Nontidal Flow Research Articles

Performance of tidal and non-tidal mangrove constructed wetlands in treating maricultural wastewater.

This study aims to evaluate the removal efficiency of nitrogen and phosphorus in the tidal and non-tidal constructed wetlands with typical mangrove (Aegiceras corniculatum) as a wetland plant model to treat simulated marine wastewater. The results showed that the average removals of NO2--N, NO3--N, NH4+-N, TN and TP were 88.4, 80.5, 81.4, 79.7 and 40.8%, respectively, in the non-tidal subsurface flow (HF) mangrove wetland, and 65.3, 61.3, 90.6, 60.1 and 19.2% in the tidal (TF) mangrove wetland, and 11.4, 64.6, 68.7, 56.6 and 16.3% in the non-tidal free water surface (FWS) mangrove wetland, respectively. Moreover, it was observed that the composition of microbial communities in the HF mangrove wetland was beneficial to the nitrogen cycle and has more quantitative associations of N-metabolism genes. The results indicated that non-tidal HF mangrove wetland has a stable and an effective capacity for potential treatment of marine wastewater compared with the non-tidal FWS mangrove wetland and tidal TF mangrove wetland.

Watershed and Estuarine Controls Both Influence Plant Community and Tree Growth Changes in Tidal Freshwater Forested Wetlands along Two U.S. Mid-Atlantic Rivers

The tidal freshwater zone near the estuarine head-of-tide is potentially sensitive to both sea-level rise and associated salinity increases as well as changing watershed inputs of freshwater and nutrients. We evaluated the vegetation response of tidal freshwater forested wetlands (TFFW) to changes in nontidal river versus estuarine controls along the longitudinal gradient of the Mattaponi and Pamunkey rivers in the Mid-Atlantic USA. The gradient included nontidal freshwater floodplain (NT) and upper tidal (UT), lower tidal (LT), and stressed tidal forest transitioning to marsh (ST) TFFW habitats on both rivers. Plot-based vegetation sampling and dendrochronology were employed to examine: (1) downriver shifts in plant community composition and the structure of canopy trees, understory trees/saplings/shrubs and herbs, tree basal-area increment (BAI) and (2) interannual variability in BAI from 2015 dating back as far as 1969 in relation to long-term river and estuary monitoring data. With greater tidal influence downstream, tree species dominance shifted, live basal area generally decreased, long-term mean BAI of individual trees decreased, woody stem mortality increased, and live herbaceous vegetative cover and richness increased. Acer rubrum, Fagus grandifolia, Ilex opaca, and Fraxinus pennsylvanica dominated NT and UT sites, with F. pennsylvanica and Nyssa sylvatica increasingly dominating at more downstream tidal sites. Annual tree BAI growth was positively affected by nontidal river flow at NT and UT sites which were closer to the head-of-tide, positively influenced by small salinity increases at LT and ST sites further downstream, and positively influenced by estuarine water level throughout the gradient; nutrient influence was site specific with both positive and negative influences. The counterintuitive finding of salinity increasing tree growth at sites with low BAI is likely due to either competitive growth release from neighboring tree death or enhanced soil nutrient availability that may temporarily mitigate the negative effects of low-level salinization and sea-level increases on living TFFW canopy trees, even as overall plant community conversion to tidal marsh progresses.

Turbulence Driven by Reflected Internal Tides in a Supercritical Submarine Canyon

