The graph we have just described is called a hydrograph . One of the most dramatic effects of urban development is to increase the amount of paved area in a watershed. Since there is so much more water running off the landscape instead of infiltrating into the ground, this has the result of causing a larger total volume of runoff from a given storm than might have occurred under natural conditions. Furthermore there is a tendency for the hydrograph to have a higher peak and a corresponding increase in the likelihood of flooding. Bed load travels either by rolling or by bouncing, which takes place in an intermittent series of jumps called saltation .
Sediment traveling along the bed of the stream often forms dunes and ripples.
Streams are able not only to carry loose sediment, but also to erode bedrock. This is accomplished by abrasion , which is the process that results when sediment particles being carried by the flow are used as tools to scrape and grind the rock surface. An eroding bedrock surface often is pockmarked by a series of potholes . The typical pattern of erosion in steep terrain is for the stream to cut a v-shaped notch in the landscape. However many stream valleys have flat or nearly flat valley floors bounded by steeper hillslopes and upland areas.