Modelling the Past and Future Evolution of Tidal Sand Waves

Round 1

Reviewer 1 Report

General comments

This manuscript applied a numerical morphodynamic model on the hindcasting and forecasting of tidal sand waves. Realistic initial bathymetry, tidal flow and bed roughness as input were used which made a further step compared with previous studies. In general, the manuscript is well organized and well written. I recommend a minor revision before publication. There are some points that confused me and should be clarified.

Specific comments

1. In figure 5, the simulation results show that some small sand waves merge gradually which does not occur in the actual measurement. This will affect the migration rate of sand waves, especially the prediction of the long-term evolution. Besides, the shape of the sand waves has changed which will affect the migration rate. I would suggest the authors add some words to explain this.
2. Line 164, a grammar error with two words “from”. Please check the full manuscript.

Author Response

We thank you for your constructive comments. In the attachment, we have provided our response.

Reviewer 2 Report

This study assessed the skill of Delft3D in capturing morphological evolution of tidal sand waves by presenting a detailed case study in the North Sea. The paper is well-written and well-organized. Arguments are supported by simulation results and field data.

I recommend moderate revision with the following two issues to be addressed by the authors:

• The authors tried to reproduce the evolution of a few selected tidal sand waves in the North Sea on a decadal time scale. Despite of a relatively good agreement between model results and measurement, I have concern on the use of simplified forcing. The authors declared that the sand waves are predominantly driven by tides, and therefore used tidal constituents only as boundary driving forcing and did not include a realistic representation of forcing which should include the impact of wind-driven currents and interaction with tides. I would like to see more details on the potential impact of wind-driven currents on the sand wave development.
• Scale interaction between smaller bedforms such as mega-ripples, dunes and larger bedforms such as the tidal sand waves is missing in the study. The authors stated that extreme events like storms mainly influence the dynamics of mega-ripples and do not affect the tidal sand waves. However, it is the smaller-scale bedforms which alter the pattern of bed-load transport that eventually impacts the development of larger-scale bedforms. Please narrate this missing feedback loop in further detail and its influence on your results.

Author Response

We thank you for your constructive comments. In the attachment, we have provided our response.

Round 2

Reviewer 2 Report

I am pleased to see that the authors have addressed my concerns from last review.