Equation 1 Interpretation

Generally, when we calculate runoff, we use a runoff coefficient, or in the case of a site with multiple types of surfaces (pavement, grass, gravel, etc.) we calculate the areas of each surface and use a table that provides us with runoff coefficients for each type of surface. Then we develope a combined run-off coefficient value for the site or drainage that can be used with the Rational Method. In the case of storage volume, LEED provides us with an emperical method that essentially calculates the runoff coefficient (Volume of captured runoff) and the "I" stands for the percent of impervious area, as a whole number in the equation. In my opinion, I would rather use a combination of runoff coefficient values and their associated areas to develop a more accurate combined ronoff coefficient volume. This is the same runoff coefficient that is used for the Rational Method. The difference is that you are just calculating a simple volume for storage based on a given rainstorm over an entire area, assuming the surface is impervious, or it isnt, using the LEED storage equation. Runoff coefficients can be easily obtained for various surfaces from the internet.