CMS Wave - Surface water Modeling System

The U.S. Army Corps of Engineers (USACE) maintains a large number of navigation structures in support of federal navigation projects nationwide. These structures constrain currents to promote scouring of the navigation channel, stabilize the location of the inlet channel and entrance, and provide wave protection to vessels transiting the navigation channel. Such structures are subject to degradation from the continual impact of currents and waves impinging upon them. Questions arise about the necessity and
consequences of engineering actions taken to rehabilitate or modify the structures. A  ong-range maintenance and rehabilitation plan to manage navigation structures and support the federal navigation projects requires a life-cycle forecast of waves and currents in District projects along with a quantification of potential evolutionary changes in wave climates decadally with impacts to analyses and decisions.

The Coastal Inlets Research Program (CIRP) of the U.S. Army Engineer Research and Development Center (ERDC) operates a Coastal Modeling System (CMS) that has established and maintained multidimensional numerical models integrated to simulate waves, currents, water level, sediment transport, and morphology change in the coastal zone. Emphasis is on navigation channel performance and sediment management for inlets, adjacent beaches, and estuaries. The CMS is verified with field and laboratory data and provided within a user-friendly interface running in the Surface-Water Modeling System (SMS).

CMS-Wave (Lin et al. 2006b, Demirbilek et al. 2007), previously called WABED (Wave-Action Balance Equation Diffraction), is a twodimensional (2D) spectral wave model formulated from a parabolic approximation equation (Mase et al. 2005a) with energy dissipation and diffraction terms. It simulates a steady-state spectral transformation of
directional random waves co-existing with ambient currents in the coastal zone. The model operates on a coastal half-plane, implying waves can propagate only from the seaward boundary toward shore. It includes features such as wave generation, wave reflection, and bottom frictional dissipation.

CMS-Wave validation and examples shown in this report indicate that the
model is applicable for propagation of random waves over complicated bathymetry and nearshore where wave refraction, diffraction, reflection, shoaling, and breaking simultaneously act at inlets. This report presents general features, formulation, and capabilities of CMS-Wave Version 1.9. It identifies basic components of the model, model input and output, and provides application guidelines.

New features added to CMS-Wave

Specific improvements were made to CMS-Wave in four areas: wave breaking and dissipation, wave diffraction and reflection, wave-current interaction, and wave generation and growth. Wave diffraction terms are included in the governing equations following the method of Mase et al. (2005a). Four different depth-limiting wave breaking formulas can be selected as options including the interaction with a current. The wavecurrent interaction is calculated based on the dispersion relationship including wave blocking by an opposing current (Larson and Kraus 2002). Wave generation and whitecapping dissipation are based on the parameterization source term and calibration using field data (Lin and Lin 2004a and b, 2006b). Bottom friction loss is estimated based on the classical drag law formula (Collins 1972).

Other useful features in CMS-Wave include grid nesting capability, variable rectangular cells, wave overtopping, wave runup on beach face, and assimilation for full-plane wave generation. More features such as the nonlinear wave-wave interaction and an unstructured grid are presently under investigation.

CMS-Wave prediction capability has been examined by comparison to comprehensive laboratory data (Lin et al. 2006b). More evaluation of the model performance is presented in this report for two additional laboratory data sets. The first laboratory data set is from experiments representing random wave shoaling and breaking with steady ebb current around an idealized inlet (Smith et al. 1998), covering a range of wave and current parameters. This data set is examined here in evaluation of wave dissipation formulations for current-induced wave breaking. The second laboratory data set is from experiments for random wave transformation accompanied with breaking over a coast with complicated bathymetry and strong wave-induced nearshore currents. Comparisons of measurements and calculations are used to (a) validate the predictive accuracy of CMS-Wave, (b) investigate the behavior of different current and depthlimited wave breaking formulas, and (c) select formulas best suitable for spectral models in nearshore applications. The diffraction calculations by CMS-Wave are tested for a gap between two breakwaters and behind a breakwater.

