2.2 Rivers Flashcards
Erosion:
Wearing away of the Earth’s surface by a moving agent, such as a river, glacier, or the sea
Discharge:
The volume of water passing a certain point per unit of time.
Expressed in cubic metres per second
Drainage basin:
an area of land where water from rain or snow melt drains downhill into a body of water
Tributary:
A stream or river that joins a larger river
Confluence:
The point at which two rivers meet
Watersheds:
A ridge or other line of separation between two river basins
Groundwater:
Water stored underground in a permeable rock
Hydrological Cycle
1) Input
- precipitation
-> Water that falls to the Earth from the atmosphere. (Rain, snow, hail..)
2) strorage
- interception
-> The precipitation that is collected and stored by vegetation
3) transfer
- infiltration
-> The movement of water into the soil.
- surface runoff
-> Overland movement of water after rainfall
- Throughflow
-> Refers to when water flows through the soil in natural pipes
4) output
- evaporation
-> The process in which a liquid turns into a vapour
- transpiration
-> The process in which the plants lose the water.
Types of erosion
- Abrasion: When the rocks (loads) grind along the river bank/bed which wears it away
- attrition: When loads in the river knock against each other, they break apart to become smaller loads and more rounded
- hydraulic action: The force of air and water on the cracks on the sides of rivers, causing the crack to increase in pressure and explodes
- solution: When river water reacts chemically with the loads and the minerals they contain, and dissolves them
Types of transportation
- suspension: Small loads are held up by the flow in the river
- saltation: Heavier loads are bounced or bumped along the river bed
- solution: The chemical load is dissolved in the water
- traction: The heaviest load is dragged or rolled along the river bed
Deposition
- Deposition occurs as a river slows down and has less energy
- The larger and heavier loads are deposited first, then the smaller and lighter ones later
V- shaped valleys
- occur in the upper course
- V-shaped valleys are when the slopes are steep. This is because vertical erosion takes place in the upper course of a river due to large loads being moved around by traction and the rivers are shallow and fast-flowing. This erodes the river bed and causes a v-shaped
Waterfalls and gorges
- occur in the upper course
- Waterfalls form as the river flows from a soft rock to a hard rock. The soft rock lies below the hard rock and the soft rock erodes, therefore causing an undercut
- The falling water from the river falls into the plunge pool and erodes the soft rock underneath the hard rock further by hydraulic action - the plunge pool then gets deeper
- The overhang of hard rock will eventually fall due to gravity. The waterfall then ‘retreats’ upstream leaving a gorge
Rapids
- occur in the upper course
- Rapids are fast-flowing water formed when the river flows over and of less-resistant and more-resistant rocks. The less-resistant rocks erode at a greater rate than the more-resistant rock making the river steeper and faster flowing
Interlocking spurs
- occur in the upper course
- Interlocking spurs are usually found with V-shaped valleys
- There will be bands of hard rock and soft rock. Where there are bands of hard rock which are harder to erode, the river will flow around these
- The bands of more-resistant rocks are called spurs and they form interlocking spurs
Potholes
- found in upper course
- Potholes are caused by hydraulic action and abrasion from loads in the river bed
- River currents trap the loads and the water swirl the trapped loads and causes erosion
Meanders:
- In the middle course, the river channel is wider and flatter.
- A meander is a bend in a river channel. It occurs due to the difference in river water speed
- Meanders form when the water in the river erodes the bank on the outside of the channel and deposits the load in the inner bank
Oxbow lakes
- in the middle course
- Oxbow lakes are the results of of erosion and deposition
- Oxbow lakes occur where there’s a meander
- Whenever there’s a flood in the river, the river water will always try to take the straightest route through the river. This means the river water will cut through the meander and flow through a straight line. The river water will then deposit its load to close off the meander, thereby forming an oxbow lake
Levées
- in the lower course
- A levées is a natural or artificial wall on the edge of the river that blocks water from overflowing
- Natural levées occur when load is deposited at the edge of the river.
-> This raises the height of the river channel and reduces risk of flooding - artificial levées could be made out of concrete
Floodplains
- in lower course
- Floodplains are the low-lying flatland next to a river/levées which is prone to flooding
- reduce risk of flood
River opportunities
- Rivers can be used to generate electricity
- to transport goods and people around
- The floodplains are flat, easy to build constructions
- the land is fertile
- rivers are a source of food
River hazards
- Erosion of river - this will lead to loss of farmland and housing. This will also destroy corps
- floods- loss of crops and infrastructure
- increase risk of water-borne diseases
