observations of the internal tide in monterey canyon abstract data from two shipboard experiments in 1994 designed to observe the semidiurnal internal tide in monterey canyon reveal semidiurnal currents of about 20 cm s 1 which is an order of magnitude larger than the estimated barotropic tidal currents the kinetic and potential energy evidenced by isopycnal displacements of about 50 m was greatest along paths following the characteristics calculated from linear theory these energy ray paths are oriented nearly parallel to the canyon floor and may originate from large bathymetric features beyond the mouth of monterey bay energy propagated shoreward during the april experiment itex1 whereas a standing wave that is an internal seiche was observed in october itex2 the difference is attributed to changes in stratification between the two experiments higher energy levels were present during itex1 which took place near the spring phase of the fortnightly 14 8 days cycle in sea level while itex2 occurred close to the neap phase further evide

modeling study of variable upwelling circulation in the east china sea response to a coastal promontory abstracta three dimensional high resolution numerical model is used to investigate processes and dynamics of an intensified upwelling that is induced by a coastal promontory over the east china sea ecs shelf the center of the intensified upwelling around the promontory has been constantly observed but so far it has been dynamically unexplained forced by an idealized southeasterly wind stress the model results well capture the observed upwelling at the lee of the coastal promontory the intensified upwelling is formed by a strengthened shoreward transport downstream of the promontory as the upwelling jet veers shoreward the jet is mainly controlled by a cross shore geostrophic balance and is largely modulated by both centrifugal acceleration associated with nonlinear advection and by bottom stress the strengthened shoreward transport is mainly attributed to the cross shore geostrophic current that is induced by a countercurrent negative pressure gradient force pgf and partly attributed to th

entrance exit losses and cross sectional stability of double inlet systems abstract this study investigates the effect of entrance exit losses on the cross sectional stability of double inlet systems the inlet is in equilibrium when the sand transport into the inlet equals the sand transport out of the inlet the velocity amplitude corresponding with the equilibrium cross sectional area is referred to as the equilibrium velocity 1 m s 1 this equilibrium is stable when after a perturbation the cross sections of both inlets return to their original equilibrium value the amplitudes of the inlet velocities are obtained using a lumped parameter model in which the basin water level fluctuates uniformly pumping mode and where the inlets are schematized to prismatic channels the system is forced by a semi diurnal tide where amplitude and phase may differ between the two inlets previous studies concluded that for double inlet systems no stable equilibriums can be found however in these studies entrance exit losses were neglected in the present study entrance exit losses are included in the dynamic equation of the inlets using an analytical model it is shown that entrance exit losses and a difference in the two ocean tidal amplitudes are a prerequisite for the existence of stable equilibriums furthermore the effects of the addition of bottom friction and inertia to the dynamic equation are investigated using a mathematical continuation method the results show that provided entrance exit losses are considerably larger than bottom friction and inertia stable equilibriums are possible these conclusions are supported by observations in the ria formosa southern portugal care should be taken in using the stability model described in this paper as a predictive tool due to simplifications in the model and the uncertainty in determining certain parameter values including inlet length entrance exit loss coefficient bottom friction factor and equilibrium velocity to alleviate these shortcomings suggestions are made for future research

the kinematic and hydrographic structure of the gulf of maine coastal current the gulf of maine coastal current gmcc which extends from southern nova scotia to cape cod massachusetts was investigated from 1998 to 2001 by means of extensive hydrographic surveys current meter moorings tracked drifters and satellite derived thermal imagery the study focused on two principal branches of the gmcc the eastern maine coastal current emcc that extends along the eastern coast of maine to penobscot bay and the western maine coastal current wmcc that extends westward from penobscot bay to massachusetts bay results confirm that gmcc is primarily a pressure gradient driven system with both principal branches increasing their transport in the spring and summer due to fresh water inflows and flowing southwestward against the mean wind forcing during this period in the spring and summer the subtidal surface currents in the emcc range from 0 15 to 0 30 ms 1 while subtidal wmcc currents range from 0 05 to 0 15 ms 1 the reduction of southwestward transport near penobscot bay is accomplished via an offshore veering of a variable portion of the emcc some of which recirculates cyclonically within the eastern gulf of maine the degree of summer offshore veering versus leakage into the wmcc varied strongly over the three study years from nearly complete disruption in 1998 to nearly continuous through flow in 2000 observations show strong seasonal and interannual variability in both the strength of the gmcc and the degree of connectivity of its principal branches r 2005 elsevier ltd all rights reserved

tidally induced cross frontal mean circulation analytical study an analytical model is developed to study the tidally induced mean circulation in the frontal zone four distinct forcing mechanisms are identified which result in the generation of the counterclockwise bernoulli cell the clockwise ekman cell the clockwise frontal cell and the stokes drift facing in the direction with the shallow water to the left the decomposition of the cross frontal circulation provides a dynamical framework for interpreting and understanding its complex structure to illustrate the underlying physics three model configurations are considered pertaining to a homogenous ocean and winter and summer fronts for a homogeneous ocean the circulation is dominated by three cells for the winter front the offshore bernoulli cell is strengthened and for the summer front two counterrotating cells are found in the vertical direction associated with the two branches of the front the dependence of the cell structure on the ekman burger and other dimensionless numbers is examined

control of estuarine sediment dynamics by interactions between currents and waves at several scales abstract the effect of interactions between continuous tidal currents and intermittent waves processes on sediment dynamics and transport is addressed by presenting detailed field measurements of waves boundary layer currents and suspended sediment from an estuarine channel and an adjacent intertidal sandflat in manukau harbour new zealand the aim is to determine in what ways it is necessary to couple waves and currents in numerical models and thereby put limits on the fundamental structure of process based estuarine sediment transport models waves were important on the intertidal flat turbidity switched on and off with the appearance and disappearance of waves wave groups dominated entrainment of bed sediment a wave current boundary layer model explained measured bed shear stress and hydraulic roughness and the measured near bed time averaged suspended sediment concentration was mostly well predicted by a pure wave model both the waves themselves and wave related processes varied markedly over the tidal cycle the variation in the former principally changes in wave height was related to changes in fetch caused by the harbour wide emergence and submergence of intertidal regions the variation in the latter was related to changes in water depth relative to the wavelength of the waves which controlled the penetration to the bed of wave orbital currents in addition to the variation over the tidal cycle in the intensity of wave processes there was also a change in kind which occurred with the arrival at the measurement site of the turbid fringe which is the narrow highly turbid edge of the estuarine water body the relationship between suspended sediment concentration and wave orbital velocity in the turbid fringe was radically different to the relationship in the estuarine water body proper which suggests a change in dynamics perhaps related to breaking waves a hybrid modelling approach is required i e one that treats discrete events but resolves tidal cycle scale variation within the event there is a need to resolve the variation in the wave train over the tidal cycle and the penetration to the bed of wave orbital motions both of which could only be done adequately within an estuary tidal model in contrast to the situation on the intertidal flat where waves intermittently entrained sediment sediment transport in the channel was continuous driven by tidal currents to predict sediment flux in the channel we need to know the upstream sediment transporting capacity of the flow including that contributed by waves the character of the bed sediment and the sediment settling time scale these factors confounded even the simplest notion of flood and ebb dominance which frequently has been applied to understand estuarine morphodynamics

coupled north atlantic slope water forcing on gulf of maine temperatures over the past millennium to investigate ocean variability during the last millennium in the western gulf of maine gom we collected a 142 year old living bivalve arctica islandica l in 2004 and three fossil a islandica shells calibrated 14cams 1030 78 ad 1320 45 ad 1357 40 ad for stable isotope and growth increment analysis a statistically significant relationship exists between modern gom temperature records shell isotope derived 30 m r 0 79 p 0 007 prince 5 50 m r 0 72 p 0 019 boothbay harbor sst r 0 76 p 0 011 and labrador current lc transport data from the eastern newfoundland slope during 1993 2003 in all cases as lc transport increased gom water temperatures decreased the following year decadal trends in the north atlantic oscillation nao and the atlantic multidecadal oscillation amo influence gom water temperatures in the most recent period with water temperatures decreasing during nao and amo negative modes most likely linked to lc transport and gulf stream interaction mean shell derived isotopic changes 18oc during the last 1 000 years were 0 47 and likely reflect a 1 2 c cooling from 1000 ad to present based on these results we suggest that observed cooling in the gom during the last millennium was due to increased transport and or cooling of the lc and decreased gulf stream influence on the gom

particle trapping in estuarine tidal flows particle trapping in estuarine turbidity maxima etm is caused primarily by convergent mean and or tidal fluxes of sediment the result is an approximately bell shaped along channel distribution of vertically integrated tidal cycle mean suspended sediment concentration observations from the columbia river estuary suggest that 1 strong two layer or internal along channel residual and overtide flows are generated by time varying stratification and 2 correlations between the near bed velocity and the suspended sediment fields at these frequencies are important in landward transport of sediment a new spatially and temporally integrated form of the sediment conservation equation has been derived to analyze this trapping process time changes in tidally averaged sediment concentration between two estuarine cross sections can be shown to be related to the divergence of the seaward river flow transport the divergence of velocity shear sediment stratification correlations for the mean flow and each tidal constituent and net erosion or deposition at the bed vertically integrated variables other than seaward river transport are absent from this integrated balance analysis of sediment fluxes using this balance supports the idea that internal residual and overtide circulations are primarily responsible for the landward sediment transport on the seaward side of etm found near the upstream limits of salinity intrusion the balance also shows that attempts to represent fluxes causing trapping of sediment in an etm as a product of a time mean vertically integrated along channel gradient and a diffusivity inevitably lead to the appearance of countergradient transport and thus a negative diffusivity on the seaward side of the etm this result occurs because the trapping process is inherently nonlinear and at least two dimensional and because a one dimensional representation is physically unrealistic

