Large bedforms and associated hydraulic conditions within microtidal-inlet channels, southern Gulf of St. Lawrence, Canada

1988 ◽  
Vol 25 (6) ◽  
pp. 916-922 ◽  
Author(s):  
P. N. Matsushita ◽  
S. B. McCann
Keyword(s):  
Tidal Current ◽  
Tidal Cycle ◽  
Average Length ◽  
Tidal Flow ◽  
Tidal Range ◽  
Sand Waves ◽  
Hydraulic Conditions ◽  
Throat Section

A variety of large bedforms, at two scales (sand waves, dunes), occur within the throat section of-small microtidal-inlet channels. The larger forms, which have an average length of 32 m and height of 1.0 m, remain ebb oriented throughout the tidal month but are only actively modified at large tides. The smaller forms, which may be superimposed on the larger, are partially reworked each tidal cycle but are also predominantly ebb oriented. Tidal-current measurements confirm the dominance of ebb-tidal flow in the inlet throats and indicate that despite the small tidal range (maximum 1.1 m), ebb currents may exceed 1.0 m s−1 with associated shear velocities of 0.14 m s−1.

scholarly journals Morphodynamic Evolution of a Nourished Beach with Artificial Sandbars: Field Observations and Numerical Modeling

2021 ◽  
Vol 9 (3) ◽  
pp. 245
Author(s):  
Cuiping Kuang ◽  
Xuejian Han ◽  
Jiabo Zhang ◽  
Qingping Zou ◽  
Boling Dong
Keyword(s):  
Sediment Transport ◽  
Tidal Current ◽  
Model Simulation ◽  
Morphological Changes ◽  
Current Model ◽  
Beach Nourishment ◽  
Tidal Range ◽  
Coastal Protection ◽  
Field Observations ◽  
One Year

Beach nourishment, a common practice to replenish an eroded beach face with filling sand, has become increasingly popular as an environmentally friendly soft engineering measure to tackle coastal erosion. In this study, three 200 m long offshore submerged sandbars were placed about 200 m from the shore in August 2017 for both coastal protection and beach nourishment at Shanhai Pass, Bohai Sea, northeastern China. A series of 21 beach profiles were collected from August 2017 to July 2018 to monitor the morphological changes of the nourished beach. Field observations of wave and tide levels were conducted for one year and tidal current for 25 h, respectively. To investigate the spatial-temporal responses of hydrodynamics, sediment transport, and morphology to the presence of three artificial submerged sandbars, a two-dimensional depth-averaged (2DH) multi-fraction sediment transport and morphological model were coupled with wave and current model and implemented over a spatially varying nested grid. The model results compare well with the field observations of hydrodynamics and morphological changes. The tidal range was around 1.0 m and the waves predominately came from the south-south-east (SSE) direction in the study area. The observed and predicted beach profiles indicate that the sandbars moved onshore and the morphology experienced drastic changes immediately after the introduction of sandbars and reached an equilibrium state in about one year. The morphological change was mainly driven by waves. Under the influences of the prevailing waves and the longshore drift toward the northeast, the coastline on the leeside of the sandbars advanced seaward by 35 m maximally while the rest adjacent coastline retreated severely by 44 m maximally within August 2017–July 2018. The model results demonstrate that the three sandbars have little effect on the tidal current but attenuate the incoming wave significantly. As a result, the medium-coarse sand of sandbars is transported onshore and the background silt is mainly transported offshore and partly in the longshore direction toward the northeast. The 2- and 5-year model simulation results further indicate that shoreline salient may form behind the sandbars and protrude offshore enough to reach the sandbars, similar to the tombolo behind the breakwater.

