Bottom Velocity Research Articles

Evaluation of a Cross-shore Outflow Rate of Suspended Sediment

A cross-shore outflow rate of suspended sediment is important in estimating coastal sediment budget. On estimating an outflow rate, vertical distributions of concentration of suspended load were evaluated as a function of bottom friction velocity due to wave action and settling velocity of suspended load. With these results, by solving numerically the conservation equation of sediment and the advective diffusion equation of the suspended load, and integrating it in the cross shore direction from the location of a berm to that of the critical depth for drift sand movement, a sediment loss flowing to a deeper region than the critical depth for drift sand movement was obtained. As a result, the bottom changes due to suspended load cannot be neglected.

AN ESTIMATION METHOD OF EQUILIBRIUM GRAIN SIZE DISTRIBUTION IN INNER BAY

A grain size distribution of suspended solids or sediment in a closed basin is closely related to habitat suitability of aquatic benthic animals such as coral or a shellfish. However, it is very difficult to get correct information about an equilibrium grain size distribution because it always changes spatially and temporally. We investigated a method to estimate grain size distributions both of bed load material and suspended one by using bottom friction velocities which were calculated by wave analysis based on statistical wave data. And then, we assume that the equilibrium grain size distribution of sediment can be approximated with the mean value of bed load material and suspended load material. We applied this method to estimate the grain size distributions of sediment in the Takegashima Marine Park which is located the southern end of Tokushima and the estimated grain size distributions coincide with the field data.

Wave Climatology in Coastal Maine for Aquaculture and Other Applications

Wind waves represent a significant hydrodynamic factor affecting many oceanographic studies such as sediment transport, design of structures, etc. In coastal Maine, wave information is needed, among other applications, for aquaculture-related activities. As few data sources exist, a question that confronts scientists pertains to the magnitudes of typical and extreme wave conditions at various times. To address this, numerical modeling was performed for a period of six and a half years (7/99–12/05) on a continuous basis by coupling National Oceanic and Atmospheric Administration’s outer ocean predictions to two coastal, high-resolution, regional domain grids encompassing the Penobscot Bay and Machias Bay regions where aquaculture activity is prevalent and expanding. As the modeling involves uncertainties because of bathymetric and wind field representations, their effect on the results was explored. It was found that although the uncertainties could create inaccuracies in real-time forecasts, their effect on the development of climatogies was minimal. Average modeled significant wave heights are found to vary between 0.6 and 1.5 m in the sub-domains. The maximum conditions are of the order of 6.5 m in the outer parts of the sub-domains and occurred in September and December. Estimated wave-induced bottom velocities were found in many areas to be in excess of the published estimates of resuspension thresholds for net-pen wastes. Estimates of “extreme” wave conditions, corresponding to a recurrence interval of 30 years (representing the nominal design life of the cage), were found to vary between 2 and 7 m in the modeled areas. Detailed contour maps have been developed for site-specific characterization of the wave climate.

Density‐dependent variations of the along‐isobath flow in the East Greenland Current from Fram Strait to Denmark Strait

The East Greenland Current (EGC) dynamically connects the Arctic Ocean to the North Atlantic on the western side of the Nordic Seas. Observations show that the speed of the EGC considerably varies along the East Greenland Slope (EGS). Here it is shown, using current meter data reported in the literature and climatological hydrographic fields, that velocity and transport variations along the EGS are supported by the cross‐isobath component of the density‐dependent geostrophic flow relative to the bottom. The relative flow impinging on (leaving) the EGS in a northern (southern) limb of the cyclonic circulation in the Nordic Seas strengthens (weakens) the along‐isobath bottom geostrophic flow. Variations of the latter are clearly associated with along‐isobath bottom density gradients. Current observations indicate an increase of the along‐isobath bottom velocity from 79°N to 75°N equal to about 9 and 10 cm s−1 on the upper (1000 m isobath) and lower (2000 m isobath) EGS, respectively. Corresponding estimates based on bottom density distribution along the 1000 and 2000 m isobaths are grossly consistent with the observations given above though we obtain a higher increase (13 cm s−1) at 1000 m and lower increase (6 cm s−1) at 2000 m. Considering the variability of the system and the poor resolution of the observations we find this to be a very convincing result, demonstrating the power of the geostrophic approximation for such estimates.