spectrum response of lj well to various stresses during non seismic and seismic periods the well water level in a deep well has significant frequency dependence on various crustal stresses which can provide an effective pathway for determining the well aquifer properties and investigating the response mechanism of groundwater however due to the limitations and complexity of the field conditions there is a lack of on site stress strain data for rocks therefore it is difficult to directly and quantitatively interpret the transfer response between the strain stress and the well water level the observation item data for the lj well in china are relatively complete including rainfall barometric pressure volumetric strain and deep water level data by calculating the spectral period spectral density coherence function and transfer function of various physical variables the spectrum response characteristics of the well aquifer system to various stresses can be effectively obtained when the crust is in a relatively stable state the semidiurnal and diurnal waves are dominant moreover the transfer functions of the well water level s response to the theoretical semidiurnal and diurnal earth tides and the barometric pressure are basically consistent with the correlation analysis results in addition when earthquakes occur the signals of the volumetric strain and the well water level can more effectively highlight the relatively intermediate and high frequency information the transfer function between the well water level and the volumetric strain is nearly an order of magnitude smaller than that in the stable state indicating that the hydrogeological conditions of the lj well aquifer change instantaneously when subjected to seismic waves all the above conclusions show that the correlation and transfer function based on spectral analysis is a feasible and advantageous method of determining the correlation of various physical variables these results provide a foundation for further research on the hydrogeological characteristics of aquifers

the influence of warm core rings on slope water entering the gulf of maine the seasonal baroclinic circulation in the gulf of maine is partly determined by the distribution of dense water that enters from the continental slope and spreads over sills into the deep basins of the gulf the slope water enters the gulf as an intermittent deep flow through the northeast channel which provides the principal connection with the atlantic ocean warm core rings from the gulf stream occasionally approach the mouth of the northeast channel and at times ring water contributes to or modifies the inflowing slope water for example sequential surveys in june and july of 1986 showed that a ring streamer crowded against georges bank and brushed obliquely across the channel mouth the resulting inflow in july flooded the channel mouth with streamer modified slope water which overwhelmed the more usual maine intermediate water outflow noted 1 month earlier compared to previous years relatively little slope water was found inside the gulf in june 1986 and it is tempting to speculate that a delayed spin up of the interior baroclinic circulation began with the major inflow episode observed in july warm core rings from the gulf stream may influence the timing intensity and structure of the circulation and dependent processes that develop each year in the gulf of maine a test of this hypothesis will require long term monitoring of the northeast channel region coupled with seasonal hydrographic surveys and current measurements at strategic locations inside the gulf of maine

the circulation of eastern canadian seas abstract the eastern canadian seas including baffin bay the labrador sea and shelf the n e newfoundland shelf the scotian shelf and the gulf of st lawrence form an integrated hydro dynamical system the circulation is investigated using current meter data and a high resolution three dimensional coupled ice ocean circulation model cecom canadian east coast ocean model covering the entire area the model is forced with realistic atmosphere fluxes and the results are compared to the current meter data collected in four selected periods between 1987 and 2008 many features of the model current fields are similar to those from the previous regional circulation models for the shelves new findings from cecom include seasonal differences of the circulation around davis strait the detailed structure of the labrador current re circulation two cross shelf currents on the scotian shelf and strong currents in halibut channel which connects the waters of the western grand banks and scotian shelf the annual variation of the circulation is investigated both the model and data show the labrador current is strong in fall and weak in spring the outflow from the gulf of st lawrence through cabot strait and the currents on the inner scotian shelf are strong in winter and fall and weak in spring and are in phase with the labrador current the model currents are compared to observations using a qualitative method of visual comparison and a quantitative method based on statistical analysis the comparisons indicate that the main features of the current fields from the observations are successfully reproduced by the model the quantitative analysis indicates that the model currents are in reasonable agreement with the observations specifically a good agreement is found in the labrador shelf newfoundland shelf and flemish pass a fair agreement is found in davis strait the inner scotian shelf and sable bank however the agreement for cabot strait and the scotian shelf break is less satisfactory an analysis of the spatial variability of the current field suggests that the degree of agreement is closely related to the spatial variability of the current field the regions with low spatial variability generally have good agreements the volume and freshwater transports through several sections from the model are in good agreement with available estimates based on data

contribution of nonlinear mechanisms in the persistence of multiple tidal inlet systems abstract multiple tidal inlet stability has been modeled following either a single inlet stability approach or a simple linear analytical approach and the results suggest that these systems are not stable however there is evidence that shallow multiple tidal inlet systems are strongly nonlinear and that they can be stable on a historical time scale based on numerical simulations of the hydrodynamics of ria formosa a shallow lagoon in the south of portugal in which multiple tidal inlets have persisted in a historical time scale the effects of tidal distortion and residual circulation on the persistence of multiple inlets in the system were analyzed numerical simulations using a 2 d vertically averaged finite element model served 1 to identify the existence of three hydrodynamically independent sub embayments in the system 2 to create realistic physical disturbances change in inlet cross sectional area and analyze the hydrodynamic response of the system to such disturbances 3 to identify and quantify the existing nonlinear hydrodynamic processes tidal distortion ebb flood dominance residual flow patterns and 4 to analyze the overall stability of the western sub embayment using the closure curve approach the results show the importance of the nonlinear processes in the hydrodynamics of multiple inlet systems and the need to consider them when analyzing inlet stability in such systems and suggest that specifically for ria formosa if the existing jetties at one of the inlets in the western sub embayment were removed this area of the system would reach natural stability and equilibrium with three inlets

transient flow to a large diameter well in an aquifer with storative semiconfining layers the hantush theory of leaky aquifers with storge in the semiconfining layers is combined with large diameter well theory to produce equations that can be used in the analysis of pumped well and observation well data for stratified formations included in the equations are storage in the pumped well and a linear resistance to flow at the sand face or well bore skin three cases proposed by hantush are considered these depend upon whether the upper boundary of the overlying semiconfining layer or the lower boundary of the underlying semiconfining layer are constant head or no flow boundaries laplace transform solutions valid for the complete time domain are given for each of the three cases for the hydraulic head in the pumped well the aquifer and each of the semiconfining layers type cures obtained by numerical inversion are selected to illustrate the effects of well bore storage well bore skin and leakage although several dimensionless parameters are involved these parameters tend to influence the character of different portions of the type curves suggesting that unique matches are possible the type curves show that well bore storage in a large diameter well may completely obliterate effects of leakage derived from compressible storage in semiconfining layers for the purposes of aquifer testing it may be possible to reduce the magnitude of well bore storage in a large diameter well and thus reveal the presence of leaky semiconfining layers this may help to prevent erroneous interpretation of the well test data and incorrect evaluation of the aquifer parameters

on the relevance of tidal forcing in modelling the mediterranean thermohaline circulation abstract the four dominant constituents of the semi diurnal and diurnal tides have been implemented in a regional eddy resolving mediterranean version of the massachusetts institute of technology general circulation model to assess the role played by tides on the simulated mediterranean thermohaline circulation to this aim we have compared two 10 year hindcast simulations differing only for the inclusion omission of tidal forcing following the recent recommendations suggested by sannino et al 2014 both simulations use the same model having a substantial increment of the horizontal resolution in the region of the strait of gibraltar the results suggest that application of explicit tidal forcing in a mediterranean model has non negligible effects on the simulated circulation in addition to the expected intensification of local mixing processes the western basin exhibits an immediate response to the different characteristics of the inflowing aw observable in the modified deep water convection processes in the gulf of lion the inclusion of tidal forcing also induces changes in the intermediate circulation of the tyrrhenian sea bringing to a better representation of local structures and a reinforcement of the global thermohaline cell liw dispersal paths in the eastern basin are also affected by tides

identification of earthquake signals from groundwater level records using the hht method summary coseismic signals of groundwater levels are generally obtained by subtracting the responses of atmospheric pressure earth tides and precipitation from the observed data however if the observations are conducted without nearby barometers pluviometers or earth tide data for correction coseismic signals are often difficult to extract in this case the hilbert huang transform hht is used to obtain the instantaneous frequencies and amplitudes for every point of the decomposed intrinsic mode functions imfs from groundwater level data for differentiating the related frequency dependent responses without a further auxiliary input the extracted coseismic signals show intense amplitude pulses that are clearly seen in the third imf in addition two types of coseismic signals can be readily distinguished in the results from the hht transform one is an instantaneous short time signal induced by the passing of seismic waves another coseismic signal is a sustained signal induced by the nearfield earthquake occurring near the hualien station taiwan and shows a positive correlation between the earthquake distance and magnitude our results generally show that using the hht transform improves our understanding of automatic detection of the coseismic signals from the groundwater level

barotropic semidiurnal tidal currents off northern california during the coastal ocean dynamics experiment code barotropic semidiurnal tidal currents measured off the coast of northern california during the coastal ocean dynamics experiment code are examined while the pressure field is consistent with the idea that the semidiurnal surface tide is dominated by a kelvin wave a high degree of variability over alongshore distances of the order of 25 km is observed in the velocity field comparison with existing models used to predict tidal velocities from sea level measurements cannot account for this spatial structure perturbation analysis of a kelvin wave propagating along a coastal boundary with bumps characterized by an alongshore length scale much less than the rossby radius of deformation shows effects on the velocity and pressure field which decay offshore with the alongshore scale of the bumps the effect on the velocity field exceeds that on the pressure field by a factor equal to the ratio of the rossby radius to the alongshore scale of the bumps we conclude that the alongshore structure observed in the measured barotropic semidiurnal tidal currents may be due in part to the local variations in the coastline geometry in the code region

structure and variability of the western maine coastal current abstract analyses of ctd and moored current meter data from 1998 and 2000 reveal a number of mechanisms influencing the flow along the western coast of maine on occasions the eastern maine coastal current extends into the western gulf of maine where it takes the form of a deep order 100 m deep and broad order 20 km wide southwestward flow with geostrophic velocities exceeding 20 cm s 1 this is not a coastally trapped flow however in fields of geostrophic velocity computed from shipboard ctd data the core of this current is roughly centered at the 100 m isobath and its onshore edge is no closer than 10 km from the coast geostrophic velocity fields also reveal a relatively shallow order 10 m deep baroclinic flow adjacent to the coast this flow is also directed to the southwest and appears to be principally comprised of local river discharge analyses of moored current meter data reveal wind driven modulations of the coastal flow that are consistent with expectations from simple theoretical models however a large fraction of the near shore current variance does not appear to be directly related to wind forcing sea surface temperature imagery combined with analysis of the moored current meter data suggests that eddies and meanders within the coastal flow may at times dominate the near shore current variance

