OS21B-1166
The semi-diurnal tide in Hudson Strait: a resonant channel oscillation
An extension of the classical Helmholtz resonator is developed to account for salient aspects of the semi- diurnal tidal resonance observed in the Hudson Bay/Hudson Strait system. The model allows for convergence/divergence of the flow in a channel connecting an inner basin, representing Hudson's Bay, to the open ocean. Accordingly, the model admits two modes of variability. One is the standard Helmholtz mode in which the largest sea level variability occurs within the inner basin. The model also supports a mode in which the greatest sea level variability occurs in the channel, with relatively weak variations in the inner basin. A distinguishing characteristic of this channel mode, the 180º phase difference in the currents at the ends of the channel, is consistent with volume transports from a tidal model of the region. Non-dimensional parameters that govern the response are identified and evaluated based on the physical dimensions of the Hudson Bay/Hudson Strait region. The results suggest that the channel mode is resonant in the strait near semi-diurnal tidal periodicities, in general agreement with observations and more complex models.
OS21B-1167
Tidal-Driven Mixing Processes in a Coastal Ocean Model With Wetting and Drying
An idealized sigma-coordinate numerical model with a Wetting and Drying (WAD) scheme and a Mellor- Yamada turbulence has been used to study how tidally-driven mixing processes in shallow areas are affected by inundation associated with WAD and by other parameters. Sensitivity studies evaluate the influence of tidal amplitudes (from 1 m to 9 m), stratification, model grid size (from 2 km to 16 km), and the impact of WAD on the mixing. The results demonstrate how the tidal amplitude impact the mixing in the surface mixed layer (SML) and in the Bottom Boundary Layer (BBL); small amplitude tides cause the thickness of the SML to increases with time, while large amplitude tides cause the thickness of the BBL to increases with time, thus the stratification resulted from the tidal mixing depends on the tidal amplitude in a non-linear fashion. In the deeper part of the domain and with tidal amplitudes less than 3 m, the SML and the BBL are separated and the water column remains stratified. In the shallow region the two layers merge, but interestingly enough the reflection of the tidal wave from the coast creates larger mixing in the case without WAD (where the artificial coastal boundary is a wall-like) than in the case where WAD is included and absorb some of the tidal energy.
OS21B-1168
Analytical Description of Tidal Dynamics in Convergent Estuaries
Analytical solutions of the one-dimensional hydrodynamic equations for tidal wave propagation are now available and, in this paper, presented in explicit equations. For given topography, friction and tidal amplitude at the downstream boundary, the velocity amplitude, the wave celerity, the tidal damping and the phase lag can be computed. The solution is based on the full non-linearised St. Venant equations applied to an exponentially converging channel, which may have a bottom slope. Two families of solutions exist. The first family consists of mixed tidal waves, which have a phase lag between zero and ð/2, which occur in alluvial coastal-plane estuaries with almost no bottom slope; the second family consists of "apparent standing" waves, which develop in short estuaries with a steep topography. Asymptotic solutions are presented for progressive waves, frictionless waves, waves in channels with constant cross-section, and waves in ideal estuaries where there is no damping or amplification. The analytical method is accurate in the downstream, marine, part of estuaries and particularly useful in combination with ecological or salt intrusion models. The solutions are compared with observations in the Schelde, Elbe and Mekong estuaries.
