Tidal Jet Research Articles

Distribution of Potentially Harmful Phytoplankton Species in the Northern Strait of Georgia, British Columbia

Spatial and temporal distributions of Chaetoceros convolutum (including C. concavicorne), Heterosigma akashiwo, Protogonyaulax (= Alexandrium) catenella, and Dinophysis are presented for the northern Strait of Georgia from March to September, 1986. In spring C. convolutum was found on the slightly stratified eastern side in concentrations just below those leading to kills of caged salmon (4-5000 cells∙L−1). The northern Strait became thermally stratified in summer. At this time the population centre of C. convolutum shifted to mid-Strait near the edge of the Discovery Passage tidal jet where it was maintained near the pycnocline (10–15 m) in concentrations up to 35,000 cells∙L−1. Heterosigma akashiwo, another fish killer, was the pbotosynthetic dominant in June and reached 200 000 cells∙L−1 in the northwest at 5 m. Protogonyaulax catenella, a source of paralytic shellfish poison (PSP), was also most abundant in the north and west, where dangerous levels of PSP often occur, particularly near Comox. Collectively, Dinophysis species exceeded the critical concentration for diarrheic shellfish poisoning (200 cells∙L−) on the western side during summer. All the potentially harmful flagellated species seem to be introduced from the northern passageways. Sheltered bays to the north are possible seed beds for cyst-forming species whereas C. convolutum remains in the Strait year-round.

Structure of the strong tidal jet in the naruto strait

In order to clarify the structure of the strong tidal current at the Naruto Strait in the Seto Inland Sea of Japan, the sea-level values were observed in the strait and the current measurements were made with an Acoustic Doppler Current Profiler (ADCP). The tidal volume transports for M2 and S2 tides were about 74×103 and 26×103 m3 sec−1, respectively. The horizontal profile of the velocity at the phase of the strong tidal current compares favorably with a theoretical profile of the two-dimensional steady turbulent jet except for the side parts of the profile. Moreover, the entrainment rate of the surrounding water into the strong tidal jet was estimated from the difference of mass flux between two cross-sections at the strait, the entrainment rate and entrainment constant for both the northward and southward flows being about 1.3–2.5×10−4m−1 and about 0.03–0.05, respectively.

Primary Production in a Tidally Energetic Fjord: Evidence of Seasonal and Inter-annual Tidal Forcing

A long term data set collected from a tidally energetic sill fjord was analyzed for its statistical relationships between primary production indices and several represented environmental variables. The analysis identified variance and covariance structure in these variables implicating changes in water column clarity, in inter-annual variability of phytoplankton carbon uptake rate, and the static stability of basin surface water in phytoplankton standing stock. The biomass–stability relationship was found to be seasonally dependent, with biomass positively correlated with stability in the summer and negatively correlated in the spring/fall, and restricted to waters under the direct mixing influence of the tidal inflow jet. These statistical patterns are discussed in terms of a possible control of primary production by seasonal and inter-annual variations in tidal inflow buoyancy.

Vertical Mixing in Basin Waters of Fjords

Abstract The rate of work against the buoyancy forces due to vertical mixing (W) has been determined from repeated measurements of vertical density profiles in a large number of fjordic sill basins (basins dammed by sills). It is found that there is a weak “background” rate of work W0, probably driven by the local wind. Superposed upon this is work driven by the tide. Thus W = W0 + RfE, where E is the mean energy flux from the surface tide to turbulence in the sill basin and Rf is an efficiency factor. We distinguish between “wave basins” and “jet basins.” In the former category progressive internal tides are generated in the mouths, while in the latter there are tidal jets at the mouths. For wave basins, about 5.6% of the energy flux E from the surface tide is used for work against the buoyancy forces in the basin water (i.e., Rf ≈ 0.056). The corresponding figure for jet basins appears to be less than 1%. We have also studied the dependence of the vertical diffusivity κ upon the vertical stratification ...