Wave and tidal power

2007 ◽  
Author(s):  
Dean L. Millar
Keyword(s):  
Wave Energy ◽  
Tidal Current ◽  
High Efficiency ◽  
Energy Resource ◽  
Energy Difference ◽  
Tidal Range ◽  
Tidal Power ◽  
Floating Structures ◽  
Wave Energy Converters ◽  
High Tidal Range

This chapter reviews how electricity can be generated from waves and tides. The UK is an excellent example, as the British Isles have rich wave and tidal resources. The technologies for converting wave power into electricity are easily categorized by location type. 1. Shoreline schemes. Shoreline Wave Energy Converters (WECs) are installed permanently on shorelines, from where the electricity is easily transmitted and may even meet local demands. They operate most continuously in locations with a low tidal range. A disadvantage is that less power is available compared to nearshore resources because energy is lost as waves reach the shore. 2. Nearshore schemes. Nearshore WECs are normally floating structures needing seafloor anchoring or inertial reaction points. The advantages over shoreline WECs are that the energy resource is much larger because nearshore WECs can access long-wavelength waves with greater swell, and the tidal range can be much larger. However, the electricity must be transmitted to the shore, thus raising costs. 3. Offshore schemes. Offshore WECs are typically floating structures that usually rely on inertial reaction points. Tidal range effects are insignificant and there is full access to the incident wave energy resource. However, electricity transmission is even more costly. Tidal power technologies fall into two fundamental categories:1. Barrage schemes. In locations with high tidal range a dam is constructed that creates a basin to impound large volumes of water. Water flows in and out of the basin on flood and ebb tides respectively, passing though high efficiency turbines or sluices or both. The power derives from the potential energy difference in water levels either side of the dam. 2. Tidal current turbines. Tidal current turbines (also known as free flow turbines) harness the kinetic energy of water flowing in rivers, estuaries, and oceans. The physical principles are analogous to wind turbines, allowing for the very different density, viscosity, compressibility, and chemistry of water compared to air. Waves are caused by winds, which in the open ocean are often of gale force (speed >14 m/s).

On submarine sand-waves and tidal lee-waves

1959 ◽  
Vol 253 (1273) ◽  
pp. 218-241 ◽  
Keyword(s):  
Wave Train ◽  
Tidal Flow ◽  
Stationary Wave ◽  
Slow Phase ◽  
Density Gradients ◽  
Sand Waves ◽  
The North ◽  
Lee Waves ◽  
The North Sea ◽  
The Stability

A simplified analysis is made of the stability of long waves in a sand bed under deep, slow, and steady (or slowly varying) water flow. Allowing for vertical variation in density and shear, the linearized hydrodynamical equations yield a symmetrical flow whose only action is to impart a slow phase velocity to existing sand-waves without altering their amplitude. The only mechanism found under which sand-waves could grow under the assumed conditions is that of a stationary wave train in the lee of a permanent obstacle. The lee-waves require density gradients greater than a certain minimum, independently of any stability due to shear. Application of this model to tidal flow in the Summer thermocline over the Continental Shelf west of Brittany yields a spectrum of wave-building increments which agrees in general wavelength and shape with that of sand-waves measured on La Chapelle Bank (47° 41' N, 7° 13' W). Changes in amplitude of a few sand-grain diameters per year would be expected. Thermal stratification would be insufficient for the same mechanism to generate waves in the North Sea, but the possibility of density gradients due to suspended sediment is suggested as a likely factor of importance.

scholarly journals Structural Design of a Horizontal-Axis Tidal Current Turbine Composite Blade

2011 ◽  
Author(s):  
Gunjit S. Bir ◽  
Michael J. Lawson ◽  
Ye Li
Keyword(s):  
Structural Design ◽  
Tidal Current ◽  
Center Of Mass ◽  
Tidal Flow ◽  
Composite Blade ◽  
Extreme Loads ◽  
Tidal Turbine ◽  
Laminate Theory ◽  
Tidal Current Turbine ◽  
Current Turbine

