Model Description

The CCHE2D-COAST is a processes-based integrated model which is capable of simulating coastal processes in different coasts with complex shorelines such as irregular wave deformation from offshore to onshore, nearshore currents induced by radiation stresses, wave set-up, wave set-down, sediment transport, and seabed morphological changes.

Main Features of CCHE2D-COAST

CCHE2D-COAST, developed by the National Center for Computational Hydroscience and Engineering (NCCHE), is a coastal processes-based area model. The coastal processes included in the model consist of irregular wave deformation from offshore to onshore, nearshore current induced by irregular waves, sediment transport due to combination of wave and current, and morphological change. The irregular wave model, which is based on a multi-directional spectral energy balance equation, has been validated by using different wave spectra. The nearshore current model for computing the nearshore currents has been validated in comparison with observed currents under oblique incident wave. By introducing the formulations of sediment transport rate under combination of wave and current, seabed changes around coastal structures (e.g. detached breakwater, groins, etc) can be simulated. The numerical models are based on a non-orthogonal mesh system so that the model is capable of solving coastal process problems in different coasts with complex bathymetries and shorelines.

Application Examples of CCHE2D-Coast

1. Validation of Wave Model by Simulating Irregular Wave Deformation over An Elliptical Shoal

In order to validate the multi-directional spectral wave model, the distributions of irregular waves over an elliptical shoal were computed. The elliptical shoal in an experimental flume built by Vincent and Briggs (1989) had a major radius of 3.96m, a minor radius of 3.05m, and a maximum height of 30.48cm at the center. The wave parameters in the cases for validations are shown in Table 1. Some results are shown in Figures 1 and 2. For the details, please refer to Ding et al (2003).

(a) Case N1

(b) Case B1

Figure 1 Normalized wave heights (Hs/H0) and wave rays for narrow and broad directional spreading (the dashed line on the figures represents the outline of the elliptical shoal)

(a) Case N1

(b) Case B1

Figure 2 Comparisons of normalized wave heights between computations and measurements (The dashed dot lines represent the locations of measurement transacts)

2. Validation of Nearshore Current Model by Simulating Uniform Longshore Currents

The experiments about uniform longshore current were conducted by Visser (1991). The computed circulations and comparisons of current profiles are shown in Figure 3.

(a) Computed nearshore currents and circulations

(b) Comparison of currents

Figure 3 Computed nearshore currents and comparison with experiments

3. Validation of Morphodynamic Models by Simulating Morphological Processes around a Detached Breakwater.

The present morphodynamic area model has been validated systematically by simulating the waves, currents, and sea bed level evolutions of a movable bed laboratory experiment conducted by Mimura et al. (1982). For the details, please refer to Ding et al (2004).

(a) Wave heights and directions

(b) Comparison of Breaking wave heights

Figure 4 Waves around a detached breakwater (experiments done by Mimura et al 1983)

(a) Measured nearshore current (Mimura et al 1983)

(b) Computed nearshore current

Figure 5 Comparison of nearshore currents around a detached breakwater

(a) Measured bed change (Mimura et al 1983)

(b) Computed bed change

Figure 6 Comparison of seabed change around a detached breakwater: the red area shows deposition of sediment (unit: cm).

4. Application to Investigation of Sediment Transport around a Harbor in a Coast

Figure 7 Nearshore current around a fishery harbor. Offshore wave conditions: H0=4.0m, T0=9s

Figure 8 Seabed change during one week around a fishery harbor (Unit: m). Offshore wave conditions: H0=4.0m, T0=9s, Direction=W

References

Ding, Y., Wang, S. S. Y., and Jia, Y. (2004), Development and validation of nearshore morphodynamic area model in coastal zone, In: Advances in Hydro-Science and -Engineering, Vol.VI, M. S. Altinakar, S. S. Y.

Wang, K. P. Holz, and M. Kawahara eds., Proceedings of the Sixth International Conference on Hydroscience and Engineering, May 30-June 3, 2004, Brisbane, Australia. (ISBN 0-937099-12-0)

Ding, Y., Wang, S. S. Y., and Jia, Y. (2003), Numerical studies on simulations of waves and nearshore currents in non-orthogonal mesh system, Proceedings of the International Conference on Estuaries and Coasts, Nov.9-11, 2003, Hanzhou, China, pp.719-726 (ISBN 7-900662-67-7/G - 79).

Mimura, N., Shimizu, T., and Horikawa, K. (1983), Laboratory study on the influence of detached breakwater on coastal change, Proc. Coastal Structure’83, ASCE, pp740-752.

Vincent, C. L., and Briggs, M. J. (1989). “Refraction-difraction of irregular waves over a mound.” J. Wtrway., Port, Coast. and Oc. Engrg., ASCE, 115(2), 269-284.

Visser, P. J. (1991). Laboratory measurements of uniform longshore currents, Coastal Engineering, 15(5), 563-593.

Wang, S. S. Y., and Ding, Y. (2003). On the verification and validation of coastal process simulation models, International Conference on Estuaries and Coasts (ICEC-2003), Nov.9-11, 2003, Hangzhou, China (Keynote Lecture).