AbstractThe La Jolla Canyon System (LJCS) is a small, steep, shelf-incising canyon offshore of San Diego, California. Observations conducted in the fall of 2016 capture the dynamics of internal tides and turbulence patterns. Semidiurnal (D2) energy flux was oriented up-canyon; 62% ± 20% of the signal was contained in mode 1 at the offshore mooring. The observed mode-1 D2 tide was partly standing based on the ratio of group speed times energy cgE and energy flux F. Enhanced dissipation occurred near the canyon head at middepths associated with elevated strain arising from the standing wave pattern. Modes 2–5 were progressive, and energy fluxes associated with these modes were oriented down-canyon, suggesting that incident mode-1 waves were back-reflected and scattered. Flux integrated over all modes across a given canyon cross section was always onshore and generally decreased moving shoreward (from 240 ± 15 to 5 ± 0.3 kW), with a 50-kW increase in flux occurring on a section inshore of the canyon’s major bend, possibly due to reflection of incident waves from the supercritical sidewalls of the bend. Flux convergence from canyon mouth to head was balanced by the volume-integrated dissipation observed. By comparing energy budgets from a global compendium of canyons with sufficient observations (six in total), a similar balance was found. One exception was Juan de Fuca Canyon, where such a balance was not found, likely due to its nontidal flows. These results suggest that internal tides incident at the mouth of a canyon system are dissipated therein rather than leaking over the sidewalls or siphoning energy to other wave frequencies.

ANALISIS PENGARUH ANGIN TERHADAP POLA ARUS PERMUKAAN DAN DISTRIBUSI SALINITAS DI MUARA SUNGAI PALU

The pattern of surface currents and salinity distribution at the mouth of the Palu River by using the 2D coherens model to show that the presence of wind factors influences the velocity and direction of the tidal and non-tidal surface flow patterns at the mouth of the Palu River. Using primary and secondary data, the results show that non-tidal currents are more dominant with the direction of spread from the North to the East to the West then turn to the South, with a velocity of 2.57 m/s. The pattern of salinity distribution with tidal and non-tidal flow generators has a different model. Still, it has the same direction, namely the flow from North East to West direction, which is deflected to the South adjacent to the mouth of the Palu River estuary.

Seasonal Variability of Tidal Currents in Tampa Bay, Florida

AbstractAn analysis of tidal current variability is performed over seasonal scales for an 11-year record of estuarine currents at two locations in Tampa Bay, Florida. From 2002 to 2012, bimonthly harmonic analyses were performed on current observations collected near the entrance to Old Tampa Bay and at the Sunshine Skyway Bridge. The resultant tidal constituents and nontidal residual were then correlated with other parameters to determine potential physical forcing. Comparison with local wind data suggests that the land-sea breeze cycle can have significant impact on diurnal tidal current flow. Periods of strong land-sea breeze are found to have up to a 30% increase in K1 amplitude compared with periods of weak land-sea breeze. Subtidal weather-scale wind forcing with periods from 2 to 7 days demonstrates a strong correlation with nontidal residual flow, likely resulting from both direct wind forcing as well as the modification of along-estuary water-level gradients. Additionally, the M2 constituent corr...

Upwelling-triggered near-geostrophic recirculation in an equatorward facing embayment

Underway current velocity profiles were combined with hydrographic profiles at the entrance to Tongoy Bay, an equatorward facing bay in north-central Chile, with the objective of determining its exchange hydrodynamics. To the west, Tongoy Bay is bounded by Lengua de Vaca Point, a ∼6 km-long northward protruding peninsula. Observations were obtained during three surveys (April 2005, December 2005, May 2009) along cross-bay transects for at least one full day. During the surveys, winds were upwelling-favorable and displayed diurnal variations. Non-tidal (tidally averaged) flows showed a consistent clockwise or southern hemisphere cyclonic, recirculation during the three surveys. This recirculation was likely part of a cyclonic gyre (10–20 km in diameter), not entirely resolved by the surveys, and formed by flow separation off Lengua de Vaca Point. Estimates of the baroclinic pressure gradient, combined with analytical solutions of density-driven and wind-driven flows, indicated that the recirculation in Tongoy Bay was nearly in geostrophic balance. An ageostrophic contribution to the dynamics was related to frictional effects derived from local upwelling-favorable winds. A linear superposition of the analytically derived density-driven and wind-driven exchange resulted in a flow pattern that resembled the observed net exchange flows at the bay mouth.

