Infiltration, Parking Lots and Bio-infiltration Islands
When precipitation falls on land, in the short term, there are two places it can go: runoff to streams or infiltration into the ground. In the long term, evaporation also matters, but during a precipitation event, it isnāt important. Runoff enables water to be used for a variety of purposes as it makes its way to the ocean. Along the way, however, it contributes to flooding, erosion, and is usually moving too fast to be captured. From an environmental and water efficiency standpoint, it is generally better to have most of the water infiltrate into the ground, reducing flooding, nurturing plant life, and later contributing to base flow in streams, flattening out runoff hydrographs. But first, a digression that always troubles me: āWhat is infiltration?ā There are at least two answers: In hydrology and some hydraulics, infiltration is the precipitation that makes its way into the ground. However, if youāre talking about sewers, infiltration is a subsurface water that leaks into sewers when it shouldnāt (i.e., the I part of I&I). The first infiltration is generally a good thing; the second is a bad thing. The result is sentences like āInfiltration into the subsurface can result in additional infiltration into