Topographic Rip Currents Around Coastal Groyne Structures

Total Page:16

File Type:pdf, Size:1020Kb

Topographic Rip Currents Around Coastal Groyne Structures TOPOGRAPHIC RIP CURRENTS AROUND COASTAL GROYNE STRUCTURES Location: Bournemouth, UK Project Dates: October 2012 Clients: Royal National Lifeboat Institution and the UK MetOffice Scope of Work: • 10-day field experiment • Observation from both fixed instruments (wave, tide and current meters) and GPS-drifters • Quantification of topographic rip currents and rip circulation patterns • Calibration and validation of an numerical model (XBeach). PROJECT DESCRIPTION Topographic rip currents are strong seaward-flowing currents that are generated in the surf zone and occur around permanent structural or geological features (e.g., groynes, breakwaters or rock outcrops) and present a hazard to water users worldwide. In the UK, topographic rip currents are potentially implicated in at least 13 accidental coastal drownings per year. The aim of this research was to gain new quantitative scientific understanding of the dynamics of topographic rip currents that occur around coastal structures, specifically those located in fetch-limited seas. A 10-day field experiment at Boscombe beach on the south coast of England measured rip currents and nearshore hydrodynamics around a groyne field. A calibrated and validated numerical model (XBeach) was then used, in support of measured data, to identify the key environmental controls on topographic rip behaviour. This work has gone on to inform practical beach safety management and guidance. Opposite: Mean Lagrangian circulation (2-hour deployment) measured with GPS-tracked surf zone drifters. Average wave height was Hs = 1.1 m and direction Dp = 145°. Contours are measured bathymetry (0.25 m interval) and shading is residual morphology. Bold black lines are groynes and red contours are mean tidal levels. Below: Vectors and shading show flow speed (uv) and direction (5 x 5 m spacing). Black lines are impermeable groynes, red line is still water shoreline and blue line is the outer edge of the surf zone where computed wave dissipation is 10% of the cross-shore maximum. COASTAL MARINE APPLIED RESEARCH WITH PLYMOUTH UNIVERSITY.
Recommended publications
  • Observations of Nearshore Infragravity Waves: Seaward and Shoreward Propagating Components A
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. C8, 3095, 10.1029/2001JC000970, 2002 Observations of nearshore infragravity waves: Seaward and shoreward propagating components A. Sheremet,1 R. T. Guza,2 S. Elgar,3 and T. H. C. Herbers4 Received 14 May 2001; revised 5 December 2001; accepted 20 December 2001; published 6 August 2002. [1] The variation of seaward and shoreward infragravity energy fluxes across the shoaling and surf zones of a gently sloping sandy beach is estimated from field observations and related to forcing by groups of sea and swell, dissipation, and shoreline reflection. Data from collocated pressure and velocity sensors deployed between 1 and 6 m water depth are combined, using the assumption of cross-shore propagation, to decompose the infragravity wave field into shoreward and seaward propagating components. Seaward of the surf zone, shoreward propagating infragravity waves are amplified by nonlinear interactions with groups of sea and swell, and the shoreward infragravity energy flux increases in the onshore direction. In the surf zone, nonlinear phase coupling between infragravity waves and groups of sea and swell decreases, as does the shoreward infragravity energy flux, consistent with the cessation of nonlinear forcing and the increased importance of infragravity wave dissipation. Seaward propagating infragravity waves are not phase coupled to incident wave groups, and their energy levels suggest strong infragravity wave reflection near the shoreline. The cross-shore variation of the seaward energy flux is weaker than that of the shoreward flux, resulting in cross-shore variation of the squared infragravity reflection coefficient (ratio of seaward to shoreward energy flux) between about 0.4 and 1.5.