2004 Indian Ocean tsunami inflow and outflow at Phuket, Thailand

At Bangtao Beach, Phuket, the 2004 Indian Ocean tsunami produced a repeated sequence in which rapid inflow of turbulent water was followed by ponding and then by gradual outflow. Photographs and eyewitness accounts show an initial withdrawal followed by series of inflows. The tsunami left behind a sand sheet as much as 25 cm thick that contains parallel, inclined, landward and seaward lamina in addition to the normal grading commonly reported from tsunami deposits. The sheet contains evidence for two times of vigorous inflow. Each of these is marked by mud rip-ups, medium to coarse sand that grades upward to fine, landward-inclined laminae, and a sharp basal contact. The top of the sand sheet, when observed in the first days after the tsunami, abounded in current dune and ripple bedforms of mostly landward orientation. The tsunami's first positive wave left no onshore sedimentary record in this pitting area. The second wave deposited sand that is much less extensive and slightly finer than that of the third wave. The deposit of both these waves contains multiple fining-upward sequences possibly due to multiple surges in one wave train. The depth-averaged flow velocity estimated from thickness and grain size are in the range 7–21 m/s, whereas, a near bottom threshold velocity calculated from bedforms reveals the order of magnitude difference from 1.74 to 1.03 m/s.

On the determination of the stable bed slope of a channel using mathematical model

The paper deals with an analysis of selected equations used for the determination of a stable longwise slope calculation of torrential rivers. Irregularity of the gradient, accompanied by heavy bed-load experiencing abrupt changes of the flow as a result of heavy rainfalls of short duration and high intensity, these are typical features impacting the behaviour and characteristics of torrential rivers. The determination of the stable bottom slope, when the river bed is kept unpaved but still provides resistence against harmfull effects of rapids, becomes an essential objective of the study. Three methods are used to determine the stable slope: the first is based on tangent tension (shear stress theory), the second observes a (critical) non-scouring cross-sectional velocity (critical mean channel velocities), and the third applies the bottom layer velocity, (the critical bed velocities). The mathematical hydraulic model HEC-RAS v. 3.1.3 has been used for the verification of the methods in the Jindřichovický creek case study in the Krušné hory.

Parameter estimation for a three‐dimensional numerical barotropic tidal model with adjoint method

AbstractThe parameters of a three‐dimensional (3‐D) barotropic tidal model are estimated using the adjoint method. The mode splitting technique is employed in both forward and adjoint models. In the external mode, the alternating direction implicit method is used to discretize the two‐dimensional depth‐averaged equations and a semi‐implicit scheme is used for the 3‐D internal mode computations. In this model the bottom friction is expressed in terms of bottom velocity which is different from the previous works. Besides, the bottom friction coefficients (BFCs) are supposed to be spatially varying, i.e. the BFC at some grid points are selected as the independent BFC, while the BFC at the other grid points can be obtained through linear interpolation with these independent BFCs. On the basis of the simulation of M2 tide in the Bohai and North Yellow Seas (BNYS), twin experiments are carried out to invert the prescribed distributions of model parameters. The parameters inverted are the Fourier coefficients of open boundary conditions (OBCs), the BFC and the vertical eddy viscosity profiles. In these twin experiments, the real topography of BNYS is installed. The ‘observations’ are produced by the tidal model and recorded at the position of TOPEX/Poseidon altimeter data, tidal gauge data and current data. The experiments discuss the influence of initial guesses, model errors and data number. The inversion has obtained satisfactory results and the prescribed distributions have been successfully inverted. The results indicate that the inversion of BFC is more sensitive to data error than that of OBC and the vertical eddy viscosity profiles. Copyright © 2007 John Wiley & Sons, Ltd.

