DOCSLIB.ORG

Relating River Plume Structure to Vertical Mixing

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Relating River Plume Structure to Vertical Mixing SEPTEMBER 2005 H E T LAND 1667 Relating River Plume Structure to Vertical Mixing ROBERT D. HETLAND Department of Oceanography, Texas A&M University, College Station, Texas (Manuscript received 30 March 2004, in final form 24 February 2005) ABSTRACT The structure of a river plume is related to the vertical mixing using an isohaline-based coordinate system. Salinity coordinates offer the advantage of translating with the plume as it moves or expanding as the plume grows. This coordinate system is used to compare the relative importance of different dynamical processes acting within the plume and to describe the effect each process has on the structure of the plume. Vertical mixing due to inertial shear in the outflow of a narrow estuary and wind mixing are examined using a numerical model of a wind-forced river plume. Vertical mixing, and the corresponding entrainment of background waters, is greatest near the estuary mouth where inertial shear mixing is large. This region is defined as the near field, with the more saline, far-field plume beyond. Wind mixing increases the mixing throughout the plume but has the greatest effect on plume structure at salinity ranges just beyond the near field. Wind mixing is weaker at high salinity classes that have already been mixed to a critical thickness, a point where turbulent mixing of the upper layer by the wind is reduced, protecting these portions of the plume from further wind mixing. The work done by mixing on the plume is of similar magnitude in both the near and far fields. 1. Introduction and Geyer 2001; García Berdeal et al. 2002; Hetland and Signell 2005). However, analysis of the plume is River plumes are central to a number of important difficult, particularly interpreting observations, because societal oceanographic problems. For example, a toxic of the changing position of the plume. In the case of dinoflagellate, Alexandrium spp., is associated with the wind forcing, the plume may change position so much the Kennebec–Penobscot River plume in the Gulf of that, at many points, the plume may be only occasion- Maine (Franks and Anderson 1992). Stratification ally present. Also, even when the plume is present, dif- caused by Mississippi–Atchafalaya outflow prevents ferent regimes of the plume may be measured, for ex- ventilation of lower-layer waters, allowing hypoxic con- ample, frontal regions versus the core of the plume. ditions to develop on the continental shelf (Rabalais et Many of these difficulties stem from a Cartesian, or al. 1999). Nearly one-half of all oceanic carbon burial Eulerian, view of the plume. occurs in large river deltas (Hedges and Keil 1995). This paper examines the plume in salinity coordi- Many papers have reported on the various features nates, a natural coordinate system for the plume. Al- of river plumes, particularly a recirculating bulge that though this approach is not Lagrangian, in that the forms in the vicinity of the outflow (e.g., Garvine 1987; plume may be steady in salinity space even while water O’Donnell 1990; Yankovsky and Chapman 1997; Fong flows through it, salinity coordinates offer the advan- 1998; Nof and Pichevin 2001; Garvine 2001; Yankovsky tage of translating with the plume as it moves or ex- et al. 2001) and the on- and offshore motion of the panding as the plume grows. For example, the addition plume in response to upwelling and downwelling wind of wind causes the plume to mix as well as to change stresses (Fong et al. 1997; Pullen and Allen 2000; Fong horizontal position. Salinity coordinates are used to here to examine changes in vertical mixing in isolation by following the plume as it is shifted by currents. The focus in this paper is buoyancy-forced flow from Corresponding author address: Robert D. Hetland, 3146 TAMU, Department of Oceanography, College Station, TX narrow estuaries, where the local internal deformation 77843-3146. radius is larger than the width of estuary mouth. For E-mail: [email protected] the narrow-estuary case, as water leaves the estuary, it © 2005 American Meteorological Society Unauthenticated | Downloaded 09/29/21 02:36 PM UTC JPO2774 1668 JOURNAL OF PHYSICAL OCEANOGRAPHY VOLUME 35 FIG. 1. This conceptual model of river plume anatomy shows the major regions and indicates the dominant mixing mechanisms. spreads and shoals, becoming supercritical. Here, the stress and by relating the size of the plume to different estuary mouth acts as a hydraulic constriction for the vertical mixing processes. upper layer (Armi and Farmer 1986). The accelerating flow soon becomes unstable, and strong shear