Stream Channel Pattern

Stream flows are generally irregular, confined to channels that give it a three-dimensional nature and are visible through variations in channel patterns. The smooth and regular-stream flow will result in straight and direct steam channels, but it is obvious that in nature very few streams exhibit straight and uniform channels over a long distance. Most steam channels tend to wind their way across the landscape, sometimes showing great sinuosity.

Stream channel patterns can be Straight, Sinuous, Meandering and Braided. Any large river system, such as Ganga or Brahmaputra, is made up of all four types of channel patterns.

Straight Channel

These are short and uncommon and reflect a strong structural control due to underlying rock formation. A straight channel would not mean that a river is running in a straight line. The deepest part of the channel, known as thalweg, hardly ever follows an absolutely straight line and may move right and left across the channel.

Sinuous Channel

These are winding channels most commonly found in various topographical structures. The channel exhibits sinuous characteristics even when the stream flows down a steep slope with a high gradient. On a flat topography with a low gradient, steam channels flow with greater sinuosity.

Meandering Channels

These are most common and are depicted by a serpentine course contorting and curving, showing twisting behaviour. The word meander means to proceed sinuously and aimlessly. Flat topography with low gradients is characteristic of meandering channels where in most streams have fine sediment loads.

The meandering channels have cohesive alluvial banks, and the sinuosity of the river is expressed as the ratio of the river channel length over the valley length. It can depict varying ratios, including one. The wavelengths are tightly clustered around a dozen times the width of a typically meandering river (Anderson & Anderson, 2010).

The inside bend of the meander may have a sandy deposit termed a point bar – forming part of the active drainage system. The thalweg will be located on the outside bend against the river’s far bank. Scroll bars and oxbow lakes are the geomorphic expressions of the meandering system.

These are commonly observed in the Mississippi Valley of North America. In India, the fluvial flood plain of River Burhi Gandak in Bihar shows several scroll bars and Oxbow lakes.

Braided Channels

These comprise multiple interwoven and interconnected channels that may be separated by low bars or islands of sand, gravel and other loose debris (McKnight, 1998). The pattern of the braided channels is explained through the process in which the banks lack cohesion, transport is by bedload only, and the flow of water in the stream fluctuates frequently.

These patterns are common in glaciated landscapes as glacial outwash plain channels where the coarse-grained bed load is supplied by a glacier to the meltwater. In arid landscapes with dry seasons and periods of low water discharge predominates the streams show the characteristic braided channel.

Since there is a deficiency of fine material and vegetation, there is a lack of cohesion in the river banks. The flow in the braided channel at any given point of time occupies two or more channel segments simultaneously. The flow threads are separated by mid-channel bars. Sometimes the entire valley cross-section may have many tens of threads.

This means that at any given point in time, active channels may cover less than one-tenth of the width of the entire channel system. But in a year, most or all of the surface sediments may be reworked by the lateral flow in the stream channel.

The flow depths may range to a few metres only. As the flow depth increases, the shear stress exerted on the bank becomes sufficient to entrain bank material, and the channel widens locally (Anderson & Anderson, 2010).

Chitina River, Alaska, shows extensive braided stream channels and is formed from major glaciers of the Wrangell Mountains.

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