Seasonal mixing of ellis fjord, vestfold hills, east antarctica

The seasonal mixing within Ellis Fjord and its relationship to the ocean are described using temperature, salinity and freshwater input data. The fjord is ice covered for 11–12 months of the year, is up to 117 m deep and has six major basins, two of which at its head are meromictic (in which some water remains partly or wholly unmixed with the main water mass at the circulation periods), hypersaline and permanently anoxic. There was a restricted water exchange during the winter and early spring between the fjord and the ocean, with the vertical mixing dominated by brine convection from salt released by the thickening ice sheet. This convection destroyed both the early winter stratification in the oxic basins and the isopycnal waters linking the sills of the meromictic basins to the deeper waters of the downstream oxic basins. Brine convection also produced waters of elevated salinity, in the shallows of all the basins, which gravitated as density currents to the bottoms of their respective basins. This process was responsible for producting hypersaline conditions at the bottoms of the two meromictic basins during the mid-holocene period. Brine continued to drain from the ice in early spring but without an increase in ice thickness. This served to convect surface waters, recently warmed through solar radiation, throughout the water columns of the oxic basins. Stratification of the surface waters, over summer, was greater in the landward basins than in the seaward basins. This may have been a result of a buoyant tidal jet emanating from the mouth of the fjord, destroying stratification in the seaward basins. As a result, warmer water of lower salinity from the basin outside the fjord had mixed down to the bottom of the first basin during late spring and summer.

Tidal jets, nutrient upwelling and their influence on the productivity of the alga Halimeda in the Ribbon Reefs, Great Barrier Reef

A field experiment was carried out to study water circulation and benthic biological productivity near a passage through the Ribbon Reefs in the northern Great Barrier Reef of Australia. The currents through the passage were phase-locked with the tide. During rising tides, strong currents through the passage generated localized upwelling on the upper continental slope, enriching the depleted surface waters in nutrients, particularly nitrate and phosphate. Simultaneously, on the shelf side of the passage, a tidal jet-vortex pair system developed, which separated from the Ribbon Reefs so that the coral reefs themselves received little of the upwelled water. This was propagated as a bottom-trapped layer towards the meadows of the calcareous alga Halimeda situated several kilometres inshore of the reefs. Halimeda can accumulate nutrients, particularly nitrate, from the relatively low concentrations available from the upwelling events. The quantity of nitrogen upwelled was more than sufficient to supply the total nitrogen requirements of the Halimeda vegetation. A tidal jet also formed, offshore from the reef passage, during falling tides and the coral-covered offshore side of the Ribbon Reefs may be sustained by the subsequent vertical turbulent entrainment into the jet of deep, nutrient-rich water immediately offshore from the reef passages. These processes require a continuous barrier reef with only narrow passages several kilometers apart. Numerical models successfully reproduce the observations of jet-driven upwelling and of the dynamics of the tidal jet-vortex pair system. The model predictions are very sensitive to the details of the bathymetry of reef passages. As such data are presently unavailable, it is not yet possible to use these models to calculate the jet-driven nutrient upwelling for the whole Great Barrier Reef.

Coastal tidal jets and tidal fringe development around the Isles of Scilly

Tidal jets are a ubiquitous feature of the coastal environment and result from strong tidal streaming off coastal features such as promontories. Around the Isles of Scilly there exist two tidal jets which tend to propagate in a clockwise sense around the island group. Currents in excess of 90 cm s −1 appear necessary for their production and the jets are characterized with a Reynolds number of about 30. It is shown that the jets indicate the direction of the maximum stream and the residual circulation around the islands. With an offshore component to the residual flow, tidal fringes may develop from the jets and such fringes were observed on the northern side of the islands.

