Based on my understanding by reading the posts on this web site, it seems to me that for option #1, all volume from the 95th or 98th percentile of rainfall to be captured and managed – either through infiltration, evaporation or harvesting. Someone even using a bowl analogy for the option #1 approach. But for my site, the 100% capture is not possible, and very costly if we have to so. We might have to have portion of the runoff drain directly offsite – especially the potion at the edge of the development.
For option #2,”Manage on site the annual increase in runoff volume from the natural land cover condition to be postdeveloped condition.
The question is “What is the definition of annual increase?” can I use 1-year 24-hour rainfall event to calculate it? I plan to use TR-55 (TR-20 HydroCAD software) to estimate the total runoff volume. Would you please let me know if my approach is correct?