a rainfall loading response recorded at 300 meters depth implications for geological weighing lysimeters abstract static pore water pressures in confined aquifers vary in response to ground surface loading changes including precipitation and evaporation under certain hydrogeological conditions such aquifers can function as giant natural weighing lysimeters referenced here as geological weighing lysimeters the extent of the land area weighed increases with aquifer depth and it is of interest to establish at what depth it is still possible to monitor surface water budgets an 86 mm rainfall event produced a clear loading signal in a well in western kansas at 300 m depth the loading effect is quantitatively consistent with elastic deformation induced by the rainfall mass and suggests that geological weighing lysimeters could operate at considerably greater depths thereby monitoring water budgets over a significant land area

morphology and composition of submarine barchan dunes on the scotian shelf canadian atlantic margin abstract submarine barchan dunes have been mapped on browns bank scotian shelf using multibeam sonar bathymetry and backscatter strength the morphology of subaerial barchans has been studied for almost a century but the advent of multibeam sonar technology now enables a quantitative investigation of their submarine counterparts the browns bank submarine barchans occur at a depth of 60 70 m and are crescentic in planform reaching almost 700 m in horn width and 5 m in height the barchans are convex to the se with steep lee faces to the nw indicating a dominant nw flowing current the barchans overlie a widespread gravel lag covered elsewhere with little or no sand obstacle marks emanate from the lee faces of the barchans and represent a lack of sand deposition and exposure of gravel lag on the sea floor the browns bank submarine barchan sediment texture is gravelly sand or sandy gravel and is primarily composed of subrounded to well rounded quartz grains the allometric relationship between submarine barchan slip face height and distance between horns is markedly different from that of subaerial barchans for the same dune height barchan horn width is about ten times greater in the marine environment the superimposition of megaripples on the stoss slopes of the submarine barchans suggests that the barchans are active and therefore represent an engineering risk to sea floor infrastructure current observations and models indicate that seasonal mean current strength is less than the critical velocity required for barchan migration however the barchans may be active under higher velocity storm induced currents repetitive multibeam sonar mapping is required to detect if barchan migration is occurring over longer time scales

determination of aquifer transmissivity from earth tide analysis the water level in an open well tapping an artesian aquifer responds to pressure head disturbance caused by earth tide dilatation of the aquifer because a finite amount of time is needed for water to flow into and out of the well there exists a phase shift or time lag between the tidal dilatation of the aquifer and the water level response in the well we derive an analytical solution that expresses the phase shift as a function of the aquifer transmissivity storage coefficient well radius and the period of the harmonic disturbance this solution is rather insensitive to the storage coefficient thus if the phase shift is known for a harmonic disturbance the transmissivity can be calculated given a rough estimate of the storage coefficient theoretical analysis shows that a significant phase shift may be present even if the disturbance is slowly varying as in the case of earth tides this opens the possibility of estimating aquifer transmissivity from water level records that show earth tide fluctuations a case study using data from a site near parkfield california is presented to illustrate application of the theory phase shifts of the o1 25 82 hour period and m2 12 42 hour period tidal constituents are chosen for analysis because they are free of systematic contamination by fluctuations in barometric pressure a brief error analysis suggests that the computed o1 phase shift is subject to large uncertainty while the computed m2 phase shift is substantially more accurate based on an assumed storage coefficient range of 10 4 to 10 6 the estimated transmissivity range is 8 10 6 to 2 10 5 m2 s while hydraulic tests have not been performed to validate these estimates the range is consistent with the transmissivity value determined by other investigators from analysis of the water level response to an earthquake

hydrological response to earthquakes in the haibara well central japan ii possible mechanism inferred from time varying hydraulic properties summary 28 coseismic groundwater level decreases have been observed at the haibara well shizuoka prefecture central japan from 1981 to 1997 these groundwater level changes cannot be explained as the poroelastic response to coseismic static strain we use the atmospheric pressure and tidal responses of the well rock properties measured on core samples from the same formation and pumping test results to characterize the hydraulic and mechanical properties of the aquifer the responses of the haibara well to the m2 earth tide constituent and to atmospheric pressure have varied over time in particular increasing amplitude and decreasing phase lags were observed after the 1993 pumping test as well as after earthquakes that caused coseismic water level changes the tidal response together with the surface load efficiency derived from the atmospheric pressure response is used to estimate the mechanical properties of the aquifer the largest amplitude of the m2 constituent 2 2 mm is small enough to imply that pore fluid in this system is approximately twice as compressible as water possibly due to the presence of a small amount of exsolved gas diffusion of a coseismic pressure drop near the well could account for the observed time histories of the water level changes the time histories of the water level drops are well matched by the decay of a coseismic pressure drop at least 80 m away from the well removal of a small amount of gas from the formation in that location might in turn explain the coseismic pressure drops

hydrodynamics and equilibrium of a multiple inlet system although it is generally acknowledged that most multiple inlets are unstable and cannot coexist there is evidence to suggest that such inlets can indeed be stable over decadal time scales multiple inlet systems servicing a single embayment in contrast to single inlet systems confer particular hydrodynamic characteristics such as the potential existence of residual discharges and currents between the inlets this paper presents detailed measurements of hydrodynamic variables obtained over complete spring and neap tidal cycles in a multiple inlet system in southern portugal ria formosa the results indicate that the two main interconnected inlets servicing an embayment can coexist at least over a time scale of several decades however their coexistence cannot be explained simply using empirical equilibrium relations or inlet hydraulics although residual flow between the inlets appears to play an important role enhancing their stability it is the availability of sediment stored in the ebb tidal deltas and its capacity to be carried into the inlets during storm events that ultimately dictates the overall equilibrium independently of the flushing capability provided by the hydraulics such movement of sediment leads to the obstruction of the inlet channels thereby affecting the hydraulic efficiency and eventually leading to inlet closure in the long term the results augment existing knowledge concerning multiple inlet systems and improve understanding of their short to medium term stability

episodic closure of the tidal inlet at the mouth of the russian river a small bar built estuary in california bar built estuaries with relatively small cross sectional area 100 m2 and shallow tidal inlets are widespread in mediterranean climates and along wave exposed coasts while similarly important to coastal sediment balances and estuarine ecosystems and more numerous than larger inlet systems they suffer from a relative lack of understanding this is especially true regarding the process of inlet closure when the channel is filled with sediment deposited by wave driven processes mouth closure is of growing concern owing to changes in inlet behavior in many systems in response to human influences the use of many existing conceptual and quantitative models for closure is precluded by rapid morphological change unsteady freshwater inputs and difficulties in scaling well established inlet relationships in these smaller systems in this paper over 60 years of daily closure records are analyzed for the russian river mouth a prototypical bar built system in northern california we show that the time dependent closure pattern can be explained by an interaction of processes that act to scour the inlet driven by tides and river with those that act to deposit sand in the inlet driven by waves tidal weather related seasonal and interannual cycles are observed we improve an existing parametric model to evaluate these separate influences and show that it works well for predicting closure events at both the tidal and seasonal scales finally we compare our data with closure records from the nineteenth and twentieth centuries to show that inlet closures have become shorter and more sporadic over time at this site and to identify anthropogenic drivers of this observed change

tidal and buoyancy driven currents in chignecto bay bay of fundy circulations in the chignecto bay system upper part of the bay of fundy were studied using current meter moorings tidal and diagnostic models and salinity and suspended sediment concentration measurements the current meter observations revealed that 1 the tides behaved basically as standing waves tidal current leads tidal elevation by about 90 2 tidal currents were typically of the order of 1 m s 1 and were almost rectilinear 3 residual currents were up to 0 17 m s 1 and the circulation pattern was quite complex and 4 a two layer residual circulation with inflow in the upper layer and outflow in the lower layer existed at the entrance to the bay most of the residual currents in the upper part of the bay were driven by tidal rectification the two layer residual circulation at the bay entrance was examined using a diagnostic model it was found that the circulation was probably induced by horizontal density variations near the entrance to cumberland basin shepody bay and chignecto bay the cross channel variation of surface suspended sediment concentration was consistent with the observed residual currents from current meter moorings and the estimated currents from the diagnostic model the cross channel variation of salinity near the entrance to chignecto bay was also consistent with the observed and computed residual currents

wind induced interannual variability of sea level slope along shelf flow and surface salinity on the northwest atlantic shelf in this study we examine the importance of regional wind forcing in modulating advective processes and hydrographic properties along the northwest atlantic shelf with a focus on the nova scotian shelf nss gulf of maine gom region long term observational data of alongshore wind stress sea level slope and along shelf flow are analyzed to quantify the relationship between wind forcing and hydrodynamic responses on interannual time scales additionally a simplified momentum balance model is used to examine the underlying mechanisms our results show significant correlation among the observed interannual variability of sea level slope along shelf flow and alongshore wind stress in the nss gom region a mechanism is suggested to elucidate the role of wind in modulating the sea level slope and along shelf flow stronger southwesterly northeastward winds tend to weaken the prevailing southwestward flow over the shelf building sea level in the upstream newfoundland shelf region whereas weaker southwesterly winds allow stronger southwestward flow to develop raising sea level in the gom region the wind induced flow variability can influence the transport of low salinity water from the gulf of st lawrence to the gom explaining interannual variations in surface salinity distributions within the region hence our results offer a viable mechanism besides the freshening of remote upstream sources to explain interannual patterns of freshening in the gom

can multiple tidal inlets be stable abstract the gorge stability of inlets connecting the same bay to the ocean is analysed the basic premise is that when the tidal maximum of the bottom shear stress in an inlet is larger than the equilibrium shear the inlet is in a scouring mode and when smaller than the equilibrium shear stress the inlet is in a shoaling mode the tidal maximum of the bottom shear stress equals the equilibrium shear stress when the inlet is in equilibrium with the hydraulic environment an inlet is called stable when after a small change the cross sectional area returns to its equilibrium value using a linearized lumped parameter model for the flow in the inlets it is shown that for a two inlet bay system neither of the two inlets can be stable this implies that when assuming the inlets to be in equilibrium with the hydraulic environment a small change in the cross sectional area of one or both of the inlets will result in the closure of one or both of the inlets starting with the results for the two inlet bay system arguments are presented that suggest a similar conclusion holds for multiple inlets i e ultimately all inlets will close or at best one will remain open