Variability in Measured Current Structure on the Southwest Continental Shelf of India

Analyses of short-duration, current meter records collected in the coastal waters off Beypore on the southwest coast of India have been made in order to understand the tidal and nontidal variability during premonsoon and summer monsoon seasons of the year 2000. The region's tidal and nontidal flows were described by means of time-series displays, simple statistics, harmonic analysis, correlation coefficients, and progressive vector diagrams. The nontidal component of current was extracted using the X0 filter. The study showed that the tidal currents were generally weak (<7 cm/s) and dominated by tidal signals only in a few records. Diurnal and semidiurnal constituents were found to be responsible for the rest of the variance. The signatures of the currents were different at the surface and bottom of the water column in the records collected during the summer monsoon season, suggesting a baroclinic nature of motion, whereas the premonsoon records showed a barotropic nature. The stratification of the water column was strong during the summer monsoon season but was well mixed during the premonsoon season. There was a strong signature of diurnal solar forcing in the surface-temperature records, which was totally lacking in the bottom records.

Spatial and temporal variability in flow at the mouth of Narragansett Bay

Results are presented from field measurements of the spatial and temporal variability of circulation and exchange between Narragansett Bay and Rhode Island Sound (RIS) at both tidal and seasonal timescales. Data were collected during 13 acoustic Doppler current profiler (ADCP) surveys between April 1998 and July 1999. Significant horizontal and vertical structure was observed in the instantaneous, tidally driven flow and the residual, nontidal flow. This was especially evident through the deeper East Passage (EP), where persistent inflow was observed along the eastern side, and outflow along the western side of the channel. The residual volume transport of water to RIS is greater through the EP than through the West Passage entrance to the Bay, particularly in summer. Data from the offshore, or coastline‐normal survey lines reveal a strong seasonal variability in RIS circulation. A residual (5–15 cm s−1) cyclonic coastal current is recorded within RIS during summer, stratified conditions. This residual current, which was not present during the winter surveys, enhances Narragansett Bay‐RIS exchange by efficiently advecting the bay outflow to the southwest, away from the entrance. Results also indicate the resupply pathways for deep water to the entrance region vary in summer versus winter. Observed differences in RIS circulation, and related estuary‐shelf exchange, have significant implications for physical, chemical, and biological models of Narragansett Bay.

Current measurements in the Halmahera Sea

A mooring with current meters at 400, 700, and 900 m at the 950‐m isobath south of the 700‐m‐deep sill across the Halmahera Sea revealed many signals between June 1993 and July 1994. Strong tidal currents of 50 cm/s dragged the mooring down by as much as 80 m on occasions when the lunar perigees corresponded with new or full moons. At 400 m the nontidal currents were southward at up to 25 cm/s from October to April and northwestward at up to 20 cm/s at other times. At 700‐m depth there was a near‐continuous nontidal southward flow of 9 cm/s across the sill into the Halmahera Basin, which accords with findings by earlier Dutch and Indonesian workers. The current meter at 900‐m depth showed the nontidal flow to be weak (∼1 cm/s) to the west. The southward transport between 350 and 700 m was inferred to reach a maximum of 5 Sv during the NW monsoon, with the annual mean being 1.5 Sv. There was a spring‐neap effect on the nontidal currents at 400 m that was most pronounced in the last few months of the mooring's life: these currents changed from ∼10 cm/s to the east during neap tides to ∼20 cm/s to the NNW during spring tides. Temperature and salinity profiles suggest that the waters of the Halmahera Sea are derived in part from the New Guinea Coastal Undercurrent.

