In swale design, what calculation is used to determine the volume reduced by an upstream BMP?

In swale design, the correct formula to determine the volume reduced by an upstream Best Management Practice (BMP) is represented as Tv = [(1 inch)(Rv)(A)]/12. This formula is important for calculating the volume of stormwater that can be managed through a swale and relates to how much runoff can be expected from a particular area.

The elements of the formula signify the following:

• The "1 inch" represents a standard depth of runoff that is often used for calculations in stormwater management, as it provides a common reference for quantifying rainfall events.
• "Rv" is the runoff coefficient, which characterizes the land surface's ability to generate runoff; it's a crucial factor in understanding how much water will ultimately flow into the stormwater system.
• "A" is the area of the land from which water will be collected, often measured in acres.

Dividing by 12 is necessary to convert the volume from cubic feet to cubic inches since the "1 inch" measurement pertains to depth, thereby allowing for consistent units in the final volume calculation.

This formula effectively links the area, the depth of runoff, and the runoff coefficient to provide a tangible estimate of the potential volume of stormwater that can be managed by