OS21B-1169
Barotropic and baroclinic tides in Philippine seas a modeling study
A Regional Ocean Modeling System (ROMS) is applied in Sulu sea and its adjacent waters to look at the barotropic and baroclinic tides. The model is initialized from results of global HYbrid Coordinate Ocean Model (HYCOM). Surface forcing from the Navy's Operational Global Atmospheric Prediction System Model is prescribed. The barotropic tide and tidal current from OSU Tidal Prediction Software are imposed on the no- tide HYCOM results and specified along the open boundary. The model runs for one year beginning March,2007. The barotropic tidal harmonics in Sulu sea and Celebes seas are compared well to the OTPS predictions and those from TOPEX/POSEIDON satellite data analysis. Dominate tides are M2, K1. In Sulu sea, tide amplitude is around 30 cm for M2 and 30 cm for K1. In contrast, in Celebes sea, the amplitude for M2 is around 60 cm and 20 cm for K1. The phase lag between these two oceans is more than 180 degree for M2 and 150 degree for K1. The large tidal difference between Sulu and Celebes seas are caused from separation by the Sulu Archipelago. The baroclinic tides generated in Sulu Archipelago propagates northward and manifests on the surface elevation. From surface elevation anomaly, the phase speed of the baroclinic tides is around 2.3~m/s. This is close to the Solition wave propogation speed 2.5m/s measured by Apel et al.(1985). The amplitude of surface signature of the baroclinic tide is around 20 cm in the south sulu sea, and decreases approaching northern bank. This baroclinic signal overlaps with barotropic tides and causes the discrepancy of barotropic tides between the OTPS results and ROMS results. The baroclinic energy flux and its divergence in this area are examined. In Sulu sea, large energy flux and divergence occur at the area close to either sides of straits open to deep ocean. This demonstrates the importance of the straits in creating baroclinic waves and tides. High energy flux convergence values in these area also indicates high dissipation. In area close to Mindoro strait, Tablas sea, Surigo strait, and San Bernardino strait, the baroclinic tide flux energy are also large compared to open ocean where topography is relatively flat. Seamounts and abrupt topography inside Sulu sea and Celebes sea also contribute to large local baroclinic flux.
OS21B-1170
Tidal Characteristics Change in the Asan Bay, Korea from 1993 to 2006
In order to identify the change of tidal characteristics on average in the Asan Bay located at the west coast of Korea, the tide data at Pyongtack (PT) inside the bay and Anheung (AH) outside the bay for the period of 1993 to 2006 were analyzed using the harmonic analysis method, and major and shallow water tidal constituents were compared. The average semidiurnal tidal amplitudes at PT increased while those at AH decreased after the Hwaong tidal barrier (HTB) construction. In particular, the amplitudes at PT increased abruptly during the period of 2002~2003 when HTB was completed. These observed phenomena suggests that the tidal characteristics change in the Asan Bay may be related to the construction of HTB. The cause of this change is different from either blocking the tidal wave propagation as in the Keum River tidal barrier or removing 'choking effect' as in the Yeongsan River tidal barrier. Rather, it may have been caused by removal of vast tidal flat where the tidal energy is dissipated through bottom friction. The M4/M2 ratio also increased and their phase difference decreased after the completion of HTB. Accordingly, these changes may result in increase of tidal range, decrease of the flood duration and increase of the flood current velocity, inducing more sediments into the Asan Bay.
OS21B-1171
Forced tidal response in the Gulf of Mexico
This study focuses on modeling the tidal dynamics in the Gulf of Mexico (GoM). In particular, the study addresses the problem of differentiating the sources of tidal energy in this semi-enclosed sea. Tidal energy can enter the basin through propagation of tidal signals through the straits connecting the GoM to the Atlantic Ocean, or by local tidal gravitational forces imparted by celestial bodies. This study provides new estimates of the tidal response in the GoM due to these different forcing mechanisms using numerical model experiments with tidal forcing imposed at the open boundaries and by the local tidal potential. It also provides new estimates of total tidal power and tidal energy fluxes in the GoM. Analyses are performed with the Navy Coastal Ocean Model run in a barotropic configuration with high horizontal resolution (1/60a). The simulations are compared with observations and previous studies. Results show that diurnal tides in the GoM are dominantly due to co-oscillation with the western Atlantic, and that a substantial amount of semidiurnal tidal energy enters the Gulf through the straits as well. However, the local tidal potential significantly modifies the propagation of the semidiurnal tidal signal within the GoM, and slightly reduces the tidal power associated with the diurnal tides in the basin.