Wind wave-forced fine sediment erosion during the slack water periods in Hangzhou Bay, China

The shallow water wave simulation model-SWAN incorporated with a simple fine sediment erosion model is applied to Hangzhou Bay, China, to model the horizontal distribution of the maximum bottom orbital velocity and corresponding fine sediment erosion rates induced by: (1) southeasterly steady winds (5, 20 and 30 m/s), (2) southwesterly steady winds (5 and 20 m/s); (3) northwesterly steady winds (5 and 20 m/s); (4) east-southeasterly steady winds (5 and 20 m/s); (5) easterly steady winds (5 and 20 m/s) under closed and unclosed boundaries; and (6) unsteady winds during the slack water periods. Results suggest: (1) the steady wind wave-induced maximum bottom orbital velocities and corresponding fine sediment erosion rates generally increased with the increasing steady winds; (2) closed and unclosed boundary conditions had more significant influences on modeled fine sediment erosion rates under 5 m/s easterly steady winds than 20 m/s; and (3) steady and unsteady wind wave-induced maximum bottom currents could be significant in eroding fine sediment bed in Hangzhou Bay. The results show implications for geomorphology, sedimentology, coastal erosion, and environmental pollution mitigation in Hangzhou Bay.

A new measure for direct measurement of the bed shear stress of wave boundary layer in wave flume

In this article, a shear plate was mounted on the bottom in a wave flume and direct measurements of the smooth and rough bed shear stress under regular and irregular waves were conducted with the horizontal force exerted on the shear plates by the bottom shear stress in the wave boundary layer. Under immobile bed condition, grains of sand were glued uniformly and tightly onto the shear plate, being prevented from motion with the fluid flow and generation of sand ripples. The distribution of the bottom mean shear stress varying with time was measured by examining the interaction between the shear plate and shear transducers. The relation between the force measured by the shear transducers and its voltage is a linear one. Simultaneous measurements of the bottom velocity were carried out by an Acoustic Doppler Velocimeter (ADV), while the whole process was completely controlled by computers, bottom shear stress and velocity were synchronously measured. Based on the experimental results, it can be concluded that (1) the friction coefficient groews considerably with the increase of the Reynolds number, (2) the shear stress is a function varying with time and linearly proportional to the velocity. Compared with theoretical results and previous experimental data, it is shown that the experimental method is feasible and effective, A further study on the bed shear stress under regular or irregular waves can be carried out. And applicability to the laboratory studies on the initiation of sediments and the measurement of the shear stress after sediment imigration.

Use of laboratory studies to develop a dispersal model for Missouri River pallid sturgeon early life intervals

Summary Understanding the drift dynamics of pallid sturgeon (Scaphirhynchus albus) early life intervals is critical to evaluating damming effects on sturgeons. However, studying dispersal behavior is difficult in rivers. In stream tanks, we studied the effect of velocity on dispersal and holding ability, estimated swimming height, and used the data to estimate drift distance of pallid sturgeon. Dispersal was by days 0–10 embryos until fish developed into larvae on day 11 after 200 CTU (daily cumulative temperature units). Embryos in tanks with a mean channel velocity of 30.1 cm s )1 and a side eddy could not hold position in the eddy, so current controlled dispersal. Late embryos (days 6–10 fish) dispersed more passes per hour than early embryos (days 0–5 fish) and held position in side eddies when channel velocities were 17.3 cm s )1 or 21.1 cm s )1 . Day and night swim-up and drift by embryos is an effective adaptation to disperse fish in channel flow and return fish from side eddies to the channel. Early embryos swam <0.50 cm above the bottom and late embryos swam higher (mean, 90 cm). A passive drift model using a near bottom velocity of 32 cm s )1 predicted that embryos dispersing for 11 days in channel flow would travel 304 km. Embryos spawned at Fort Peck Dam, Missouri River, must stop dispersal in <330 km or enter Lake Sakakawea, where survival is likely poor. The model suggests there may be a mismatch between embryo dispersal distance and location of suitable rearing habitat. This situation may be common for pallid sturgeon in dammed rivers.