Microstructure Observations of Turbulent Mixing in a Partially Mixed Estuary. Part II: Salt Flux and Stress

Abstract Turbulent mixing in the water column was observed with a microstructure profiler in the Hudson River estuary during two cruises in summer and fall 1995. The focus is on the estimation of turbulent salt flux and turbulent stress from measured viscous dissipation rates (e), and on the tidal and fortnightly variability of these fluxes. In estimating eddy viscosity (Km) and eddy diffusivity (Kρ), the authors follow measurement/modeling techniques of Busch and Osborn, while prescribing a variable flux Richardson number (Rf) dependent upon the gradient Richardson number (Ri). It is argued that a steady-state production–dissipation balance holds in the turbulent kinetic energy budget. All turbulence characteristics varied strongly over semidiurnal tidal cycles and over the fortnightly cycle. Subject to complications arising from nontidal flows, the “strongest” mixing occurred during flood on neap tides, and during ebb on spring tides. In the lower part of the water column during floods and spring ebb Km...

Observations of Shallow-Water Transport and Shear in Western Florida Bay*

Abstract Acoustic Doppler profiler (ADP) data are used to describe depth-integrated transport and vertical shear at two study sites along the open western boundary of Florida Bay. During a 404-day study period, transport was into the bay at the northern study site, where the depth-averaged 3.2 m. Transport at the southern study site, where the depth averaged 2.0 m, was out of the bay during a 266-day time period. A comparison of flow in the top and bottom layers of the ADP profile at the northern study site reveals patterns that are very different from each other, and very different from the depth-integrated transport. Nontidal flow in the surface layer is nearly consistently out of the bay and highly correlated with wind forcing. East–west near-bottom flow is inversely correlated with the rise and fall of water level in northwest Florida Bay. Nontidal east–west flow in the bottom layer is negligible, suggesting a near balance between westward directed wind stress and eastward directed barotropic pressure...

Spatial and Temporal Entry Patterns of Fish Larvae into North Carolina Estuaries: Comparisons Among One Pelagic and Two Demersal Species

A sampling programme targeting larvae of winter spawning fishes immigrating from the oceanic domain into the Pamlico-Albemarle Sounds system (NC, U.S.A.) was performed at the four major inlets of the lagoon system. Sampling yielded abundant catches of three species, a Clupeid (Atlantic menhaden,Brevoortia tyrannus) and two Sciaenids (Atlantic croaker,Micropogonias undulatusand spot,Leiostomus xanthurus). In this article, the author documents the differences in the mechanisms developed for estuarine recruitment among the three species. Abundance at the tidal inlets was dependent upon numerous factors, such as sampling month, inlet, luminosity, tide flow direction and depth. The spatial and temporal positioning of the larvae differed among the species and affected their capabilities to be transported through the inlets. More specifically, spot and croaker migrated vertically within the water column in accordance with the direction of the water flow. Sciaenids minimized the outwelling effects of ebb tides by migrating into the slowest ebbing currents, near the bottom. Menhaden did not rely on vertical migrations for estuarine transport and retention. For this species, landward transport is provided either when dusk and flood onset are coincident or through non-tidal flows developing under meteorological forcing. The Sciaenids were less, or not, dependent upon these conditions. In one inlet, the retention was dependent upon the strength of the flooding and ebbing flows. In this case, the retention of the pelagic species was lower than the retention of demersal species.

Generalized inverse with shipboard current measurements: Tidal and nontidal flows in Long Island Sound

A simple linear shallow-water model forced by tidal boundary conditions can capture most of the tide height variability in Long Island Sound. In this sense, the tides are easy to model. The modeled tidal currents can be subtracted from measurements in order to obtain estimates of subtidal circulation. But linear shallow-water dynamics is not accurate enough for this purpose. Allowing for dynamical errors with a generalized inverse model leads to improved estimates of tidal and nontidal flow. The analysis provides expected errors for the prior (before inversion) and posterior (after inversion) tidal velocity field. Estimates of the flow field in central Long Island Sound are obtained with current measurements from a ship-mounted Acoustic Doppler Current Profiler (ADCP) survey. Inversion of data from a single ten-hour survey improves tidal predictions, as verified with independent data. Furthermore, the posterior penalty functional is shown to be an effective test statistic for the existence of nontidal flow. The inverse model reduces model-data misfit, using interior dynamics and open-boundary conditions as weak constraints. Model-data misfit can also be reduced by tuning the friction parameter in the prior tidal model. However, in contrast with inversion, tuning degrades predictability.