    [Show full text]
  • Mapping Turbidity Currents Using Seismic Oceanography Title Page Abstract Introduction 1 2 E
    Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Ocean Sci. Discuss., 8, 1803–1818, 2011 www.ocean-sci-discuss.net/8/1803/2011/ Ocean Science doi:10.5194/osd-8-1803-2011 Discussions OSD © Author(s) 2011. CC Attribution 3.0 License. 8, 1803–1818, 2011 This discussion paper is/has been under review for the journal Ocean Science (OS). Mapping turbidity Please refer to the corresponding final paper in OS if available. currents using seismic E. A. Vsemirnova and R. W. Hobbs Mapping turbidity currents using seismic oceanography Title Page Abstract Introduction 1 2 E. A. Vsemirnova and R. W. Hobbs Conclusions References 1Geospatial Research Ltd, Department of Earth Sciences, Tables Figures Durham University, Durham DH1 3LE, UK 2Department of Earth Sciences, Durham University, Durham DH1 3LE, UK J I Received: 25 May 2011 – Accepted: 12 August 2011 – Published: 18 August 2011 J I Correspondence to: R. W. Hobbs ([email protected]) Published by Copernicus Publications on behalf of the European Geosciences Union. Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion 1803 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract OSD Using a combination of seismic oceanographic and physical oceanographic data ac- quired across the Faroe-Shetland Channel we present evidence of a turbidity current 8, 1803–1818, 2011 that transports suspended sediment along the western boundary of the Channel. We 5 focus on reflections observed on seismic data close to the sea-bed on the Faroese Mapping turbidity side of the Channel below 900m. Forward modelling based on independent physi- currents using cal oceanographic data show that thermohaline structure does not explain these near seismic sea-bed reflections but they are consistent with optical backscatter data, dry matter concentrations from water samples and from seabed sediment traps.
    [Show full text]
  • Infragravity Wave Energy Partitioning in the Surf Zone in Response to Wind-Sea and Swell Forcing
    Journal of Marine Science and Engineering Article Infragravity Wave Energy Partitioning in the Surf Zone in Response to Wind-Sea and Swell Forcing Stephanie Contardo 1,*, Graham Symonds 2, Laura E. Segura 3, Ryan J. Lowe 4 and Jeff E. Hansen 2 1 CSIRO Oceans and Atmosphere, Crawley 6009, Australia 2 Faculty of Science, School of Earth Sciences, The University of Western Australia, Crawley 6009, Australia; [email protected] (G.S.); jeff[email protected] (J.E.H.) 3 Departamento de Física, Universidad Nacional, Heredia 3000, Costa Rica; [email protected] 4 Faculty of Engineering and Mathematical Sciences, Oceans Graduate School, The University of Western Australia, Crawley 6009, Australia; [email protected] * Correspondence: [email protected] Received: 18 September 2019; Accepted: 23 October 2019; Published: 28 October 2019 Abstract: An alongshore array of pressure sensors and a cross-shore array of current velocity and pressure sensors were deployed on a barred beach in southwestern Australia to estimate the relative response of edge waves and leaky waves to variable incident wind wave conditions. The strong sea 1 breeze cycle at the study site (wind speeds frequently > 10 m s− ) produced diurnal variations in the peak frequency of the incident waves, with wind sea conditions (periods 2 to 8 s) dominating during the peak of the sea breeze and swell (periods 8 to 20 s) dominating during times of low wind. We observed that edge wave modes and their frequency distribution varied with the frequency of the short-wave forcing (swell or wind-sea) and edge waves were more energetic than leaky waves for the duration of the 10-day experiment.
    [Show full text]
  • Climate Change Report for Gulf of the Farallones and Cordell
    Chapter 6 Responses in Marine Habitats Sea Level Rise: Intertidal organisms will respond to sea level rise by shifting their distributions to keep pace with rising sea level. It has been suggested that all but the slowest growing organisms will be able to keep pace with rising sea level (Harley et al. 2006) but few studies have thoroughly examined this phenomenon. As in soft sediment systems, the ability of intertidal organisms to migrate will depend on available upland habitat. If these communities are adjacent to steep coastal bluffs it is unclear if they will be able to colonize this habitat. Further, increased erosion and sedimentation may impede their ability to move. Waves: Greater wave activity (see 3.3.2 Waves) suggests that intertidal and subtidal organisms may experience greater physical forces. A number of studies indicate that the strength of organisms does not always scale with their size (Denny et al. 1985; Carrington 1990; Gaylord et al. 1994; Denny and Kitzes 2005; Gaylord et al. 2008), which can lead to selective removal of larger organisms, influencing size structure and species interactions that depend on size. However, the relationship between offshore significant wave height and hydrodynamic force is not simple. Although local wave height inside the surf zone is a good predictor of wave velocity and force (Gaylord 1999, 2000), the relationship between offshore Hs and intertidal force cannot be expressed via a simple linear relationship (Helmuth and Denny 2003). In many cases (89% of sites examined), elevated offshore wave activity increased force up to a point (Hs > 2-2.5 m), after which force did not increase with wave height.
