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River processes & landforms
- 1. River Processes &Landforms Chapter 5
- 2. River Processes • Erosionremoves material from a river bed making it deeper/wider • These pebbles, sand, silt, etc. get transported downstream (river’s load) • Deposition occurs after a river no longer has enough energy to carry the load and drops it on the river bed-boulders first, silt & mud last
- 3. How a RiverTransports
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- 5. Factors Affecting RiverWork • Velocity/energy-the faster the river the larger the material able to be transported • After rain rivers may look brown due to suspension
- 6. Factors Affecting RiverWork • Volume-the more water the greater the volume of the load • Bedrock-harder rocks- i.e. granite- erode slowly, soft rocks-shale- erode easily & some rocks- i.e. limestone- can be dissolved completely
- 7. Deposition • Occurs whenrivers lose velocity – Decrease in the gradient – Decrease in river flow as water drains after a heavy rain – River meets the sea/lake – River flows slower on the inside of bends
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- 9. Upper Course ofa River Source • Where the river starts in a highland or mountainous area • Vertical erosion can be great in some areas and create gorges, canyons, potholes • Potholes-smooth rounded hollows formed by stones trapped in the hollows of a river bed
- 10. Upper Course ofa River Rapids • Form where the water is shallow and the river bed is rocky & irregular making the water rough • Usually in steeper areas • Can make river travel difficult unless white water rafting/kayaking
- 11. Upper Course ofa River Waterfalls & Gorges
- 12. Victoria Falls Zambia& Zimbabwe
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- 14. Waterfalls & Gorges Positives •Brings in tourists • Hydroelectricity Negatives • Can cause navigation problems, makes the river difficult to cross
- 15. Upper Course Interlocking Spurs •Narrow valleys force the river to create a winding path
- 16. Middle and LowerCourses • As the river valley begins to widen and become less steep • Begin to see more lateral (sideways) erosion • Vertical erosion may stop completely by the time we reach the lower course
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- 18. Meanders & OxbowLakes
- 19. Floodplains & Levèes •Flat land next to a river liable to flood • Occasionally the river flows above the level of the surrounding plain but is enclosed by raised embankments called levèes
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- 22. Deltas • Low-lying flatmarshy land where a river meets a sea/lake • Formed from a river with carrying a lot of sediments that meets a still sea/lake and the sediments build up • May cause distributaries
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- 25. The Long Profileof a River • A line drawn from the source of the river to the mouth showing how the gradient changes • Typically steep in the upper course and more gentle and smooth in the lower course • Erosion & deposition remove irregularities in the profile making it smooth and concave
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- 28. Living in RiverFlood Plains & Deltas • Often densely populated • Offer flat land (easy to build) • Fertile soils • River valleys are natural route ways • Navigable rivers allow transport & trade • Provide drinking water and food source
- 29. Living in RiverFlood Plains & Deltas • Tropics can suffer from diseases carried by insects i.e. malaria (mosquitoes) & sleeping sickness (tsetse flies)
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- 32. Flooding • Discharge-the volumeof water flowing down the river at any one time • When the discharge can no longer be contained within the channel & overflows to the surrounding area it floods • Dense population can make flooding severe • When it rains, very little of it actually falls into the river, so where does the water come from?
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- 35. Factors Affecting Discharge •Rainfall • Relief – Rainwater runs over steep slopes vs. infiltration on gentle • Land Use • Weather Conditions – Hi-temps reduce discharge • Rock & Soil Type – Permeable vs. impermeable
- 37. Hydrographs • Graph showinghow a river responds to a storm • Shows rainfall and discharge
- 38. Flood Prevention Planting Vegetation •Planting vegetation (trees) allows rainwater to be taken in by roots & go out through transpiration • Acts like a sponge that releases water slowly so flood peaks are reduced
- 39. Flood Prevention • Reservoirscan trap water and release it slowly
- 40. Flood Prevention Straightening theChannel • Shortens the river and gets the water away faster.
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- 42. Flood Prevention Artificial Levèes •Increase the capacity of the channel • Usually banks are strengthened with concrete or stone so less likely to break
- 44. Flood Prevention Dredging theChannel • By making it deeper this increases the capacity and makes it less likely to overflow
- 45. Flood Prevention Bridge Design •Bridges with wide pillars and walls on top act like dams which hold back water; modern bridges are slim and prevent this from happening
- 46. Flood Prevention Wash Lands •Control land on flood plains areas for recreation instead of residential to minimize damage
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