the structure of three dimensional tide generating currents experimental verification of a theoretical model in an earlier paper tee 1979 a simple model for computing the three dimensional structure of the tidal current in a well mixed water column was presented to examine the validity of the theoretical model 12 current meters were moored at three locations at the head of the bay of fundy four meters were moored in each location at different depths in order to investigate the significance of the small semi minor axis and the small vertical variation of phase and inclination of the semi major axis the error of the analysed harmonic constants has been examined in detail new formulas for estimating the error for non separated constituents and for the semi major axis semi minor axis and the phase and inclination of the semi major axis have been derived a discussion of when the simple formulas for limiting cases can be applied has also been included by comparing the analysed coefficients with tee s 1979 simple model it was found that by using realistic forms of the vertical eddy viscosity the simple theoretical model reproduced the observed vertical variation of the tidal currents in the well mixed estuary reasonably well

observations of wind induced subtidal variability in the delaware estuary sea level and current observations made in the delaware estuary during autumn of 1982 were examined for evidence of wind forced subtidal variability the large subtidal sea level fluctuations at the mouth of the delaware were found to be forced primarily by the wind stress component over the continental shelf nearly parallel to shore indicating coastal ekman transport to the right of the wind local wind forcing within the estuary is shown to be insignificant the subtidal sea level in the interior of the estuary was found to be driven by the wind through a combination of two remote forcing mechanisms one acting at the mouth of the delaware through direct estuary shelf coupling and a second acting locally over the chesapeake bay and being transmitted from the upper chesapeake through the chesapeake and delaware canal which links the two estuaries in the upper delaware estuary we found predominantly barotropic subtidal current fluctuations superimposed on a much weaker two layer gravitational circulation these current fluctuations were produced primarily by the local subtidal surface slope generated by the difference between the two remote forcing mechanisms the evidence strongly suggests that the chesapeake and delaware canal plays a critical role in the subtidal circulation of the delaware estuary

coastal upwelling and eddy development off nova scotia satellite photos during the summer of 1984 show the development of a band of cool water along the seaward coast of nova scotia during a month long period of upwelling favorable winds the timing of the appearance of the cool water band the rate at which it broadened and the bottom temperature evolution at several representative points along the coast are shown to be in good agreement with an idealized two layer model of the wind driven shelf circulation the presence of the cool water is clearly attributable to upwelling after the temperature front moves offshore wavelike features develop rapidly with alongshore wavelengths of 50 75 km and similar maximum cross shore displacement amplitudes the associated alongshore propagation speed is at most 0 02 m s 1 to the northeast the length and time scales of these features are shown to be consistent with results from simple linear instability models which allow for both potential and kinetic energy release from the mean state by perturbations results suggest that the wavelike features are primarily due to baroclinic instability of the upwelling associated base state rough estimates suggest that upwelling and subsequent eddy development can play an important role in the supply of nutrients to the surface waters of the shelf

estimating aquifer parameters from analysis of forced fluctuations in well level an example from the nubian formation near aswan egypt 2 poroelastic properties we discuss the in situ estimation of aquifer poroelastic properties from observed water level fluctuations in five wells sampling the 0 30 porosity nubian sandstone near aswan reservoir egypt the study area is close to ideal for the application of poroelastic theory because of the relatively simple stratigraphy and the absence of cultural and climatological noise in this paper we use approximately 2 years data sampled at 0 2 hour intervals to calculate frequency dependent admittances between the well levels and the recognized forcing functions of the earth tides and barometric fluctuations the effect of variations in lake level is treated in a companion paper the time series analysis techniques that we employ are described in detail three of the wells show equilibrium confined response at tidal frequencies which allows various in situ poroelastic parameters of the aquifer to be derived from the tidal and barometric admittance values we make extensions to earlier treatments of poroelastic theory in order to include the effect of horizontal strain resulting from barometric loading the modifications proved of minor importance for our data set because of the high compliance of the aquifer material and the shallow depth to basement in situ shear modulus is determined as 5 4 6 4 109 pa and uniaxial strain loading efficiency as 0 33 each of these parameters depends on the field measurements of well level and air pressure and also depends strongly on a theoretical estimate of the solid earth areal strain tides the principal source of error in lies in these areal strain estimates we measured poisson s ratio in the laboratory and found that it lies in the range 0 13 0 18 this together with the admittance values allows estimates of uniaxial strain modulus 13 19 109 pa with the smaller values at shallower depth specific storage 1 5 1 9 10 6 m 1 with the larger values at shallower depth porosity 0 2 0 3 skempton s constant 0 54 0 58 and biot s constant 0 78 0 85 laboratory measurements of uniaxial strain modulus are about 50 higher than the in situ estimates probably reflecting scale effects despite the high porosity use of a theory of aquifer response in which the solid constituent is considered incompressible produces significant errors in these estimates

seasonal variability of sea surface temperature fronts on georges bank abstract sea surface temperature sst fronts extracted from archived 1985 1996 advanced very high resolution radiometer avhrr data are determined in the georges bank region resulting frontal locations clearly show the tidal mixing front on georges bank the probability of detecting an sst front at an individual pixel on georges bank is presented as a monthly climatology variations in the probability position and associated water depth of sst fronts in the georges bank region show the development of the tidal mixing front during the summer as well as the presence of a persistent front near the shelfbreak from the 12 yr time series of fronts 144 individual monthly frontal probability images are decomposed into the mean frontal position and empirical orthogonal functions eof using singular value decomposition svd spatial and temporal information from the first eof mode reveals the seasonal development of the tidal mixing front spatial patterns associated with the first mode also reveal the winter occurrence of fronts on the northeast peak area of georges bank which is most likely associated with scotian shelf water flow across the northeast channel the second mode also indicates the development of the hot spot often observed over georges bank during the late summer and early fall further evidence indicates that the mean position of detected sst fronts on southern georges bank changes approximately 10 km on bank from late spring to mid summer monthly mean positions are also compared to the distribution of simpson and hunter s 1974 tidal mixing parameter with resultant positions compared to historical stratification at those locations comparison of detected sst fronts to historical hydrographic data on georges bank points to the fronts being located in increasingly stratified water from may through august

spatial and temporal structure of the barotropic response of the scotian shelf and gulf of maine to surface wind stress a model based study the barotropic current and pressure field responses of the scotian shelf and gulf of maine region to spatially uniform wind stress are examined using a three dimensional finite element numerical model the model is linear and harmonic with spatially varying eddy viscosity and bottom friction coefficients obtained from a nonlinear m2 tidal solution the solutions for low frequency 20 day period wind stress and upstream boundary forcing are generally consistent with previous depth averaged model results showing a substantially stronger response for along shelf compared to cross shelf stress and strong topographic shaping of the associated arrested topographic waves with their expanded domain and dimensionality the present solutions reveal important additional features of the responses such as the northeast channel being the primary conduit for cross shelf subsurface flow compensating the cross shelf ekman transport over the scotian shelf widespread areas of near bottom upwelling and downwelling along the coast and shelf break and leakage of the response across the shelf break model solutions for stress forcing with periods in the storm band 2 5 days show similar structures and elevation current gains to those in the low frequency solutions with the primary exception that the large northeast channel transport for along shelf stress excites a topographic wave over the continental slope south of georges bank the strength of bottom stress dependent on the magnitudes of both the bottom friction coefficient and near bottom viscosity in the model has a significant quantitative influence on the inner shelf response coastal elevation amplitudes and cross shelf decay scales in particular the implications of the model solutions for the interpretation of various observational features of the region s response to wind stress are discussed including coastal elevations offshore bottom pressures currents transports upwelling zones frequency dependences and seasonal and frictional influences

stability of tidal inlets pass cavallo texas many tidal inlets are scoured in loose granular material and the morphological changes in these inlets are discussed the changes are the result of the predominantly fortnightly variations in the tide the seasonal variations in storm activity and the occurrence of extreme meteorological events the adjustment of an inlet to changes in the hydraulic environment and sudden changes in its morphology associated with extreme meteorological events is primarily via a change in the cross sectional area for a single inlet bay system the response of the inlet cross sectional area can be determined using the stability analysis presented by escoffier 1940 rather than one inlet many bays are connected to the ocean by several inlets in this study escoffier s analysis is expanded to include the interaction of these inlets in the analysis the sediment carrying capacity of the inlet currents is characterized by the bottom shear stress the stability analysis is applied to pass cavallo texas assuming the absence of future influences of tropical storms and hurricanes the analysis shows that as a result of the opening of a companion inlet pass cavallo ultimately will close

suspended sediment transport processes in cumberland basin bay of fundy cumberland basin located at the head of chignecto bay bay of fundy exhibits a seaward exponential decreasing time dependent surface sediment concentration there is a strong correlation between suspended sediment concentration and longitudinal concentration gradient a similar correlation was found in shepody bay chignecto bay and minas basin suggesting that an equilibrium condition exists between the two variables total suspended mass in cumberland basin was constant over 2 years of observation 1011 g despite changes in sediment concentration and concentration gradient temporal controls on suspended sediment concentration are river influx ice melting dispersion settling on the intertidal mud flats and water mass exchange at the mouth of the basin this exchange is due to cross channel velocity variations exchanges due to tidal current asymmetry and settling lag are small a simple box model was developed to study the temporal variation of total suspended sediment in the basin the results show that the water mass exchange at the basin mouth varies with time and is the dominant factor controlling suspended mass due to efficient dampening of temporal fluctuations in suspended mass