Estuarine Boundary Layer Mixing Processes: Insights from Dye Experiments*

Abstract A series of dye releases in the Hudson River estuary elucidated diapycnal mixing rates and temporal variability over tidal and fortnightly time scales. Dye was injected in the bottom boundary layer for each of four releases during different phases of the tide and of the spring–neap cycle. Diapycnal mixing occurs primarily through entrainment that is driven by shear production in the bottom boundary layer. On flood the dye extended vertically through the bottom mixed layer, and its concentration decreased abruptly near the base of the pycnocline, usually at a height corresponding to a velocity maximum. Boundary layer growth is consistent with a one-dimensional, stress-driven entrainment model. A model was developed for the vertical structure of the vertical eddy viscosity in the flood tide boundary layer that is proportional to u2*/N∞, where u* and N∞ are the bottom friction velocity and buoyancy frequency above the boundary layer. The model also predicts that the buoyancy flux averaged over the bottom boundary layer is equal to 0.06N∞u2* or, based on the structure of the boundary layer equal to 0.1NBLu2*, where NBL is the buoyancy frequency across the flood-tide boundary layer. Estimates of shear production and buoyancy flux indicate that the flux Richardson number in the flood-tide boundary layer is 0.1–0.18, consistent with the model indicating that the flux Richardson number is between 0.1 and 0.14. During ebb, the boundary layer was more stratified, and its vertical extent was not as sharply delineated as in the flood. During neap tide the rate of mixing during ebb was significantly weaker than on flood, owing to reduced bottom stress and stabilization by stratification. As tidal amplitude increased ebb mixing increased and more closely resembled the boundary layer entrainment process observed during the flood. Tidal straining modestly increased the entrainment rate during the flood, and it restratified the boundary layer and inhibited mixing during the ebb.

A three-dimensional hydrodynamic model of estuarine circulation with an application to Southampton Water, UK

A three-dimensional hydrodynamic model has been developed to simulate water mass circulation in estuarine systems. This model is based on the primitive equation in Cartesian coordinates with a terrain-following structure, coupled with a Mellor–Yamada 2.5 turbulence scheme. A fractional-step method is applied and the subset of equations is solved with finite volume and finite element methods. A dry–wet process simulates the presence of the tidal flat at low water. River inputs are introduced using a point-source method. The model was applied to a partially mixed, macrotidal, temperate estuary: Southampton Water, UK. The model is validated by comparisons with sea surface elevation, ADCP measurements and salinity data collected in 2001. The mean spring range 2( M 2 + S 2) and the mean neap range 2( M 2 − S 2) are modelled with an error relative to observation of 12 and 16%, respectively. The unique tidal regime of the system with the presence of the ‘young flood stand’ corresponding to the slackening conditions occurring at mid flood and ‘double high water’ corresponding to an extension of the slackening conditions at high tide is accurately reproduced in the model. The dynamics of the modelled mean surface and bottom velocity closely match the ADCP measurements during neap tides (rms of the difference is 0.09 and 0.01 m s −1 at the bottom and at the surface, respectively), whereas at spring the difference is greater (rms of the difference is 0.25 and 0.20 m s −1 at bottom and surface, respectively). The spatial and temporal variation of the degree of stratification as indicated by salinity distributions compares well with observations.

