Water Quality Volume

07/21/25

“How do we classify the amount of stormfall runoff that we want to capture and clean?”

Stormwater runoff is infamous for carrying pollution to water bodies. Infrastructure operators will need to size the volume of stormwater they plan to hold and treat before releasing to the environment. But how can they do this? Well, we know that we will need to treat most storm events (let’s say 90 percent), but not all storm events, otherwise it would be too expensive. And we also know that we will need to treat a certain area that we’re designing for, and that a certain amount of runoff may get absorbed. Well, what if we were to combine these factors into a single variable? Well, this is the idea behind Water Quality Volume. Water quality volume is given by the equation WQV = R_V*P*A, where R_V is the volumetric runoff coefficient (the percentage of runoff that is generated by a single rain drop), P the 90th percentile rainfall depth, and A the area that’s drained.