are a cosmopolitan shark species frequently found in shallow shelf ocean waters and, occasionally, in several tropical river systems around the world. Due to bull shark’s capability to enter riverine systems, the documentation of its occurrence is essential for future fisheries inspections and studies. In this way, this study aims to report the presence of a medium sized specimen of C. leucas in an equatorial river system. The specimen was caught by fishermen at Mearim River, located in Northern Brazil and well known for the occurrence of tidal bores during the highest spring tides of the dry season. The event coincided with the occurrence of one of the strongest spring tides of 2015. The captured female specimen measured approximately 1300 mm and weighted 35 kg. The occurrence of this species was not known in this river basin until now. We recommend and support future ichthyologic studies in the Mearim River basin in order to provide data for the delimitation of the territory used by C. leucas in Maranhao State, specially looking into its age, growth, diet, spatial, and temporal movement patterns in this area.

A novel approach to measurement of underwater sound levels in a dangerous tidal fjord using a miniature self-contained acoustic recorder

Recent plans for highway construction along the shore of Turnagain Arm, Alaska, raised concerns about acoustic impact on the critically endangered Cook Inlet subpopulation of beluga whales (Delphinapterus leucas). Evaluation of possible impact required estimates of normal background sound levels. However, as a shallow fjord with profound (9-m mean) tides, hazardous currents, tidal bores, and quicksand-like tidal flats, Turnagain Arm has historically defied most vessel operations and thwarted vessel-based sound measurements. In August 2014, the first documented acoustic measurements in Turnagain Arm of which we are aware took place using a novel technique based on a miniature, self-contained acoustic recorder developed as a marine-mammal tag (Acousonde™, Greeneridge Sciences, Inc.). The recorder’s small size allowed it to be suspended from a motorized buoy and towed up to 80 m from shore. Measurements took place off a point known as Windy Corner at high and low tide as well as near maximum flood and ebb current. Data showed Turnagain Arm to be quieter than expected, with broadband (40 Hz to 9.3 kHz) sound pressure levels as low as 74 dB re 1 μPa and below a 125-dB provisional regulatory assumption. [Work supported by Alaska Department of Transportation and Public Facilities.]

Unsteady turbulence, dynamic similarity and scale effects in bores and positive surges

A tidal bore is a positive surge or compression wave formed in an estuarine system during the early flood tide under macro-tidal conditions. A series of physical experiments were conducted in a large facility to investigate the unsteady free-surface properties, velocity characteristics and Reynolds shear stresses. Both instantaneous and ensemble-averaged measurements were performed. The results demonstrated the intense turbulence and turbulent mixing under breaking and undular tidal bores. A range of dimensionless unsteady turbulent properties were carefully compared based upon both Froude and Morton similitudes with two different Reynolds number ranges. The data showed that several parameters were affected by scale effects, including velocity and Reynolds stress fluctuations during the bore propagation. The finding implies that laboratory study data might not be up-scaled to prototype conditions without some form of scale effects.

Are breaking waves, bores, surges and jumps the same flow?

The flow structure in the aerated region of the roller generated by breaking waves remains a great challenge to study, with large quantities of entrained air and turbulence interactions making it very difficult to investigate in details. A number of analogies were proposed between breaking waves in deep or shallow water, tidal bores and hydraulic jumps. Many numerical models used to simulate waves in the surf zone do not implicitly simulate the breaking process of the waves, but are required to parameterise the wave-breaking effects, thus relying on experimental data. Analogies are also assumed to quantify the roller dynamics and the energy dissipation. The scope of this paper is to review the different analogies proposed in the literature and to discuss current practices. A thorough survey is offered and a discussion is developed an aimed at improving the use of possible breaking proxies. The most recent data are revisited and scrutinised for the use of most advanced numerical models to educe the surf zone hydrodynamics. In particular, the roller dynamics and geometrical characteristics are discussed. An open discussion is proposed to explore the actual practices and propose perspectives based on the most appropriate analogy, namely the tidal bore.