hydrographic and transport variability on the halifax section 1 archived data and geostrophic computations are used to examine variability in hydrographic properties and along shelf transport on the scotian shelf with focus on the halifax section and a decadal scale hydrographic anomaly during the late 1950s and early mid 1960s the long term annual cycle shows strong seasonal variations in baroclinic transport on the inner shelf and at the shelf edge and an associated steric change in adjusted sea level asl at halifax regional wind forcing and barotropic currents make smaller contributions to the annual cycle in asl in contrast regional wind forcing contributes about 40 of the asl variability for periods of 6 30 days hydrographic sections indicate that the 1950s 1960s anomaly arose from episodic extensions of labrador slope water along the shelf edge followed by on shelf intrusions primarily during the fall spring periods of 1958 1959 and 1963 1964 it ended with excursions of warm slope water into the region in 1967 1968 an analysis of monthly temperature anomalies indicates that slope temperatures can account for 50 of the variance of deep shelf temperatures 3 6 months later correlations between the hydrographic and baroclinic transport variations indicate increased southwestward flow associated with lower temperatures and salinities but no evidence was found for large local current events at the onset and termination times of the 1950s 1960s anomaly positive correlations between wind adjusted asl and steric anomalies point to the potential for sea level being helpful in monitoring baroclinic transport variability

specific storage as a poroelastic coefficient a definition for the specific storage coefficient ss is given which is unambiguous for general isotropic three dimensional aquifer elasticity in every representative elementary volume ss is the fluid volume released from storage per unit decline in hydraulic head per unit bulk volume under conditions such that there is no strain in two orthogonal directions and the total normal stress in the third orthogonal direction is constant the specific storage coefficient is a point property of the aquifer and is defined independently of problem domain stress and head boundary conditions the expression for ss in terms of aquifer and fluid compressibilities is identical to the familiar forms obtained assuming zero horizontal strain and constant overburden in an aquifer although it is not restricted to these conditions as a point property of the fluid saturated material the specific storage coefficient is one of four constants in the general constitutive poroelastic equations relating three dimensional aquifer stress and strain to fluid pressure and dilatation written in terms of ss these equations show that pore fluid mass diffusion is governed by a diffusivity equal to the ratio of hydraulic conductivity to specific storage under arbitrary boundary conditions it is shown that ss controls slow compressional body wave velocity in the low frequency limit and that the uniaxial aquifer compressibility is not necessarily related to the vertical direction

quaternary geology and surficial sediment processes browns bank scotian shelf based on multibeam bathymetry abstract browns bank is located on the glaciated continental shelf off southern nova scotia geological mapping of browns bank is based on interpretation of multibeam bathymetric and backscatter data in conjunction with 220 line km of seismic reflection profiles and sidescan sonograms sea floor sediment samples and bottom photographs the fundian moraine part of the previously identified end moraine system on the continental shelf off nova scotia is a prominent west east flat topped multi lobate ridge identifiable in the multibeam bathymetric data and in geophysical records the fundian moraine was subjected to erosion in the surf zone during sea level rise in depths less than 100 m a series of north south roughly parallel till ridges continuous in the subsurface with the fundian moraine is interpreted as interlobate moraines suggesting formation by a tidewater glacier the browns bank moraine connected to the fundian moraine is evidence of a newly identified grounded ice position farther seaward than the latter bedforms including obstacle marks comet marks sand waves and megaripples are evidence of a vigorous anticyclonic current pattern on browns bank the combination of multibeam bathymetric imagery with high resolution geoscientific information represents a powerful technique for sea floor geological investigations

some estimates of transport processes in long island sound a parametric description of lateral and vertical oscillatory transport in two segments of long island sound is presented the vertical eddy viscosity and diffusivity coefficients are estimated on the basis of a model for turbulent kinetic energy transfer characteristics of horizontal mixing are examined by means of dimensional analysis the relative importance of the mechanisms controlling mass distribution in the estuary is evaluated by calculating longitudinal dispersion coefficients in a form introduced by fisher 1972 it is shown that the mass transport in long island sound is governed mainly by two processes lateral turbulent dispersion and net longitudinal transport caused by the density gradients

a 250 year decadally resolved radiocarbon time history in the gulf of maine reveals a hydrographic regime shift at the end of the little ice age

spring neap tidal effects on satellite ocean color observations in the bohai sea yellow sea and east china sea 1 eight year ocean color observations between 2002 and 2009 from the moderate resolution imaging spectroradiometer modis onboard the aqua satellite are used to quantitatively assess the spring neap tidal effects on variability of ocean optical and biogeochemical properties in the bohai sea yellow sea and east china sea we demonstrate that spring neap tidal variation is one of important ocean processes that drive both the synoptic scale and mesoscale changes of the ocean optical biological and biogeochemical properties in the coastal region normalized water leaving radiance spectra nlw water diffuse attenuation coefficient at the wavelength of 490 nm kd 490 and total suspended matter tsm concentration show significant spring neap variations in the coastal region within a lunar cycle of 29 53 days in the open ocean however spring neap tidal effects on ocean color data are negligible the entire areal coverage of the turbid waters kd 490 0 3 m 1 showing significant spring neap tidal variations is 4 5 105 km2 similar coverage of moderately turbid waters 0 1 kd 490 0 3 m 1 is also impacted by the spring neap tides the magnitude of the spring neap tidal effects on the variations of the satellite ocean color properties e g kd 490 and tsm is in the same order as the seasonal variations in the coastal region highest kd 490 and largest turbid water coverage lag the new moon or full moon about 2 3 days while the lowest kd 490 and smallest turbid water coverage are also 2 3 days behind the one quarter or three quarter moon this is attributed to the seawater inertia and the friction against the seabed as well as the sediment resuspension process

depth dependent studies of tidally induced residual currents on the sides of georges bank abstract using a depth dependent tidal model the tidally induced residual currents on the northern and southern sections of georges bank are computed and the effects of various physical parameters on the current are examined because of significant on bank stokes drift the rigid lid approximation is not appropriate for the shallow region of the southern section also in the same shallow region the curvilinear structure of isobaths significantly increases the one off bank residual flow in the lower upper portion of the water column and thus enhances the upwelling near the shallow end of the section although the amplitudes of the residual current and the center of gyres in the cross bank circulation vary significantly with the values and forms of the vertical eddy viscosity and the stratification in the water column the overall residual circulation is generally insensitive to these physical parameters the only exception is that for a sharp density front or a large horizontal variation in the vert

hydraulic study of multiple inlet system east matagorda bay texas the hydrodynamic feasibility of a proposed third inlet to east matagorda bay texas was examined by application of a two dimensional depth averaged hydrodynamic model wind driven flows in this remote shallow bay frequently dominate the weak astronomical tide the bay presently has two connections to the gulf of mexico one through a short flood relief channel and the other through a long and circuitous navigation channel the study had to consider whether installation of a third inlet would cause the relief channel to close or increase the already strong current velocity in the navigation channel that is a concern for boating safety the model was calibrated with measurements of wind water level and current taken in this study it is concluded that the new inlet will be ebb dominated because of the wind induced current and that the relief channel will not close in the presence of the new inlet in addition the peak current at a critical maneuvering area in the navigation channel that presently poses a hazard to vessel traffic will be reduced by as much as 25 as a result of opening the new inlet

mass transport velocity in shallow water waves reflected in a rotating ocean with a coastal boundary abstract the mass transport velocity in shallow water waves reflected at right angles from an infinite and straight coast is studied theoretically in a lagrangian reference frame the waves are weakly nonlinear and monochromatic and propagate in a homogenous viscous and rotating ocean unlike the traditional approach where the domain is divided into thin boundary layers and a core region the uniform solution is obtained here without constraints on the thickness of the bottom wave boundary layer it is shown that the mass transport velocity is not only sensitive to topography but depends heavily on the interplay between the vertical length scales similarities and differences between the cases of a constant depth a linearly sloping bottom and a wavy and linearly sloping bottom are discussed the mass transport velocity can be divided into two main categories that induced by waves with a frequency close to the inertial frequency and that induced by waves with a much larger frequency for waves signi

assessment of tidal inlet evolution and stability using sediment budget computations and hydraulic parameter analysis abstract research into the response of coastlines to the opening and stabilisation of inlets has been limited by the availability of suitable data the shortcomings of existing formulae when applied to different inlets and the difficulties particular to multi inlet situations our appraisal of methodologies for studying inlet dynamics leads us to formulate a new approach for investigating inlet evolution and stability based on combining sediment budget computations using best estimates and uncertainty analysis and inlet hydraulic parameter analysis the approach developed is applied to a stabilised inlet located within a multi inlet system faro olhao inlet ria formosa southern portugal which was opened starting 1929 and has since been dredged periodically to maintain navigability a series of digital maps was produced based on multi year data acquired from charts surveys and aerial photos the maps were used to compute sediment volumes for six coastal cells delineated on the basis of the morphological features of the inlet cell volumes and fluxes were calculated for three periods 1929 1962 1962 1978 and 1978 2001 and overall sediment budgets were calculated for the latter two periods inlet hydraulic parameters measured included tidal prism inlet channel cross sectional area and hydraulic radius and maximum depth of the inlet throat and were tracked over 9 bathymetric surveys from 1947 2004 the computed budget reveals that the inlet is only at present reaching volumetric equilibrium however the analysis of channel cross sectional area and radius indicates parameter stability around 1978 1985 20 25 years before the inlet started to reach volumetric equilibrium it is hypothesised that the observed stability in parameters for the inlet post 1978 is related to the presence of fixed jetties and to a stratigraphic control that prevents further deepening and not to the achievement of a dynamic equilibrium the findings indicate that the coupling of sediment budget computation and inlet parameter analysis is useful for understanding historical sediment pathways and magnitudes and for analysing the evolution of an inlet towards equilibrium although the analysis of inlet parameter evolution is valuable for examining the locational geometrical stability of an inlet it needs to be used in conjunction with sediment budget computations in order to properly infer inlet equilibrium moreover existing formulae used to infer inlet stability which relate cross sectional area to tidal prism should be reviewed with a view to including other external variables e g stratigraphic controls and to making their application more flexible to cope with the range of different inlet conditions for multi inlet systems the coupling of morphology and hydrodynamics analysis should be extended to all inlets in order to infer the stability of the overall system based on the distribution of the tidal prism through time and the patterns of inlet circulation and sediment transport

seasonal circulation on the western and central scotian shelf abstract a realistic representation of 3d seasonal circulation and hydrography on the western and central scotian shelf has been obtained from historical observations and a combination of diagnostic and prognostic numerical models with forcing by tides wind stress and baroclinic and barotropic pressure gradients the major current features the southwestward nova scotian and shelf edge currents and partial gyres around browns and sable island banks are found to persist year round but with significant seasonal changes comparison with current meter observations shows good agreement for the browns bank southwest nova scotia and inner shelf regions and poorer agreement in the sable island bank and shelf edge regions where current and density observations are sparser and tidal influences weaker there is significant spatial structure in the seasonal circulation and hydrography and in the underlying dynamical processes on the shelf scale there are substantial changes in stratification potential energy

