Date post: | 04-Jan-2016 |
Category: |
Documents |
Upload: | ferdinand-bennett |
View: | 225 times |
Download: | 1 times |
Chapter 4: Weathering and Erosion
TOPIC 6 : River Deposits ; Flooding
Deposition
• The amount and size of a river’s load depends on discharge, which in turn depends on speed.
• When a river slows down, it loses it’s ability to carry some of it’s load.
• Some of the load gets deposited where the river loses speed. Heaviest load (bedload) is the first to get deposited.
Deposition locations
• The inside bank of meanders (looping bends)– In sharp turns, water on the inside of the turn
slows down while it speeds up on the outside bank. (inside = deposition ; outside = erosion)
• Near and at the mouth of a river– As rivers approach their base level (elevation
of what they are flowing into) they lose most of their gradient and speed.
Depositional Features of Rivers
• POINT BARS and FLOODPLAINS– Form along the inside bank of meanders– Point bars = rocks, gravel, sand– Floodplains = soil (sand, silt, clay)
• Flat areas of fertile soil that form along the banks of a river and are covered by water during flood stage.
• DELTAS and ALLUVIAL FANS– Fan-shaped land formed at the mouth of a
river from deposits of fertile sediment.
CUT BANK
POINT BAR
Cut Bank
CUT BANK
Cut Bank Erosion
meandersfloodplain
Formation of Point Bars and Floodplains
• http://csdms.colorado.edu/wiki/Movie:Floodplain_Evolution
• Stream table meandering
The Nile Delta (Eqypt)
Benefits and dangers of rivers
• In addition to providing fresh water, river deposits produce very fertile farmland.
• Floodplains and deltas are among the most fertile areas for farming.
• Floodplains and deltas are prone to flooding when rivers overflow their banks (known as “flood stage”). Crops and structures built on these may be destroyed during floods.
Controlling the river
• The risk of flooding can be controlled by the construction of:– Dams – a barrier that redirects the flow of
water to another area; controls how much water flows through the channel.
• Dams can also use the energy of a river to produce mechanical or electrical energy.
– Levees – a barrier built along the banks of a river to prevent overflow during flood stage.
Taming the River- Dams
A dam
Levee
This guy really wants to be left alone!