EGU2020-20305
https://doi.org/10.5194/egusphere-egu2020-20305
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

The effect of the choice of time resolution on the prediction of deep drainage rates in rocky covers

Thomas Baumgartl1 and Mandana Shaygan2
Thomas Baumgartl and Mandana Shaygan
  • 1Federation University Australia, GHERG, Churchill, Australia (t.baumgartl@federation.edu.au)
  • 2The University of Queensland, Brisbane, Australia (m.shaygan@uq.edu.au)

Numerical modelling is a tool allowing the prediction of water flow and water balance based on material properties and time dependent input information at defined boundaries. Long time series are often required for a well informed assessment of the performance of a site. It has been shown that covers as a preferred option constructed in semi-arid and arid climates on mine sites to manage water flows and to prevent deep drainage have a characteristic bi-modal pore system largely caused by a large fraction of coarse rocks. Bi-modal water retention curves have been established for such covers which have proven to describe the response to precipitation with higher accuracy. Meteorological data as input information are in many cases only available on a daily basis if time series over decades are used for modelling. For a bi-modal pore system with often very high values for saturated hydraulic conductivity, a daily time-step may be to large to capture numerically the response in water flow. The objective of the presented work is the comparison of modelled deep drainage data for a specific cover design where hourly data are compared with daily input data. The latter were aggregated from the hourly information.

The results from the numerical modelling showed that for environments with high intensity rainfall events the calculated amount of deep drainage was by up to 10% smaller for the aggregated daily input data compared to the hourly data.

The presentation will inform which rainfall events contributed primarily to the difference in the water balance parameters and to which extent a generalisation can be made on the choice or requirement to choose an appropriate time step for specific climatic conditions.

How to cite: Baumgartl, T. and Shaygan, M.: The effect of the choice of time resolution on the prediction of deep drainage rates in rocky covers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20305, https://doi.org/10.5194/egusphere-egu2020-20305, 2020

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Presentation version 2 – uploaded on 02 May 2020
Correction text; update figure page 6
  • CC1: Comment on EGU2020-20305, Teamrat Ghezzehei, 05 May 2020

    Interesting finding Thomas. What solver do you use?

    • AC1: Reply to CC1, Thomas Baumgartl, 05 May 2020

      Hi Teamrat,

      We used Hydrus. I cannot really think of a physical reason to explain this.

      Cheers,
      Thomas

      • CC2: Reply to AC1, Teamrat Ghezzehei, 05 May 2020

        Do you allow runoff? It could be those heavy rain events when applied at hourly resolution would exceed maximum infiltration and generate runoff. But the same volume, when spread over a day, can infiltrate completely. 

        • AC2: Reply to CC2, Thomas Baumgartl, 05 May 2020

          I think we did not allow for runoff, but I have to check.  very good point. But then ksat is 230cm/day, i.e. per hour that would be 100mm/hour rain intensity. This can happen, but would still be a rare event.

          -- back on the reply - I just send an email to your normal email address.

          • AC4: Reply to AC2, Thomas Baumgartl, 06 May 2020

            We did actually allow for runoff. The calculated surface runoff volume was zero in all cases.

  • CC3: Comment on EGU2020-20305, Dani Or, 05 May 2020

    Nice work Thomas,

    What are the time scales of travel to 2 m (its unclear from the images...) - hrs days?

    • AC3: Reply to CC3, Thomas Baumgartl, 05 May 2020

      Thanks, Dani.

      The infiltration down to 2m is in the half day - 1day scale. But it requires the cliamte where it has been tested, i.e. heavy rainfall events. We have also done rainfall simulation tests above the sensor station and could follow the infiltration front.

Presentation version 1 – uploaded on 02 May 2020 , no comments