mixing 2. Salinity coordinates occurs in the near field (Wright and Coleman 1971; Interpreting measurements of a river plume in Car- MacDonald 2003). Beyond this region, mixing is pri- tesian space may be difficult—for instance, the plume marily caused by wind stress through a mechanism de- may be only occasionally present at certain locations. scribed by Fong and Geyer (2001). Ekman transport in The analysis methods presented below are less sensitive the upper layer may become large enough that shear to the motions of the plume, because these methods instability is induced. At this point, the plume will mix consider the water mass structure of the plume as a and thicken until the local Richardson number is again whole using a coordinate system based on salinity. This above the critical value. This model of wind mixing salinity-based coordinate system follows the plume as it considers only the local wind stress and stratification. It moves and allows the freshwater introduced into the is not yet clear how this balance affects, and is affected domain to be followed as it is mixed with the back- by, the horizontal plume structure. A cartoon of the ground waters. The analysis presented below is based various dynamical regions within the plume shown in on the approach of MacCready et al. (2002), who ex- Fig. 1 demonstrates the mixing history of a water parcel amine long-term estuarine salt balances by calculating as it leaves the river/estuary and eventually becomes salt fluxes across isohalines. The derivation below ex- part of the background waters. tends MacCready et al.’s analysis by demonstrating The goal of this paper is to relate vertical mixing in how changes in isohaline surface area can be used to different dynamical regions of the plume to changes in estimate salt flux at particular salinity classes within the plume structure. In particular, this paper will compare plume, rather than across the entire isohaline surface. the relative importance of different dynamical pro- Here, we will consider a volume V bounded by the cesses acting within different parts of the plume, the sea surface and ocean floor, a face within the river structure of the plume, and the role of wind mixing in where s ϭ 0, and on the seaward edge by an isohaline, determining that structure. Garvine (1999) notes that s (the shaded area in Fig. 2). A portion of the bound- the steady-state alongshore scale of a river plume with- A ing area A defined by the isohaline surface s com- out wind forcing depends on, among other things, the A pletely divides fresher plume water (s Ͻ s ) from the value of background mixing, the minimum value for A rest of the ocean. There is a net freshwater flux of Q diffusivity, and viscosity in a turbulence closure scheme. R across the face of the volume within the river. Garvine’s results show that increasing the background The three-dimensional salt balance equation, mixing decreases the alongshore scale of the plume (roughly related to the total area of the plume). This Ѩs f, ͑1͒ · su͒ ϭϪ١͑ · ١ ϩ paper expands Garvine’s basic result by including wind Ѩt Unauthenticated | Downloaded 09/29/21 02:36 PM UTC SEPTEMBER 2005 H E T LAND 1669 FIG. 2. The volume V, bounded on the seaward edge by area A, is shaded gray; the area A ϭ is defined by isohaline s sA. A freshwater flux, QR, is input into the volume on the opposite Ϫ ␦ Ͻ face of V. The second isohaline, sA s sA, is used in an example in the text. The difference Ϫ ␦ ␦ in isohaline area between sA s and sA is A. integrated over volume V is is the freshwater content within V, relative to sA.IfEq. (4) is divided by s , an intuitive freshwater balance is Ѩ A ͵ sdVϪ s ͵ u · dA ϩ s ͵ u · dA formed—the freshwater from the river, QR, must either Ѩt A A A V A A increase VfA in time or be compensated by a freshwater flux, f/sA, across A. ϭϪ͵ ͑ ͒ By knowing Q and the change in freshwater content f · dA, 2 R A over time, the average salt flux, f across A may be es- timated. However, it is expected that within the river where u is the three-dimensional flow vector, uA is the Ϫ plume the flux will change at different points within the normal velocity of the surface A itself (such that u uA is the flow through A), and f is the diffusive salt flux. plume, so that an area average of the salt flux over a The generalized Leibnitz theorem (Kundu 1990, p. 75) large isohaline may be difficult to interpret: are changes is used to take the time derivative outside the integral in average flux due to intense localized mixing or in the first term. The advective and diffusive salt fluxes broad-scale changes? through the faces of V are nonzero only on the isoha- Assuming a thin pycnocline, the salt flux across two isohalines within the pycnocline will be similar.
