Modelling Hydrodynamics in the Nearshore. Jim Gunson, Graham Symonds, Liejun Zhong & Nick Mortimer CMAR. 21 May 2009. Setting.
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Jim Gunson, Graham Symonds, Liejun Zhong & Nick Mortimer CMAR
21 May 2009
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.
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.
Marine habitat types correspond to wave energy experienced
Low relief reef
Mean wave height
Dwave, Hwave, Lwave,
Ub_swan, Wave_dissipDynamic feedback between ROMS & SWAN
BLUElink II Nearshore Experiment
Secret Harbour, WA
Feb 9 to Mar 6, 2009
To measure wave driven, alongshore currents and compare with numerical simulations using selected models.
Nortek Vector (u,v,w,P,T)
Cross-shore distance (m)
Seabird SBE26 (P,T)
Nortek AWAC (u(z),v(z),z)
Choice:- Extends over instruments- Resolve surf-zone- Rotated grid
- Model domain: 1150m x 1450m, Δx=Δy=5m- Forced by swell (Hs=.8m, Tp=10s, Dir=10º) on seaward boundary.
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)
Capabilities:- NearCoM- Xbeach- Scouring- Sand-bar formation- Changing sea-level
Challenges:- Rebuilding a beach- 3D circulation- Long time-scales with short time-scales- Knowledge of bathymetry crucial- Data assimiliation / sensitivity studies