Percent Connected Impervious Areas and Percent Unconnected Impervious Areas

Hi, 

I am getting the same error that i found with the question asked regarding the percent connected impervious. I have read through the other question and answer and I think it did answer my question, however if we do have it shown like i have below

will the results be very altered? i believe reading the other post i would have to change it to 0% but what are the impacts on the model results if its kept at that 100%.

thanks,

Paola 

  • Paola,

    Can you please clarify the link you are referring to? Is it a forum post, or perhaps this article in our Wiki knowledgebase? - Percent Connected Impervious Areas and Percent Unconnected Impervious Areas

    As seen in the above article, you will not be able to enter 100% because the sum of the Percent Connected Impervious Area and Percent Unconnected Impervious Area cannot exceed 30%.

    See the additional details in the above article for more details. If your entire "asphalt road" drains directly to the catchment collection point (outflow node) instead of part of it flowing over the "industrial lawn", then you could consider splitting the catchment into two catchments, one with only the impervious road and the other with only the pervious lawn. 

    If you set the percentages to zero and leave the two line items in a single catchment, SewerGEMS will compute an overall single CN representing the whole area, and will use that in the runoff calculations. Consider using scenarios to try both ways and compare the runoff hydrograph.


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.