Load more

Recommended publications
  • James T. Kirby, Jr
    James T. Kirby, Jr. Edward C. Davis Professor of Civil Engineering Center for Applied Coastal Research Department of Civil and Environmental Engineering University of Delaware Newark, Delaware 19716 USA Phone: 1-(302) 831-2438 Fax: 1-(302) 831-1228 [email protected] http://www.udel.edu/kirby/ Updated September 12, 2020 Education • University of Delaware, Newark, Delaware. Ph.D., Applied Sciences (Civil Engineering), 1983 • Brown University, Providence, Rhode Island. Sc.B.(magna cum laude), Environmental Engineering, 1975. Sc.M., Engineering Mechanics, 1976. Professional Experience • Edward C. Davis Professor of Civil Engineering, Department of Civil and Environmental Engineering, University of Delaware, 2003-present. • Visiting Professor, Grupo de Dinamica´ de Flujos Ambientales, CEAMA, Universidad de Granada, 2010, 2012. • Professor of Civil and Environmental Engineering, Department of Civil and Environmental Engineering, University of Delaware, 1994-2002. Secondary appointment in College of Earth, Ocean and the Environ- ment, University of Delaware, 1994-present. • Associate Professor of Civil Engineering, Department of Civil Engineering, University of Delaware, 1989- 1994. Secondary appointment in College of Marine Studies, University of Delaware, as Associate Professor, 1989-1994. • Associate Professor, Coastal and Oceanographic Engineering Department, University of Florida, 1988. • Assistant Professor, Coastal and Oceanographic Engineering Department, University of Florida, 1984- 1988. • Assistant Professor, Marine Sciences Research Center, State University of New York at Stony Brook, 1983- 1984. • Graduate Research Assistant, Department of Civil Engineering, University of Delaware, 1979-1983. • Principle Research Engineer, Alden Research Laboratory, Worcester Polytechnic Institute, 1979. • Research Engineer, Alden Research Laboratory, Worcester Polytechnic Institute, 1977-1979. 1 Technical Societies • American Society of Civil Engineers (ASCE) – Waterway, Port, Coastal and Ocean Engineering Division.
    [Show full text]
  • Observations of Shoaling Density Current Regime Changes in Internal Wave Interactions
    JUNE 2020 S O L ODOCH ET AL. 1733 Observations of Shoaling Density Current Regime Changes in Internal Wave Interactions AVIV SOLODOCH,JEROEN M. MOLEMAKER, AND KAUSHIK SRINIVASAN Department of Atmospheric and Oceanic Sciences, University of California in Los Angeles, Los Angeles, California MARISTELLA BERTA Istituto di Scienze Marine, Consiglio Nazionale delle Ricerche, La Spezia, Italy LOUIS MARIE Institut Francais de Recherche pour l’Exploitation de la Mer, Plouzané, France ARJUN JAGANNATHAN Department of Atmospheric and Oceanic Sciences, University of California in Los Angeles, Los Angeles, California (Manuscript received 1 August 2019, in final form 16 April 2020) ABSTRACT We present in situ and remote observations of a Mississippi plume front in the Louisiana Bight. The plume propagated freely across the bight, rather than as a coastal current. The observed cross-front circulation pattern is typical of density currents, as are the small width (’100 m) of the plume front and the presence of surface frontal convergence. A comparison of observations with stratified density current theory is conducted. Additionally, subcritical to supercritical transitions of frontal propagation speed relative to internal gravity wave (IGW) speed are demonstrated to occur. That is in part due to IGW speed reduction with decrease in seabed depth during the frontal propagation toward the shore. Theoretical steady-state density current propagation speed is in good agreement with the observations in the critical and supercritical regimes but not in the inherently unsteady subcritical regime. The latter may be due to interaction of IGW with the front, an effect previously demonstrated only in laboratory and numerical experiments. In the critical regime, finite- amplitude IGWs form and remain locked to the front.