Profiling float measurements of the recirculation gyre south of the Kuroshio Extension in May to November 2004

During May to November 2004, 20 profiling floats were deployed in the recirculation gyre (RG) region south of the Kuroshio Extension (KE). With the KE and RG being in a stable state, most of these floats remained within the RG, resulting in a large number of satellite position fixes for estimating the velocities at the parking depth (1500 db) and a large number of temperature/salinity profiles for estimating the geostrophic velocities above the parking depth. The flows of the RG at different depths in the upper 1500 db are found to be approximately parallel to each other, with the speed at the surface (35 cm s−1) being about three and a half times larger than that at the parking depth (10 cm s−1). By analyzing the full‐depth conductivity‐temperature‐depth profiles in the RG, in addition to the velocity estimates, we found that the vertical structure of the RG velocity field was dominated by the barotropic and first baroclinic modes. The two modes are combined in such a way that the resulting RG circulates anticyclonically in the same direction from the surface to the bottom and has an anticyclonic bottom velocity on the order of 5 cm s−1. From the barotropic component (depth‐averaged) of the RG velocity field, the RG transport with one standard error is estimated at 101 ± 8 × 106 m3 s−1.

Reconstructing the Meridional Overturning Circulation from Boundary Densities and the Zonal Wind Stress

Abstract Numerical models are used to test whether the meridional overturning circulation (MOC) can be reconstructed from boundary densities and the wind stress. In idealized model setups without topography the strength as well as the temporal and spatial variability of the MOC cell can largely be reproduced from boundary densities and the zonal wind stress. With added slopes along the meridional boundaries, most of the depth-averaged flow is missed and neither strength nor spatial structure of the MOC is well reproduced. However, the temporal evolution of both MOC and its estimate are similar. In an eddy-permitting model with realistic bottom topography the contribution of the depth-averaged meridional flow to the MOC is captured at some places while it is missed at others. Nevertheless, boundary densities and the zonal wind stress allow the leading modes of the temporal and spatial MOC variability to be reproduced. On seasonal time scales most of the MOC variability is due to the wind stress but changes in the boundary density affect the MOC as well. On interannual time scales the MOC variability largely reflects changes in the boundary density. Generally, the MOC reconstructions are accurate when bottom velocities are small, an assumption made in the reconstruction approach. The results are relevant for estimates of both the modern and the past MOC. In the real ocean, boundary densities can be obtained from measurements of temperature, conductivity, and pressure in the water column, whereas past seawater densities have left their imprint in sea sediments.

Teleseismic tomography of the southern Tyrrhenian subduction zone: New results from seafloor and land recordings

Teleseismic traveltime data, recorded by temporary ocean bottom seismographs deployed in Tyrrhenian Sea around the Aeolian Islands (Tyrrhenian Deep‐sea Experiment (TYDE)), have been used for the first time in Italy to refine the 3‐D model for the deep P wave velocity structure of the southern Tyrrhenian subduction zone. The arrival times of 35 teleseisms have been combined with those recorded by the Italian National Network. In order to obtain a more complete azimuthal coverage of teleseismic rays, 80 events recorded by land stations from 1990 to 2002 have been included in the data set. In total, 2904 P and 314 PKPdf phases, 1300 recorded by ocean bottom instruments, have been collected. The upper mantle structure is reconstructed down to 500 km by a nonlinear inversion of the relative residuals computed with respect to the reference 1‐D velocity model ak135. The obtained tomographic model has a higher resolution than those previously published thanks to the recordings of TYDE seafloor stations. Tomographic results confirm the presence of the Tyrrhenian slab imaged as a high‐velocity body extending from the uppermost mantle down to the bottom velocity model with dip 70–75° NW. The model better defines the geometry of the seismogenic part of the slab. Its lateral extension is about 200 km in the depth interval 150–300 km, where most of the deep seismicity is concentrated. At uppermost mantle depths the fast structure has smaller lateral dimensions (about 100 km). The inversion also points out a wide well‐resolved low‐velocity zone completely surrounding the steeply dipping fast structure from the lower crust down to about 300 km. This feature suggests the presence of a three‐dimensional circulation of asthenospheric flow around the Ionian slab caused by retreat and roll‐back of the slab. Our results are in agreement with recent laboratory experiments, mantle anisotropy studies, geochemical and isotopic analyses, and modeling based on residual topography.