This paper describes the structural design of a tidal turbine composite blade. The structural design is preceded by two steps: hydrodynamic design and determination of extreme loads. The hydrodynamic design provides the chord and twist distributions along the blade length that result in optimal performance of the tidal turbine over its lifetime. The extreme loads, i.e. the extreme flap and edgewise loads that the blade would likely encounter over its lifetime, are associated with extreme tidal flow conditions and are obtained using a computational fluid dynamics (CFD) software. Given the blade external shape and the extreme loads, we use a laminate-theory-based structural design to determine the optimal layout of composite laminas such that the ultimate-strength and buckling-resistance criteria are satisfied at all points in the blade. The structural design approach allows for arbitrary specification of the chord, twist, and airfoil geometry along the blade and an arbitrary number of shear webs. In addition, certain fabrication criteria are imposed, for example, each composite laminate must be an integral multiple of its constituent ply thickness. In the present effort, the structural design uses only static extreme loads; dynamic-loads-based fatigue design will be addressed in the future. Following the blade design, we compute the distributed structural properties, i.e. flap stiffness, edgewise stiffness, torsion stiffness, mass, moments of inertia, elastic-axis offset, and center-of-mass offset along the blade. Such properties are required by hydro-elastic codes to model the tidal current turbine and to perform modal, stability, loads, and response analyses.

scholarly journals SAR Imaging Features of Shallow Water Bathymetry

2020 ◽  
Vol 27 (3) ◽  
Author(s):  
P. D. Pivaev ◽  
V. N. Kudryavtsev ◽  
E. A. Balashova ◽  
B. Chapron ◽  
◽  
...  
Keyword(s):  
Shallow Water ◽  
Tidal Current ◽  
Bottom Topography ◽  
Tidal Flow ◽  
Imaging Features ◽  
Sar Images ◽  
Current Divergence ◽  
Sar Imagery ◽  
Convergence Zones ◽  
Synthetic Aperture Radars

Purpose. The aim of the article is to study manifestations of the underwater topography features in the northern part of the White Sea in the images made by the spaceborn synthetic aperture radars (SAR) Sentinel-1A, Sentinel-1B. Methods and Results. In the SAR images, the bottom features are revealed as bright and dark brightness anomalies. The anomalies were observed at the wind speed ranging from 2.6 to 10.8 m/s, and became reverse (bright anomalies turned dark and vice versa), when a tidal current changed its direction. It is shown that the observed SAR imagery contrasts correlate to divergence of a current formed by interaction of a tidal flow with the bottom topography inhomogeneities. The simulated SAR contrasts agree with the observations, and confirm the relation between the observed SAR contrasts and the current divergence. Together with modeling the SAR contrasts, the contribution of different mechanisms to formation of the observed modulations of the normalized radar cross section was qualitatively estimated. The wave breaking effect was especially accentuated. The method for retrieving the underwater bottom topography based on the relationship between the bottom gradient and the SAR imagery contrasts is proposed. Conclusions. Location of the bottom inhomogeneities in the shallow water region on the whole coincides with that of the tidal current divergence and convergence zones, which are observed as brightness anomalies in the SAR images. Breaking of surface waves is the main contributor to the observed SAR contrasts. The bottom topography reconstructed from the SAR contrasts, and the actual one resulted from the bathymetry maps are in good agreement. Some discrepancies are interpreted as possible changes in depth and shape of the bottom topography features induced by action of strong currents and waves.

scholarly journals NUMERICAL SIMULATIONS ON INFLUENCE OF LONG-TERM FLUCTUATION OF MEAN WATER LEVEL ON SAND WAVES IN THE KANMON WATERWAY, JAPAN

2020 ◽  
pp. 45
Author(s):  
Shiro Yamagata ◽  
Shouya Orishikise ◽  
Masaru Yamashiro ◽  
Yasuyuki Nakagawa ◽  
Noriaki Hashimoto ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Water Level ◽  
Tidal Current ◽  
Ocean Model ◽  
Spatial Difference ◽  
Sand Waves ◽  
Mean Water Level ◽  
Simulation Results ◽  
Term Fluctuation

