Landforms that result from erosion by water flowing on land surfaces. This water may concentrate in channels as streams and rivers or flow in thin sheets and rills down slopes. Essentially all land surfaces are subjected to modification by running water, and it is among the most important surface processes. Valleys are cut, areas become dissected, and sediment is moved from land areas to ocean basins. With increasing dissection and lowering of the landscape, the land area may pass through a series of stages known as the fluvial erosion cycle.
The most distinctive fluvial landform is the stream valley. Valleys range greatly in size and shape, as do the streams that flow in them. They enlarge both through down and lateral cutting by the stream and mass wasting processes acting on the valley sides.
Waterfalls occur where there is a sudden drop in the stream bed. This is often the case where a resistant rock unit crosses the channel and the stream is not able to erode through it at the same rate as the adjacent less resistant rock. Waterfalls also occur where a main valley has eroded down at a faster rate than its tributary valleys which are left hanging above the main stream. With time, waterfalls migrate upstream and are reduced to rapids.
Many streams flow in a sinuous or meandering channel, and stream velocity is greatest around the outside of meander bends. Erosion is concentrated in this area, and a steep, cut bank forms. If the river meander impinges against a valley wall, the valley will be widened actively.
A stream terrace represents a former floodplain which has been abandoned as a result of rejuvenation or downcutting by the stream. It is a relatively flat surface with a scarp slope that separates it from the current floodplain or from a lower terrace. Terraces are common features in valleys and are the result of significant changes in the stream system through time. Floodplain
Fluvial erosion also has regional effects. Streams and their valleys form a drainage network which reflects the original topography and geologic conditions in the drainage basin. A dendritic drainage pattern, like that of a branching tree, is the most common and reflects little or no control by underlying earth materials. Where the underlying earth materials are not uniform in resistance, streams develop in the least resistant areas, and the drainage pattern reflects the geology. If the rocks contain a rectangular joint pattern, a rectangular drainage pattern develops; if the rock units are tilted or folded, a trellis pattern of drainage is common. Topography also controls drainage development; parallel and subparallel patterns are common on steep slopes, and a radial pattern develops when streams radiate from a central high area. Erosion River Stream transport and deposition