Water on The Land Flashcards
What is a river’s course?
The path of the river as it flows downhill
Describe the valley and channel shape in the UPPER COURSE:
V-shaped valley, steep sides. Narrow, shallow channel
Describe the valley and channel shape in the MIDDLE COURSE:
Gently sloping valley sides. Wider, deeper channel
Describe the valley and channel shape in the LOWER COURSE:
Very wide, almost flat valley. Very wide, deep chanel
What effect does vertical erosion have?
It deepens the river valley and channel, making it V-shaped. Dominant in the upper course.
What effect does lateral erosion have?
Widens the river valley and channel. Dominant int he middle and lower course.
What are the 4 processes of erosion?
Hydraulic Action, Solution, Abrasion and Attrition
What are the 4 methods of transportation?
Traction, Solution, Saltation and Suspension
What is Hydraulic Action?
The force of the water breaks rocks and particles away from the river channel
What is Solution?
River water dissolves some times of rock, and carries the dissolved particles with it
What is Abrasion?
Eroded rocks picked up by the river scrape and rub against the channel, wearing it away.
What is Attrition?
Eroded rocks picked up by the river smash into each other and break into smaller fragments. Their edges are also rounded off.
What is Traction?
Large particles like boulders re rolled along the river bed by the force of the water.
What is Saltation?
Pebble sized particles are bounced along the river bed by the force of the water
What is Suspension?
Small particles like silt and clay are carried along by the water
What is deposition?
When a river drops eroded material as it looses velocity and energy
What causes a river to slow down enough for deposition to occur?
- The volume of water in the river decreases
- The amount of eroded material in the river increases
- The water is shallower
- The river reaches its mouth
What are meanders?
Large bends in the rivers middle or lower course
What are the 2 main features of a meander bend?
River cliff and slip off slope
How are the features of a meander formed?
- The current is faster on the OUTSIDE of the bend because the river channel is deeper there
- More erosion takes place on the outside of the bend, forming a river cliff
- The current is slower on the inside of the bend, because the water is shallower and slower
- More deposition occurs, forming a slip off slope
Why does more erosion occur on the outside of a meander bend?
The river channel is deeper, so there is less friction to slow the water down and more erosion takes place via hydraulic action
How are ox bow lakes formed?
- Erosion on the outside bends cause them to get closer, forming a neck of the meander
- The river breaks through the neck, usually during a flood
- The river flows it shortest course
- Depostion eventually cuts of the meander completely, and the ends of the oxbow lake will dry up over time
Name 4 more river landforms:
- Waterfalls
- Gorges
- Levees
- Floodplains
How are waterfalls formed?
- A band of hard rock and a bad of soft rock must lay parallel to each other for a waterfall to form
- The soft rock is eroded ore than the hard rock, creating a ‘step’ in the river
- The water flows over the step, leading to more erosion of the soft rock
- A steep drop is eventually created, and the hard rock is undercut by erosion
- The hard rock is unsupported and collapses. A plunge pool is also formed by erosion
- After more undercutting and more collapses, the waterfall retreats and a gorge is formed
Where are waterfalls found?
In the upper course
What do contour lines on a map tell you about a river?
Which direction it flows in
What evidence could there be on a map to show a river is in its upper course?
- Nearby high land
- It crosses a lot of contour lines in a short distance, meaning it’s steep
- The river is narrow
- The contour lines are close together and the valley floor is narrow
How is a waterfall marked on a map?
With a label, but the cliff symbol and close contours are evidence for one
What evidence is there for a river in its lower course on a map?
- Low nearby land
- River only crosses a few contours
- Joining a sea or lake
- The river is wide (thick blue line)
- The river meanders
What is river discharge?
The volume of water flowing in a river
What is discharge measured in?
Cumecs: m3/s
What do hydrographs show?
How the discharge at a certain point in a river changes over time
What is peak discharge?
The highest discharge in the period of time you’re looking at
What is lag time?
The delay between peak rainfall and peak discharge
What is a rising limb?
The increase in river discharge as rainwater flows into the river
What is a falling limb?
The decrease in river discharge as the river returns to its normal level
How is discharge affected by the amount and type of rainfall?
Lots of rain in short, heavy periods of rainfall means there’s more runoff. Lag time is decreased, so discharge increases
How is discharge affected by temperature?
Hot, dry condition and cold, freezing conditions both result in hard ground - this increases runoff. Lag time is decreased, so discharge increases
How is discharge affected by previous weather conditions?
After lots of rain, soil can become saturated, so can’t absorb any more water. Runoff will increase and lag time will decrease, so discharge increases
How is discharge affected by rock type?
Water infiltrates through porous rocks and flows along cracks in previous rocks, so there isn’t much runoff. Lag time increased, so discharge decreases. Opposite for impermeable rock
How is discharge affected by land use?
Urban areas have drainage systems and are covered with impermeable surfaces, increasing runoff. Lag time is decreased, so discharge increases
How is discharge affected by relief?
Lots of runoff occurs on steep slops. Lag time decreased, discharge increased