On the salt transport in the Cananéia sea during a spring tide experiment

Observations of the velocity, salinity, water depths and tides in the southem region of the Cananeia Sea were sampled at an anchored station during two complete tidal cycles. The measurements were made during spring tides on 5-6 December, 1991. The observed non-tidal current profile for this weakly stratified tidal channel is found to be in close agreement with the results of a simple steady state unidimensional analytical model of a well-nuxed estuary. This comparison indicates that the primary driving mechanisms are the longitudinal salinity gradient and the fresh water discharge. The contribution to the advective salt transport is dominateo by the freshwater discharge through the down-stream non-tidal flow and the up-stream dispersive term due to Stokes wave transporto This dispersive term is almost one order of magnitude smaller than the down-stream non-tidal transport inouced bythe fresh water discharge. TidaI correlation, acting as a counter-dispersion term, and the steady shear dispersion term are two orders of magnitude smaller than the oown-stream salt transporto The remaining dispersive terms, which are dependent on the deviations from the mean deptb, are smaller than eitlier of these terms by one order of magnitude. The computed total salt transport per unit width of a section perpendicular to the mean flow was in close agreement (within 12 %) with the sum of the individual advective and dispersive terms. On the assumption that the tidal channel sampled is laterally homogeneous, an imoalance of the salt budget across the section was observed.

On the salt transport in the Cananéia sea during a spring tide experiment

Observations of the velocity, salinity, water depths and tides in the southem region of the Cananéia Sea were sampled at an anchored station during two complete tidal cycles. The measurements were made during spring tides on 5-6 December, 1991. The observed non-tidal current profile for this weakly stratified tidal channel is found to be in close agreement with the results of a simple steady state unidimensional analytical model of a well-nuxed estuary. This comparison indicates that the primary driving mechanisms are the longitudinal salinity gradient and the fresh water discharge. The contribution to the advective salt transport is dominateô by the freshwater discharge through the down-stream non-tidal flow and the up-stream dispersive term due to Stokes wave transporto This dispersive term is almost one order of magnitude smaller than the down-stream non-tidãl transport inôuced bythe fresh water discharge. TidaI correlation, acting as a counter-dispersion term, and the steady shear dispersion term are two orders of magnitude smaller than the ôown-stream salt transporto The remaining dispersive terms, which are dependent on the deviations from the mean deptb, are smaller than eitlier of these terms by one order of magnitude. The computed total salt transport per unit width of a section perpendicular to the mean flow was in close agreement (within 12 %) with the sum of the individual advective and dispersive terms. On the assumption that the tidal channel sampled is laterally homogeneous, an imoalance of the salt budget across the section was observed.

Observations of currents and water properties in the Amazon Frontal Zone

Measurements of currents and water properties were obtained at various locations in the frontal zone of the Amazon River outflow plume during four cruises in 1989–1991 as part of A Multidisciplinary Amazon Shelf Sediment Study. A salinity front resembling a salt wedge is found approximately 150 km seaward of the river mouth. It continues northwestward more than 400 km along the shelf between the 10‐ and 20‐m isobaths. Tidal currents, which are oriented principally in the cross‐shelf direction, reach 200 cm s−1 during spring tides and drop to less than 80 cm s−1 during neaps in the vicinity of the river mouth. The nontidal flow is strongly sheared, with near‐surface speeds of up to 100 cm s−1 and weak near‐bottom velocities. The direction of the near‐surface flow is generally northwestward except near the river mouth, where river discharge leads to a significant offshore component of flow. The strong velocity shears are stabilized by strong stratification by salinity and by highly concentrated suspended sediment (or fluid mud) near the seabed. Variations in stratification and frontal position are due principally to spring‐neap variations in tidal mixing and seasonal variations in runoff.