OS21B-1172
Detiding shipboard-mounted ADCP data in a pelagic region with large-amplitude geostrophic flows
Tidal currents in the southern region of the California Current are obtained from 10 years (1998-2007) of
shipboard-mounted ADCP data using a spatial least-square technique. The ADCP data together with CTD
data were collected by the Mexican Research of the California Current (IMECOCAL) program. The ADCP
data were screened to remove outliers. The sensitivity and alignment errors were calculated by least-square
technique. Previous studies show that the displacement of isopycnal surfaces is large, which enhances the
geostrophic currents. In this work, geostrophic velocity was obtained from the 10 years of CTD data, and
extracted from the ADCP data. The depth-averaged nongeostrophic velocity was spatially interpolated to
derive tidal and residual currents. We tested several interpolation functions, and found that the better was a
Gaussian function. The semidiurnal (12.42 hours) tidal current ellipses derived from the ADCP data compare
well with the predictions of a global ocean tidal model.
http://imecocal.cicese.mx
OS21B-1173
Remote Sensing of Salinity Intrusion in a Marine Estuary
We seek to measure electrical conductivity over the entire water column from a bottom mounted instrument. In some instances, electrical conductivity is a useful surrogate for salinity. The approach is to produce low- frequency electrical currents while observing the resulting electric field at a nearby dipole receiver. The received electric field is a function of the electrical conductivity of the water column and the sediments. An EM source dipole 2.5-m long and a receive dipole of 2.5-m length are mounted 6-m apart on a plastic pipe frame. The frame was deployed in the Snohomish and Columbia Rivers in WA and OR in water about 6 to 14-m deep at high tide. The support vessel was anchored heading upstream and the frame was then lowered onto the riverbed. A lowered CTD was used to provide profiles of electrical conductivity and salinity at least every half hour. The observations were of the received voltage difference normalized by the corresponding source current. As the layer of seawater thinned, the electrical conductance of the water column decreased. The increased resistance of the water column caused the receiver voltage to increase for the same amount of source current. The pattern of the received voltage divided by the transmitter current, Rx/Tx, is almost the inverse of height of the seawater layer or the electrical conductance (vertical integral of conductivity) of the water column. A simple equation relates the conductance of the river to the inverse of Rx/Tx.
OS21B-1174
Changes in Tidal Circulation in Saemangeum, Korea due to the Construction of Tidal Dykes
Saemangeum is a shallow coastal area located at the southwestern part of Korea. It had very well developed intertidal zones with tidal range of about 5 m and the tidal currents of about 1 m/sec at the maximum, and riverine estuaries of the Keum, Mankyung and Donjin Rivers. Between 1992 and 2006, a series of 33km long tidal dykes resembling the inequality symbol with the vertex pointing west (<) and surrounding the Mankyung and Donjin riverine estuaries and intertidal zones was constructed. Using a finite volume coastal ocean model (FVCOM), which is based on triangular grid, the effects of the dykes on the tidal circulation in Saemangeum has been investigated by comparing cases with ("disturbed") and without ("undisturbed") the dykes. The model domain is about 100 km wide and 90 km long and the model is forced by tidal forcing at the open boundaries. Earlier studies suggest that the dykes weaken the tidal amplitudes along the open boundary of the current model domain by about 1 cm, but this effect is not considered. The tidal amplitude and phase from the model ("disturbed") agree well with observations within 4 %. By comparing the "undisturbed" and "disturbed" we find that in front of the dykes the tidal amplitude was reduced by up to 7 cm. The effect of the dykes is stronger along the southern part of the dykes because it is parallel to the cophase line of the M2 tide, and more effective in blocking the propagation of the tidal energy. The northern branch is parallel to the undisturbed M2 tidal co-phase line and less effective in disturbing the tidal energy propagation. The tidal energy reflected by the southern branch accumulates around the Gogunsan island chains that are located west of the dykes.
OS21B-1175
Modeling of M2 Tidal Circulation in Kyounggi Bay, Korea
Kyounggi Bay located along the western coast of Korea is a macrotidal zone of 7.9 m tidal range during the spring tide and tidal flats very well developed. Within the bay there are several islands, and the coast lines are crooked significantly so that the geometry of the bay is very complex. To study the tidal circulation of this area, we conducted numerical modeling using a finite volume coastal ocean model, FVCOM, which could represent the complex topography properly. The model domain is about 40 km × 53 km, and the smallest grid is about 72 m. Therefore, the narrowest waterway, Yeomha, is well resolved. Only M2 tidal forcing is considered at the open boundary. There are three rivers in the bay and experiments were conducted with or without the fresh water discharge from the three rivers. Some of the previous modeling studies showed that the fresh water discharge could reverse the direction of the residual flows in Yeomha Waterways, but in the present experiment the river discharge could not reverse the residual flow. Other aspects of the tidal flow in this area were examined.
