From Source to Sea
Follow one river the whole way and the changes are systematic: steeper and rockier near the source, wider and slower near the mouth. That pattern is why upland and lowland landscapes look so different.
What a learner can do afterwards
- Describe how width, depth, gradient and load change between source and mouth
- Match three landforms to the part of the course where each is usually found
- Explain why a river usually gets faster downstream even though the slope gets gentler
1 · Read
Every river starts at a source, often high in the hills, and ends at a mouth where it meets the sea, a lake, or a larger river.
Upstream the channel runs narrow, shallow and steep over stones where fast water wears rock away. Downstream it grows wide, deep and gentle, carrying fine mud. Deeper water passing more each second usually runs faster despite a gentle slope, but flat lower reaches can slow.
Small streams called tributaries join along the way and add their water. When two channels match in size, shape, slope, and bed with equal water-filled space, the one passing more water each second usually flows faster. A dam stores and releases water on its own schedule, so the timing and size of flow below can shift.
Where a river meets still water it slows, and dropped mud can build a fan called a delta.
From source to sea the channel often widens and deepens. Deeper flow with more water each second usually runs faster despite a gentle slope, but flat lower reaches can slow. With matching size, shape, slope, and bed, the flow passing more water each second usually runs faster.
2 · Watch
Take it off screen
Where it sits
Learn first
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.