a hydrologic and geomorphic model of estuary breaching and closure abstract to better understand how the hydrology of bar built estuaries affects breaching and closing patterns a model is developed that incorporates an estuary hydrologic budget with a geomorphic model of the inlet system erosion of the inlet is caused by inlet flow whereas the only morphologic effect of waves is the deposition of sand into the inlet when calibrated the model is able to reproduce the initial seasonal breaching seasonal closure intermittent closures and breaches and the low streamflow closed state estuary hydrology of the carmel lagoon located in central california model performance was tested against three separate years of water level observations when open during these years the inlet was visually observed to drain directly across the beach berm in accordance with model assumptions the calibrated model predicts the observed 48 h estuary stage amplitude with root mean square errors of 0 45 m 0 39 m and 0 42 m for the three separate years for the calibrated model the probability that the estuary inlet is closed decreases exponentially with increasing inflow streamflow plus wave overtopping decreasing 10 fold in probability as mean daily inflow increases from 0 2 to 1 0 m 3 s seasonal patterns of inlet state reflect the seasonal pattern of streamflow though wave overtopping may become the main hydrologic flux during low streamflow conditions infrequently causing short lived breaches in a series of sensitivity analyses it is seen that the status of the inlet and storage of water are sensitive to factors that control the storage transmission and inflow of water by varying individual components of the berm system and estuary storage the amount of the time the estuary is open may increase by 57 or decrease by 44 compared to the amount of time the estuary is open during calibrated model conditions for the 18 2 year model period the individual components tested are berm height width length and hydraulic conductivity estuary hypsometry storage to stage relationship two factors that control wave swash sedimentation of the inlet and sea level rise the elevation of the berm determines the volume of water that must enter the estuary in order to breach and it modulates the wave overtopping flux and frequency by increasing estuary storage capacity the estuary will breach less frequently 27 change in time open for modeled excavation scenario and store water up to 3 months later into the summer altering beach aquifer hydraulic conductivity affects inlet state and patterns of breaching and water storage as a result of sea level rise of 1 67 m by 2100 and a beach berm that remains in its current location and accretes vertically the amount of time the estuary remains open may decrease by 44 such a change is an end member of likely scenarios given that the berm will translate landwards model results indicate that the amount of time the estuary is open is more sensitive to changes in wave run up than the amount of sand deposited in the inlet per each overtopping wave

groundwater pressure changes in central japan induced by the 2011 off the pacific coast of tohoku earthquake 1 in the 2011 off the pacific coast of tohoku earthquake groundwater pressure changes were observed in and around the mizunami underground research laboratory miu in central japan where two vertical shafts and horizontal research galleries are excavated in the granitic rock mass coseismic changes of groundwater pressure are believed to correspond to crustal dilation contraction induced by earthquakes in this study we calculated volumetric strain changes due to the tohoku earthquake based on previously reported fault slip models the calculation indicates approximately 2 10 7 of dilational strain around the miu based on the strain sensitivities calculated from tidal responses at the monitoring boreholes the dilation corresponds to drawdowns of several tens of centimeters and is almost the same as the drawdown observed in the boreholes at distances greater than 1 km from the miu in contrast rapid elevation of groundwater pressures associated with the earthquake was observed in the boreholes within the 500 m vicinity of the miu the anomalous elevation is explained by a temporary recovery of the drawdown due to excavation of the shafts and a unique permeability increase induced by the coseismic dilation of heterogeneous local geological structures such as impervious faults controlling the hydrogeological environment

influence of diurnal heating on stratification and residual circulation of georges bank 1 the influence of the diurnal heat flux on summer stratification and residual circulation over georges bank was examined using a three dimensional primitive equation numerical circulation model for a given spatially uniform and time varying heat flux the model results show that the surface water is heated much faster on the southern flank than on the northern flank and much faster in the stratified region than in the mixed region heating significantly strengthens the tidal mixing front and intensifies the frontward convergence near the surface as seasonal stratification develops the location of the tidal mixing front gradually shifts on bank on the southern flank while remaining almost unchanged on the northern flank response of the tidal currents to the diurnal variation in the heat flux varies across georges bank it changes periodically with tidal cycles on the southern flank but is locked to the phase of the eastward tidal current on the northern flank this phase lock feature directly contributes to the intensification of the along bank residual current jet on the northern flank diagnostic analysis suggests that this intensification is mainly caused by the heat enhanced cross bank momentum flux modelcomputed variations of near surface temperature and residual currents are in good agreement with satellite derived sea surface temperature data and drifter measurements index terms 4219 oceanography general continental shelf processes 4227 oceanography general diurnal seasonal and annual cycles 4255 oceanography general numerical modeling 4279 oceanography general upwelling and convergences 4528 oceanography physical fronts and jets keywords heat flux tidal mixing front residual current stratification frontward convergence

an optical study of the water masses of the gulf of maine optical studies of the suspended load in the gulf of maine have been performed in conjunction with hydrographic and biological analyses between late winter and early fall major particle sources are coastal runoff benthic resuspension and biological activity analysis of the optical efficiencies of the particles suggests that runoff and resuspension sources are restricted to the nearshore and shallow regions the variabilities in the coupling and discoupling of the optical and hydrographic features of the gulf demonstrate that advection is primarily responsible for the distribution of clear water masses while settling vertical mixing and productivity are the processes behind the distribution of particles

model simulations of the bay of fundy gyre 1 climatological results 1 the characteristics of a persistent gyre in the mouth of the bay of fundy are studied using model simulations a set of climatological runs are conducted to evaluate the relative importance of the different forcing mechanisms affecting the gyre the main mechanisms are tidal rectification and density driven circulation stronger circulation of the gyre occurs during the later part of the stratified season july august and september october the density driven flow around the gyre is set up by weak tidal mixing in the deep basin in the central bay of fundy and strong tidal mixing on the shallow flanks around grand manan island and western nova scotia spring river discharge has an important influence on near surface circulation but only a small effect when averaged over the entire water column retention of particles in the gyre is controlled by the residual tidal circulation increased frontal retention during stratified periods wind stress and interactions with the adjacent circulation of the gulf of maine residence times longer than 30 days are predicted for particles released in the proximity of the gyre

tidal flow and residual flow in the ems estuary tidal water flow and residual tidal flow between and within channels was ascertained for 20 cross sections in the ems estuary the netherlands the tidal prism of the estuary is approximately 1 10 9 m 3 in the middle reaches the residual ebb and flood transports over the cross sections varied between 1 and 18 of the tidal water transport increasing to 43 near the river proper and near the tidal watersheds the overall mean is c 11 tidally averaged residual current velocities in the cross sections varied from less than 0 01 to 0 33 m s 1 with an overall mean of 0 06 m s 1 the distribution of the tidally averaged residual currents along and over the cross sections studied corresponds very well with the results of a horizontally two dimensional water transport simulation model the data from this study show that the distribution of large scale between channels and small scale within channels residual currents is reflected in the local cross sectional bathymetry it is hypothesized that deviations from a good correspondence between the location of residuals and bathymetry indicate a hydraulically unstable situation which implies a changing local morphology

interaction between the tidal and seasonal variability of the gulf of maine and scotian shelf region abstractas part of a broader study of ocean downscaling the seasonal and tidal variability of the gulf of maine and scotian shelf and their dynamical interaction are investigated using a high resolution 1 36 circulation model the model s seasonal hydrography and circulation and its tidal elevations and currents are compared with an observed seasonal climatology local observations and results from previous studies numerical experiments with and without density stratification demonstrate the influence of stratification on the tides the model is then used to interpret the physical mechanisms responsible for the largest seasonal variations in the m2 surface current that occur over and to the north of georges bank the model generates a striation pattern of alternating highs and lows aligned with georges bank in the m2 surface summer maximum speed in the gulf of maine the striations are consistent with observations by a high frequency coastal radar system and can be explained in terms of a li

modelling the mean barotropic circulation in the bay of fundy and gulf of maine abstract two dimensional nonlinear numerical models are used to study the residual barotropic circulation generated by tides and steady winds in the bay of fundy and gulf of maine the first a multi grid model is used to examine the bay of fundy with a coarse look at the gulf of maine the circulation in the upper bay of fundy is predominantly tidally driven the model clearly reproduces the major gyres observed at the head of the bay steady wind stresses have some effect on the strength of these currents but little cited on the pattern the counterclockwise gyre observed in the body of the bay of fundy is not reproduced in the model the second model covers the lower bay of fundy and the gulf of maine with a single fine grid and is used to look at details in the gulf of maine a clockwise circulation around georges bank and nantucket shoals is clearly indicated from tidal forcing alone as is a gyre over the shallow part of browns bnak different steady wind stress fields give rise to variations in

the adjustment of a shelfbreak jet to cross shelf topography abstract a rigid lid finite difference numerical model is used to study the adjustment of inviscid along shelf barotropic shelfbreak jets to cross shelf channel topography the channel is embedded in the shelf topography perpendicularly to the shelfbreak the shelfbreak jet flows with the direction of propagation of long wavelength topographic rossby waves and the coast is sufficiently distant so as not to affect the flow three models are used that vary the strength of the channel topography s f hd uh where f is the coriolis parameter h is the difference between the shelf depth and the channel depth d is the width of the slope into the channel u is the maximum speed of the jet at the inflow and h is the depth of the shelf estimation of the path of the jet from the inflow parameters and the geometry of the channel is possible in some cases generally for large s the flow follows the topography of the channel and for small s the flow crosses the channel the motivation for this study is the episodic flow of scotian shelf water from the scotian shelf across the northeast channel to georges bank the steady inviscid non linear barotropic dynamics studied here do not allow such a flow for a channel of similar dimensions to the northeast channel and for flow speeds within the oceanographic range other factors such as stratification wind stress and time variability need to be introduced to account for this phenomenon

