Rivers Flashcards
What is a river
A river is fresh water flowing across the surface of the land, usually to the sea. It flows in a channel. The bottom of the channel is called the bed and the sides of the channel are called the banks.
Where do rivers begin?
Rivers begin at their source in higher ground such as mountains or hills, where rain water or melting snow collects and forms tiny streams.
How are rivers formed?
When one stream meets another and they merge together, the smaller stream is known as a tributary. It takes many tributary streams to form a river.
What do rivers provide?
Most settlements were built along major rivers. Rivers provide us with food, energy, recreation, transportation routes, and of course water for irrigation and for drinking.
Rainfall and melting and snow
Some rivers begin in mountains or hills, where rain water or snowmelt collects and forms small channels, . At first, the channels are small and are called rills. As more water enters the channels they grow forming gullies (larger channels). The streams in the gullies eventually become big enough to form a river.
Meanders
As the river makes its way to the middle course, it gains more water and therefore more energy. Lateral erosion starts to widen the river. When the river flows over flatter land they develop large bends called meanders.
Hydraulic action
Erosion caused by the force of river water hitting cracks in the side of the river bank. The air in the cracks becomes compressed and then explodes outwards, breaking off bits of rock.
Abrasion
When rocks carried by the sea water wear away the landscape, eg cliff face/headland.
River cliff
Steep bank created on the outside of a river bend by the erosive effect of fast-flowing water undercutting the bank.
Slip-off slope
Gently sloping bank found on the inside of a river bend because of slow-flowing water, depositing sediment.
Middle course
The middle section of a river which has sloping land.
Lateral erosion
The wearing away of the landscape when a river erodes sideways.
Discharge
The volume of water in a river passing a point in a given time. Measured in cumecs (cubic metres per second).
Step 1 on formation of a meander
As a river goes around a bend, most of the water is pushed towards the outside. This causes increased speed and therefore increased erosion (through hydraulic action and abrasion).
Step 2 on formation of a meander
The lateral erosion on the outside bend causes undercutting of the bank to form a river cliff.
Step 3 on formation of a meander
Water on the inner bend is slower, causing the water to slow down and deposit the eroded material, creating a gentle slope of sand and shingle.
Step 4 on formation of a meander
The build-up of deposited sediment is known as a slip-off slope (or sometimes river beach).
