Rivers Flashcards
Describe Lateral erosion
It widens the valley, dominant in the middle and lower courses.
Describe Vertical erosion
It deepens the valley, making it V-shaped. Dominant in the upper courses.
Name and describe the four processes of erosion.
Hydraulic action - Waves breaks rocks from the river channel
Abrasion - Rocks, picked up by the channel, rub against sides of the channel.
Attrition - Rocks, picked up and smashed together
Solution - River water dissolves some rocks (chalk)
Name and describe the four types of transportation.
Traction - Large particles are pushed along the river bed by the force of the wave.
Suspension - Small particles carried along by river
Saltation - Bounced along the riverbed by waves
Solution - Materials are dissolved and carried along
What does Transportation and deposition mean?
Transportation - The movement of eroded material
Deposition - When a river drops eroded materials
How does a river slow down
Volume of water falls
Amount of eroded material in the water increases
Water is shallower
River reaches its mouth
Describe how meanders are formed
Formed by erosion and deposition.
Current faster on the outside. More erosion occurs on the outside forming river cliffs. It is slower on the inside, as it is shallower allowing material to be deposited.
How are ox-bow lakes formed?
Erosion causes the outside bend to get closer, until there is a bit of land left. The river breaks through the land and the river flows through the shortest course. Deposition cuts off the meander, forming an ox-bow lake.
How are waterfalls and gorges formed?
Area of hard rock then soft rock. The water flows through both areas eroding the soft rock creating a step. As more rock is eroded the step gets bigger. Creating a waterfall. Eventually the hard rock is undercut by erosion and can no longer support it, collapsing. After more undercutting/collapsing the waterfall will retreat.
What is a flood plain?
A wide valley floor that gets flooded. When the river floods is deposits materials, building up the land.
What are levees?
These are natural embankments along the river. During a flood the heaviest materials are deposited, as it gets dropped first. Overtime the material builds up.
What is river discharge?
The volume of water flowing in a river
Describe a hydrograph
Peak discharge - Highest discharge in a period Lag-time - Time between peak rainfall/discharge Rising limb - The increase in river discharge as rainwater flows into the river. Falling limb - The decrease in river charge, as it returns to normal level.
What 6 things affect river discharge
Rainfall - Amount and time periods (runoffs)
Previous weather conditions - Lots of rain saturated soil no infiltration into the soil (runoff)
Land use - Urban areas have drainage, impermeable materials.
Temperature - Hot, dry, cold result in hard ground
Rock type - Impermeable decrease Permeable increase
Relief - Height of the land, lag time decre dis incre
What are the four physical factors affecting flooding?
Prolonged rainfall - Soil becomes saturated no infiltration increasing discharge.
Snowmelt - When snow/ice melts lots of water goes into the river increasing discharge quickly.
Heavy Rainfall - A lot of runoff increasing discharge
Relief - A steep valley water will run faster
increasing discharge vice versa.
