Features Of The Upper, middle and lower courses Flashcards
How is the levee formed?
Levees are the raised edges of the bank. They form as a river overflows, increasing friction and resulting in deposition. The coarsest material is dropped first. Further floods increase the size of the bank. At periods of low discharge the channel bed builds up sediment, raising the height of the river. Some authorities reinforce the levees, such as on the Mississippi River. Levees can cause deferred tributaries (tributaries that cannot join the main river).
How are deltas formed?
River flows into slow moving water body. Falling velocity=deposition of load. Flocculation=Meeting of salt and fresh water produces electric charge causing clay particles to coagulate. Deposits: bottom set beds (finest materials travel furthest), forest beds(silts and clays) and top set beds (coarse). Distributaries: separate channels giving several river mouths.
Delta types?
Arcuate: Nile Delta Bird’s Foot: Mississippi
Describe an arcuate delta
Shaped like the letter delta. Composed of coarse sediments such as sand and gravel. Curved convex outer edge Wave action smoothed out edge
Describe a birds foot delta
Huge load of sediment is carried into shallow low energy water. Sediment deposited on the side of channel. Additional distributary channels extend into the sea. The Bird’s foot shape is created.
What are Deltas uncommon in the UK?
Large tidal range and high energy environment prevent deposition
Problems and benefits of deltas?
Nutrient rich land But are easily flooded
Outline the conditions necessary for delta formation?
Flocculation Small tidal range Weak currents Shallow
What are pools and riffles?
Pool=area of deeper water Riffle=area of shallow water
How do meanders begin with pools and riffles?
Water forced to flow in a curved shape around the riffles. Riffles direct water flow towards zone of maximum velocity and deepest water. Causes erosion. Deposition on inside bank. Movement sustained by HELIOCOIDAL FLOW( corkscrew movement). Line of fastest flow is moved from side to side within the channel, increasing the amplitude of the meander.
How are meanders formed?
Waters flows fastest on the outside bend (discharge and velocity are the greatest, friction minimum). This results in erosion (via abrasion and hydraulic action) creating steep sided river cliff. Water flows slowest on inside bend (discharge and velocity are lowest, friction at its greatest deposition occurs resulting in a slip off slope/point bar.
How is a floodplain formed?
-When a river overflows its banks, it will spread out across the surrounding flat land. -A sudden increase in the wetted perimeter and hydraulic radius (ratio between CSA and wetted perimeter). This leads to increase in friction and decrease in velocity, resulting in the deposition of suspended materials. -A thin layer of silt (alluvium) is deposited when the river floods, building up the height of the floodplain. The land is very fertile. -The edge of floodplain is marked by the bluff line.
How are oxbow lakes formed?
Over time the meander becomes so pronounced the neck of land is cut through to shorten the course. The main current flows in the middle of the channel. Deposition takes place need to the banks, and the old curve is abandoned to form an oxbow lake. The lake silts up and forms a marsh.
Draw a delta
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Draw a waterfall
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Draw a floodplain
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Draw a meander cross section
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