TIDICS—Control of tidal residual circulation and tidal exchange in a channel-basin system

A self-excited oscillation of tidal flow occurs in a tidal channel-basin system with a narrow and high speed inflowing tidal jet. The mechanism of this oscillation was examined through hydraulic experiments. Results show that the oscillation is caused by alternation in the strength of asymmetric residual circulation caused by a biased supply of vorticity by asymmetric tidal vortex pairs, and that the mechanism of alternation also depends on negative feed-back between the residual circulation and the vorticity supply.

NOAA satellite and air-borne sensing of a small-scale, coastal tidal jet

Koombana Bay, on the south-west coast of Australia, contains a tidal jet that emanates from Leschenault Inlet via a man-made channel 150 m wide. The tides are of mixed diurnal-semidiurnal character. The strongest jets are induced by the diurnal tide and flow at night in summer and during daytime in winter. The duration of the discharge is about 9 h, after which the maximum length of the jet is a few kilometres. Extensive field studies together with numerical and analytical modelling have recently been completed on the jet. These allowed predictions of optimum times for viewing the jet via an air-borne thermal scanner aboard the CSIRO Fokker F27 aircraft, and a NOAA7 satellite image. The air-borne image mapped the late-summer jet, which consisted of night-cooled water from the shallow Inlet. Because the satellite pass occurs in late afternoon, the seasonality of the tide limits visibility of the jet in the imagery to late winter. The NOAA7 image shows a jet composed of warm water that has been heated during the day inside the Inlet. These observations confirm the sea data and model results and are believed to be the first use of NOAA imagery to resolve a coastal oceanographic feature of this scale.

Tidally induced jet in Koombana Bay, Western Australia

A study is made of a coastal tidal jet, based on a field program together with numerical and analytical modelling of the tidal discharge and jet dynamics. A new criterion is demonstrated for bottom attachment of low-aspect-ratio buoyant jets. The slightly buoyant jet is attached to the seabed over the initial 2 km of its trajectory, which lies in shallow coastal waters of less than 10 m depth. The jet is about 200 m in width and so its ratio of depth to half-width (aspect ratio) is much lower than for previously reported bottom-attached jets. The longitudinal retardation of the axial speed of the jet is due to bottom friction and entrainment. The jet widens only slowly with distance along its trajectory because entrainment is limited to its sides and is compensated by bathymetric deepening. The jet attaches to the coastline by turning, without loss of speed, to move parallel to the shore. The coastal attachment width is found to be a simple function of the ratio of the jet discharge velocity to the speed of the prevailing alongshore current.

A Case Study of Wave–Current–Bathymetry Interactions at the Columbia River Entrance

Abstract A unique set of field observations has documented intense wave–current–bathymetry interactions in a tidal inlet, providing a severe test of existing wave theory. Hourly wave spectral estimates were acquired over ten complete tidal cycles at locations offshore of, and on, the Columbia River Bar. This site has long been recognized as an extreme hazard to navigation due to the interaction of incident waves with a strong tidal jet typified by ebb currents in excess of 2 m s−1. During the five-day observational period, offshore significant wave height ranged from 1 to 5 m; in contrast, the Bar wave height oscillated at tidal periods, sometimes doubling during a single six-hour flood-to-ebb cycle. In one case, the Bar wave height was 7.0 m with an offshore wave height of 2.9 m. A one-dimensional model, based on linear wave action–density conservation and incorporating shoaling, refraction and radiation stress, fits the data remarkably well; 85% of the observed variance in Bar swell height and 57% of th...

Circulation Induced by Tidal Jets

Steady potential motion induced by a tidal jet in an ebbing ocean is analyzed by representing the jet as a distribution of sink singularities and relating the sink strength to jet solutions for steady bottom‐frictional turbulent jets over constant bathymetry. Circulation patterns are determined for various inlet configurations of practical interest and for different values of the bottom friction parameter. Particular attention is given to the jet induced alongshore current which is shown to be sensitive to the presence of jetties and also to the bottom friction experienced by the jet. The present theory is applied to Fort Pierce Inlet, Florida, where severe erosion is known to exist on both sides of the inlet. It is suggested that the alongshore current, albeit small in magnitude, is a potential contributor to the movement of suspended beach material toward the inlet due to its continual occurrence during every ebb tide.

