Once flow is confined in a channel, the erosional power of a stream is related to its slope and discharge. When the flow of water is sufficiently strong, it can dislodge particles from the channel and lift them into the moving water In this manner, the force of running water swiftly erodes poorly consolidated the bed and sides of a stream channel on occasion, materials on banks of the channel may be undercut, dumping even more loose debris into the water to be carried downstream. In addition to eroding unconsolidated materials, the hydraulic force of streamflow can also cut a channel into solid bedrock. A stream's ability to erode bedrock is greatly enhanced by the par ticles it carries. These particles can be any size, from large boulders in very fast-flowing waters to sand and gravel-size particles in somewhat slower flow. Just as the particles of grit on sandpa- per can wear away a piece of wood, so too can the sand and gravel carried by a stream abrade a bedrock channel. Moreover, pebbles caught in swirling eddies can act like"drills" and bore circular potholes into the channel floor(Figure 5.10).