1 / 24

Modelling Hydrodynamics in the Nearshore

Modelling Hydrodynamics in the Nearshore. Jim Gunson, Graham Symonds, Liejun Zhong & Nick Mortimer CMAR. 21 May 2009. Setting.

kasper-finch
Download Presentation

Modelling Hydrodynamics in the Nearshore

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Modelling Hydrodynamics in the Nearshore Jim Gunson, Graham Symonds, Liejun Zhong & Nick Mortimer CMAR 21 May 2009

  2. Setting Purpose:- Operational prediction of nearshore conditions (Bluelink)- Better understanding of surf-zone circulation.Outline of talk: - Overview of nearshore hydrodynamic modelling - Marmion lagoon- Secret Harbour beach- Linkages with other models.

  3. Background When incoming waves break in the surf zone, they can drive currents. Need model that couples a wave model to a current model. Critical elements:- Knowledge of boundary conditions- Knowledge of bathymetry- Computational costWave model: - Conservation of wave action (SWAN, Xbeach) phase-averaging.- Mild-slope equation (Ref-Dif), phase-resolving.Circulation model: - 2D (shallow-water equations): Storm-surge models, Curvcirc, Xbeach.- 3D (Navier-Stokes equations): Ocean models, PolCOMMS, ROMS, SHOC.

  4. Marmion Lagoon habitat distribution Marine habitat types correspond to wave energy experienced • Algae in high energy • Seagrass in low energy Bare sand Seagrass Low relief reef Algae dominated Benthic habitat Mean wave height

  5. Lagoon Measurement Program • From July 2007 to May 2008 • An area of order 5km x 10km • Reef lines of 1~3m depth • About 10m deep inside lagoon • Measurements of wave, current, pressure, T, S, Chlorophyll, nitrate, etc RDIN AQ1 AQ2 RDIS

  6. CTD Survey - 6/2/2008 • High nutrient levels over reef • Use the numerical model to identify the possible sources of nutrient over the reefs

  7. Wind, wave and currents during July 2007 • Southerly wind component at all times • Low variation in wave direction • Low correlation between currents and wind

  8. Marmion Lagoon Region • Complex bathymetry with depth change of 5-10m over several hundred meters across a reef. Deep channels exist between reefs in reef lines. • Weak stratification although there are seasonal variations of temperature and salinity • Weak tidal currents but tidal sea level may be important in terms of wave breaking over the reefs

  9. Marmion Lagoon Model • ROMS Configuration • Physical domain, 10km x 30km • Grid size, 120 x 240 x 8 • Horizontal resolution, 50~150m • Tidal forcing from 8 tidal constituents K1, O1, P1, Q1, M2, S2, N2 and K2 whose harmonic constants are derived from TPXO6 • surface momentum, heat and moisture fluxes calculated from bulk parameterizations • Wave data from AWAC site

  10. ubar, vbar, h Dwave, Hwave, Lwave, Pwave_top, Pwave_bot, Ub_swan, Wave_dissip Dynamic feedback between ROMS & SWAN

  11. Wind, wave and currents during July 2007 • Southerly wind component at all times • Low variation in wave direction • Low correlation between currents and wind

  12. Model-data comparison OBS No coupling Two-way coupling

  13. Wind, wave and currents during July 2007 • Southerly wind component at all times • Low variation in wave direction • Low correlation between currents and wind

  14. Model-data comparison OBS No coupling Two-way coupling

  15. Nearshore Experiment BLUElink II Nearshore Experiment Secret Harbour, WA Feb 9 to Mar 6, 2009 Aim: To measure wave driven, alongshore currents and compare with numerical simulations using selected models.

  16. Instrument array (not to scale) Radar 10 Shore break Surf zone Depth (m) 0 SBE26-1 -1 VEC2 VEC3 VEC1 -2 VEC4 SBE26-2 -10 AWAC 0 50 100 1000 Nortek Vector (u,v,w,P,T) Cross-shore distance (m) Seabird SBE26 (P,T) Nortek AWAC (u(z),v(z),z)

  17. Vector current meter deployment

  18. The Surf Zone

  19. Wind and wave observations Sea-breeze cycle

  20. Secret Harbour – model domain Choice:- Extends over instruments- Resolve surf-zone- Rotated grid

  21. Secret Harbour – NearCoM, preliminary run - Model domain: 1150m x 1450m, Δx=Δy=5m- Forced by swell (Hs=.8m, Tp=10s, Dir=10º) on seaward boundary.

  22. Linkages with other models Biogeochemistry Hydrodynamic variables of interest to BGC:- Wave orbital velocity- Wave-induced vertical mixing- Bottom pressure variations- Bottom velocity- Stokes drift- Tidal signal (local amplitude and phase)

  23. Linkages with other models Morphodynamics Capabilities:- NearCoM- Xbeach- Scouring- Sand-bar formation- Changing sea-level

  24. Linkages with other models Morphodynamics Challenges:- Rebuilding a beach- 3D circulation- Long time-scales with short time-scales- Knowledge of bathymetry crucial- Data assimiliation / sensitivity studies

More Related