NUMERICAL STUDY ON WAVE AND WAVE-INDUCED CURRENT NEAR JETTIES IN COASTAL INLET

1. CHINA – NETHERLANDS Bilateral Workshop on Waterways, Harbours, Estuaries and Coastal Engineering, Shanghai, CHINA NUMERICAL STUDY ON WAVE AND WAVE-INDUCED CURRENT NEAR JETTIES IN COASTAL INLET Jinhai ZHENG Nov. 3, 2009

2. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 1 INTRODUCTION The combined wave-current processes at coastal inlets determine navigation risk, frequency of dredging requirements for the channel maintenance, repair of inlet structures, and extent of channel sedimentation and morphology change.

3. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 1 INTRODUCTION Objective Evaluation of predictive numerical models for coastal inlets, with a special focus on the hydrodynamic models’ performance in close proximity to inlet jetties, and their ability to describe the complex wave and current field in inlets and connecting back bays. Method Coupling WABED, a spectral wave model, and CMSFLOW, a 2D circulation model, to investigate the spatial and temporal behavior of waves and wave-induced currents in the vicinity of two types of jetties of an idealized coastal inlets, a highly absorbing one and a fully reflective one. Comparison of numerical results with extensive datasets obtained from the idealized inlet laboratory experiments conducted for different wave conditions and for the above types of jetty structures.

4. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 1 INTRODUCTION Physical modeling Phase I experiments (wave measurements alone) [Seabergh et al., 2002, Report ERDC/CHL-TR-02-27]

5. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 1 INTRODUCTION Physical modeling Phase II experiments (wave and current measurements) [Seabergh et al., 2005, Report ERDC/CHL-TR-05-8]

6. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 1 INTRODUCTION Physical modeling Phase II experiments [Seabergh et al., 2005, Report ERDC/CHL-TR-05-8] The waves for the reflecting jetty experiment created a clockwise circulation in the region along the shoreward half of the jetty length. The incoming longshore current was deflected by this circulation seaward further up-drift than for the absorbing jetty experiment.

7. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 2 MODEL DESCRIPTION WABED wave model A 2-D phase-averaged model A practice-oriented random wave model for coastal engineering studies at estuaries and inlets Inclusion in the Coastal Modeling System of Coastal Inlets Research Program Examination with wave shoaling and breaking around an idealized inlet, waves breaking on plane beach, wave generation in fetch-limited condition, wave transformation over complicated bathymetry with strong nearshore currents, wave generation at Rich Passage in southern Chesapeake Bay, and large wave events at Mouth of Columbia River Field applications for Matagorda Bay, Grays Harbor Entrance, Southeast Oahu Coast in USA, and Hangzhou Bay, Nanri Coast in China.

8. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 2 MODEL DESCRIPTION Governing equationsof WABED Wave diffraction is implemented by adding a term derived from the parabolic wave equation. The effect of currents on waves is included as a Doppler shift in the solution of intrinsic frequency calculated through wave dispersion equation. κ is a diffraction intensity parameter. εb is a parameterization of wave breaking function for energy dissipation, and a bore based formulation is suggested to parameterize the breaking energy dissipation associated with both depth-variation and ambient currents.

9. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 2 MODEL DESCRIPTION Numerical schemes of WABED A quadratic upstream interpolation for convective kinematics is used to solve in a staggered rectangular grid system. WABED operates on a half-plane to allow waves to propagate from the sea-ward boundary toward shore with forward marching calculations. The backward marching can perform for the seaward reflection computation.

10. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 2 MODEL DESCRIPTION CMSFLOW Circulation Model A time-dependent, 2D rectangular grid circulation model [Camenen and Larson, 2007, Report ERDC/CHL CR-07-1] that can be forced by tides, waves, surface winds, and flow influx along the computational domain boundary. Models Coupling The wave and flow models are coupled in the present study to calculate wave-current interaction at inlets. Wave radiation stresses from wave model are input to the flow model to calculate wave-induced current. The coupling of circulation and wave models is ideal for long-term hydrodynamics simulations when wave fields are updated at a fixed time interval.

11. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 3 MODEL TESTING Models setup The grid numerical origin is at x = 450 m and y = 300 m, grid cells are each 10 m by 10 m, and thirteen cells covered the inlet width of 130 m. The dimensions of the numerical grid are 1600 m (or 160 cells) in the cross-shore direction (x-axis) and 1800 m (180 cells) along shore (y-axis), with the inlet located approximately in the grid center. The model domain covered an area of approximately 2 km by 1.5 km, extending 940 m to the left, 730 m to the right of the inlet, 790 m offshore to a depth contour of 15 m, and 570 m bay-ward of the two barrier islands. Coupling between wave and flow models is at a 3-hr interval and the simulation duration is 6hrs.

12. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 3 MODEL TESTING Comparisons with Phase I experimental data Three types of numerical wave simulations were performed for each physical model test condition: (a) wave alone simulation for the fully absorbing jetty with R=0, (b) wave simulation for the fully reflecting jetty with R = 1, (c) coupled wave and flow simulation with R = 1 for wave-current interaction.

13. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 3 MODEL TESTING Comparisons with Phase I experimental data

14. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 3 MODEL TESTING Comparisons with Phase I experimental data

15. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 3 MODEL TESTING Comparisons with Phase II experimental data

16. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 3 MODEL TESTING Comparisons with Phase II experimental data

17. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 3 MODEL TESTING Comparisons with Phase II experimental data

18. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 3 MODEL TESTING Comparisons with Phase II experimental data

19. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 4 SUMMARY The results of the coupled WABED wave model and CMSFLOW circulation model are presented and evaluated using two laboratory datasets for fully- absorbing and fully-reflecting jetties. In general, model predictions follow closely the trends of data for different range of current and wave conditions studied in laboratory experiments. Its performance very near the jetties would require further testing with both laboratory and field data. Calibration parameters obtained for each evaluation examples and testing conditions, and lessons learned in this research are presently being used in the field application. Additional data for different structures and inlets could be used in the calibration of model parameters and to guide users in applying to real cases.

20. Bilateral workshop on waterways, harbours, estuaries and coastal engineering,, Shanghai, CHINA 5 PUBLICATIONS • Demirbilek Zeki, Lin Lihwa, Seabergh WC, Mase Hajime & Zheng Jinhai (2009) Laboratory and numerical studies of hydrodynamics near jetties. Coastal Engineering Journal, 51(2), 143-175. • Zheng Jinhai & Tang Yu (2009) Numerical simulation of spatial lag between wave breaking point and location of maximum wave-induced current. China Ocean Engineering, 23(1), 59-71. • Zheng Jinhai, Mase Hajime, Demirbilek Zeki & Lin Lihwa (2008) Implementation and evaluation of alternative wave breaking formulas in a coastal spectral wave model. Ocean Engineering, 35(11-12), 1090-1101.

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