| 17 Jul 2026
The Regional Oceanic Modeling System with Non-Conservative Surface Gravity Wave Effects on Currents (ROMS-NCWEC v1.0.0)
Abstract. We present ROMS-NCWEC, an updated and extended implementation of non-conservative Wave Effects on Currents (WEC) in the Regional Ocean Modeling System (ROMS). It is either one-way coupled to the spectral wave model WaveWatch3 (WW3) to resolve a broadband wave field or fully coupled to a spectrum-peak (WKB) wave model with Doppler-shift Current Effects on the waves (CEW). The implementation of three non-conservative (NC) effects includes the following: wave breaking and wave-induced bottom streaming, each represented as either a boundary stress or a 3D body force, and wave-enhanced bottom drag. The turbulent mixing from wave breaking is parameterized as a near-surface eddy viscosity enhancement to the K-Profile Parameterization (KPP) model. The bottom boundary layer mixing scheme is modified to account for the influence of wave streaming and wave-enhanced bottom drag. The implementation is validated against the Duck 1994 experiment, recovering the essential nearshore flow features with normalized RMS errors comparable to past studies. ROMS-NCWEC is then applied in a realistic regional setting near Pt. Arguello, CA. It uses an intermediate grid resolution (dx = 30 m) that is inner-shelf-resolving, surfzone-permitting that bridges the gap between coarse-grid regional models and more fully surfzone-resolving simulations. A momentum balance analysis reveals dynamically distinct offshore and nearshore regimes. Offshore, WEC amplifies the terms in the turbulent thermal wind balance while preserving it as the governing balance, consistent with prior findings on wave-enhanced frontogenesis. Nearshore, breaking stress emerges as the dominant WEC contribution, producing at times vorticity enhancements of order 20 times relative to a no-wave control case and shifting the balance from wind-versus-drag to breaking-plus-wind-versus-drag. Wave streaming is found to compete with bottom drag on the inner shelf (depths 10 m < h < 100 m). Just seaward of the breaking zone, streaming meets the wave-driven undertow return current; the resulting near-bed convergence drives upwelling that closes a wave-forced overturning cell and generates strongly sheared alongshore jets at the surface.
This manuscript presents an updated implementation of the UCLA ROMS wave–current interaction framework together with a realistic regional application of the model at 30 m horizontal resolution forced by offline WW3 wave fields. The topic is timely and relevant, as the community increasingly seeks physically consistent representations of wave-driven coastal circulation at regional scales. The manuscript is well written, the numerical implementation is carefully documented, and the effort invested in modernizing the ROMS-NCWEC codebase is appreciated.
In my opinion, however, the manuscript currently attempts to address two rather different objectives within a single paper: (i) the presentation of several methodological developments of the ROMS-NCWEC framework, and (ii) the demonstration of its application to a realistic coastal domain. Both contributions are potentially valuable, but neither is developed in sufficient depth. The methodological developments deserve a more comprehensive validation, while the regional application would benefit from a more balanced discussion of its strengths and limitations. I therefore encourage the authors to clarify the scope of the paper and moderate several claims regarding novelty and nearshore capability.
Major comments
1. Validation of the updated ROMS-NCWEC implementation
The first half of the manuscript introduces several modifications and extensions of the original ROMS-NCWEC framework, including updates to the wave-current interaction terms, accounting for wave spectra, and code organization. These developments represent a substantial methodological contribution, although they appear to be largely presented in Romero et al. (2021). Could you clarify what is genuinely new in the present study? Is the manuscript intended to provide a summary of the novel aspects introduced by Romero et al. (2021) compared to Uchiyama et al. (2011)?
Given the extent of these modifications, I expected a more comprehensive validation. The Duck94 experiment is an excellent benchmark and has become a standard reference for wave-averaged coastal circulation models. However, only a relatively limited subset of the available observations is presented. Earlier studies, such as Uchiyama et al. (2010), devoted significant effort to validating multiple aspects of the wave-driven circulation, including mean current profiles and sensitivity to parameterizations (vertical mixing, CEW, wave roller …). Since the present manuscript introduces new formulations, a more complete validation would considerably strengthen confidence in the updated implementation.Â
It should be noted that Case 8 in the study by Uchiyama et al. (2010) yields one of the poorest solutions (in terms of current profiles) among all the cases presented, largely due to the absence of a "wave roller," which would otherwise transfer a significant portion of the breaking-induced momentum into the trough between the bar and the shore. Further reading of the article reveals that the validation based on Duck94 data is intended to be purely qualitative; it serves as a precursor to the regional study, which also relies heavily on a qualitative approach to compare dynamic balances between the nearshore and offshore zones.
2. Scope of the manuscript
The manuscript effectively contains two papers:
* a methodological paper describing an updated ROMS-NCWEC implementation;
* a regional application demonstrating its use.
Each topic is substantial enough to justify publication, but combining them leaves both somewhat underdeveloped. The first part provides only limited validation, while the second focuses largely on qualitative interpretation of a single regional case. The authors should consider either expanding the validation section substantially or, alternatively, better presenting the objectives of the regional application as an illustrative demonstration rather than the primary scientific result.
3. Novelty claims regarding the regional application
Several statements describing the regional simulation appear stronger than warranted. The manuscript repeatedly emphasizes the 30 m ROMS resolution and describes the application as "surfzone permitting", "capturing both inner shelf and surfzone", or even as a first realistic simulation spanning both regimes.
I believe these statements require more careful qualification.
The circulation model indeed operates at 30 m resolution, but the wave forcing is provided offline by a WW3 simulation with approximately 300 m resolution. Consequently, the nearshore wave transformation is fundamentally limited by the WW3 solution rather than by the ROMS grid itself. Increasing the circulation resolution cannot recover wave processes that are absent from the prescribed forcing.
The regional application provides an interesting demonstration of the updated framework, and many aspects of the simulated circulation appear physically plausible. Nevertheless, the discussions seem to imply a level of realism that exceeds what can reasonably be expected given the wave forcing. For example, statements suggesting that the model captures the surfzone balance should be moderated if the prescribed offshore wave field does not contain the appropriate depth-induced wave transformation.
4. Gray zones
On a few occasions, the authors suggest that reducing the grid resolution below 30 m would be problematic due to entering a gray zone for turbulence closure — thus apparently justifying the chosen coarse resolution. I do not share this point of view. The reference to Chen et al. (2025) is completely misleading in this context. In a free surface model of the breaking zone, the turbulence linked to breaking is never resolved; these are the large eddies of the surf zone. All wave-resolving free-surface models (SWASH, CROCO, NHWAVES) successfully employ a RANS-type closure, as they cannot resolve the large eddies directly generated by wave breaking, even though their resolution can sometimes reach a few centimeters.
5. Discussion of offline wave forcing
The implications of the offline one-way coupling deserve a more explicit discussion.
Unlike fully coupled systems such as COAWST (SWAN) or CROCO (WW3), the present framework does not allow feedback from the evolving circulation to the wave field. Current-induced refraction, modifications of breaking, and water-level feedbacks are therefore absent. This does not diminish the usefulness of the approach, but these limitations should be acknowledged when discussing the applicability of the model and comparing it with two-way coupled systems.
Minor comments
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Recommendation
Overall, I believe this manuscript contains valuable developments that will be of interest to the coastal modeling community. However, the current presentation tends to overstate the capabilities of the regional application while providing only limited validation of the methodological developments. A more comprehensive validation of the updated ROMS-NCWEC implementation, together with a more balanced discussion of the limitations of the regional simulation, would strengthen the manuscript.
I therefore recommend publication after major revision.