Hydromechanics of Tidal Jets

A unified theoretical investigation of the fully-developed region of a tidal jet is presented. The jet is treated as a vertically-averaged flow and the effects of lateral mixing, bottom friction, and variable bathymetry are included. It is shown, without assuming any specific form of the similarity function, that the cross-stream length scale and the centerline velocity of the jet must satisfy certain differential equations in order for the jet to be self-similar. Solutions of these equations are obtained for some simple forms of bottom topography. For a flat, frictional bottom, the jet exhibits exponential growth and decay of the centerline velocity which is in agreement with earlier investigations. An exact analytical solution for the similarity function is obtained upon introduction of Prandtl's eddy viscosity hypothesis. The theory contains two free constants which must be determined in future experimental investigations.

Evolution of a shoal retreat massif, North Carolina Shelf: Inferences from areal geology

The Albemarle Shelf Valley Complex on the northern North Carolina Shelf is a leveed shelf-floor channel trending seaward from the modern Albemarle estuary. Vibracores and seismic profiles indicate that the levees have a twofold internal structure. Levee cores consist of fine sand interbedded with mud lenses. The cores are mantled with a generally coarser, cleaner sand. The levees are interpreted as shoal retreat massifs; deposits formed as the littoral-drift depositional centers on either side of the ancestral Albemarle estuary retreated landward during the Holocene transgression. The shelf-valley complex underwent systematic changes in bottom morphology and sediment character as the reversing tidal jet of the estuary mouth was replaced by the intermittent south-trending storm flows of the open shelf. A pattern of ridges and troughs with 10 m of relief was incised into north sides of the massifs flanking the shelf valley. The coarser surficial sand into which the bedform pattern has been impressed appears to be a lag deposit formed by the winnowing of the massifs during storm flow. On ridge crests this surficial sand sheet has been molded into sand waves up to 3 m high. The relative orientations of sand waves, ridges, and the shoreline indicate that the structure of the velocity field during peak flows must be quite complex. Ridges converge southward with the shoreline at angles of 15–20°, while the sand waves atop them make angles of about 75° with the shoreline; the sand waves are thus neither orthogonal with respect to the shoreline nor with respect to the ridges. Sand-wave orientation indicates southward bottom flow with an offshore component. Existing hydrodynamical theory does not adequately explain this pattern. Extensive hydraulic measurements of careful design will be required so we can interpret the bedform pattern and its role in the coastal sand budget.

Dynamic Diversion: Influence of Longshore Current-Tidal Flow Interaction on Chenier and Barrier Island Plains