OS21B-1176
Effects Of Tide And Wind On Changjiang River Plume
The response of Changjiang River plume to combined tidal and wind forcing is investigated using a three- dimensional hydrodynamic model (ROMS) developed for East China and Yellow Seas. Both tide and wind exert strong influences on the plume's dispersal trajectory, vertical structure and rate at which freshwater is transported down the coast. Without tidal forcing, the Changjiang River plume appears to be a surface trapped plume. With tidal forcing, however, the plume resembles a bottom-controlled buoyancy plume. The spring-neap tidal cycle causes periodic destratification in the bulge region and periodic detachment of fresh water patches away from the river mouth. Upwelling favorable winds advect the plume in the offshore direction and decrease the plume thickness, but the tides act to reduce the plume spreading. Downwelling favorable winds confine the plume to the coast and increase the plume thickness, but the onshore Ekman transport is weaker in the presence of tides. In addition, residual tidal currents modify the plume trajectory, particularly in the Hangzhou Bay which is located to the south of Changjiang River estuary.
OS21B-1177
The influence of the Kennebec River discharge on estuarine and reverse estuarine flow in eastern Casco Bay, Gulf of Maine
Harpswell Sound and the New Meadows estuary are narrow coastal embayments on the eastern side of Casco Bay, in the Gulf of Maine. Hourly oceanographic data was collected at both locations, including ADCP profiles of current velocity vs. depth. It was found that net circulation in both inlets displays both estuarine and inverse estuarine characteristics at various times. During periods of low discharge from the neighboring Kennebec River there is little connection between the two inlets, with New Meadows developing a three- layered circulation regime and Harpswell Sound having periods of negligible net flow punctuated by brief wind-driven events. However, when the discharge of the Kennebec River is high both inlets experience considerable freshening of surface water with corresponding increases in vertical stratification. In addition both inlets act in concert, experiencing near-simultaneous alternation between estuarine and inverse estuarine current regimes of relatively high strength. It is hypothesized that this coordinated reverse estuarine flow is caused by the passage of the leading edge of a bolus of fresher Kennebec discharge past the entrances of the inlets. Water flowing down the sloping surface of this bolus is deflected by the Coriolis force, running into the inlets at the surface and triggering a compensating outflow at depth. Conversely, coordinated estuarine flow is caused by the passage of the trailing edge of the bolus past the entrances, causing the sea surface slope to switch direction.
OS21B-1178
Obstacle Effects on the River sea Interaction
The river discharged flow behavior in the ROFI (Regions of Freshwater Influence; Simpson, 1997) is studied using FVCOM (Chen et al, 2006), an unstructured grid primitive equation model. In the present study we can resolve detailed motion near the river mouth and consider the effect of an obstacle (a sea mount or an island) placed in front of the river mouth. The unstructured grid zooms up the behavior of a bulge which was widely observed in earlier estuarine model studies and we could investigate the separation of the bulge by the anti-cyclonic motion due to the river discharge. An obstacle of a sea mount seems to play a similar role as the core of a bulge, but in the case with an island as an obstacle, totally different flow patterns were observed compared with other cases, since island can affect the surface motions. With the same geometrical conditions, we also consider tide, which enhances vertical mixing and changes flow patterns induced by the river discharge.
OS21B-1179
Material flux in mangrove forest based on the field observation.
