In Hydrology, throughfall is the process which describes how wet leaves shed excess water onto the ground surface. These drops have erosive power because they are larger than rain drops, however, if they travel a shorter distance their erosive power is reduced. In the case of a high canopy, higher than what is required for the drops to reach terminal velocity, about 8 metres (26 ft), the erosive power is increased.
Rates of throughfall are higher in areas of forest where the leaves are broad-leaved. This is because the flat leaves allow water to collect. Drip-tips also facilitate throughfall. Rates of throughfall are lower in coniferous forests as conifers can only hold individual droplets of water on their needles.