    [Show full text]
  • FAU Institutional Repository
    FAU Institutional Repository http://purl.fcla.edu/fau/fauir This paper was submitted by the faculty of FAU’s Harbor Branch Oceanographic Institute Notice: ©2002 Elsevier Science Ltd. This is the author’s version of a work accepted for publication by Elsevier. Changes resulting from the publishing process, including peer review, editing, corrections, structural formatting and other quality control mechanisms, may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. The definitive version has been published at http://www.elsevier.com/locate/csr and may be cited as Lee, Thomas N., Ned Smith (2002) Volume transport variability through the Florida Keys tidal Channels, Continental Shelf Research 22(9):1361–1377 doi:10.1016/S0278‐4343(02)00003‐1 Continental Shelf Research 22 (2002) 1361–1377 Volume transport variability through the Florida Keys tidal channels Thomas N. Leea,*, Ned Smithb a Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, USA b Harbor Branch Oceanographic Institution, 5600 US Highway 1, North, Ft. Pierce, FL 34946, USA Received 28 February 2001; received in revised form 13 July 2001; accepted 18 September 2001 Abstract Shipboard measurements of volume transports through the passages of the middle Florida Keys are used together with time series of moored transports, cross-Key sea level slopes and local wind records to investigate the mechanisms controllingtransport variability. Predicted tidal transport amplitudes rangedfrom 76000 m3/s in LongKey Channel to 71500 m3/s in Channel 2. Subtidal transport variations are primarily due to local wind driven cross-Key sea level slopes.
    [Show full text]
  • Redalyc.Study of Atrato River Plume in a Tropical Estuary
    Dyna ISSN: 0012-7353 [email protected] Universidad Nacional de Colombia Colombia Montoya, Luis Javier; Toro-Botero, Francisco Mauricio; Gomez-Giraldo, Andrés Study of Atrato river plume in a tropical estuary: Effects of the wind and tidal regime on the Gulf of Uraba, Colombia Dyna, vol. 84, núm. 200, marzo, 2017, pp. 367-375 Universidad Nacional de Colombia Medellín, Colombia Available in: http://www.redalyc.org/articulo.oa?id=49650910043 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Study of Atrato river plume in a tropical estuary: Effects of the wind and tidal regime on the Gulf of Uraba, Colombia 1 Luis Javier Montoya a, Francisco Mauricio Toro-Botero b & Andrés Gomez-Giraldo b a Universidad de Medellin, Medellin, Colombia. [email protected] b Facultad de Minas, Universidad Nacional de Colombia, Medellin, [email protected], [email protected] Received: January 7th, 2016. Received in revised form: October 6th, 2016. Accepted. December 20th, 2016 Abstract This study focuses on the relative importance of the forcing agents of Atrato River plume as it propagates in a tropical estuary located in the Gulf of Uraba in the Colombian Caribbean Sea. Six campaigns of intensive field data collection were carried out from 2004 to 2007 to identify the main features of the plume and to calibrate and validate a numerical model. Field data and numerical models revealed high spatial and temporal plume variability according to the magnitudes of river discharges, tidal cycles, and wind stress.
    [Show full text]
  • A Satellite View of Riverine Turbidity Plumes on the Ne-E Brazilian Coastal Zone
    BRAZILIAN JOURNAL OF OCEANOGRAPHY, 60(3):283-298, 2012 A SATELLITE VIEW OF RIVERINE TURBIDITY PLUMES ON THE NE-E BRAZILIAN COASTAL ZONE Eduardo Negri de Oliveira1*, Bastiaan Adriaan Knoppers2, João Antônio Lorenzzetti3, Paulo Ricardo Petter Medeiros4, Maria Eulália Carneiro5 and Weber Friederichs Landim de Souza6 1Universidade Estadual do Rio de Janeiro - Departamento de Oceanografia Física (Rua São Francisco Xavier, n. 524, Maracanã, Rio de Janeiro, RJ, Brasil) 2Universidade Federal Fluminense (UFF) - Departamento de Geoquímica (Morro do Valonguinho s/n, 24020-141 Niterói, RJ, Brasil) 3Instituto Nacional de Pesquisas Espaciais (INPE) - Divisão de Sensoriamento Remoto (Av. Astronautas, 1758, 12227-010 São José dos Campos, SP, Brasil) 4Universidade Federal de Alagoas - Laboratório Natural e Ciências do Mar (Rua Aristeu de Andrade, 452, 57021-090 - Maceió / AL, Brasil) 5Petrobras SA - Monitoramento e Avaliação Ambiental (Av. Horácio de Macedo, 950, Ilha do Fundão, 21941-915 Rio de Janeiro, RJ, Brasil) 6Instituto Nacional de Tecnologia - Laboratório de Metrologia Analítica e Química (Av. Venezuela, 82, 20081-312, Rio de Janeiro, RJ, Brasil) *Corresponding author: [email protected] A B S T R A C T Turbidity plumes of São Francisco, Caravelas, Doce, and Paraiba do Sul river systems, located along the NE/E Brazilian coast, are analyzed for their dispersal patterns of Total Suspended Solids (TSS) concentration using Landsat images and a logarithmic algorithm proposed by Tassan (1987) to convert satellite reflectance values to TSS. The TSS results obtained were compared to in situ collected TSS data. The analysis of the satellite image data set revealed that each river system exhibits a distinct turbidity plume dispersal pattern.
