Erosion is a natural stream process. When left to its own devices, a stream channel is a dynamic thing. Banks move and erosive forces shape, and reshape, the channel and floodplain. Soils scour out here and deposit there in a healthy balance. Sediments deliver nutrients that support aquatic life.
But when development and urbanization put stresses on natural stream systems, erosion can accelerate beyond the norm. This leads to decreased bank stability, a diminished capacity to handle flood waters, and excess sediment clouding of the stream. In other words, excess erosion can cause property damage and degrade water quality and habitat.