Experimental Study of Sediment Transport in Meandering Channels

Sediment transport in a meandering channel is measured in a laboratory flume. The measurements are evaluated and compared with previous studies. The values of the calculated sediment transport rates using previous formulas are generally overestimated. Under these circumstances, in this research, it is noticed that the sediment transport rates as measured in the laboratory, and sediment transport capacities computed with the Einstein’s approach, behave in a quite similar way, seemingly closely related to the varying bottom shear velocity or stress. Einstein’s approach for bed load comparison is chosen in this experimental research because it has been tested to some extent.

Trends in Caribbean Paleoproductivity related to the Neogene closure of the Central American Seaway

This study tests the hypothesis that the late Miocene to early Pliocene constriction and closure of the Central American Seaway (CAS), connecting the tropical Atlantic and East quatorial Pacific (EEP), caused a decrease in productivity in the Caribbean, due to decreased coastal upwelling and an end to the connection with high-productivity tropical Pacific waters. The present study compared paleoceanographic proxies for the interval between 8.3 and 2.5 Ma in 47 samples from south Caribbean ODP Site 999 with published data on EEP DSDP Site 503. Proxies for Site 999 include the relative abundance of benthic foraminiferal species representing bottom current velocity and the flux of organic matter to the sea floor, the ratio of infaunal/epifaunal benthic foraminiferal species and benthic foraminifer accumulation rates (BFARs). In addition, we calculated % resistant planktic foraminifers species and used the previously published % sand fraction and benthic carbon isotope values from Site 999. During early shoaling of the Isthmus (8.3–7.9 Ma) the Caribbean was under mesotrophic conditions, with little ventilation of bottom waters and low current velocity. The pre-closure interval (7.6–4.2 Ma) saw enhanced seasonal input of phytodetritus with even more reduced ventilation, and enhanced dissolution between 6.8 and 4.8 Ma. During the post-closure interval (4.2–2.5 Ma) in the Caribbean, paleoproductivity decreased, current velocity was reduced, and ventilation improved, while the seasonality of phytodetrital input was reduced dramatically, coinciding with the establishment of the Atlantic–Pacific salinity contrast at 4.2 Ma. Our data support the hypothesis that late Miocene constriction of the CAS at 7.9 Ma and its closure at 4.2 Ma caused a gradual decrease in paleoproductivity in the Caribbean, consistent with decreased current velocity and seasonality of the phytodetrital input.

Field Study on the Characteristic of the Eelgrass Bed under the Severe Wave Condition and Development of an Erosion-Proof Base for its Transplantation

The field observation revealed that eelgrass bed was gravel, on which they can take root, in the place where strong wave was observed. This finding gave a new idea of the base for eelgrass transplantation using gravel. Laboratory experiments showed that the eelgrass planted in the base was stable against the strong wave action, which the maximum amplitude of bottom velocity was 1.2 m/s. An erosion-proof base for transplantation of eelgrass was developed. The field test of transplantation was conducted at the place where theycannot survive by any conventional transplantation procedure because of the strong wave action. It was confirmed that transplanted eelgrass by the developed base grew stably and increased the number there.

Six circumpolar currents—on the forcing of the Antarctic Circumpolar Current by wind and mixing