    [Show full text]
  • Wave Breaking Turbulence at the Offshore Front of the Columbia River
    GeophysicalResearchLetters RESEARCH LETTER Wave breaking turbulence at the offshore front 10.1002/2014GL062274 of the Columbia River Plume 1 1 1 1 2 Key Points: Jim Thomson , Alex R. Horner-Devine , Seth Zippel , Curtis Rusch , and W. Geyer • Strong currents at fronts cause 1 2 wave breaking University of Washington, Seattle, Washington, USA, Woods Hole Oceanographic Institution, Woods Hole, • Wave breaking generates strong Massachusetts, USA turbulence • Surface turbulence (from wave breaking) can affect subsurface Abstract Observations at the Columbia River plume show that wave breaking is an important source mixing of turbulence at the offshore front, which may contribute to plume mixing. The lateral gradient of current associated with the plume front is sufficient to block (and break) shorter waves. The intense whitecapping Correspondence to: that then occurs at the front is a significant source of turbulence, which diffuses downward from the J. Thomson, [email protected] surface according to a scaling determined by the wave height and the gradient of wave energy flux. This process is distinct from the shear-driven mixing that occurs at the interface of river water and ocean water. Observations with and without short waves are examined, especially in two cases in which the background Citation: Thomson, J., A. R. Horner-Devine, conditions (i.e., tidal flows and river discharge) are otherwise identical. S. Zippel, C. Rusch, and W. Geyer (2014), Wave breaking turbu- lence at the offshore front of the Columbia River Plume, Geo- phys. Res. Lett., 41, 8987–8993, 1. Introduction doi:10.1002/2014GL062274. The local effects of waves and wave breaking on river plumes and the mixing of estuarine waters is largely unknown.
    [Show full text]
  • Nearshore Drift-Cell Sediment Processes And
    Journal of Coastal Research 00 0 000–000 Coconut Creek, Florida Month 0000 Nearshore Drift-Cell Sediment Processes and Ecological Function for Forage Fish: Implications for Ecological Restoration of Impaired Pacific Northwest Marine Ecosystems David Parks†, Anne Shaffer‡*, and Dwight Barry§ †Washington Department of Natural Resources ‡Coastal Watershed Institute §Western Washington University 311 McCarver Road P.O. Box 2263 Huxley Program on the Peninsula Port Angeles, Washington 98362, U.S.A. Port Angeles, Washington 98362, U.S.A. Port Angeles, Washington 98362, U.S.A. [email protected] ABSTRACT Parks, D.; Shaffer, A., and Barry, D., 0000. Nearshore drift-cell sediment processes and ecological function for forage fish: implications for ecological restoration of impaired Pacific Northwest marine ecosystems. Journal of Coastal Research, 00(0), 000–000. Coconut Creek (Florida), ISSN 0749-0208. Sediment processes of erosion, transport, and deposition play an important role in nearshore ecosystem function, including forming suitable habitats for forage fish spawning. Disruption of sediment processes is often assumed to result in impaired nearshore ecological function but is seldom assessed in the field. In this study we observed the sediment characteristics of intertidal beaches of three coastal drift cells with impaired and intact sediment processes and compared the functional metrics of forage fish (surf smelt, Hypomesus pretiosus, and sand lance, Ammodytes hexapterus) spawning and abundance to define linkages, if any, between sediment processes
    [Show full text]