Mangrove ecosystems play important roles in conservation of seashore lines and spawning and nursery of aquatic creatures. It is important to understand nutrient budgets and links between human activities and their effects on mangrove ecosystems. However, we have less knowledge about mangrove ecosystems than that about many other ecosystems. To quantify total material balances in the estuary centered in mangrove forest, we have measured nutrient cycling and CH4 and CO2 gas fluxes in Fukido mangrove creek, Ishigaki island, Okinawa, Japan. It was conducted over tidal cycles from 2006 to 2008. To understand the difference between weather conditions, we investigated on both of rainy day and fine day. Water budget in the river was controlled by tidal exchange at estuary and the input budget from upriver was not dominant for the total budget even if itfs rainDFrom estimation of suspended solids (SS) budgets, SS was flowed in the river from upriver significantly on rainy day (more than 5 times inflow of fine day). The amount of SS accumulation in mangrove forest on rainy day (316 kg/day) was about 10 times amount of fine day. Total nitrogen (T-N) and total phosphorus (T-P) budgets also showed accumulation in mangrove. The outflow of T-P to coastal area on rainy day was 0.046 kgPO4/day and nearly equal to fine day. In contrast, T-N outflow to coastal on rainy day (0.58 kgN/day) was about 100 times of fine day. T-N budget showed different behavior from T-P. Ammonia nitrogen (NH4+-N) was dissolved from mangrove forest (~3.83 kgN/day by the nutrient dissolution experiments) and flowed out to estuary under certain conditions. In additionCconcentrations of total organic carbon (TOC) in mangrove creeks increased on fine days (11.2~15.5 mgC/L) and decreased on rainy days(1.8~4.9 mgC/L). It suggested the TOC dissolution to creek water from mangrove carbon-rich sediments and dilution effects by rain. Continuous measurements of gas fluxes showed that the CH4 and CO2 emissions from the water were accelerated due to the drop in hydrostatic pressure during the falling tide. The magnitude of total carbon gas fluxes (~116kgC/day) was about ~50 percent of the carbon accumulation in the creek. Estimation of net carbon cycling in Fukido mangrove estuary including carbon gas emission indicated that the estuary functioned as sinks for carbon. We conclude that a mangrove ecosystem had unique functions different from common urban rivers, preventing excess sediment outflow on rainy day and supplying nutrients to coastal area on fine day. It would affect the coastal ecosystems and offer habitats to marine life including fish and coral.
OS21B-1180
A tidally-driven flushing process in a coastal bay
Lunenburg Bay, on the south eastern coast of Nova Scotia, is the site of an interdisciplinary coastal observatory with permanent moorings recording hydrodynamic, atmospheric and biological data. The Bay is characterised by complex bathymetry with a narrow shallow channel connecting the main bay to two adjacent coves. During the ebb phase of the tide a strong jet exits the channel and enters the main bay with maximum velocities reaching 1m/s. The flow in the channel and the jet is strongly baroclinic. We report observational data from a series of field experiments examining the circulation. The channel and cove system forms a 'cold water pump' every tidal cycle. During flood tide, relatively cold near-bottom water is drawn from the bay into the channel, resulting in large and sudden temperature drops in the channel at the bottom. This bottom water mixes with warmer surface water from the coves, and as ebb tide commences, the ebb-tide jet flushes the relatively cold water into the bay at the surface. The subsequent spreading of the cold pulse as it enters the bay appears to be strongly influenced by winds over the bay particularly when the wind is aligned along the axis of the bay (in either direction). Mixing in the channel and jet likely represent one of the primary mechanisms driving the residual (estuarine) circulation in the Bay. The observations, in particular the temperature stratification and fluxes, are compared with predictions from the hydrodynamic model Delft3d.
OS21B-1181
Eulerian and Lagrangian Observations of Circulation in Pamlico Sound, North Carolina
Pamlico Sound, North Carolina, may have the weakest tidal influence of any North American estuary. This broad, shallow lagoon is connected to the ocean only by a few narrow inlets, and circulation is primarily wind- driven. We will present Eulerian and Lagrangian observations of circulation in the Sound, and discuss the spatial and temporal variations in wind and tidal forcing. Eulerian data were collected in the fall of 2004 and Eulerian and Lagrangian data in the summers of 2006 and 2007. These data reveal that currents have a vertical distribution consistent with barotropic forcing and significant bottom friction; vertical stratification is not significant. Currents are essentially in phase with the wind, while the along-estuary surface slope lags the wind by a few hours. This is consistent with prior observations of wind-driven seiching. On average, currents throughout the sound are straight downwind at about one percent of the wind speed. Lagrangian data were averaged to reveal typical vector fields during northeasterly and southwesterly wind conditions. Tidal period Eulerian currents are observed only near Oregon Inlet at the north-eastern corner of the sound, and further analysis of the the Lagrangian data may reveal finer-scale spatial variations in tidal amplitude.