CMS-Wave Interface

Demirbilek et al. (2007) described the computer graphical interface in the SMS (Zundel 2006) for CMS-Wave applications. A summary of key features of the interface is provided in this chapter to familiarize users with guidelines for the interface usage and implementation of CMS-Wave. The SMS is a graphically interactive computer program designed to facilitate the operation of numerical models and creates input files and output visualization for CMS-Wave. The CMS-Wave interface in the SMS is similar to that of the half-plane model of STWAVE Version 5.4 (Smith 2001b). The SMS can generate CMS grids with variable rectangle cells and half-plane STWAVE grids with constant square cells. Both wave models can use the same grid domain with identical grid orientation and layout, and the same file formats for their bathymetric and spectral energy files. This was done to facilitate the usage of CMS-Wave and allow users to utilize the same settings and files to run both models without modifications.

CMS-Wave files

Depending on which options are selected in the *.std file, CMS-Wave may generate one to six output files. A wave field conditions file (*.wav) is always generated. Optional output files are calculated spectra (*.obs) and wave parameters with the maximum water level (selhts.out) at selected cells, wave breaking indices (*.brk), wave radiation stress gradients (*.rad), wave setup and maximum water level field (setup.wav), and nesting spectral data (*.nst). Figure 1 shows a chart of input and output files involved in a CMS-Wave simulation. Table 1 presents a list of the type and use of all I/O files, where “projname” is a prefix given by users.

The simulation file (*.sim) stores the coordinates of the origin and orientation of the computational grid, and a list of names of all files used in the simulation. All input and output files, required and optional, are listed in Figure 1 and is described in Table 1. Abbreviated output from sample files was provided in Technical Note ERDC/CHL CHETN-I-74 (Demirbilek et al. 2007) and presented in Appendix A to familiarize users with these files.

Users can run CMS-Wave with the input files of STWAVE Version 5.4 without making changes. In this case, CMS-Wave runs in a basic mode. Although doing this may be useful in some project applications, the basic mode does not take advantage of certain features of CMS-Wave, such as reflection. Users should run CMS-Wave with its special set of parameters as defined in the *.std file. That is, one can edit *.std, without modifying *.sim and *.dep, to add a few additional parameters that are specific to CMS-Wave. Guidance on various parameters and recommended values is given below.

File used simulation

Users can provide up to 15 control parameters in the *.std. They are (in
sequential orders) iprp, icur, ibrk, irs, kout, ibnd, iwet, ibf, iark, iarkr,
akap, bf, ark, arkr, iwvbk, which represent:

iprp	= 0, for wave generation and propagation (use wind input if provided)

= 1, for propagation only (neglect wind input)
= -1, for fast-mode simulation (for wave generation and
propagation)
icur = 0, no current
= 1, with current input (*.cur), using data sets in the sequential
order
= 2, with current input (*.cur), using only the first set current data

ibrk	= 0 (no *.brk file) = 1, for output of wave breaking indices (*.brk) = 2, for output of energy dissipation fluxes (*.brk) = 0 (no *.rad file)
irs

= 1, for output of wave radiation stresses (*.rad)
= 2, for output of wave radiation stresses (*.rad) and wave setup/maximum water level (setup.wav) kout = 0 (no *.obs and selhts.out files)
= n, for output of spectra (*.obs) and parameters (selhts.out) at n selected cells ibnd = 0 (no *.nst file)
= 1, for nested grid, with linear interpolation of boundary input spectra (*.nst)
= 2, for nested grid, with morphic interpolation of boundary input spectra (*.nst)

iwet	= 0, for normal wetting/drying (use water level input) = 1, no wetting/drying (neglect water level input) = 0, no bottom friction
ibf

= 1, for bottom friction with constant Darcy-Weisbach type coefficient (= bf)
= 2, for bottom friction with variable Darcy-Weisbach type coefficient (friction.dat)
= 3, for bottom friction with constant Manning coefficient (= bf)
= 4, for bottom friction with variable Manning coefficient (friction.dat)

iark	= 0, no forward reflection = 1, with forward reflection

iarkr = 0, no backward reflection = 1, for backward reflection
akap = diffraction intensity factor (0 for no diffraction, 4 for strong diffraction)

bf ark	= constant bottom friction coefficient = constant forward reflection coefficient (0 for no reflection, 1 for maximum forward reflection) = constant backward reflection coefficient (0 for no reflection, 1 for maximum backward reflection)
arkr

iwvbk = option for selection of wave breaking formula = 0, for Extended Goda (Sakai et al. 1989) = 1, for Extended Miche (Battjes 1972; Mase et al. 2005b) = 2, for formula by Battjes and Janssen (1978) = 3, for formula by Chawla and Kirby (2002)