turbidity and sediment transport in a muddy sub estuary abstract sub estuaries i e tidal creeks and also larger estuaries that branch off the stem of their main estuary are commonplace in many estuarine systems their physical behaviour is affected not only by tributary inflows winds and tides but also by the properties and behaviour of their main estuary measurements extending over more than an annual cycle are presented for the tavy estuary a sub estuary of the tamar estuary uk generally waves are small in the tavy because of the short wind fetch a several hour period of up estuary winds blowing at speeds of between 7 and 10 m s 1 generates waves with significant wave heights of 0 25 m and a wave periodicity of 1 7 s that are capable of eroding the bed over the shallow ca 1 5 m deep mudflats waves also influence sedimentation within and near salt marsh areas an estuarine turbidity maximum etm occurs in the tavy s main channel close to the limit of salt intrusion at hw suspended particulate matter spm concentrations typically are less than 40 mg l 1 at hw although concentrations can exceed 80 mg l 1 when tides and winds are strong flood tide spm inputs to the tavy from the tamar are greater during high runoff events in the river tamar and also at spring tides when the tamar has a high concentration etm higher spm concentrations are experienced on the mudflats following initial inundation without wave resuspension this is followed by a rapid decrease in spm for most of the tide indicating that the mudflats are depositional at those times spm concentrations on the mudflats again increase sharply prior to uncovering peak ebb tidal speeds at 0 15 m above the mudflat bed can exceed 0 26 m s 1 at spring tides and 0 4 m s 1 following high runoff events which are sufficient to cause resuspension time series measurements of sediment bed levels show strong seasonal variability higher and lower freshwater flows are associated with estimated monthly mean sediment transport that is directed out of or into the upper sub estuary respectively seasonal sediment transfers between the estuary and its sub estuary are discussed

longitudinal mixing in the upper reaches of the bay of fundy a time dependent one dimensional advection diffusion equation is used to predict the salinity distribution in the vertically well mixed upper regions of the bay of fundy it is shown that the longitudinal diffusion coefficient must increase in a seaward direction from the head of the bay to give a good agreement between the model and observations and a simple parameterization of the coefficient is sought in terms of the product of appropriate length and velocity scales a coefficient equal to b1u0l0 where b1 is a constant u0 the amplitude of the tidal current and l0 the tidal excursion is tried but does not give this increase and produces a poor description of the salinity distribution however a diffusion coefficient of the form cu h where c is a constant u the r m s friction velocity from the tidal current averaged over the m2 tide h is the water depth and the overbar denotes a cross sectional average does give the required increasing value and allows a good agreement between the model and observations for c 200 this form of parameterization is the same as that for shear dispersion except that the coefficient c is in order of magnitude too large it is suggested instead that the diffusion process results from the interaction of tidal residual eddies with the oscillatory tidal flow a mechanism described by zimmerman 1976 and capable of producing large diffusion coefficients preliminary estimates show that the construction of a tidal power barrage across minas basin would considerably reduce the salinity in the headpond of the barrage but have little effect seaward a sinusoidally varying freshwater input to the estuary is shown to have a significant effect on the salinity distribution only for periods of oscillation exceeding a month while variations in the longitudinal diffusion coefficient due to an apogee perigee tidal cycle have little effect on the salinity distribution

observations of the eastern maine coastal current and its offshore extensions in 1994 cold surface temperatures reflecting scotian shelf origins and local tidal mixing serve as a tracer of the eastern maine coastal current and its offshore extensions which appear episodically as cold plumes erupting from the eastern maine shelf a cold water plume emanating from the eastern maine coastal current in may 1994 was investigated using advanced very high resolution radiometer avhrr imagery shipboard surveys of physical and biochemical properties and satellite tracked drifters evidence is presented that suggests that some of the plume waters were entrained within the cyclonic circulation over jordan basin while the major portion participated in an anticyclonic eddy at the distal end of the plume calculations of the nitrate transported offshore by the plume show that this feature can episodically export significant quantities of nutrients from the eastern maine coastal current to offshore regions that are generally nutrient depleted during spring summer a series of avhrr images is used to document the seasonal along shelf progression of the coastal plume separation point we speculate on potential causes and consequences of plume separation from the coastal current and suggest that this feature may be an important factor influencing the patterns and overall biological productivity of the eastern gulf of maine

historical and recent evidence of scotian shelf water on southern georges bank abstract historical data from 1912 1987 indicate that low salinity less than 32 0 psu near surface water occurs occasionally on southern georges bank during may while none occurs during april composite monthly plots of historical near surface salinity and estimated advection rates show that the southwestern scotian shelf is the immediate upstream source of this low salinity water optimally interpolated satellite derived sst and hydrographic data reveal that very cold less than 2 0 c low salinity less than 32 0 psu scotian shelf water ssw initially located south of the 200 m isobath off southern georges bank in early march 1992 moved north onto southern georges bank during april 1992 ssw was not as extensive during the same period in 1993 as evidence by significantly higher temperatures and salinities these differences show large interannual variability in the transport and or properties of ssw flowing onto georges bank lower higher salinities measured during spring 1992 1993 on southern georges bank are consistent with higher lower st lawrence river discharge noted during spring 1991 1992 and the nine month lag between annual discharge maxima from rivers located upstream and minimum salinity at cape sable in february however comparisons between historical occurrences of low salinity less than 32 0 psu ssw on southern georges bank noted for may 1966 1971 and 1978 and cumulative st lawrence river discharge from the spring prior to each occurrence show no relationship this suggests that the occurrence of low salinity water on southern georges bank is not directly related to variations in upstream river discharge although an idealized model of wind forcing on a bank trapped density front shows that near surface flow is related to superposition of an ekman layer and the along bank gyral circulation evidence from late winter spring 1992 and 1993 on georges bank shows that except for on bank movement of the shelf slope front during late spring 1992 simple ekman theory does not explain on bank movement of the ssw plume during 1992 nor the immobile nature of the shelf slope front during late winter 1992 and late winter spring 1993 surface heat flux and satellite derived sst from georges bank and the scotian shelf together with a slab mixed layer model allows estimation of the advective heat flux and transport of ssw flowing onto georges bank from the scotian shelf during late winter spring 1992 mean advective heat flux onto georges bank during march may 1992 is 14 5 mw cm 2 with an estimated error of 3 5 mw cm 2 demonstrating that advection of cold ssw onto georges bank is required mean velocity and transport of ssw flowing onto georges bank during march may 1992 are 13 4 cm s 1 and 0 21 sv assuming a ssw depth width of 40 m 40 km demonstrating that flow of ssw onto georges bank was robust during the period at this time the dynamics that control the flow of ssw across northeast channel are unknown

subtidal water flux through a multiple inlet system observations before and during a cold front event and numerical experiments 1 this paper examines the net transport through a multiple inlet bay under a combined force of strong wind and tide with observations and a model experiment the observations were made in central georgia in sapelo and altamaha sounds between 13 and 17 september 2000 wind was weak in the beginning of the survey an air pressure trough as a weak cold front passed the area on 16 september when the wind changed to the northeast and increased in magnitude this front was associated with a midlatitude cyclone in the new england area this weather event with an episode of strong northeasterly winds prompted a numerical model experiment on an idealized three inlet bay with a set of nonlinear 2 d shallow water equations on an f plane which provides some insight to the wind driven circulation under the presence of tidal forcing it is found that tidally induced currents are small compared to wind induced flows when the wind direction is not perpendicular to the alignment of the three inlets the net outward flow tends to occur at the inlet farther away in the downwind direction this is associated with a net inward transport in the inlet opposite of the downwind direction as a result the middle inlet has the minimum of the net flow when the wind is perpendicular to the barrier islands and if the three inlets have different maximum depth values the deeper inlet tends to have a net flow against the wind while the shallower inlet tends to have a net flow in the direction of the wind offshore onshore currents may develop outside of the inlet with outward inward flow as an effect of fluxes through the inlets on the coastal ocean

currents at lindenkohl sill in the southern gulf of maine from june 22 to september 3 1986 current speeds and directions were measured at depths of 76 127 and 212 m over lindenkohl sill 225 m which controls an important deepwater spreading path from georges basin into wilkinson basin in the gulf of maine most 70 of the low frequency subtidal variability occurred in a barotropiclike mode in which the inward currents were coherent with alongshore wind stress for 5 day periods early in the record and for 3 day periods late in the record the coherence weakened during the central part of the record when dense atlantic slope water from georges basin moved over the mooring site most of the remaining variance appeared in a baroclinic mode that added constructively to produce surprisingly large 1 m s 1 near bottom currents during the wind coherent intervals at other times the modes interfered to produce near zero currents over the sill while middepth and upper level currents were intensified the relationship between the wind stress and the currents suggests the action of a density modulated coastal upwelling mechanism in which the deep inward currents over the sill respond directly to northeastward alongshore wind stress at times of weak stratification increased density stratification caused by water mass adjustments or seasonal heating produces a more complex baroclinic response it is suggested that the springtime onset of northeastward winds over the gulf of maine may play an indirect but important role in the yearly intensification of the baroclinic circulation in the gulf by controlling or modulating the indraft of slope water into the inner basins

surface heat flux horizontal advection and the seasonal evolution of water temperature on the scotian shelf seasonal temperature variations on the scotian shelf penetrate to a depth of about 75 m the net surface heat flux q can explain about 85 of the annual cycle in the rate of change of mean temperature over this depth range the long term mean heat budget for a midshelf location shows that horizontal advection 40 w m 2 is almost exactly balanced by the combined contributions of q 25 w m 2 horizontal mixing 11 w m 2 and vertical diffusion 6 w m 2 the seasonal evolution of temperature structure on the mid scotian shelf is modeled with a one dimensional vertical diffusion equation modified to include the effect of horizontal advection the model features a vertical eddy diffusivity k that varies with the background density stratification n according to the parameterization k k0 1 np 1 the three free parameters k0 and p are estimated by best fitting in a least squares sense the predicted temperatures to observations at standard depths between the surface and 100 m typical values of k lie in the range 0 2 20 10 4 m2 s 1 with the highest values found in winter and close to the surface as expected the root mean square of the differences between observed and predicted monthly temperatures is small and equal to 1 0 c the root mean square of the errors increases significantly from 1 0 c to 3 1 c on fitting with a constant k highlighting the importance of allowing k to vary with depth and time the diffusion model is finally used to examine the role of q and horizontal advection in the seasonal evolution of the temperature profile on the scotian shelf and in particular the cold intermediate layer which is a prominent feature of the hydrography on the midshelf

