Rivers from source to sea
Geography · Key Stage 2 · The School
The journey
A river starts at its SOURCE, usually high ground. The narrow fast part near the top is the UPPER COURSE. It widens through the MIDDLE COURSE, meanders across flatter land in the LOWER COURSE, and reaches the sea at its MOUTH. Each part looks and behaves differently.
Three things a river does
EROSION: it wears away rock, most powerfully near the fast upper course. TRANSPORT: it carries the material downstream. DEPOSITION: it drops that material where it slows, which is why the lower course has mud banks and the mouth often has a delta. One river doing three jobs in different places.
Meanders and floods
On flat land a river swings in wide curves. The outside of a bend flows faster and erodes; the inside is slower and deposits. Over years the bends move. When heavy rain sends more water than the channel can hold, it spills onto the FLOODPLAIN — which is exactly what a floodplain is for, and why building on one is a decision with consequences.
UPPER COURSE: steep, narrow, fast over boulders. Erosion is downwards, cutting a V-shaped valley with waterfalls. MIDDLE: the valley widens, the river meanders, eroding the outside bends and depositing on the inside. LOWER: wide, slow, carrying fine silt, building a floodplain and often a delta. Same water; what changes is gradient and load, and everything else follows from those two.