Effect of Helium Concentration on Experimental Upper Airway Obstruction

This study investigates the effect of helium concentration in inspired gas on resistance to breathing during experimental upper airway obstruction. Obstruction was modeled by use of a series of four polyvinyl endotracheal tubes narrowed progressively in their midportions with C clamps. Percentage ratios of helium-oxygen gas mixtures were 0:100, 40:60, 60:40, and 80:20. Gas flow was provided by two methods: 1) nontidal flow from compressed gas tanks from which resistance was calculated from pressure and flow measurements, and 2) tidal respiratory flow from human volunteers from whom respiratory effort was evaluated by using airway pressure measurements integrated over 90-second trial periods. The results derived from both methods demonstrated that the effect of helium in reducing resistance and pressure in an obstructed airway is linear (p less than .016) and inversely proportional to helium concentration. Reductions in resistance and pressure were larger for the tighter obstructions (p less than .007). As helium was added to the gas mixture (from 0% to 80%), resistance and airway pressure measurements dropped 42% and 58%, respectively. The major conclusions are that 1) even low concentrations of helium may have therapeutic value and 2) helium is effective only for more severe obstructions.

Episodic changes in lateral transport and phytoplankton distribution in South San Francisco Bay

Observations in South San Francisco Bay during 1982 showed that substantial cross‐channel, nontidal flows accompanied episodic increases in the longitudinal, nontidal flows. Along the channel the nontidal circulation was enhanced during the monthly minima in tidal energy or as a result of wind forcing, producing upestuary flows 2–3 times greater than normal. These longitudinal pulses modified the horizontal and vertical salinity distributions and generated cross‐channel flows of up to 0.07 m s−1 that persisted for several days. The increased lateral flows were directed to the west and may explain the large fluctuations in phytoplankton biomass observed over the broad eastern shoal during spring.

Upwind Return Flow in A Coastal Lagoon: Seasonal-Scale Barotropic Transport

Current and wind data collected during a 223-d study period from early June 1983 through early January 1984 are used to document net upwind return flow over seasonal time scales in the Indian River Lagoon near Sebastian Inlet on the Atlantic Coast of central Florida. Spectral analysis of wind and current meter data suggests that wind forcing accounts for the majority of nontidal flow. The two time series are highly coherent at periodicities of 2,3–3.5, 4, and 6 d. The serial correlation coefficient of −0.49 is significant at the 99.9% confidence level. Historical water level and wind data recorded simultaneously at Sebastian Inlet and Eau Gallie, 34.5 km to the north, suggest that longitudinal pressure gradients are established in response to seasonal wind patterns. The upwind near-bottom return flow is interpreted as a response to the seasonal set up of the longitudinal pressure gradients. The study documents the importance of windstress in forcing low-frequency transport over seasonal time scales.

The decomposition and simulation of the longitudinal circulation in a coastal lagoon

Current measurements during a 32-day study period in late spring, 1977, are used to quantify the magnitude and relative importance of tidal and wind-driven motion in the interior of the Indian River lagoon, on the Atlantic coast of Florida. Harmonic analysis of the total longitudinal flow along the axis of the lagoon isolates the tidal component of the current; non-tidal flow is revealed by subtracting the tidal current from the total current, and making corrections for non-linear relationships between the current and both surface wind stress and bottom friction. A one-layer, one-dimensional model is developed to simulate wind drift. A quadratic bottom friction term with a drag coefficient of 15 × 10 −3 gives results which compare most favourably with observations. Results indicate that tidal forcing explains approximately 45% of the total variance at the study site, 25 km from the nearest inlet. Local wind forcing accounts for 44% of the non-tidal flow. The remainder of the variance is attributed to freshwater outflow through the lagoon and non-local forcing.