Users can assign 0 for 15 control parameters in CMS-Wave to run in the basic mode. If only the first six parameters, iprp, icur, ibrk, irs, kout, and ibnd, are provided (minimum requirement) in *.std, a zero will be assigned to the remaining parameters, except that a default value of 1.0 is assigned to the diffraction intensity factor (akap = 1.0) to simulate a weak diffraction condition. If only the first ten parameters, iprp, icur, ibrk, irs, kout, ibnd, iwet, ibf, iark, and iarkr, are provided in *.std (no other information provided for the bottom friction and reflection coefficients), default values of bf = 0.0, ark = 0.5 (for 50 percent energy forward reflection), arkr = 0.3 (for 30 percent backward energy reflection), and akap = 1.0 are used by the model. CMS-Wave calculates wave transmission, wave runup, and overtopping as special features on selected cells. These cells can represent a floating breakwater, a bottom mound breakwater, a beach segment and the land adjacent to it, jetties, seawalls, or underwater features such as reefs or submerged structures. A trench, submerged mound, or structure can be added to the bed as features without modifying the input depth file. These feature cells need to be specified in the *.struct file. Each feature cell is described by four parameters, istruc, jstruc, kstruc, and cstruc in a line format in the *.struct

istruc = i-th column in the grid

jstruc = j-th row in the grid

kstruc = feature cell identity

= 1, for adding alternative feature or structure (immersed or

exposed) without modifying the input depth

= 2, for calculation of wave runup and overwash on beach face or

structure, and adjacent land

= 3, for calculation of transmitted waves of a floating breakwater

= 4, for a vertical wall breakwater

= 5, for a composite or rubble-mound breakwater

cstruc = feature structure depth, for kstruc = 1 (assume a land cell if not

provided)

= beach/structure elevation above mean water level, for kstruc = 2

(use the input depth if not provided; no effect for cstruc < 0)

= floating breakwater draft, for kstruc =3 (skip if not provided or

cstruc < 0.05 m)

= breakwater/structure elevation, for kstruc = 4 or 5 (use the input

depth if not provided; immersed if cstruc < 0)

Model Validation

Numerical models are validated by comparing model calculations to data and analytical solutions to determine the reliability of a model’s individual or combined features. Data for model validation come from laboratory and field measurements, whereas analytical solutions are available in the literature and engineering manuals. Validation tests are essential benchmarks for evaluating both general features and the unique capabilities of numerical models.

This chapter describes and discusses nine examples, or cases, and four depth-limited breaking wave formulas. The CMS-Wave validation is shown for eight data sets from laboratory and field studies, two sets of analytical solutions, and two sets of semi-empirical calculations. The laboratory data are from experiments that have been conducted for idealized inlets, plain sloping beaches, and jetties. These data are examined for validation of wave breaking formulas, wave-current interaction, wave runup, and overall model performance at inlets and nearshore.

Theoretical solutions for wave diffraction at a semi-infinite breakwater, a single gap, and multiple gaps in breakwaters are examined to evaluate the reliability of CMS-Wave calculations for simulating wavestructure interaction problems. The wind-wave growth capability of CMSWave is validated with semi-empirical relations given in the U.S Army Corps of Engineers Shore Protection Manual (1984) and Coastal Engineering Manual (Headquarters (HQ), USACE 2002). The wave reflection capability of CMS-Wave was tested based on a laboratory experiment conducted for an idealized inlet protected by dual jetties (Seabergh et al. 2005). Both fully reflected and absorbing jetties were tested in the experiment. Details of the experiment, data, and CMSWave predictions and comparisons were summarized in (Lin et al. 2006b). This Technical Note also includes additional tests comparing CMS-Wave results to data for wave diffraction around and behind a shore-parallel breakwater and wave diffraction measurements by Seabergh et al. (2002)
at the bay side of an inlet