    [Show full text]
  • Download Presentation
    WaveWave drivendriven sea-levelsea-level anomalyanomaly atat MidwayMidway AtollAtoll RonRon HoekeHoeke CSIROCSIRO SeaSea LevelLevel andand CoastsCoasts JeromeJerome AucanAucan LaboratoireLaboratoire d'Etudesd'Etudes enen GéophysiqueGéophysique etet OcéanographieOcéanographie SpatialeSpatiale (LEGOS),(LEGOS), IRDIRD MarkMark MerrifieldMerrifield SOESTSOEST –– UniversityUniversity ofof HawaiiHawaii Funding:Funding: ••NOAANOAA CRCPCRCP ••JIMARJIMAR –– UniversityUniversity ofof HawaiiHawaii ••AustralianAustralian InstituteInstitute ofof MarineMarine ScienceScience (AIMS)(AIMS) ••CSIROCSIRO SeaSea LevelLevel andand CoastsCoasts ((AusAID)AusAID) photo: Scott Smithers WaveWave set-upset-up atat PacificPacific atollsatolls andand islandsislands “..the power of the breaking waves is utilized to maintain a water level just inside the surf zone about 1.5 ft above sea level.” Munk and Sargent (1948) Adjustment of Bikini Atoll to waves, Transactions, Am. Geo. Union, 29(6), 855-860. Wave set-up may be “as much as 20% of the incident wave height.” Tait, R. J. (1972) Wave Set-Up on Coral Reefs, J. Geophys. Res., 77(12). WaveWave set-upset-up atat PacificPacific atollsatolls andand islandsislands Steep-sloped Continental Shelf: islands/atolls: Wave dissipation Wave dissipation close farther offshore to shore/reef edge Smaller waves Larger waves Larger storm surge Smaller storm surge Graber et al. (2006) Coastal forecasts and storm surge predictions for tropical cyclones: A timely partnership program, Oceanography, 19(1), 130–141. PacificPacific wavewave climateclimate Hoeke et al. (2011) J. Geophys. Res., 116(C4), C04018. WaveWave set-upset-up inundationinundation eventsevents Nov. 28, 1979 Pohnpei Majuro Dec. 8, 2008 Fiji T imes,May 21, 2011 Takuu Dec. 10, 2008 Caldwell,Vitousek, Aucan (2009), Frequency and Duration of Coinciding High Surf and Tides along the North Shore of Oahu, Hawaii, 1981-2007, J.
    [Show full text]
  • Stratospheric Transport
    Journal of the Meteorological Society of Japan, Vol. 80, No. 4B, pp. 793--809, 2002 793 Stratospheric Transport R. Alan PLUMB Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA (Manuscript received 3 July 2001, in revised form 15 February 2002) Abstract Improvements in our understanding of transport processes in the stratosphere have progressed hand in hand with advances in understanding of stratospheric dynamics and with accumulating remote and in situ observations of the distributions of, and relationships between, stratospheric tracers. It is conve- nient to regard the stratosphere as being separated into four regions: the summer hemisphere, the tropics, the wintertime midlatitude ‘‘surf zone’’, and the winter polar vortex. Stratospheric transport is dominated by mean diabatic advection (upwelling in the tropics, downwelling in the surf zone and the vortex) and, especially, by rapid isentropic stirring within the surf zone. These characteristics determine the global-scale distributions of tracers, and their mutual relationships. Despite our much-improved understanding of these processes, many chemical transport models still appear to exhibit significant shortcomings in simulating stratospheric transport, as is evidenced by their tendency to underestimate the age of stratospheric air. 1. Introduction have opposite large-scale gradients (HF has a stratospheric source and tropospheric sink, It has long been recognized that strato- CH a tropospheric source and stratospheric spheric trace gases with sufficiently weak 4 sink); nevertheless, the shapes of their iso- chemical sources and sinks have similar global pleths are very similar, with isopleths bulging distributions, in the sense that their isopleths upward in the tropics and poleward/downward (surfaces of constant mixing ratio) have similar slopes in the extratropics.
