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How to setup global tidal model

Hello. We are using Open Flows Flood to model the tide in northern Patagonia (South America). We have the problem that the FES model does not calculate harmonic constants (M4) well for this site. Is it possible to use another model? Is it really a model error? Attached screenshot for a tidal point, this error is repeated at all points.

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  • Hello Gabriel,

    Which FES version are you using? In OpenFlows FLOOD we recommend that you use the latest FES2014 dataset to setup tidal open boundary conditions. 

    You can find more information in the wiki article: Global tide solution for coastal hydrodynamics

    From the screenshot of the Tide file you've posted, I believe you are using FES2004, right? 

    The shallow water tide component M4 may not be present (or with amplitude and phase set to zero) when you extract tidal harmonic constituents at some locations, simply because it is either not relevant or not considered/computed by the global scale solution. Typically you have to set your open boundary condition in deep areas and let the hydrodynamic model compute the non-linear tide propagation over shallow waters within the computational domain (explicitly and dynamically computing M4). This is especially true in a large continental shelf like the one you're trying to model. 

    FES2014 has improved a lot the older since FES2004 especially in this areas, so you may want to try and use FES2014 and see how that improves your results. 

    It's always possible to use another global tide solution, but OpenFlows FLOOD does not have any support tools to do it. You can configure your Tide.dat file manually setting "virtual" tide gauges with the respective harmonic constituents along the open boundary, but my suggestion is still to use FES2014. 

    Let me know if you were able to improve your results. 

    Kind regards,
    Luis

  • FES Tide 2004 vs FES Tide 2014

    Hello. I am trying to generate the tide file for the MOHID Water model from the FES model. The interface to generate it only allows to use the file Tide.FES.nc, this is the file that I have used to generate the tide and the interface does not support another extension.
    When configuring the hydrodynamic model, this is where it is only possible to use the 2014 version of the global FES model.
    I think that is why the harmonic constant M4 is not generated, is it?

  • Hello Gabriel,

    FES2014 is much easier to use in OpenFlows FLOOD. You simply have to follow the instructions in the wiki article: Global tide solution for coastal hydrodynamics.

    No need to use the tool that was necessary in FES2004.

    Kind regards,
    Luis

  • Hi Luis. Thanks for the help and answers. I have managed to obtain a model for the tides in the Río Negro region (Argentina), but now I want to improve the model. For that, I designed a new digital terrain but I have the difficulty that tidal currents are not generated when I run the hydrodynamic model. Although I have followed the detailed instructions on modeling coastlines, I can't find any help for this particular problem. I would like if someone can see my model to know if it is a corruption in the FES2014 file.
    What's more. OpenFlows presents a problem in the graphic display of the results. Although the aerial map is in the Mercator projection, and the grids, topography and coastline in WGS1984, there are no problems when designing the digital terrain but there are problems when displaying the results. Thank you very much and I look forward to your help.
    Gabriel

  • Hi Gabriel,

    In order to run a model with FES2014, please keep in mind that FES2014 has a resolution of ~7km, so if your model domain open boundary is too close to the coastline it's possible that FES2014 does not have data to provide. 

    You can upload your model as described here: https://communities.bentley.com/help/w/be_communities_help/7079/communities-secure-file-upload. To export the FLOOD workspace please follow instructions as described here: https://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/51090/how-to-export-and-import-workspaces

    Please when exporting export don't check the box "Include Result files" and make sure the FES2014 is not inside the project folder (this will reduce the size of the workspace significantly). 

    Regarding the coordinates problem, can you open the Digital Terrain Model Grid Data file (aka bathymetry) in the File Editor and check what is the coordinate type? Check for keyword COORD_TIP, it should be 4 which sets it to WGS84. Could you please confirm that?

    Please find more about coordinate systems and grid generation by clicking the links. 

    Thanks and regards,
    Luis

  • Thanks for your response Louis. I just attached the files called "rio_negro_digital_terrain_huck_gabriel.own" and "rio_negro_digital_terrain_huck_gabriel.rar", they both contain the same files.
    Regarding the visualization of the results in the Open Flows Flood GIS, the problem occurs once the program is closed and reopened because the projected base map is in World Mercator coordinates and the rest of the layers ( bathymetry, grid, shoreline) are in WGS1984 format. This problem started in the month of October 2021 and I have not found a solution.

  • Hello Gabriel,

    The problem with your model is that the bathymetry referential is not correct. In OpenFlows FLOOD, when running a coastal application with MOHID Water, the digital terrain model Grid Data file (bathymetry file) must have positive values for bathymetry. Meaning a value of 50 is 50m deep (below water surface) and -2 mean it's 2 meters above the reference water level. You must invert the referential of the original bathymetry data and multiply it by -1 and then regenerate the Grid Data file. 

    After that you it should be all OK. 

    Regarding the coordinates problem I am not able to reproduce your error. Keep in mind that if you save the workspace and then move the files (bathymetry, coastline, etc) to another folder, FLOOD will not be able to load the files. Can you be a bit more specific with what the problem is please? 

    Thank you very much and kind regards,
    Luis

Reply
  • Hello Gabriel,

    The problem with your model is that the bathymetry referential is not correct. In OpenFlows FLOOD, when running a coastal application with MOHID Water, the digital terrain model Grid Data file (bathymetry file) must have positive values for bathymetry. Meaning a value of 50 is 50m deep (below water surface) and -2 mean it's 2 meters above the reference water level. You must invert the referential of the original bathymetry data and multiply it by -1 and then regenerate the Grid Data file. 

    After that you it should be all OK. 

    Regarding the coordinates problem I am not able to reproduce your error. Keep in mind that if you save the workspace and then move the files (bathymetry, coastline, etc) to another folder, FLOOD will not be able to load the files. Can you be a bit more specific with what the problem is please? 

    Thank you very much and kind regards,
    Luis

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