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    Hi There,

    I am trying to run a RORB model with a catchment that drains to a dam. I need to specify an initial existing water level in the dam of 1m. How do I go about doing this? Would I have to alter the H-S tables or is there a more straight-forward way?


    • This topic was modified 4 months ago by  ThaneshGaneson. Reason: added tags


    Check the discussion of this in section 2.4.4 of the manual. Also item 2.3 in Table 5.2.
    If you look at the storage node in the graphical editor, there is an Initial Drawdown box where you can enter a numeric value – you might be able to use this to get the effect that you need.



    Hi Tony,

    Thanks for the reply. Your blog has been helpful to me many times

    After consulting the manual at the sections you suggested, I can see that I can specify an initial drawdown of 1m to simulate a 1m ‘dead’ storage in the dam.

    Thank you



    Furthering on from this, trying out an initial drawdown level of 1m caused errors. So I tested out different values and found that even a 0.1m initial drawdown was giving me an error claiming a surcharge, which seems highly improbable, as the model was working fine with 0m of initial drawdown. Any advice on how to troubleshoot this?


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    Benson Liu

    Hi Thanesh,

    How are you putting in your initial drawdown?

    In RORB, there are 2 ways of specifying drawdown, one is to specify it in volume (m³) and the other is to input it as water level. If you put it in as volume it needs to be a negative number. Water level is a positive number.

    I think you are putting it in as drawdown in metres which RORB won’t deal with correctly. If you are putting in “1” RORB will assume that it is a starting water level of 1m not 1m drawdown. This will give an error as your H-S relationship is not defined at 1m (it starts at 949.5m)

    Let me know if this helps.

    Kind regards,




    Hi Benson,

    Yes my initial drawdown was specified as 949.6m when I was testing an initial water level of 0.1m
    Since my initial troubles, I’ve moved away from initial drawdown and I altered the H-S table to simulate a dead storage instead

    Thanks for the assistance


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