residual transport model in correlation with sedimentary dynamics over an elongate tidal sandbar in the gironde estuary southwestern france abstract this study qualitatively describes by a multidisciplinary approach hydrodynamic and residual sediment transport over a sandbar in a macrotidal environment the sandbar is elongated and attached to a headland that is located in the gironde estuary southwestern france bathymetric surveys side scan sonar sonograms grain size trends of surficial sediment and 2dh numerical simulations of current patterns were used to define a conceptual model for the dynamics of this sandbar the sandbar is oriented anticlockwise with respect to the main flow the channel oriented bar face is ebb dominated whereas the opposite face is flood dominated resulting in a clockwise residual transport the line of sediment flux convergence corresponds to the crest of the bar the residual flow over the bar appears to originate from the regional estuarine flow the dominant process responsible for the maintenance of the sandbar seems to be the depth averaged main tidal flow rather than secondary circulation due to headlands or the interaction between the tidal flow and the seabed to generalize this regional conceptual model a qualitative comparison is made with the theories of sandbar dynamics due to tidal currents pingree and maddock 1979 zimmerman 1981 huthnance 1982 and others the seabed stability approach developed by huthnance 1982 seems to be the most reliable theory to explain the saint georges bank dynamics even though many natural factors are not taken into account

temperature and salinity variability on the scotian shelf and in the gulf of maine 1945 1990 examination of temperature and salinity data from the scotian shelf gulf of maine gulf of st lawrence and the adjacent continental slope has shown that the dominant low frequency event over the last 45 years was a cooling and subsurface freshening of the water masses from 1952 to 1967 followed by a rapid reversal of these trends the largest temperature and salinity changes 1952 1967 were 4 6 c and 0 7 respectively and occurred at about 100 m over the slope exchanges with shelf waters and vertical mixing gave rise to the surface manifestation of this variability the westward transport of the labrador current was found to have similar variability increasing from about 1 106 m3 s 1 in the early 1950s to about 4 106 m3 s 1 in the mid 1960s a simple model that accounts for this variation of transport and has a constant entrainment of north atlantic water indicates that changes of the westward flow of the labrador current could contribute significantly to the t s fluctuations

seasonal variation of the three dimensional mean circulation over the scotian shelf the seasonal mean circulation over the scotian shelf is studied numerically by computing mean and tidal current fields for winter spring and summer using a three dimensional nonlinear diagnostic model the mean current fields are forced by seasonal mean baroclinic pressure gradients tidal rectification uniform wind stresses and associated barotropic pressure gradients a historical hydrographic database is used to determine the climatological mean baroclinic forcing upstream open boundary conditions are estimated from the density fields to give no normal geostrophic bottom flow and are specified as either along boundary elevation gradients or depth integrated normal velocities the numerical solutions for nominal bimonthly periods january february april may and july august reveal the dominant southwestward nearshore and shelf break flows of relatively cool and fresh shelf water from the gulf of st lawrence and newfoundland shelf with speeds up to about 20 cm s the seasonal intensification of the southwestward flows is reproduced by the model with the transport increasing from 0 3 sv in summer to 0 9 sv in winter on the inner halifax section there are also pronounced topographic scale influences of submarine banks basins and cross shelf channels on the circulation such as anticyclonic gyres over banks and cyclonic gyres over basins baroclinicity is the dominant forcing throughout the domain but tidal rectification is comparable on the southwestern scotian shelf e g about 0 2 sv recirculating transport around browns bank for all the periods the mean wind stress generates offshore surface drift in winter the solutions are in approximate agreement with observed currents and transports over the scotian shelf although there are local discrepancies

the mean and seasonal circulation off southwest nova scotia abstract long term measurements off southwest nova scotia reveal the following features of the mean circulation a a westward longshore coastal current 4 10 cm s 1 b an anticyclonic gyre around brown bank 5 15 cm s 1 and c an upwelling circulation off cape sable 1 2 cm s 1 at bottom the gyre circulation appears permanent but the coastal current and upwelling exhibit annual variations of the same order as the means there is a distinct annual signal in the longshore transport at cape sable maximum westward in winter whereas the mean transport 0 14 106 m4 s 1 is consistent with both geostrophic estimates and budget requirements in the gulf of marine strong seasonal cycles are also found in the salinity and density fields at cape sable which appear to be controlled both by buoyancy input from the coastal current and local mixing effects a linear diagnostic model indicates that the primary dynamical balance for the circulation is between a longshore pressure gradient and longshore mean

stability analysis of a two inlet bay system abstract the stability analysis for a double inlet bay system is applied to an inlet system resembling big marco pass and capri pass on the lower west coast of florida since the opening of capri pass in 1967 the length of big marco pass has increased from 2000 m in 1967 to 3000 m in 1988 and the cross sectional area has decreased from 1200 m 2 in 1967 to 1000 m 2 in 1988 since 1967 the cross sectional area of capri pass has steadily increased and in 1988 was 700 m 2 tides off the inlets are of the mixed type with a diurnal range of 1 m the gross littoral transport rate in the vicinity of the inlets is estimated at 150 000 m 3 yr 1 for each inlet the maximum tidal velocities are calculated as a function of the gorge cross sectional areas using a lumped parameter model to describe the hydrodynamics of the flow in the model it is assumed that the bay level fluctuates uniformly and the bay surface area remains constant the velocities are used to calculate the tidal maximum of the bottom shear stress in each inlet as a function of the cross sectional areas of the two inlets closure surface values of the equilibrium shear stress are derived from an empirical relationship between cross sectional area and tidal prism for stable inlets along the west coast of florida closure surfaces and equilibrium stress values are calculated for values of friction factors ranging from f 4 10 3 to f 6 10 3 using the closure surfaces and equilibrium stress values the equilibrium flow curve for each inlet is determined the equilibrium flow curve represents the locus of the combination of cross sectional areas for which the actual bottom shear stress in the inlet equals the equilibrium shear stress based on the equilibrium flow curves and the known values of the cross sectional areas of the two inlets in 1988 it is expected that ultimately big marco pass will close and capri pass will remain as the sole inlet with a cross sectional area of 1250 m 2 and a maximum tidal velocity pertaining to a diurnal tide of 0 85 m s 1

suspended sediment transport on a temperate microtidal mudflat the danish wadden sea abstract time series measurements of suspended sediment transport and bed level change on a microtidal mudflat of the danish wadden sea were carried out between february 1997 and september 2000 the data show that the mudflat is generally accreting except for periods with onshore winds when wave induced erosion takes place during periods of low water levels at the site in general a continuous net input of mud was recorded during periods of weak or offshore winds i e the import is not event controlled and this was interrupted by episodic loss of mud during a few tidal periods with onshore winds the net landward transport of suspended sediment during calm weather or periods of offshore wind is caused by settling and scour lag and tidal asymmetry a very large input of suspended material was observed in the period following a strong storm the landward directed net transport during the five tidal periods following the storm being equivalent to approximately 40 of the net annual accumulation in the area the typical depth of sediment reworking at the intertidal study site is 2 5 cm some seasonal variation can be deduced from the data set with a tendency for deposition during spring and summer and erosion in the winter period the seasonality was especially clear at the most landward station where accretion following periods of ice formation in the area is due to grounding of sediment transported by ice floes but otherwise deposition is mainly taking place in the warmer seasons net accretion over the three year measuring period along the transect varies between 0 6 and 1 9 cm a 1 deposition is largest at the most landward station and the accretion found on the basis of repeated bed level measurements compares well with 210 pb and 137 cs dating

hydrological response to earthquakes in the haibara well central japan i groundwater level changes revealed using state space decomposition of atmospheric pressure rainfall and tidal responses summary for the groundwater level observed at the haibara well shizuoka prefecture central japan time series analysis using state space modelling is applied to extract hydrological anomalies related to earthquakes this method can decompose observed groundwater level time series into five components atmospheric pressure tidal and precipitation responses observation noise and residual water level the decomposed responses to atmospheric pressure and precipitation are independently determined and are consistent with the expected response to surface loading in the groundwater level at the haibara well 28 coseismic changes can be discerned during the period from 1981 april to 1997 december there is a threshold in the relationship between earthquake magnitude and the well hypocentre distance above which earthquakes cause coseismic changes in the residual water level all of the coseismic water level changes at the haibara well are decreases although 33 per cent of the estimated coseismic volumetric strain steps are contraction which would be expected to cause water level increases the coseismic changes in groundwater level are more closely proportional to the estimated ground motion than to coseismic volumetric strain steps suggesting that ground motion due to earthquakes is the major cause of the coseismic water level drops and that the contribution from static strain is rather small possible pre or inter earthquake water level changes have occurred at the haibara well and may have been caused by local aseismic crustal deformation

vernal circulation in the gulf of maine the circulation in the gulf of maine has an important baroclinic component it appears to be driven mostly by the density contrast between high salinity slope water which enters from the atlantic and fresher waters which are formed in the gulf or which enter from the scotian shelf hydrographie surveys in three successive spring seasons suggest that slope water accumulates in georges basin driving a counterclockwise surface circulation which brings scotian shelf water westward into the gulf and contributes to the eastward jet along the inner edge of georges bank the slope water also crosses a sill and enters jordan basin where it provides a potential energy source which may enhance a counterclockwise gyre partly driven by nearshore buoyancy sources and perhaps the wind the coastal limb of the gyre turns offshore east of penobscot bay part of the separated coastal current recirculates in jordan basin and part of it continues into wilkinson basin generating a clockwise eddy as it passes over jeffreys bank there is little evidence for recirculating surface flow in wilkinson basin instead the surface water appears to split into branches feeding the jordan basin gyre the georges bank jet and an export path to nantucket shoals the jordan and georges branches seem to be divided by the denser slope water in georges basin and this may be the central process controlling the vernal intensification of the circulation in the gulf a more complete dynamical understanding awaits models which include the baroclinic influence of boundary waters