First of all, we wish to thank the referee for their extensive review and comments which have raised some very valid points. 

The purpose of LOCATE is to provide a system to facilitate the study of the dispersion of marine debris in small-scale coastal settings. To achieve this, the use of nested hydrodynamic grids with high-resolution data is applied, and although this could be done using Parcels alone as suggested by the referee, the main purpose of LOCATE’s methodology is to do so in conjunction with an appropriate method for detecting when and where particles arrive on land with as much precision as possible from the hydrodynamic data available and often given the complex coastal geometry. Given that coastal areas can experience very high amounts of beaching, special emphasis has been placed on the detection of the beaching of particles. This is especially relevant for areas such as the Barcelona coastline described in this study characterized by a complex geometry with a major harbour and several marinas (Port Olimpic, Forum), groynes, breakwaters and so on. Barcelona experiences discharge of debris on the coastline from various sources, such as rivers or other discharge outlets commonly found in urbanised coastal areas where debris is transported and interacts with the described complex geometry.  

A beaching module based on a distance-to-shore parameter that detects the pre-calculated real shoreline by using distance data within grids during the simulation is included in LOCATE, which could be adapted to other areas where high-resolution coastline data may be available. The beaching module developed within LOCATE allows for a precise determination of which areas can be more affected by particle beaching. The beaching module adapts to each computational grid. In small-scale studies, such as this one, such precision and highly granular information which can be determined in the post-simulation analysis when using the distance-based beaching module, is pertinent to being able to determine which areas, such as specific beaches or port structures, could be more at risk of receiving debris. 

In the present work, it is shown that LOCATE’s use of high-resolution hydrodynamic data that resolves coastal processes in conjunction with the distance-to-shore beaching module, allowed for substantially greater precision in terms of the measurements of where particles became beached. The reason for this is that by using these data together, complex geometric structures can be solved to a much greater extent than using the IBI-CMEMS grid alone where such structures are not taken into account or ‘seen’ due to the grid’s coarse resolution. Furthermore, using the current velocity as a land detection parameter to determine when and where a particle becomes beached has been shown in this study to be insufficient and imprecise at localised scales, even if this has been widely used by other studies, albeit at much larger, even global scales. 

The LOCATE model offers areas of functionality tailored towards use for coastal areas that would require substantial time investment and programming using Parcels from scratch. As mentioned above, the distance-to-shore beaching module can be used as a tool to determine where exactly particles become beached independently of hydrodynamic data resolution, while recreating real-life scenarios such as the continuous release of particles by a river or other discharge outlet can be easily achieved with relatively minor configurations. LOCATE can also be easily configured to track particle dispersion of one-off releases, such as runoff events, or even track drifters or tracers. Since there are high-resolution circulation data available throughout the Spanish coastline via the Spanish Port Authority (Puertos del Estado), LOCATE could be easily applied for similar studies in any of those areas with relative ease. Although Parcels is the engine behind the LOCATE model, it lacks the necessary considerations and requirements, which are included within LOCATE, to provide precise simulations of marine debris at localised coastal scales.

The concern about the model’s accuracy is duly noted and in return, what we propose is that the model can be used for more precise measurements of particle beaching at localised settings. The abstract and conclusion have been edited to reflect this change. The model’s validation has been extended with data on two more drifters that serve to increase the model’s confidence to be used in coastal settings, where more consistent good skill scores were achieved when using the nested grids than using only the IBI-CMNEMS grid. However, the use of nested grids alone is not the sole focus of LOCATE as outlined above.

It is hoped that the concerns shown in the comments by the referee are addressed in the above statement and in the response to each of their points. Far from being a “detailed supplement” to other published works which have also used LOCATE to simulate the dispersion of particles, this work sets out to present a complete outline of the purpose and functionality available in LOCATE for use in coastal areas which may be affected by high amounts of beaching of debris. 

With this in mind, the abstract (below), section 1.4 (objectives) and conclusion have been modified to reflect the points made above to offer greater clarity regarding the purpose of the study and the objectives. To avoid further confusion and add clarity the title has been shortened to:



LOCATE v1.0: Numerical Modelling of Floating Marine Debris Dispersion and Beaching in Coastal Regions Using Parcels v2.4.2

Thank you very much for the comments which are addressed accordingly:

1. Line 55: Use density instead of specific gravity
   • Agree, will change this term
2. Line 126: Some scripts and folders are cited but not given in the Appendix
   • In section 2.1 The following sentence will be added:
     
     “The scripts used for LOCATE and preprocessing scripts mentioned hereon can be found in the code availability section”
   • Mention is already made in line 123 to the LOCATE repository, referenced as Hernandez, et al., 2023
3. Line 145: Regarding citing the environment variables for CMEMS. 
   • Reference to these will be removed as this is in the instructions provided in the repository, and agree that it is not necessary.
4. Lines 274 and 305: A map showing the release points would be useful.
   • Such a map is already provided in Figure 7, where the release points are displayed in 7a, 7c and 7e. Figure 3, however, has also been edited to show these release points in the next version of the manuscript.
5. Line 372 and 382: Showing validation results in section 3.1 in a table
   • These results are already shown as a plot in Figure 6 instead of a table because it was considered by the authors that it could be better understood that way. Better referencing in the text of section 3.1 to the individual plots will be included in the updated manuscript. 
6. Line 394: Include a short description of each test in Table 4. 
   • This will be included.
7. Line 483: 
   • This has already been changed in the next version of the manuscript to “wave-induced Eulerian (mean) currents” as per the recommendation of Referee 1. 
8. Final comments on the conclusion:
   
   
   • It is hoped that an updated version of the manuscript will be clearer and easier to read. The LOCATE model required substantial outlining and explaining, as well as the different tests contained within, such as the validation process which has been extended to include more drifter data, the beaching sensitivity test to define the beaching parameter at coastal scale moving forward, and the simulation using realistic debris discharge data to test the model output and beaching patterns.
     
     
     
     Regarding the conclusion, this has been reworked given the comments from referee1 as well. The point of this study and in turn, its scientific contribution, which perhaps was not made strongly enough, is that while using high-resolution hydrodynamic data is important at coastal scales because they can resolve (some) coastal processes not available using coarse-resolution data, it can also resolve complex geometric structures which are otherwise indistinguishable using low-resolution data that used in many other studies. This was seen in the port area where particles spent 18 times longer with the nested grids compared to the IBI-CMEMS grid. Resolving complex strucutres is especially relevant at coastal scales to identify which areas were most affected by the beaching of particles. The distance-to-shore-based beaching module was developed to calculate a particle’s distance to the shoreline in real-time using high-resolution shoreline data to adequately consider coastal areas in the model in terms of land-water boundary detection in areas of high complexity. Using the high-resolution hydrodynamic and shoreline data in conjunction can provide much more precise information regarding the affected areas around the coastline. This beaching module can also be used independently of the resolution of the hydrodynamic data and still provide more precise beaching measurements even when not applying nested grids as can be seen in the beaching sensitivity test.
     
     
     
     While the ability to implement this development can be scale-dependent, if the shoreline data is available at coastal scales then the beaching module and methodology presented in this study would be beneficial, as the beaching parameters used in previous studies e.g. when a particle moves into a dry cell or stagnation based on current velocity, are insufficient to determine which local areas are more at risk from the deposition of plastic pollution. These points will be extensively presented in the discussion for referee 1, which made similar observations, and will be included in the updated version of the manuscript.