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LID Simulation

Posted by Sunny on September 10, 2013 at 10:50am

Hi! I have a question about simulation of LID. How does SWMM 5 simulate the runoff reduction from LID? Are there any principles or equations? 

In addition, when soil becomes saturated after long-term precipitation or certain time of precipitation, LID is not as useful as the initial stage. In this case, how does SWMM model runoff reduction from LID? Does it take into account this situation?

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Replies

  • Robert Dickinson September 12, 2013 at 6:24am

    The soil becomes unsaturated over time in the LID unit the same as the soil on a Subcatchment becomes unsaturated.  I will show you how this works in graphs over the weekend.

    • Sunny > Robert Dickinson September 12, 2013 at 4:12pm

      Hi! Thank you! I really appreciate your help! 

      Today I simulated the very short time with relatively heavy rainfall and made a graph compared with different situations. Green Ampt was used as infiltration model. But i get a little bit confused about the final result. I attached the graph I made.

      Under scenario 1, there is no any LID, only impervious area; in the current situation, there are some bio-retention and under scenario 2, more LID were implemented compared with current situation, such as green roof and porous pavement. 

      At some point, the losses are the same in three situations. I think that's because water holding capacity is reached. Water cannot enter into the soil anymore. Please correct me if I'm wrong.

      At some point, why are losses in scenario 2  less than other two situations? I couldn't find the answer about it. Because scenario 2 has the greatest percentage of LID, but why sometimes losses is even lower? 

      In addition, at 22:00, why are the losses from scenario 1 much higher than that in current situation? Scenario 1 has no any LID. How can I explain this phenomenon? 

      The x axis is the time of that day (o:00 to 23:00) and the hourly rainfall data are 

      0:00:00 0
      1:00:00 0
      2:00:00 0
      3:00:00 0.6
      4:00:00 0.6
      5:00:00 0.2
      6:00:00 0.6
      7:00:00 0.4
      8:00:00 0
      9:00:00 0
      10:00:00 0
      11:00:00 0.8
      12:00:00 0.4
      13:00:00 0.8
      14:00:00 0
      15:00:00 0
      16:00:00 0
      17:00:00 0.6
      18:00:00 0.4
      19:00:00 0.8
      20:00:00 0
      21:00:00 0
      22:00:00 0
      23:00:00

      0

      Could you please help me to figure them out when you have time? Thank you! I'm looking forward to your reply!

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