Pre-Event Water

Some of the interflow that quickly finds its way to the stream is not necessarily from the current rainfall. In these cases there is considerable water already in the soil layers that gets displaced as new water infiltrates. The water that appears in the stream immediately following a rainfall or rapid snowmelt period may be from previous precipitation events, or pre-event water. In humid climates, studies have shown that pre-event water is often the greatest contributor to rapid rises in stream level.