Rivers Flashcards
What percent of the worlds water is found in seas and oceans?
97%
What is a drainage basin?
The area of land drained by a river
What is the catchment area?
The area within the drainage basin
What is the watershed?
The boundary between two or more drainage basins
Where are watersheds usually found?
The edge of highlands surrounding a drainage basin
What is a confluence?
The point at which two rivers or streams join together
What is a tributary?
A stream or smaller river which joins a larger river
Describe a cross section of the land near to the source of a river
V-shaped valley Narrow and shallow river
What is the name of the process that causes a river to erode downwards?
Vertical erosion
Name the four main forms of erosion
Hydraulic action Solution Attrition Abrasion
Explain hydraulic action
The force of the river causes air to be trapped in cracks of the bank. This pressure weakens the banks and slowly causes them to wear away
Explain abrasion
Erosion caused by the rubbing of materials carried by rivers
Explain attrition
Erosion caused when rocks and boulders transported by rivers and waves bump into each other and get smaller
What does attrition do to the size of the rocks?
Smaller Smoother Rounder
Name the four different transport processes in rivers
Solution Suspension Traction Saltation
Explain solution for erosion and transportation
Small pieces of rock and minerals are dissolved in the river and then carried along
Explain suspension
Fine, light materials are carried along the water
Explain saltation
Small pebbles and stones bounce along the river bed
Explain traction
Larger rocks and boulders are rolled along the river bed
What is required for traction to occur?
High energy level in the river
Where are energy levels usually at their highest in a river?
In the lower course
What causes deposition?
The river losing energy : Inside of a meander
Estuary
Where is deposition the most common?
Near to the mouth Shallow areas Low volume of water
Name the upper course features
-V shaped valleys -Interlocking Spurs -Rapids -Waterfalls -Gorges
Name the features of the middle course
-Wider, shallower valleys -Meanders -Oxbow lakes
Name the features of the lower course
-Wide, flat bottomed valleys -Floodplains -Levees -Deltas
Why do interlocking Spurs occur?
The river avoids areas of hard rock due to its low energy
How does a waterfall occur?
-A layer of hard rock above a thicker layer of soft rock causes the soft layer to erode faster -The soft rock slowly undercuts the hard rock due to it eroding faster and a steep edge is created -This overtime develops to be a waterfall as the height difference increases -Eventually the overhanging rock falls and the waterfall slowly retreats
How do Rapids form?
Ridges of hard rock cause an uneven slope. This creates Rapids
Why does water travel faster in the middle course compared to the upper course?
The channel has been widened and deepened and therefore less friction
Why do meanders form?
-The river erodes laterally -Deposition on inside -Erosion on outer side
What happens on the inside bend of a meander?
-The river flows slower -Material is deposited -More friction
What happens on the outside bend of a meander?
-Water erodes and undercuts the bank -Most energy -Less friction
What is the result of meanders being cut off?
An oxbow lake
When is an oxbow lake most to form?
In times of flood
What happens when oxbow starts to form?
-Sediment builds up, blocking it from the rest of the river -Over time the stagnant water could be replaced by land as sediment is deposited
What is it called when a meander is replaced by land?
Meander scar
What happens to interlocking Spurs if they occur in the middle course?
Bluffs (Truncated Spurs) are created
What are created by floods in the middle course?
Levees
What is the material which is deposited in the event of a flood?
Alluvium deposits
What is precipitation?
Rainfall
What is interception?
When trees and plants catch rainfall.
What is infiltration?
When water on the surface enters the ground.
What is percolation?
The gravity flow of water in soil.
What is infiltration?
When water on the surface enters the ground.
What is throughflow?
Sideways flow of water under ground.
What is transpiration?
The flow of water up a plant and, eventually, its evaporation.
What can cause flooding?
• A steep-sided channel • A lack of vegetation or woodland • A drainage basin, consisting of mainly impermeable rock • A drainage basin in an urban area • Heavy rainfall
What can cause river erosion?
• Stream bed lowering• Saturation of banks• Redirection and acceleration of flow • Removal or disturbance of protective vegetation • Bank soil characteristics such as poor drainage or seams of readily erodible material within the bank profile• Wave action generated by wind or boat wash;• Excessive or inappropriate sand and gravel extraction• Intense rainfall events (e.g. cyclones).
What are the advantages of living near a river or a delta?
• Fertile soil • Fishing • Tourism • Protection against hurricanes (only delta) • Sand and gravel for construction
What are the two main ways river flooding can be managed?
Hard-engineering Soft-engineering
What are some examples of hard engineering?
• Dams • River engineering
What are some examples of soft engineering?
• Afforestation • Managed flooding • Planning
What is the Bradshaw model?
A graphic representation of the change of characteristics as you go downstream
What is the cross section?
A profile of the shape of the river channel
What is the channel width?
The measuremeant from one bank to the other, either present flow or bankfull flow
Increases going downstream
What is the mean depth?
Water’s surface to the river bed across the entire width
Increases going downstream
What is the discharge of a river?
Volume of water which flows past a point in a given time.
Usually measured in cubic meters/second (cumecs) and increases going downstream
What is the wetted perimeter?
The surface of the channel bottom and sides in direct contact with water
What is the hydraulic radius?
Measure of a channel flow efficiency
cross-sectional area / wetted perimeter
Increases going downstream
How does the channel bed roughness change as you go downstream?
Decreases: due to ersosional processes which increase due to a higher discharge
How does turbulance and friction change as you go downstream?
Decreases: due to the smaller particle size
What is evaporation?
When water particles heat up to a point where they become a gas
What is the source?
The place where the river begins
What is the mouth of a river?
Where the main river meets the sea/ocean/lake
What is drainage denisty?
Total length of the rivers / area
What type of rock underlys high drainage denisty?
Non-porous hard rocks such as clay
What does high and low drainage density look like?

What drainage density is more likely to flood?
High Drainage density
What is groundwater flow?
Water flowing through rocks underground
What is surface storage?
Water which is stored in rivers, lakes reservoirs etc.
What is a rivers load?
The material which the river is carrying
What is a meander scar?
The feature left behind when the water in an ox-bow lake dries up
What are natural levees?
A raised river bank formed by deposition
What are man-made levees?
Artificial raised banks to increase the channel capacity and reduce flood risk
What is a floodplain?
An area of land around a river channel which is formed during times of flood when deposition occurs
Why is alluvium useful?
Rich with minerals and is essential for fertile lands
What is the bluff line?
Outer limits of the floodplain
What is the strand line?
Outer limit of floodplain where material is left
How is a delta formed?
A delta is formed when the river deposits its material faster than the sea can remove it
Name and give an example of 3 types of deltas
- Bird’s foot delta (Mississipi)
- Arcuate delta (Nile)
- Cuspate delta (Ebro)
What is flocculation?
Salt from the sea causes the load from a river to join together and heavier so it is more likely to be deposited
What are the disadvantages of living near/on a delta?
- Risk of flood
- Mosquitos (malaria, dengue)
- Dirty and polluted water
- Rising sea levels
- Defences cost