Major flooding effects on a Virginia river included the flattening of riparian forest trees. The most visible effect on a nearby small stream was soil erosion.

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Agents of Natural Change in Watersheds

Natural Change Processes: Flooding
In rivers and streams, floods are critical for several reasons. They redistribute organic material and living organisms downstream and create an opportunity for exchange of sediment and nutrients with the floodplains. Major structural elements of the channel are redistributed during floods and new surfaces are exposed. During particularly intense floods entirely new channels can form, riparian forests can be displaced, and major landslides and debris torrents can be triggered, leading to a more extensive ecological recolonization and recovery period.

Variation in flow on a seasonal and interannual basis is a primary selective force for organisms living in rivers and their associated watersheds. Floodwaters also play a major role in shaping the physical environment of the stream channel and floodplains. For example, the bankfull flood stage (a flood level which fills the main channel and just begins to spill onto the floodplain), which is a flood level that recurs approximately every 1.5 years on average, is recognized as the primary force in determining the shape of the channel and the location of its floodplains. The amount and velocity of streamflow and the shape of the channel affect the size of materials transported and the stability of the streambed, which in turn affect the density and composition of benthic organisms. Across much of North America, seasonal floods are associated with the spring snowmelt. In other parts of the country, floods occur during extreme weather events such as hurricanes (southeast coastal areas) or periods of extended rain.