OS21B-1182
Simulating particle dispersion in a tidal flat and channel system: Skagit Bay, WA (USA)
In order to gain a better quantitative understanding of factors controlling mixing rates in a tidal flat environment, a Lagrangian particle tracking approach was employed. The Delft modeling system was applied to an idealized tidal channel/flat system and Skagit Bay, WA (USA) (48 19N, 122 24W) for the purpose of computing the flow and particle trajectories under a range of environmental conditions. Time varied particle distribution statistics were examined for each condition, and the ensemble particle tracks were analyzed and compared with field deployed drogues. Results of the simulations are compared with field- deployed drogues dropped in at various time intervals and locations.
OS21B-1183
Estuarine Energy Pathways
A conceptual framework for the tidally-averaged, volume-integrated mechanical energy balance in an estuary is developed. Five energy reservoirs are defined: tidal, subtidal KE, and subtidal APE of surface height, stratification, and along-channel density gradient. Primary fluxes between all reservoirs are defined, and scaling expressions are developed. The APE is found to be dominated by the subtidal along-channel gradient of the depth-averaged density.
OS21B-1184
Lateral Mixing Processes in an Estuary: San Francisco Bay and its Exchange With Perimeter Habitat
Observations from the South San Francisco Bay are presented to examine lateral mixing processes in an estuary. Irregularities in the shoreline lead to lateral density gradients that are set up by tidal trapping, which disrupts the phasing of flows and scalar concentrations along the estuary's axis. In South San Francisco Bay, thousands of acres of salt ponds are being breached to the Bay's influence for the first time in decades as part of a landscape-scale salt marsh restoration project. The tides deliver salt, sediment, and nutrients to the subsided ponds, aggrading their surfaces and converting them to marsh. These newly inter-tidal ponds around the perimeter of the South San Francisco Bay constitute a highly irregular shoreline, capable of initiating steep, periodic lateral density gradients. In this study, we focus on a small cluster of salt ponds and the tidal slough to which they were breached. The exchange between the tidal slough and the ponds is representative of the larger estuary, but of a spatial scale small enough that we can conduct field experiments to examine the flows and transport of scalars in detail. We conducted two boat-mounted transecting surveys of the tidal slough in June and July of 2008, during which we collected profiles of velocity with a down-looking 1200 kHz ADCP, continuous CTD measurements of surface water temperature and salinity, and discrete CTD profiles of salinity and temperature. We have observed that water and salt are trapped in the ponds on the flood tide, and released on the ebb out of phase with the slough's primary salinity gradient. Additionally, the momentum of the ebbing flow in the channel confines the pond effluent to the near bank just down-estuary of the breach. This leads to the coincidence of two distinct water masses, and a sharp change in salinity of 3 PSU over a distance less than 10 meters. We use our data to construct detailed velocity and density fields across and along the tidal slough as the lateral salinity gradients are induced and relaxed. We then explore the resulting periodic, buoyancy-driven cross-sectional mixing, and its implications for estuarine transport on two time and spatial scales: first, the cross-sectional mixing affects shear dispersion, which influences the tidally averaged, longitudinal flux of salt and other scalars, such as suspended sediment. Second, the variability of buoyancy-driven mixing within the tidal cycle affects the quantity of salt and sediment delivered to habitat areas, as well as the grain size distribution and source of sediment transported.
OS21B-1185
Mapping the Transverse Structure of Tidal Velocity in the Channel of a Saltmarsh Creek
The tidal exchange through the Scott Creek saltmarsh estuary was measured near Big Bay Creek, in Edisto, South Carolina. The techniques used for data collection stemmed from those recommended in previous studies. A bottom-mounted ADCP was used to sample data for 35 days, from the thalweg. A vessel-mounted ADCP was used for 13- hour durations, repeatedly surveying Scott Creek's 50m width. These surveys were performed during 4 different tidal cycles, capturing 1.2, 1.5, 2.3, and 2.4m amplitude events. Survey data were then spatially segregated into 3m wide bins along the transverse axis of the creek. Data in each bin were then depth-integrated, treated as distinct time series of data, and analyzed for 14 significant harmonic frequencies. Resultant constituents were used to construct individual time series for axial current speed through each transverse bin and were compared with both the bottom-mounted and vessel-mounted ADCP datasets. Correlations, between transversely segregated measurements and each constructed time series, averaged 0.88, and varied between 0.71 and 0.93. Standard deviations were 8-14cm/s. This effort was completed to provide both the boundary forcing function to drive a 2-D hydrodynamic model and the baseline to evaluate the effect of tidal restoration for the Scott Creek estuary.