    [Show full text]
  • Turbulence in the Swash and Surf Zones: a Review
    Coastal Engineering 45 (2002) 129–147 www.elsevier.com/locate/coastaleng Turbulence in the swash and surf zones: a review Sandro Longo a,*, Marco Petti b,1, Inigo J. Losada c,2 aDepartment of Civil Engineering, University of Parma, Parco Area delle Scienze, 181/A, 43100 Parma, Italy bDipartimento di Georisorse e Territorio, Faculty of Engineering, University of Udine, Via del Cotonificio, 114, 33100 Udine, Italy cOcean and Coastal Research Group, Universidad de Cantabria, E.T.S.I.C.C. y P. Av. de los Castros s/n, 39005 Santander, Spain Abstract This paper reviews mainly conceptual models and experimental work, in the field and in the laboratory, dedicated during the last decades to studying turbulence of breaking waves and bores moving in very shallow water and in the swash zone. The phenomena associated with vorticity and turbulence structures measured are summarised, including the measurement techniques and the laboratory generation of breaking waves or of flow fields sharing several characteristics with breaking waves. The effect of air entrapment during breaking is discussed. The limits of the present knowledge, especially in modelling a two- or three-phase system, with air and sediment entrapped at high turbulence level, and perspectives of future research are discussed. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Swash zone; Surf zone; Breaking waves; Turbulence; Length scales; Coastal hydrodynamics 1. Introduction short and long waves, currents, turbulence and vorti- ces may be present. Therefore, the hydrodynamics to The swash zone is defined as the part of the beach be found in the swash zone is largely determined by between the minimum and maximum water levels the boundary conditions imposed by the beach face during wave runup and rundown.
    [Show full text]
  • A Coupled Wave-Hydrodynamic Model of an Atoll with High Friction: Mechanisms for flow, Connectivity, and Ecological Implications
    Ocean Modelling 110 (2017) 66–82 Contents lists available at ScienceDirect Ocean Modelling journal homepage: www.elsevier.com/locate/ocemod Virtual Special Issue Coastal ocean modelling A coupled wave-hydrodynamic model of an atoll with high friction: Mechanisms for flow, connectivity, and ecological implications ∗ Justin S. Rogers a, , Stephen G. Monismith a, Oliver B. Fringer a, David A. Koweek b, Robert B. Dunbar b a Environmental Fluid Mechanics Laboratory, Stanford University, 473 Via Ortega, Y2E2 Rm 126, Stanford, CA, 94305, USA b Department of Earth System Science, Stanford University, Stanford, CA, 94305, USA a r t i c l e i n f o a b s t r a c t Article history: We present a hydrodynamic analysis of an atoll system from modeling simulations using a coupled wave Received 18 April 2016 and three-dimensional hydrodynamic model (COAWST) applied to Palmyra Atoll in the Central Pacific. Revised 11 October 2016 This is the first time the vortex force formalism has been applied in a highly frictional reef environ- Accepted 28 December 2016 ment. The model results agree well with field observations considering the model complexity in terms Available online 29 December 2016 of bathymetry, bottom roughness, and forcing (waves, wind, metrological, tides, regional boundary condi- Keywords: tions), and open boundary conditions. At the atoll scale, strong regional flows create flow separation and Coral reefs a well-defined wake, similar to 2D flow past a cylinder. Circulation within the atoll is typically forced by Hydrodynamics waves and tides, with strong waves from the north driving flow from north to south across the atoll, and Surface water waves from east to west through the lagoon system.
    [Show full text]
  • Beach Nourishment Profile Equilibration: What to Expect After Sand Is Placed on a Beach By
    ASBPA WHITE PAPER: Beach nourishment profile equilibration: What to expect after sand is placed on a beach By Kenneth Willson, Gordon Thomson, Tiffany Roberts Briggs, Nicole Elko, and Jon Miller ASBPA Science & Technology Committee March 2017 each nourishment is a commonly implemented solution to mitigate long-term erosion, provide habi- tat,B and reduce storm-damage to coastal communities. During a beach nourish- ment project, large volumes of sand (with similar properties as the native sand) are added to the beach from upland, offshore, or nearby inlet sources to establish a de- signed level of protection and/or restore sand that has eroded. During the construction of a beach nourishment project, sand is brought to the beach by dredges or truck hauling to Figure 1. Diagram showing the basic features of a beach profile typical of widen the beach. Bulldozers are then used many U.S. beaches. to grade the sand into a pre-determined refers to the typically dry area between the natural processes by including a vol- construction template. Nourishment the (high) water level and dune/upland ume of sand intended to be transported projects are designed and constructed region. Seaward of the beach is the surf offshore (Figure 2). to take advantage of the natural forces, zone, extending beyond the region where The constructed beach nourishment such as waves and currents, to move sand waves break. The dune, beach, surf zone, project includes a total volume of sand, offshore. This process results in a natural and dune comprise the beach profile “constructed fill,” which consists of sloping beach within the littoral zone, and (Figure 1).