  • A Conceptual Model of the Strongly Tidal Columbia River Plume
    Submitted to Journal of Marine Systems manuscript No. (will be inserted by the editor) Alexander R. Horner-Devine, David A. Jay, Philip M. Orton and Emily Y. Spahn A conceptual model of the strongly tidal Columbia River plume Received: date / Accepted: date Abstract The Columbia River plume is typical of large-scale, high discharge, mid-latitude plumes. In the absence of strong upwelling winds, freshwater from the river executes a rightward turn and forms an anticyclonic bulge before moving north along the Washington coast. In addition to the above A.R. Horner-Devine Civil and Environmental Engineering University of Washington Tel.: 206-685-3032 E-mail: [email protected] David Jay Civil and Environmental Engineering Portland State University E-mail: [email protected] Philip Orton Lamont-Doherty Earth Observatory Columbia University E-mail: [email protected] Emily Spahn Civil and Environmental Engineering University of Washington E-mail: [email protected] 2 dynamics, however, the river plume outflow is subject to large tides, which modify the structure of the plume in the region near the river mouth. Observations based on data acquired during a summer 2005 cruise indicate that the plume consists of four distinct water masses; source water at the lift-off point, and the tidal, re-circulating and far-field plumes. In contrast to most plume models that describe the discharge of low-salinity estuary water into ambient high-salinity coastal water, we describe the Columbia plume as the superposition of these four plume types. We focus primarily on a conceptual summary of the dynamics and mutual interaction of the tidal and re-circulating plumes.
    [Show full text]
  • Encountering Shoaling Internal Waves on the Dispersal Pathway of the Pearl River Plume in Summer Jay Lee1, James T
    www.nature.com/scientificreports OPEN Encountering shoaling internal waves on the dispersal pathway of the pearl river plume in summer Jay Lee1, James T. Liu1*, I‑Huan Lee1, Ke‑Hsien Fu1,2, Rick J. Yang1, Wenping Gong3 & Jianping Gan4 Fundamentally, river plume dynamics are controlled by the buoyancy due to river efuent and mixing induced by local forcing such as winds and tides. Rarely the infuence of far‑feld internal waves on the river plume dynamics is documented. Our 5‑day fx‑point measurements and underway acoustic profling identifed hydrodynamic processes on the dispersal pathway of the Pearl River plume. The river plume dispersal was driven by the SW monsoon winds that induced the intrusion of cold water near the bottom. The river efuent occupied the surface water, creating strong stratifcation and showing on‑ofshore variability due to tidal fuctuations. However, intermittent disruptions weakened stratifcation due to wind mixing and perturbations by nonlinear internal waves (NIWs) from the northern South China Sea (NSCS). During events of NIW encounter, signifcant drawdowns of the river plume up to 20 m occurred. The EOF deciphers and ranks the contributions of abovementioned processes: (1) the stratifcation/mixing coupled by wind‑driven plume water and NIWs disruptions (81.7%); (2) the variation caused by tidal modulation (6.9%); and (3) the cold water intrusion induced by summer monsoon winds (5.1%). Our fndings further improve the understanding of the Pearl River plume dynamics infuenced by the NIWs from the NSCS. Significant physical and biogeochemical effects caused by internal waves (IWs) have been ubiquitously recognized1–3.