ABSTRACT Chenier and barrier island plains are characteristic products of post-Pleistocene sedimentation along the northern and western coasts of the Gulf of Mexico, but similar features may be recognized throughout the world. These plains have been formed by net progradational displacement of the sea throughout the latest 3000 to 5000 year period of sea level stability. They consist of low, narrow, well-sorted shell and sand ridges that are elongate parallel with the former shoreline, and which are separated by tidal mud flats or zones of poorly sorted, fine sand. A correlation has been established in the vicinity of the Mississippi River delta, by means of radiocarbon dating, between low rate of fine sediment discharge into westward moving longshore currents, stability or minor recession of the downdrift shoreline, and slow accretion of well-sorted chenier beach ridge sand. High rate of sediment discharge into nearshore currents, however, coincides with rapid progradation of sandy, silty mudflat deposits along the downdrift shoreline. It is suggested that the presence of a high content of fine sediment in longshore currents changes their fluid characteristics in such a way as to enhance traction transport, inhibit separation of differing grain size modes, and thus promote deposition of unsorted detritus. Light sediment loads halt rapid progradation and induce reworking of previously accumulated sediment. Thus no change in general wave regime is required to account for alternation of chenier sand accumulation with interchenier mudflat deposition. Barrier island plains closely resemble chenier plains, except the barrier island beach ridges are separated by clayey, silty, poorly-sorted fine sand, but cheniers are separated by unsorted, sandy, shoreface mud deposits. Comparison of sublittoral beach profiles show that, rising from equivalent depths of water, the barrier island profile has a seaward gradient that is approximately twice that of the non-barred shore. This steeper profile is related to the coarser average grain size of barrier island shoreface sediment compared to chenier plain shoreface detritus. The greater coarseness is in part the result of tidal jet winnowing of clay from longshore-moving sediment as it sweeps past estuary mouths. As a consequence of the steep barrier Island profile, a higher rate of wave energy issipation takes place in shallow offshore water. This higher rate of energy transfer contributes to the further winnowing of barrier island sand that is initiated by longshore current-tidal flow interaction. The textual differences between barrier island interridge sand and sandy, interridge chenier plain mud appear to mask similarities of origin. A close geographic association invariably exists between chenier deposits and river or estuary mouths. Although major rivers are the ultimate source of sediment composing chenier plains, cheniers are not uncommonly located adjacent to estuaries receiving little or no sediment from the rivers passing through them to the sea. This suggests that sand build-up is related primarily to interaction between sediment-bearing longshore currents and tidal flow from estuary months, and is not necessarily dependent upon the rivers as sediment sources. The interaction, here termed the dynamic diversion effect, is particularly important to chenier plain growth because of its influence on deposition of in-transit sediment that approaches an estuary during ebb tide. Both surf suppression by he issuing jet and decrease in velocity of nearshore transport associated with current deflection cause deposition of sediment on the updrift shoreface of mainland or developing spit. Some sediment stranding may also take place during flood tide. A second important site of ebb flow deposition is offshore, and downdrift, from the estuary mouth. Here longshore flow reasserts its dominance over the tidal jet, and energy dissipating gyral flow occurs as the seaward-displaced longshore drift moves back toward the shoreline. Deposition at this site results in barrier island plain development. Exploration for subsurface chenier and barrier plains sands might well be pursued in the vicinity of provable intersection between paleoshorelines and ancient river systems.

The Stratospheric Tidal Jet

Rotation of the earth introduces a diurnal perturbation into the heating experienced by the ozonosphere through absorption of solar ultraviolet radiant energy. This diurnal heat wave induces perturbations in the stratospheric wind field which are principally meridional at low latitudes and are largely zonal at high latitudes. This asymmetric situation is shown to power a tidal-type circulation system which has its maximum strength in the high latitude nighttime upper mesosphere of the summer hemisphere. This “stratospheric tidal jet” is zonal as it skirts the periphery of the continuously heated polar region, and presumably serves to transport and mix the summer mesosphere as well as provide the vertical flow required for formation of noctilucent clouds.

Patterns of Flow and Channeling in Tidal Inlets

ABSTRACT Tidal inlets penetrating narrow barriers and with or without tidal deltas typically have a central trough with terminal channel fans. The trough is centrally narrowly branched at each end with multiple, lesser, converging lateral channels. Deltaic sand, where present, tends to form peripheral shoals and shoals separating the two sets of channels. The trough is a narrow horizontal slot, ratio 1/24 to 1/75 in typical examples. Deep holes occur in axial and other narrows. Detailed studies by others show that the individual channels of an inlet can usually be identified as either entering or issuing channels, subject to being shifted by longshore currents as the tidal phases change. Without further direct current studies, the gross flow characteristics of the channel systems may be interpreted from the described conditions. In both flood and ebb (rising and falling) phases, the water level is higher on one side of the barrier than the other. For the high sheet of water to get through the inlet, it must drain centripetally into it along all unobstructed radii, a tidal drain. The wide distribution of the minor lateral channels gives them most of the drainage. The inlet flow issues with appreciable velocity, scouring the trough and hole and forming a local maximum of current energy in its flow direction. The trough typically has two major branches at each end separated by shoals but narrowly and sub-centrally confined. If unobstructed and unbranched, the issuing channel flares like a horizontal jet, which ideally flares at 20 degrees. Whether single or branched, the issuing current is a tidal jet. Thus, at the ends of the inlet both the flood and ebb tides are drains on the high side and jets on the low side of the barrier, in both cases being there local maxima of hydraulic energy. The mouths of shallow estuaries, but not those of deep straits, show the type of channel pattern characteristic of the tidal inlet.

