Floodplain: A floodplain, or flood plain, is flat or nearly flat land adjacent to a stream or river that experiences occasional or periodic flooding. It includes the floodway, which consists of the stream channel and adjacent areas that carry flood flows, and the flood fringe, which are areas covered by the flood, but which do not experience a strong current.
Levee: is a natural or artificial slope or wall to prevent flooding of the land behind it. It is usually earthen and often parallel to the course of a river or the coast. The ability of a river to carry sediments varies very strongly with its speed. When a river floods over its banks, the water spreads out, slows down, and deposits its load of sediment. Over time, the river's banks are built up above the level of the rest of the floodplain. The resulting ridges are called natural levees.
Deferred Tributary: A tributary is a stream or river which flows into a mainstem (or parent) river. A tributary does not flow directly into a sea. Tributaries and the mainstem river serve to drain the surrounding drainage basin of its surface water and groundwater by leading the water out into an ocean or some other large body of water. A confluence is when two or more bodies of water meet together, usually referring to the action of tributaries.
Distubritary:An affluent is synonymous to the word 'tributary', being defined as a stream or river that simply flows into a larger one.A parallel to tributaries is the distributary, a river that branches off of and flows away from the main stream.
Middle Course features:
The river channel has become much wider and deeper as the channel has been eroded and the river has been fed by many tributaries upstream. Consequently, despite the more gentle gradient the velocity of flow may be as fast as in the uplands. As well as changes in the river channel, its surrounding valley has also become wider and flatter in cross-section with a more extensive floodplain. One of the most distinctive features of the river in the middle course is its increased sinuousity. Unlike the relatively straight channel of the upper course, in the middle course there are many meanders (bends) in the river.
Meanders: A meander in general is a bend in a sinuous watercourse, also known as an oxbow loop, or simply an oxbow. A meander is formed when the moving water in a river erodes the outer banks and widens its valley creating a meander.
Ox-bow lake: Oxbow lakes are created when growing meanders intersect each other and cut off a meander loop, leaving it without an active cutting stream. Over time, these oxbow lakes tend to dry out or fill in with sediment
Braided Stream: Braided streams occur in rivers with high slope and/or large sediment load. Braided channels are also typical of environments that dramatically decrease channel depth, and consequently channel velocity, such as river deltas, alluvial fans and peneplains.
River Cliff - a small cliff formed on the outside of a meander bend due to erosion in this high energy zone.
Slip off Slope - a small beach found on the inside of a meander bend where deposition has occured in the low energy zone.
Tuesday, February 24, 2009 ♥
Rivers The course of river
Nearly all rivers have a lower, middle and upper course. Upper Course: A river always starts from the upper course of the river which can be found at glaciers, springs, rills and lakes that can be found at the top of mountains. The river can create waterfalls where it carves out layers of soft rock and leaves a cliff of hard rock standing. Middle Course: When the river descends to lower levels, it runs more slowly over the gently sloping land of its middle course. Its current no longer has the force to carry stones or gravel. This material drops to the riverbed, where it forms bars of sand or gravel or builds islands. It consists of rapids, waterfall, canyon, alluvial fan, tributary and intermittent stream.
Lower Course: As the river flows downstream it reaches the still gentler slope of its lower course. It drops more of its load than it did upstream and begins to build up its bed instead of tearing it down. The valley has been eroded into a wide plain. The river swings in great S-shaped curves, forming loops called meanders.
Upper course features:
Spurs: An interlocking spur is a natural feature which occurs in a river's upper course, where upward erosion is the dominant force in determining the river's course.
Potholes: Potholes are formed when rock fragments are dragged along the river bed or against river banks known as corrasion or abrasion and it is particularly effective during a flood.
Rapids: A rapid is a section of a river where the river bed has a relatively steep gradient causing an increase in water flow and turbulence. Rapids occur where the bed material is highly resistant to the erosive power of the stream in comparison with the bed downstream of the rapids
Waterfalls: Waterfalls are sudden, steep, vertical flows of fast-flowing water falling from great heights. Waterfalls are normally formed in two ways, erosion of rocks of different resistance or faulting. 1st Way: Waterfalls are formed through erosion of rocks when the river flows erodes the less resistant rocks more rapidly and this causes a change in the gradient of the river cause and over time the river would plunge from a great height. This repeated pouncing will leave a depression which would deepen as rocks and boulders swirl around at the base of the waterfall creating a plunge pool. 2nd Way: Faulting involves the movement of rocks along large cracks in the Earth's Crust. This movement may result in the lifting of one block of land above the other. When a river flows down from the edge of uplifted block, a waterfall and a plunge pool are formed.
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This is our geography project on rivers:D