    [Show full text]
  • Effect of Winds and Waves on Salt Intrusion in the Pearl River Estuary
    Ocean Sci. Discuss., https://doi.org/10.5194/os-2017-73 Manuscript under review for journal Ocean Sci. Discussion started: 5 September 2017 c Author(s) 2017. CC BY 4.0 License. Effect of winds and waves on salt intrusion in the Pearl River Estuary Wenping Gong1,2, Zhongyuan Lin1,2,Yunzhen Chen1,2, Zhaoyun Chen1,2, Heng Zhang1,2,3 1School of Marine Science, SunYat-sen University, Guangzhou, 510275, China 5 2Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, Sun Yat-sen University, Guangzhou, 510275, China 3Guangdong Provincial Key Laboratory for Climate Change and Natural Disaster Studies, Sun Yat-sen University, Guangzhou, 510275, China Correspondence to: Heng Zhang ([email protected]) 10 Abstract. Salt intrusion in the Pearl River Estuary (PRE) is a dynamic process that is influenced by a range of factors and to date, few studies have examined the effects of winds and waves on salt intrusion in the PRE. We investigate these effects using the Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system applied to the PRE. After careful validation, the model is used for a series of diagnostic simulations. It is revealed that the local wind considerably strengthens the salt intrusion by lowering the water level in the eastern part of the estuary and increasing the bottom 15 landward flow. The remote wind increases the water mixing on the continental shelf, elevates the water level on the shelf and in the PRE, and pumps saltier shelf water into the estuary by Ekman transport. Enhancement of the salt intrusion is comparable between the remote and local winds.
    [Show full text]
  • Laurentian Great Lakes, Interaction of Coastal and Offshore Waters Introduction
    1Encyclopedia of Earth Sciences Series IEncyclopedia of Lakes and Reservoirs ISpringer Science+Business Media B.V. 2012 110.1007/978-1-4020-4410-6_264 ILars Bengtsson, Reginald W. Herschyand Rhodes W. Fairbridge Laurentian Great Lakes, Interaction of Coastal and Offshore Waters 1 21S3 Yerubandi R. Rao IS3 and David J. Schwab (1) Environment Canada, National Water Research Institute, Canada Center for Inland Waters, 867 Lakeshore Road, Burlington, ON, Canada (2) Great Lakes Environmental Research Laboratory, 2205 Commonwealth Blvd, Ann Arbor, MI 48105, USA IS::l Yerubandi R. Rao (Corresponding author) Email: [email protected] [;] David J. Schwab Email: [email protected] Without Abstract Introduction The Laurentian Great Lakes represent an extensive, interconnected aquatic system dominated by its coastal nature. While the lakes are large enough to be significantly influenced by the earth's rotation, they are at the same time closed basins to be strongly influenced by coastal processes (Csanady, 1984). Nowhere is an understanding of how physical, geological, chemical, and biological processes interact in a coastal system more important to a body of water than the Great Lakes. Several factors combine to create complex hydrodynamics in coastal systems, and the associated physical transport and dispersal processes of the resulting coastal flow field are equally complex. Physical transport processes are often the dominant factor in mediating geochemical and biological processes in the coastal environment. Thus, it is critically important to have a thorough understanding of the coastal physical processes responsible for the distribution of chemical and biological species in this zone. However, the coastal regions are not isolated but are coupled with mid-lake waters by exchanges involving transport of materials, momentum, and energy.
    [Show full text]
  • Effects of Waves on Coastal Water Dispersion in a Small Estuarine Bay M
    JOURNAL OF GEOPHYSICAL RESEARCH: OCEANS, VOL. 119, 1–17, doi:10.1002/2013JC009466, 2014 Effects of waves on coastal water dispersion in a small estuarine bay M. T. Delpey,1 F. Ardhuin,2 P. Otheguy,1 and A. Jouon1 Received 27 September 2013; revised 2 December 2013; accepted 9 December 2013. [1] A three-dimensional wave-current model is used to investigate wave-induced circulations in a small estuarine bay and its impact on freshwater exchanges with the inner shelf, related to stratified river plume dispersion. Modeled salinity fields exhibit a lower salinity surface layer due to river outflows, with typical depth of 1 m inside the bay. The asymmetric wave forcing on the bay circulation, related to the local bathymetry, significantly impacts the river plumes. It is found that the transport initiated in the surf zone by the longshore current can oppose and thus reduce the primary outflow of freshwater through the bay inlets. Using the model to examine a high river runoff event occurring during a high-energy wave episode, waves are found to induce a 24 h delay in freshwater evacuation. At the end of the runoff event, waves have reduced the freshwater flux to the ocean by a factor 5, and the total freshwater volume inside the bay is increased by 40%. According to the model, and for this event, the effect of the surf zone current on the bay flushing is larger than that of the wind. The freshwater balance is sensitive to incident wave conditions. Maximum freshwater retention is found for intermediate offshore wave heights 1m< Hs < 2 m.
    [Show full text]