Patterns of Flow and Channeling in Tidal Inlets: ABSTRACT

Tidal inlets penetrating narrow barriers and with or without tidal deltas typically have a central trough with terminal channel fans. The trough is centrally narrowly branched at each end with multiple, lesser, converging lateral channels. Deltaic sand, where present, tends to form peripheral shoals and shoals separating the two sets of channels. The trough is a narrow horizontal slot, ratio 1/24 to 1/75 in typical examples. Deep holes occur in axial and other narrows. Detailed studies by others show that the individual channels of an inlet can usually be identified as either entering or issuing channels, subject to being shifted by longshore currents as the tidal phases change. Without further direct current studies, the gross flow characteristics of the channel systems may be interpreted from the described conditions. In both flood and ebb (rising and falling) phases, the water level is higher on one side of the barrier than the other. For the high sheet of water to get through the inlet, it must drain centripetally into it along all unobstructed radii, a tidal drain. The wide End_Page 366------------------------------ distribution of the minor lateral channels gives them most of the drainage. The inlet flow issues with appreciable velocity scouring the trough and hole and forming a local maximum of current energy in its flow direction. The trough typically has two major branches at each end separated by shoals but narrowly and sub-centrally confined. If unobstructed and unbranched, the issuing channel flares like a horizontal jet, which ideally flares at 12°. Whether single or branched, the issuing current is a tidal jet. Thus, at the ends of the inlet, both the flood and ebb tides are drains on the high side and jets on the low side of the barrier, in both cases being there local maxima of hydraulic energy. The mouths of shallow estuaries, but not those of deep straits, show the type of channel pattern characteristic of the tidal inlet. End_of_Article - Last_Page 367------------

The control of river floods with special reference to the miami conservancy district of ohio

The Albemarle Shelf Valley Complex on the northern North Carolina Shelf is a leveed shelf-floor channel trending seaward from the modern Albemarle estuary. Vibracores and seismic profiles indicate that the levees have a twofold internal structure. Levee cores consist of fine sand interbedded with mud lenses. The cores are mantled with a generally coarser, cleaner sand. The levees are interpreted as shoal retreat massifs; deposits formed as the littoral-drift depositional centers on either side of the ancestral Albemarle estuary retreated landward during the Holocene transgression.The shelf-valley complex underwent systematic changes in bottom morphology and sediment character as the reversing tidal jet of the estuary mouth was replaced by the intermittent south-trending storm flows of the open shelf. A pattern of ridges and troughs with 10 m of relief was incised into north sides of the massifs flanking the shelf valley.The coarser surficial sand into which the bedform pattern has been impressed appears to be a lag deposit formed by the winnowing of the massifs during storm flow. On ridge crests this surficial sand sheet has been molded into sand waves up to 3 m high. The relative orientations of sand waves, ridges, and the shoreline indicate that the structure of the velocity field during peak flows must be quite complex. Ridges converge southward with the shoreline at angles of 15–20°, while the sand waves atop them make angles of about 75° with the shoreline; the sand waves are thus neither orthogonal with respect to the shoreline nor with respect to the ridges. Sand-wave orientation indicates southward bottom flow with an offshore component.Existing hydrodynamical theory does not adequately explain this pattern. Extensive hydraulic measurements of careful design will be required so we can interpret the bedform pattern and its role in the coastal sand budget.