The transport of the Antarctic Circumpolar Current (ACC) is influenced by a variety of processes and parameters. A proper implementation of basin geometry, ocean topography and baroclinicity is known to be a fundamental requisite for a realistic simulation of the circulation and transport. Other, more subtle parameters are those of eddy-induced transports and diapycnal mixing of thermohaline tracers or buoyancy, either treated by eddy resolution or by a proper parameterization. Quite a number of realistic numerical simulations of the circulation in the Southern Ocean have recently been published. Many concepts on relations of the ACC transport to model parameters and forcing function are in discussion, however, without much generality and little success. We present a series of numerical simulations of circumpolar flow with a simplified numerical model, ranging from flat-bottom wind-driven flow to baroclinic flow with realistic topography and wind and buoyancy forcing. Analysis of the balances of momentum, vorticity, and baroclinic potential energy enables us to develop a new transport theory, which combines the most important mechanisms driving the circulation of the ACC and determining its zonal transport. The theory is based on the importance of the bottom vertical velocity in generating vorticity and shaping the baroclinic potential energy of the ACC. It explains the breaking of the \(f/h\)-constraint by baroclinicity and brings together in one equation the wind and buoyancy forcing of the current. The theory emphasizes the role of Ekman pumping and eddy diffusion of buoyancy to determine the transport. It also demonstrates that eddy viscosity effects are irrelevant in the barotropic vorticity balance and that friction arises via eddy diffusion of density. In this regime, the classical Stommel model of vorticity balance is revived where the bottom friction coefficient is replaced by \(K/\lambda^2\) (with the Gent–McWilliams coefficient \(K\) and the baroclinic Rossby radius \(\lambda\)) and a modified wind curl forcing appears.

Numerical model simulations of continental shelf flows off northern California

Abstract The three-dimensional circulation on the continental shelf off northern California in the wind events and shelf transport (WEST) experiment region during summer 2001 is studied using the primitive equation regional ocean modeling system (ROMS). The simulations are performed with realistic topography and initial stratification in a limited-area domain with a high-resolution grid. Forcing consists of measured wind-stress and heat flux values obtained from a WEST surface buoy. The general response shows a southward coastal upwelling jet of up to 1 m s - 1 and a weakening or reversal of currents inshore of the jet when upwelling winds relax. Model results are compared to WEST moored velocity and temperature measurements at five locations, to CODAR surface current observations between Pt. Reyes and Bodega Bay, and to hydrographic measurements along shipboard survey lines. The model performs reasonably well, with the highest depth-averaged velocity correlation (0.81) at the inshore mooring (40 m water depth) and lowest correlation (0.68) at the mid-depth mooring (90 m depth). The model shows generally stronger velocities than those observed, especially at the inshore moorings, and a lack in complete reversal of southward velocities observed when upwelling winds relax. The comparison of surface velocities with CODAR measurements shows good agreement of the mean and the dominant mode of variability. The hydrography compares closely at the southern and northern edges of the survey region (correlation coefficients between 0.90 and 0.97), with weaker correlations at the three interior survey lines (correlation coefficients between 0.44 and 0.76). Mean model fields over the summer upwelling period show slight coastal jet separation off Pt. Arena and significant separation off Pt. Reyes. The cape regions also experience relatively strong bottom velocities and nonlinearity in the surface flow. Across-shelf velocity sections examined along the shelf reveal a double jet structure that appears just north of Bodega Bay and shows the offshore jet strengthening to the south. We examine the dynamics during an upwelling and subsequent relaxation event in May 2001 in which the WEST measurements show evidence of a strong flow response. The alongshelf variability in the upwelling and relaxation response introduced by Pt. Reyes is evident. Analysis of term balances from the depth-averaged momentum equations helps to clarify the event dynamics in different regions over the shelf. A clear pattern in the nonlinear advection term is due to the spatial acceleration of the southward jet around the capes of Pt. Arena and Pt. Reyes during upwelling. Results from a three-dimensional Lagrangian analysis of water parcel displacement show significant southward displacement in the coastal jet region, including a strong signal from the double jet. Alongshelf variability in parcel displacements and upwelling source waters due to the presence of Pt. Arena and Pt. Reyes is also apparent from the Lagrangian fields. A cyclonic eddy-like recirculation feature offshore of Pt. Arena prior to the upwelling event causes large patches of onshore-displaced parcels. Additionally, across-shelf variability in the response of water parcels along the D line includes decreased vertical displacement and increased alongshelf displacement in the offshore direction.