Impact of a large cylindrical roughness on tidal bore propagation

A tidal bore is a hydrodynamic shock, surging upstream in some shallow-water bays and estuaries during the flood tide under large tidal range. This study investigates experimentally the propagation of tidal bores over a large cylindrical roughness element, representative of damaged bridge pier foundation. In the initially steady flow, the large cylindrical element generated a wake region, with extents comparable to steady flow literature. During the tidal bore propagation, the presence of the element had negligible effect on the free-surface properties, but a significant impact in terms of the instantaneous velocity and Reynolds stresses. This resulted in longer transient recirculation both upstream and downstream of the element and larger maximum velocity recirculation magnitudes, as well as enhanced turbulent stress levels and potential bed erosion around the large element, within two diameters from the element centre. The results showed the potential development of a large scour hole around the cylindrical element.

Application of positivity-preserving well-balanced discontinuous Galerkin method in computational hydrology

Abstract The positivity-preserving well-balanced discontinuous Galerkin (DG) method (Xing et al. J Sci Comput 57 , 2013) is employed to solve the shallow water equations on an unstructured triangular mesh and to study their applications in computational hydrology. The grid convergence of the DG method is verified via the steady state oblique hydraulic jump problem. The dam-breaking problems with wet and dry river beds are conducted to demonstrate the positivity-preserving property of the scheme. The tidal bores in an idealized estuary problem are simulated to study the development and evolution of the tidal bores from different amplitudes of incoming tidal waves and topography of the river bed bottom. The numerical experiments above demonstrate that the DG method can be applied successfully to these class of problems in computational hydrology.

High frequency (hourly) variation in vertical distribution and abundance of meroplanktonic larvae in nearshore waters during strong internal tidal forcing

We related the vertical distribution and abundance of nearshore meroplankton at hourly time scales with internal tidal wave events. We proposed that significant changes in plankter abundance would occur across internal tidal fronts, and that surface and bottom strata would respond in opposite fashions. First-mode internal tidal bores propagating in the alongshore direction were detected in water-column currents and baroclinic temperature changes. Surface and bottom currents always flowed in opposite directions, and abrupt flow reversals coincided with large temperature changes during arrival of bores. Crab zoeae and barnacle cyprids were more abundant in the bottom strata, whereas barnacle nauplii showed the opposite pattern. Significant changes in vertical distribution and abundance of target meroplankters occurred across internal tidal fronts, especially for crabs at depth, with surface and bottom organisms responding in opposite fashions. Changes in plankter abundance were significantly correlated with current flows in the strata where they were most abundant. The manner in which plankters were affected (increasing or decreasing abundance) appeared to be modulated by their vertical position within the water column. The significant differences found at the high frequencies of this study, maintained across sampling days, suggest that nearshore meroplankton populations may have greater and more consistent temporal and vertical variability than previously considered.

Sediment transport induced by tidal bores. An estimation from suspended matter measurements in the Sée River (Mont-Saint-Michel Bay, northwestern France)

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 (qs) associated with the tidal bore passage (up to 40kg/m2/s).

Conditions for tidal bore formation in convergent alluvial estuaries

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 ε0, the convergence ratio δ0 and the friction parameter ϕ0. 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 δc. A new proposed definition of the friction parameter highlights a clear separation on the parameter plane (ϕ0,ε0) 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, εc, which is an increasing function of the friction parameter ϕ0. 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 Q0.

Atmospheric noise of a breaking tidal bore.

A tidal bore is a surge of waters propagating upstream in an estuary as the tidal flow turns to rising and the flood tide propagates into a funnel-shaped system. Large tidal bores have a marked breaking roller. The sounds generated by breaking tidal bores were herein investigated in the field (Qiantang River) and in laboratory. The sound pressure record showed two dominant periods, with some similarity with an earlier study [Chanson (2009). J. Acoust. Soc. Am. 125(6), 3561-3568]. The two distinct phases were the incoming tidal bore when the sound amplitude increased with the approaching bore, and the passage of the tidal bore in front of the microphone when loud and powerful noises were heard. The dominant frequency ranged from 57 to 131 Hz in the Qiantang River bore. A comparison between laboratory and prototype tidal bores illustrated both common features and differences. The low pitch sound of the breaking bore had a dominant frequency close to the collective oscillations of bubble clouds, which could be modeled with a bubble cloud model using a transverse dimension of the bore roller. The findings suggest that this model might be over simplistic in the case of a powerful breaking bore, like that of the Qiantang River.