    [Show full text]
  • Physical Oceanography in Coral Reef Environments: Wave and Mean Flow Dynamics at Small and Large Scales, and Resulting Ecological Implications
    PHYSICAL OCEANOGRAPHY IN CORAL REEF ENVIRONMENTS: WAVE AND MEAN FLOW DYNAMICS AT SMALL AND LARGE SCALES, AND RESULTING ECOLOGICAL IMPLICATIONS A DISSERTATION SUBMITTED TO THE DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING AND THE COMMITTEE ON GRADUATE STUDIES OF STANFORD UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Justin Scott Rogers December 2015 © 2015 by Justin S Rogers. All Rights Reserved. Re-distributed by Stanford University under license with the author. This work is licensed under a Creative Commons Attribution- Noncommercial 3.0 United States License. http://creativecommons.org/licenses/by-nc/3.0/us/ This dissertation is online at: http://purl.stanford.edu/fj342cd7577 ii I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. Stephen Monismith, Primary Adviser I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. Rob Dunbar I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. Oliver Fringer I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. Curt Storlazzi Approved for the Stanford University Committee on Graduate Studies. Patricia J. Gumport, Vice Provost for Graduate Education This signature page was generated electronically upon submission of this dissertation in electronic format.
    [Show full text]
  • Concept Designs for a Groyne Field on the Far North Nsw Coast
    CONCEPT DESIGNS FOR A GROYNE FIELD ON THE FAR NORTH NSW COAST I Coghlan 1, J Carley 1, R Cox 1, E Davey 1, M Blacka 1, J Lofthouse 2 1 Water Research Laboratory (WRL), School of Civil and Environmental Engineering, The University of New South Wales, Manly Vale, NSW 2Tweed Shire Council (TSC), Murwillumbah, NSW Introduction On the open coast of NSW, many options exist to adapt to the hazards of erosion and recession. Perhaps the most common historical approach to counter the erosion and recession hazard is to construct a seawall or revetment to protect the existing foreshore. Other alternatives include the construction of a submerged breakwater, assisted beach recovery and/or beach nourishment. For beaches with a littoral drift imbalance, the construction of one or more groyne structures is a further possibility. This paper presents two different concept designs for a long term groyne field at Kingscliff Beach. Background Information Case Study: Kingscliff Beach Kingscliff Beach, located at the southern end of Wommin Bay on the far north coast of NSW (Figure 1), is a section of the Tweed coastline with built assets at immediate risk from coastal hazards. Ongoing erosion in the last few years has resulted in substantial loss of beach amenity and community land. Storm erosion episodes between 2009 and 2012 severely impacted the Kingscliff Beach Holiday Park (KBHP). This section is also affected by moderate ongoing underlying shoreline recession (WBM, 2001). To manage the Kingscliff Beach foreshore (Figure 2) in the longer term, Tweed Shire
    [Show full text]
  • Chapter 43 Turbulence Scales in the Surf And
    CHAPTER 43 TURBULENCE SCALES IN THE SURF AND SWASH Reinhard E. Flick California Department of Boating and Waterways and Ronald A. George Center for Coastal Studies-0209 Scripps Institution of Oceanography La Jolla, California, USA 92093-0209 Abstract Ocean surface gravity waves breaking on gently sloping beaches generate sub- stantial turbulent velocity fluctuations, both from overturning at the surface bore and from shear stresses at the bottom. We have used measurements made with laboratory-style hotfilm anemometers in the surf and swash on a natural beach to determine the relevant length and velocity scales. Battjes (1975) has pointed out the importance of determining the turbulence scales in the surf zone. Modelers, such as Svendsen and Madsen (1984), for example, rely on length and velocity scale esti- mates to parameterize and solve the complicated equations that govern surf zone flows. We find that turbulence length scales depend essentially on the bore height, and therefore on the local depth, but may decrease sharply under the bore. We also determine that at least the horizontal velocities approach isotropy at frequencies of 2 to 3 Hz, which turn out to also correspond to length scales on the order of the local depth. Introduction The determination of "scales" plays an important role in turbulence research, since turbulent flows must be described by their characteristic times, lengths, veloci- ties, kinetic energies, Reynolds stresses, eddy viscosities and dissipation rates. Much of the theory of turbulence is concerned with establishing connections and relationships between these parameters and much experimental effort has gone into guiding these concerns. The basic reason why this approach is necessary, is that tur- bulent flows typically contain velocity fluctuations at a broad range of length scales, particularly small ones, so that direct analytical or numerical solution of the govern- ing equations is unmanageable.
    [Show full text]