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:
- Youthful stage (Upper)
- Mature Stage (Middle)
- Old stage (Lower)
| Youthful Stage | Mature stage | Old stage | |
|---|---|---|---|
| Gradient | Steep | Gently sloping | Levelling off |
| Speed | Fast-flowing | Starts to slow down | Slow-moving |
| Water quantity | Low volume | Higher volume | Largest volume |
| Erosion/deposition | Erosion | Erosion and deposition | Deposition |
| Characteristics | SteepV-Shaped valleyNarrowShallow channelHigh level of material on river bed | OpenGently sloping valley with a flood plainWiderDeeper channelSuspended sediment | Flat and wide flood plainVery wide and deepHigh levels of suspended suspended |
| Landforms | V-shaped valleyInterlocking spursWaterfalls | MeandersOxbow lakes | Flood plaindLevees |
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 riverās 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 āVā
- 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