L4 ap middle and lower course features
- 2. Landforms of a River – Middle and Lower Lesson Objectives: • Understanding how processes of erosion and deposition create landforms along a river in its middle and lower course.
- 3. Middle Course landforms • The main process in the middle course are erosion and deposition
- 4. 1. Meanders and Oxbow Lakes • Video here
- 5. • Meander on a map
- 9. RIVER CLIFF POINT BAR SLIP OFF SLOPE
- 10. Pont bar
- 11. Water is pushed to the outer bend . This reduces friction with the bed and banks. So the river has more energy for transporting material which can erode the outside bank via abrasion. In the middle course lateral erosion dominates as the river swings in large bends known as meanders. Meanders constantly change their shape and position. What do you think happens on the inside of the bend?
- 12. Point Bar As the river loses energy on the inside of the bend (less water and more friction) it also cannot carry as much of its load and so deposits it. Deposited material builds up on the slip off slope and it forms a point bar.
- 14. Ox Bow Lakes
- 16. Ox bow lakes
- 20. 2. Features from erosion and deposition: Oxbow Lakes 1. Meander formed through erosion and deposition. A point bar develops on the inside of the meander (due to deposition) and a river cliff on the outside (due to undercutting) 2. During periods of flooding the meander neck is breached and the water takes the fastest route across the meander.
- 21. 2. Features from erosion and deposition: Oxbow Lakes 3. Erosion (Hydraulic action especially) continues and the neck is finally breached. Deposition begins in the old meander. 4. Deposition continues and eventually a lake is formed that is totally cut off from the river channel – an oxbow lake.
- 22. 3. Landforms resulting from deposition in the lower course: Levees & Floodplains
- 24. Levees
- 26. 3. Landforms resulting from deposition: b. Levees • Levees are _______ banks found along the side of a river in its lower course. • They form as a result of _________. • The increase in _______ as the flooding river moves over the land results in ______ it down. Therefore it has less energy as it moves away from the channel. • It then deposits its largest/heaviest material first along the river ______ taking the finer/lighter material further over the floodplain. • Subsequent floods serve to ______ up the material along the bank thereby creating levees. bank flooding build friction slowing raised
- 27. 3. Landforms resulting from deposition: a. Floodplain • Meanders widen the valley in the lower course by eroding laterally as they move across it. • In _________ conditions – water contained in the channel • In flood conditions – Water floods onto the ____ land adjacent to the river and ___________ material. • _________ sediment is deposited first because the river lacks energy. Then lighter sediment is carried ________ across the flood plain as the ______ requires less _______ to move lighter sediment. • This creates a wide, flat area of land either side of the river called the floodplain. • Further Flat Heavier Normal Deposits Energy River