LID Infiltration Facility Calculator (a.k.a. Rain Garden Calculator)
This calculator was created to provide a more user-friendly interface to the typical spreadsheet model engineers use for sizing infiltration facilities. The tool is a reservoir-routing spreadsheet model that uses a standardized NRCS Type 1a 24-hour rainfall distribution (typical of Western and parts of Central Oregon) with variables input by the user to approximate the performance of various low impact development vegetated infiltration facilities. It is to be used for modeling runoff from impervious surfaces of less than 0.25 acres (approx. 11,000 sq. ft.).
THE INNER WORKINGS OF THE LID INFILTRATION FACILITY CALCULATOR
An LID Infiltration Facility web calculator has been provided to help designers in public and private sectors size vegetated infiltration facilities including rain gardens, planters, and vegetated swales with check dams. Since the web calculator does not show the user how the calculations are being performed, this webpage presents the assumptions and calculations on which the web calculator is based and allows you to download the model in Excel format. The advantage of this format over the web calculator is that you can use it to size rain gardens for runoff from any area, not just impervious areas, and you can use it to justify the design calculations for permits.