ABSTRACT
The unique importance of stormwater infiltration comes from the role of subsurface water in the hydrologie balance. The defining process of infiltration is to transfer surface water to the subsurface. Water occurs in the subsurface of almost all landscapes. All subsurface water has an intrinsic sustaining role in landscapes and watersheds. Understanding how water moves through the subsurface provides a foundation for evaluating the impacts of urban development on landscape hydrology, and planning stormwater management in response to them. Immediately below the ground surface, outside of wetland areas, the earth pores are unsaturated. This part of the subsurface is called the vadose zone, from the Latin vadosus for shallow, akin to wade as in a shallow ford. In any landscape, any difference between hydrologie inflow and outflow is resolved by a change in storage, in some combination of surface, vadose and phreatic forms. Stream flow is characteristically variable, within limits defined by the drainage area and the climate.
