The Journey of a River
Every river has a start, a middle, and an end. Understanding each part helps us explain the different features (landforms) found at each stage.
- Source: where the river begins — often a spring, snowfield, lake, or area of high rainfall on a hillside or mountain
- Mouth: where the river ends — it flows into the sea, a large lake, or another river
The Upper Course
Near the source, the land is steep. The river:
- Is narrow and shallow
- Flows fast, but carries little water
- Erodes the riverbed downwards (vertical erosion), cutting a V-shaped valley
- Forms features like waterfalls and gorges
The Middle Course
As the river moves into gentler land:
- Widens and deepens
- Erodes the banks sideways (lateral erosion)
- Forms sweeping bends called meanders
- Tributaries join, adding more water
The Lower Course
Near the mouth, the land is nearly flat:
- River is wide and slow
- Carries large amounts of sediment
- Deposits sediment (silt) on the valley floor, creating a flood plain
- May form a delta where it enters the sea (wide, fan-shaped deposit of sediment)
- The widening zone where fresh and salt water mix is called an estuary
A drainage basin is the total area of land that drains into a river. All the rainwater falling in that area eventually flows into the river (unless it evaporates or is absorbed into the ground). The boundary of a drainage basin is called the watershed.
Major Rivers and Their Mouths
| River | Source | Mouth |
|---|---|---|
| Nile | Lake Victoria, East Africa | Mediterranean Sea, Egypt |
| Amazon | Andes, Peru | Atlantic Ocean, Brazil |
| Thames | Cotswold Hills, England | North Sea, Essex/Kent |
| Mississippi | Lake Itasca, Minnesota, USA | Gulf of Mexico |
Long profile: if you plotted a side view of a river from source to mouth, the slope would be steep at the source and nearly flat at the mouth. This is called the long profile and it shows how the river's energy and processes change along its course.
Real world: The Amazon — the world's mightiest river
The Amazon begins in the Andes mountains of Peru at over 5,000 m altitude — its source (the Apacheta River) is a spring on a snowy mountain. Over 6,400 km later, it drains into the Atlantic Ocean in Brazil through a mouth so wide (up to 325 km) that early European explorers thought they had reached a new sea. On the way it collects over 1,000 tributaries and carries 20% of all the fresh water that flows into the world's oceans.
Real world: The Thames from Cotswolds to London
The Thames begins as a trickle from a spring in the Cotswold Hills in Gloucestershire — you can step over it at the source. By the time it reaches Oxford it is wide enough for rowing, and by London it is a major shipping route over 200 m wide. Near its mouth, it becomes tidal — the Thames Estuary stretches 100 km into the North Sea, mixing salt and fresh water. This source-to-mouth journey is only 346 km long, but every river feature (V-valley, meanders, floodplain, estuary) appears in sequence.
Real world: The Nile — longest river, life-giving source
The Nile's most distant source was not confirmed until modern exploration — it is a stream in Burundi/Rwanda feeding into Lake Victoria, which feeds the White Nile. The Blue Nile, from Lake Tana in Ethiopia, carries most of the water. Together they join near Khartoum, Sudan, and flow north through desert for 3,000 km before reaching the Mediterranean. Without the Nile's source waters, Egypt would be almost entirely uninhabitable.
Where do you see this in real life? Look up your nearest river on a map. Can you find where it starts (its source in the hills or springs) and where it ends (its mouth at the sea or another river)? Trace its full journey and notice how it changes shape along the way.