Rivers *

Key Words

• $Source$: The $beginning$ or start of a river
• $Course$: The $route$ a river takes to the sea
• $Confluence$: The point at which two rivers or streams $join$ together
• $Tributary$: A stream or $smaller river$ that flows into a larger stream or river
• $Mouth$: The point where a river comes to the $end$, usually when entering the sea
• $Drainage basin$: The area of land $drained$ by a river
• $Watershed$: The area of $high ground$ which $separates$ two drainage basins
• $Estuary$: The part of a river mouth that is $tidal$
• $Surface processes$: the ways in which $weathering$ and erosion create different features on the Earth's surface, and so shape the landscape.

Stages of a river

A number of $surface processes$ take place on rivers. These surface processes create many $features$ along the route of the river.

The river course can be divided into $three$ stages that reflect the change in $gradient$ (slope) from the river's $source$ high up in the mountains to its $mouth$ at sea level. The three stages are:

1. Youthful stage (Upper)
2. Mature Stage (Middle)
3. Old stage (Lower)

The work of rivers

Erosion

Hydraulic Action

• The physical force of moving water erodes pieces of rock from banks and beds of river.
• The eroded material is transported down through river’s course => load

Abrasion

• The load erodes and wears away riverbed and banks
• This deepens and widens river channel

Solution

• The river water dissolves rock particles

Attrition

• The load is also in collision with itself
• Pebbles and stones rub against one another and are worn down and smoothened

Transportation

Traction

• Larger stones are rolled along the riverbed

Saltation

• Smaller pebbles bounced along riverbed

Suspension

• Light materials => sand + silt => float along water

Solution

• Materials dissolve in water

Deposition

Deposition: dropping of the load

• Shapes the land => leaves sediment in new places

Rivers deposit their load when:

• They lose speed
• There is a reduction in waters
• They flow into a lake or sea
• The slope of river is reduced

River landforms

Youthful stage

• V-shape valleys: a steep-sided valley in the shape of ‘V’
• Interlocking spurs: areas of high ground that jut out at both sides of the V-shaped valley
• Waterfalls: a vertical drop in a river

V-shape valley

Mature stage

• Meanders: curves or bends in a river
• Oxbow lakes: a horseshoe shaped lakes

Oxbow lake

The old stage

• Flood plains: wide + flat area at either side of a river
• Levees: build up of alluvium on the banks of a river
• Deltas: a triangular shapes area of land at the mouth of a river

Levee