Rivers Flashcards
What is the river course
The path of the river as it flows downhill
Where is the upper course
Closest to the source of the river
Where is the lower course
Closest to the mouth of the river
How do rivers form channels and valleys
- The ERODE the landscape
- They transport the material somewhere where it is deposited
- The shape depends on whether erosion or deposition has the most impact
Upper course properties
- Steep
- V-shaped valley, steep sides
- Narrow, shallow channel
Middle course properties
- Medium
- Gently sloping sides
- Wider, deeper channel
Lower course properties
- Gentle
- Very wide, almost flat valley
- Very wide, deep channel
Vertical erosion
- This DEEPENS the river valley, making it a V-SHAPED valley
- Dominant in the UPPER course of the river
Lateral erosion
- This WIDENS the river valley
- Dominant in the MIDDLE and LOWER courses
Name the four process of erosion
- Hydraulic action
- Abrasion
- Attrition
- Solution
Hydraulic action
The force of water breaks rock particles away from the river channel
Abrasion
Eroded rocks picked up by the river SCRAPE and RUB against the channel, wearing away.
Most erosion happens by abrasion
Attrition
Eroded rocks picked up by the river SMASH into each other breaking into smaller fragments.
The edges are rounded off as they rub together
Solution
River water DISSOLVES some type of rocks e.g. chalk and limestone
Name the four processes of transportation
- Traction
- Saltation
- Suspension
- Solution
Traction
Large particles (like boulders) are PUSHED along the river bed by the water FORCE
Saltation
PEBBLE sized particles are BOUNCED along the river bed by the water FORCE
Suspension
SOLUBLE materials DISSOLVE in the water and are CARRIED along
Solution
River water DISSOLVES some type of rocks e.g. chalk and limestone
When does deposition happen and why
- When a river drops eroded material
- Happens when a river slows down (loses velocity)
Why do rivers slow down and deposit material
- Volume of water falls
- Amount of eroded material in the water increases
- Water is shallower e.g. inside of a bend
- River reaches the mouth
What happens when a river is eroding and depositing material
Meanders and ox-bow lakes
Where are meanders found
In the middle and lower courses
Formation of a meander
- The water current flows faster on the outside of the bend, because the river channel is deeper (less friction to slow water down)
- More erosion on the outside of the bends, forming river cliffs
- Current is slower on the inside bend (channel is slower) More friction -> Slow water down
- Eroded material is deposited on the inside of the bend, forming slip-off slopes
Formation of an ox-bow lake
- Water flows in a corkscrew pattern causing lateral erosion. Erosion causes the outside bends to get closer
- Water flows fastest on the outside and slowest on the inside bends leading to deposition
- Two meanders will erode coming closer together The river breaks through this land, usually during a flood
- The river flows the shortest course
- Deposition eventually cuts of the meander, forming an ox-bow lake
Waterfalls and gorges are formed by what
Erosion
Formation of a waterfall and a gorges
- The river flows over the cliff of horizontal bands of soft and hard rock
- The soft rock is undercut by Hydraulic action and abrasion. A steep drop is created -> waterfall
- Eventually the soft rock erodes so much that the more resistant rock is left unsupported.
- This rock will eventually fall, the erode the softer rock by abrasion forming a plunge pool at the base of a cliff
- Overtime the cliff will retreat backwards and the process repeats forming a gorge
Where are waterfalls and gorges found
The upper course of the river
How are flood plains and levees formed
By deposition
Formation of a flood plain
- The wide valley floor gets flooded
- The water slows down on the flood plain and deposits the eroded material that its transporting -> Builds up the flood plain
- Meanders migrate (move) across the flood plain making it wider
- Deposition that happens on the slip-of slopes of meanders also build up the flood levees
Formation of levee’s
- During a flood, eroded material is deposited over the flood plain
- The heaviest material is deposited closest to the river channel (dropped first) when the river slows down
- Over time the deposited material builds up creating levee’s along the edges of the channel
What is river discharge
The volume of water flowing in a river
What is river discharge measured in
Cumecs
What do Hydrographs show
How the discharge at a certain point in a river changes over time
Peak discharge
The highest discharge in the period of time your looking at
Lag time
The delay between peak rainfall and peak discharge
Rising limb
The increases in river discharge as rainwater flows into the river
Falling limb
The decrease in river discharge as the river returns to its normal level
Why does lag time happen
Most rainfall doesn’t land directly in the river channel
Gets there by surface run off or infiltration
Surface run off
If the ground is hard already saturated, no more rain can infiltrate so it travels over the lands surface to the sea
Infiltration
When water soaks into the sea
Ground water flow
Infiltrated water flowing through solid rock, to the sea
Through flow
Water travelling through the soil
Interception
Trees catching rainfall before it reaches the ground
What is river discharge affected by
- Amount/ type of rainfall
- Temperature
- Previous weather
- Rock type
- Land use
- Relief (how the height of the land changes)
Amount/type of rainfall as a factor
Lots of rain and short, heavy periods of rainfall means more surface run off. Lag time DECREASES and so discharge INCREASES
Temperature as a factor
Hot, dry conditions and cold, freezing both result in HARD ground -> Increases run off -> Lag time is DECREASED, so discharge INCREASES
Previous weather as a factor
After lots of rain, soil becomes saturated. More rainwater wont be able to infiltrate in to soil -> Runoff will INCREASE -> Lag time is DECREASED, so discharge INCREASES
Rock type as a factor
Water infiltrates through pore spaces in PERMEABLE rock and flows along cracks in previous rocks -> Not much runoff -> Lag times INCREASES -> Discharge INCREASES Water cant infiltrate into IMPERMEABLE rock -> A lot of runoff -> Lag time DECREASES -> Discharge INCREASES
Land use as a factor
Urban areas have drainage systems and are covered with impermeable materials
- > INCREASES runoff
- > Lag time DECREASES
- > Discharge INCREASES
Relief as a factor
LOTS of runoff occurs on STEEP SLOPES
- > Lag time DECREASES
- > Discharge INCREASES
