Uk Physical 2 - Rivers Flashcards
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
