What are the features of a drainage basin
Source- Where the river starts
Confluence- The point where two rivers meet
Watershed-High area that makes up the edge of the basin
Tributary- A small river than joins to a larger one
Mouth- End of river
Which types of mass movement occur on rivers
- Soil creep~ individual soil particles move down the side of the slope due to gravity. They gather at the bottom of the valley where they are eroded by the river .
- Slumping-Happens when river erodes the bottom of river valley . The slope becomes unstable and the material higher up on the slope slides down , rotating as it does so . This can often also happen when the material is saturated
Define the long profile,the cross profile and the river profile of a river
The river profile is the path of the river as it flows
The cross profile is the cross section of the river
The long profile is how the gradient of the river changes along its course
What is the discharge of a river
The discharge of a river is the volume of water flowing in a river at a particular point
How are waterfalls formed (upper course)
Waterfalls occur in areas where there are layers of more resistant rock on top of layers of less resistant rock. The less resistant rock is eroded first (hydraulic action).
A plunge pool is created at the bottom of the waterfall as the rivers bed load swirls and erodes the river bed at the foot of the waterfall.
Erosion of the less resistant rock continues until eventually the overhang of the more resistant rock collapses under its own weight
How are v shaped valleys and interlocking spurs formed (upper course)
In the upper course of the river . The river erodes vertically downwards- creating steep sided V shaped valleys. The river does not have the erosive power to erode laterally so it flows around hills (interlocking spurs)
How is a meander formed (middle course)
When a river reaches its middle and lower courses it begins to erode sideways creating large bends called meanders.
- The meander erodes the outside of the bend , where the current is strongest .
- This washes away the river bank and creates a river cliff
- On the inside of the meander ,where the current is weakest, the river deposits its load. Creating a slip off slope.
- Over time this deposition and erosion continues and changes the course of the river
- When the meander reaches the river valley sides it erodes them .widening the flood plain and valley floor
How is an oxbow lake formed (middle course)
Meanders get larger over time.
Erosion causes the outside bends of the meander to get closer until their is only a small strip of land between the bends.
The river breaks through this land , usually during a flood , and the water chooses the fastest pathway.
This cuts off the meander.
The new river path then deposits material on its banks , causing the meander to get further cut off and turned into an oxbow lake
( see an image)
How is a delta formed (lower course)
- When a river meets a sea or a lake it is forced to slow down , causing it to deposit the material it is carrying
- If the sea does not wash it away the material builds up and blocks the river channel
- The river has to split up into smaller rivers(distributaries)
- Eventually a low lying area of land forms called a delta
How is a levee formed (lower course)
- A levee is a natural embankment along the side of a river channel.
- When a river floods it deposits material on its embankments .
- The heaviest material is deposited first when the river slows down
- Over time the deposited material builds up and creates a levee along the side of the river channel
How is a floodplain formed (lower course)
- When a river is in its lower course the meanders move downstream and outwards
- Over time they erode hills
- This leaves a large flat area next to the meander called a floodplain
- When the river floods water spreads out over the floodplain
- Friction of the river increases with the river bed over time.This adds sediment to the floodplain and makes it fertile
What are the key features of a storm hydrograph
Peak discharge-The highest amount of river discharge recorded in a time period
Lag time-Time difference between peak rainfall and peak discharge
Rising limb-The increase in river discharge as rainfall flows into river
Falling limb-The decrease in river discharge as river returns to normal levels
Name four factors affecting discharge
- Precipitation
- Geology - There is more run off with impermeable rocks
- Soil type-more impermeable soil can absorb less water than more sandy soil and shallower soils become saturated faster and cant absorb as much as deeper soils
- Slope-Steeper slopes mean there is higher run off and less infiltration
What are four more factors affecting discharge
1.Antecedent conditions-Previously wet or cold conditions make the ground saturated and mean no water can infiltrate in
2.Drainage base type/ size-Circular basins have a shorter lag time and a higher discharge because all run off reaches the river channel at the same time.In Narrower basins the water takes longer to reach the main river channel
3.Urbanisation-More impermeable surfaces mean that less water can be absorbed and there is higher run off; more drains means that water is taken to the river rapidly , increasing discharge
4-Deforestation-Trees absorb water and store it in the ground
How do you work out flood risk
Flood risk = Flood likelihood x flood severity
Why is flood risk increasing in the uk
- Storm frequency is increasing due to climate change
- Storm severity is increasing because there is more intense rainfall due to climate change
- There are more frequent periods of wet weather meaning the ground is more likely to be saturated
- There has been an increase in impermeable surfaces due to urbanisation
- Vegetation and other permeable surfaces are being destroyed for housing
- There has been development of floodplains
Describe the features of embankments
Embankments are high banks built along a river to protect built up areas and stop flooding there
Pros:protects built up area and infrastructure in that area , made from natural resources so not ugly
Cons: expensive and ineffective in severe flooding
Hard engineering
Describe the features of flood walls
Flood walls are barriers built to increase the height of river banks
Pros: Allows the river channel to hold more water so it doesn’t flood
Cons:Expensive , ugly
Hard engineering
Describe the features of demountable flood barriers
Demountable flood barriers provide temporary protection against floods and are put up when a flood is forecast.
Pros: provide temporary protection from flood , dont ruin scenery and environment permanently
Cons:May not be put up in time, expensive
Hard engineering
Describe the features of flood barriers
Flood barriers are built in river estuaries to stop flooding during high tides or storm surges
Pros: can be shut during storm surges, protect large areas
Cons:Expensive, ugly
Hard engineering
What are the features of flood plain retention
Flood plain retention involves maintaining the floodplain and making sure it isn’t built on
Pros:Maintains flood plains ability to store water, relatively inexpensive, slows flood water down
Cons:Restricts development , not possible in urban areas
Soft engineering
What are the features of river restoration
River restoration involves removing any man made levees from the floodpain so the river can flood naturally
Pros:Stops flooding downstream as discharge is lower,no maintenance required
Cons:Can lead to local flooding
Soft engineering
What are the physical factors affecting the river Eden that could increase flood risk
- Cumbria is on the west coast and it faces the SW prevailing wind direction meaning it is wet and windy
- The area is one of the wettest in the UK and often experiences intense periods of rainfall
- The river is next to both the pennines and the lake district.Both these areas are made up of impermeable rock meaning there is high run off into the river
- There is high snowfall. Meltwater increases discharge
What are the human factors affecting the river Eden that could increase flood risk
- Carlisle is a built up area and there has been development on Eden’s floodplain
- There is a lack of Vegetation and soil. Meaning little infiltration or interception leading to high surface run off
- Woodland and heathland have been cleared , increasing runoff
- Parts of the Eden valley basin have been drained to make suitable farmland. Drainage ditches increase runoff into river channel