In this study, the numerical simulation of tidal current and sediment transport in the Kanmon Waterway were performed by using a numerical simulation model FVCOM (Finite Volume Community Ocean Model (Chen et al. 2003)), in order to discuss the influence of the long-term fluctuation of mean water level on the sand waves. The numerical simulation results suggested that the spatial difference of the long-term fluctuation of mean water level in the Kanmon Straits slightly changes the tidal current around Tanoura Area, and consequently affects the development of sand waves.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/kfMfIVGiLKM

Tidal-current and tidal-range power

2021 ◽  
pp. 413-441
Author(s):  
John Twidell
Keyword(s):  
Tidal Current ◽  
Tidal Range

Response of estuarine wetlands to reinstatement of tidal flows

2010 ◽  
Vol 61 (6) ◽  
pp. 702 ◽  
Author(s):  
Alice J. Howe ◽  
José F. Rodríguez ◽  
Jennifer Spencer ◽  
Geoff R. MacFarlane ◽  
Neil Saintilan
Keyword(s):  
Primary Productivity ◽  
Tidal Flow ◽  
Tidal Range ◽  
Natural Conditions ◽  
Buffer Zones ◽  
Estuarine Wetlands ◽  
Tidal Flows ◽  
Height Datum ◽  
Tidal Pools ◽  
Flood Attenuation

The importance of estuarine wetlands to ecosystem services such as primary productivity and flood attenuation, as well as their function as habitat for threatened species has prompted efforts to restore tidal flows to degraded wetlands. We tracked the response of estuarine vegetation to tidal-flow reinstatement over 12 years (1995–2007) in a wetland of the Hunter estuary, Australia. This site provides important habitat for migratory shorebird species, which favour shallow tidal pools and saltmarsh over mangrove forest. Increased tidal flows following culvert removal reduced shorebird roost habitat by 17% because of mangrove encroachment on saltmarsh and shallow tidal pools. Saltmarsh occurred in areas with a spring tidal range <0.3 m, hydroperiod <1.0 and elevation >0.4 above the Australian height datum (mAHD), whereas mangrove occupied areas with spring tidal range >0.3 m, hydroperiod <0.45 and elevation <0.4 mAHD. By using these parameters, it is possible to exclude mangrove from saltmarsh areas and to establish saltmarsh at lower elevations in the tidal frame than would occur under natural conditions, effectively expanding saltmarsh area. These measures can be useful where landward migration of estuarine communities is restricted by infrastructure; however, they should not be considered a substitute for conservation of remnant saltmarsh or establishment of landward buffer zones.

Tidal-current control of submarine morphology at the mouth of the Miramichi estuary, New Brunswick

1977 ◽  
Vol 14 (11) ◽  
pp. 2524-2532 ◽  
Author(s):  
G. E. Reinson
Keyword(s):  
New Brunswick ◽  
Tidal Current ◽  
Barrier Island ◽  
Current Control ◽  
Tidal Range ◽  
Tidal Prism ◽  
Artificial Channel ◽  
Ebb Tidal Delta ◽  
Island System ◽  
Natural Channel

The mouth of the microtidal Miramichi estuary, New Brunswick, is enclosed by a barrier-island system which is cut by two major tidal inlets. The submarine morphology adjacent to these inlets indicates the presence of large tidal deltas which formed predominantly by tidal-current processes. The extensive shoal water on the landward side of the barrier is due to the landward transport of sand through the inlets and the deposition of this sand as coalescing flood-tidal delta deposits. The creation of an artificial channel inside the main inlet in the late 19th century, and its maintenance since that time, have resulted in substantial channel-flow bypassing of the natural channel seaward of the barrier. This promoted the scouring of a new channel through the ebb-tidal delta shoal.Large tidal deltas apparently are not common morphological features of estuaries on microtidal, barrier-island coastlines, but they do occur at the entrances of very large microtidal estuaries such as the Miramichi. In such cases they are usually completely subtidal, and much larger than tidal deltas of mesotidal estuaries reported in the literature. Rather than tidal range, the tidal prism, which takes into account both tidal range and estuary surface area, may play the major role in the formation of tidal deltas in both mesotidal and microtidal estuaries.

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