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rachel.jensen

Beginners Troubleshooting and Model Review Guide

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We often get asked about instability troubleshooting and how to have a basic review of model health. Below is a short workflow for how we normally start checking mo dels, typically for instabilities but also for schematisation problems or general health. The below is for basic 2D models but also applies to 1D/2D models. 

How do you go about checking for instabilities? What do you find most helpful when it comes to picking up problems?

Is there anything on your wishlist that your Tuflow simulation could tell you about how to get to the bottom of these?

 

  1. Check the Tuflow log file (.tlf)
    • Search for the words WARNING, CHECK and ERROR in the tlf. If there are messages that you don't understand, then use the wiki messages page to help you look for what the codes means and suggestions for how to solve them
    • What's are the cell size and time step? Is the time step around half or one quarter of the cell size (or down to one eighth for direct rainfall models)? Is the cell size appropriate for the results that you expect (ie: no depths much larger than the cell size)
    • Scroll to the bottom of the tlf and check the simulation summary – image one below shows two examples on how to read the summary in your tlf
      • Has the model finished?
      • Are there any negative depths? If so, import the layer into your GIS package to find out where these instabilities are occurring. 
      • What is the peak mass balance in the model? As a rule-of-thumb this should be between ±1%.
  2. Look at your messages layer
    • If it goes unstable, is it in the 1D or 2D?
    • Find the first UNSTABLE errors that occur and visualise those in your GIS package, along with you model inputs, are there any correlations?
  3.        Topography

    o    Load your zpt_check file (or DEM_Z check) and review the topography around your area of interest. If you’re using topographic modifiers, also load you zsh_zpt_check file to review what changes you’re making. Are there any sharp edges or quick changes?

    4.      Materials

    o    Load your grd_check file and thematically map by material or load your DEM_M to look at your materials. Are there any big changes in roughness?

    5.      Results

    o    Step through the depth results and velocity vectors, look for sudden changes

    o    Check for circulations or oscillations, particularly around boundaries. Are there circular flow paths or undulating water surface levels?

forum_tlf.png

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This workflow is great, thanks for that Rachel!

It is generally what I do and how I assess the health of a model however, on top of all that I also use Crayfish in QGIS. I display MB1 in Crayfish and I can see where the MB errors happen but as this is based on cells and not in the overall model is not coinciding with what is seen in the csv file output (good to display dvol in comparison to Cum ME (%)  to assess if the MB errors are out of +-1% at the peak of the simulation which is the most important point generally).

My question here is... would you give more credit to what is seen in the csv and in the tlf as summary than what is seen in Crayfish?

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