![]() ![]() All the streams flow away from the peak in all directions, yielding a radial pattern.ĭrainage patterns are also influenced by the local geologic history. Radial Drainage Radial drainage develops on domes or volcanoes that have a singular peak.Because joints tend to have a rectangular pattern, the streams also have a rectangular morphology. The joints, therefore, control the path of the tributaries and river. Water travels the path of least resistance, and joints are natural linear zones of weakness in the bedrock. Rectangular Drainage Rectangular drainage develops on jointed bedrock that controls the direction of flow.Trellis Drainage Trellis drainage develops on folded bedrock that exposes rocks with different rates of erosion, creating trunks and tributaries that are roughly parallel to each other.Just like branches of a tree joins the main trunk, so too do tributaries join the main “trunk” of a river. Dendritic Drainage Dendritic drainage is characterized by a branching stream pattern.The pattern that the stream channels make as they move through the basin defines the drainage network as follows (Figure 8.4): Water that falls in the same area but ends up in another river belongs to an entirely different catchment or drainage basin. All the water in a particular catchment basin will flow in streams, which will eventually become tributaries to the river. Water that falls on land and flows over the surface in streams will eventually end up in one major channel called a river. Stream floodplain developmentĬlick on the image to load the animation.ĭrainage networks are contained within a drainage basin separated from other basins by drainage divides (Figure 8.3). These levees help to constrain the stream to the channel even during high flow between floods. Most of the sediments are deposited along the border of the stream’s channel, building up into levees. Because the area the stream is spread over is very large, its velocity decreases significantly, allowing fine-grained material to be deposited (Animation 8.1). During a flood, the water no longer flows in the channel instead, it inundates the valley. It consists of fine-grained sediment layers deposited by intermittent floods. Click on each pattern to see an example.Īs previously stated, the floodplain is the flat part of the valley immediately adjacent to the channel. If the cut-off meander has water in it, it is called an oxbow lake. During a flood, the stream can cut across the adjacent cutbanks, creating a cut-off meander. Therefore, the banks on the outside curve of a meander are called cutbanks and the banks on the inside curve are built up into point bars.Īs the erosion along the cutbanks and the deposition along the point bars continues, it causes the “curviness” of the meander to increase, resulting in adjacent meanders’ growing closer together (Figure 8.2). The water travelling on the outside of the bend moves faster than the water travelling on the inside of the bend, leading to erosion of the banks on the outside curves and deposition on the inside curves. This creates alternating bends in the channel called meanders. A meandering channel pattern is a positive feedback loop created when a stream in a straight channel pattern loses energy (because of, for example, a decrease in slope) and starts to develop a side-to-side motion in plan view. This is called a braided channel pattern.Ĭonversely, low-velocity/low-sediment-load streams will occupy one channel at a time and begin to meander (Figure 8.2). ![]() When a stream carries a high sediment load and/or has a high velocity, it will flow in many channels at the same time (Figure 8.2). The channel is essentially the bottom of the valley in which the stream flows. The floodplain is the area of low relief that is level with the top of the stream’s channel. The valley consists of the sloping areas around the stream and has the distinctive V shape. Looking at a stream in cross-section, three main components are visible: the valley, the floodplain, and the channel (Figure 8.1). Furthermore, the amount of flow over the surface depends on the porosity and structure of the bedrock, as determined by its geology. Flow also depends on rainfall and the like, as determined by the climate. The flow of a stream depends on gravity as a function of the slope, and as such depends on plate tectonics that drive uplift. Streams are any flowing body of water however, the term riveris reserved for the major branches of a stream system. Explain and calculate stream discharge.Describe and explain how sediment is transported by flowing water.Describe drainage patterns and networks.Define what a stream is and describe its anatomy.After completing this chapter, you should be able to: ![]()
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