OS21B-1186
Classification of Gyeong-Gi Estuary (Korea) with Tidal Propagation Characteristics at Difference Waterways
The characteristics of tidal wave propagation at Gyeonggi Bay (west coast of Korea) are studied with tide observation data and numerical model. The estuary consists of 3 main channels and 3 rivers, through which major tidal flow and river discharge meet each other. It is found that the type of this estuary can be characterized by different tidal propagation pattern along the 3 main channels. Although 3 major channels show a hyper-synchronous type in general, the maximum tidal amplitude and asymmetry of tidal current occur in different way at different channel. Numerical model study is performed to find out the major physical factors that influence channel-dependent tidal propagation. Model results show that the important factor for the change of tidal amplitude and phase along ecah channel is bottom friction, compared with river discharge and tidal flat existence. On the other hand the river discharge modifies phase lag at high and low tide. Model experiment shows the topographical characteristics of Gyeong-Gi estuary is the most important factor for the generation of hyper-synchronous pattern in Gyeong-Gi Estuary.
OS21B-1187
Characterizing Estuarine Turbulence and Testing Turbulence Closure
Turbulent mixing has significant consequences for a wide array of estuarine processes. As scientists and resource managers rely more heavily on numerical models that utilize two-equation turbulence closure schemes to study estuarine systems, it becomes increasingly important to test these closure models with high quality field data. We present data collected with the Mobile Array for Sensing Turbulence (MAST) in three different estuarine systems. The data from the MAST provide estimates of the turbulent length scale, the rate of dissipation of TKE and scalar variance, the turbulent fluxes of buoyancy and momentum, as well as highly resolved measurements of the gradient Richardson number. These data highlight the importance that the large variations in stratification have on estuarine turbulence and demonstrate that turbulence in these systems often deviates significantly from local equilibrium where turbulent production and dissipation balance at first order. Our data demonstrate that the distance to the boundary or the Ozmidov scale sets the turbulent length scale, depending on which is smaller. We present evidence for growing turbulence due to shear instability, as well as decaying turbulence in a turbulent wake zone. We use these data to test how well several commonly used turbulence closure schemes account for the impact of stratification and non-local turbulence on the turbulent fluxes, mixing efficiency and critical gradient Richardson number. The general approach employed by these models is largely consistent with our observations, with the stability functions proposed by Kantha and Clayson (1994) demonstrating the best agreement with our data. Their formulation not only is more consistent with our observations of a critical gradient Richardson number of 0.25, but it also accounts for the large deviations from equilibrium in a manner more consistent with our observations.
OS21B-1188
Lateral circulation driven by axial winds in an idealized, partially mixed estuary
A 3D hydrodynamic model (ROMS) is used to investigate lateral circulation driven by axial wind events in a partially mixed estuary. The channel is straight with a triangular cross-section. The model results suggest that driving mechanisms for lateral circulation during axial wind events are different between stratified and unstratified conditions. When the water column is stratified, the lateral flow and salinity structures below the halocline closely resemble those driven by boundary mixing, and rotational effects are important. When the water column mixes vertically, rotational effects do not drive significant lateral circulation. Instead, differential advection of the axial salinity gradient by wind-driven axial flow is responsible for controlling lateral salinity gradients that in turn drive bottom-divergent lateral circulation during down-estuary wind and bottom- convergent lateral circulation during up-estuary winds. The wind-induced and tidally-induced lateral shear interacts to drive the variability of lateral flow. A Hansen-Rattray-like scaling is applied and shows good predictive skills for lateral flows under unstratified conditions. Supporting observations from the Hudson River estuary is provided.