The hydrology of small forest streams in western Oregon varies by time and space in terms of both streamflow and channel hydraulics. Overland flow rarely occurs on undisturbed soils. Instead, water is transmitted rapidly through soils to stream channels by displacement of stored soil water. Drainage networks expand and contract according to the interaction between precipitation characteristics and soil's capability to store and transmit water. Drainage networks are more extensive in winter than in summer. Streamflow may he 1,000 to 5,000 times greater during winter storms than during summer low flow. A stream's kinetic energy varies along with streamflow. Channel width and depth, heterogeneity of bed materials, and the accumulation of large, organic debris affects the dissipation of kinetic energy. Clearcutting can increase relatively small peak flows, but forest roads and extensive areas of soil compacted by other means may increase larger peak flows. Both roadbuilding and clearcutting can cause soil mass movements, which can drastically alter a stream's channel hydraulics by adding debris or scouring the charnel to bedrock. Removal of naturally occurring organic debris that has become part of a stable channel can accelerate bed and bank erosion.