Rivers and their landforms
Geography · Key Stage 3 · The School
Three processes
A river ERODES — wears material away; TRANSPORTS it downstream; and DEPOSITS it when it slows. Which dominates depends on speed and volume. Fast upper courses erode, cutting steep V-shaped valleys; slow lower courses deposit, building flat land. Every river landform is one of these three processes acting where conditions favour it.
Meanders
Water flows fastest on the OUTSIDE of a bend, so it erodes there, cutting a steep river cliff. On the inside it slows and deposits, building a shallow slip-off slope. That asymmetry makes the bend grow, so meanders migrate sideways over time. If a neck is eventually cut through, the loop is abandoned as an oxbow lake.
Floodplains
When a river overflows, the water slows abruptly and drops its load, laying fine silt across the valley floor. Repeated over centuries this builds a FLOODPLAIN — flat and unusually fertile, which is why so many settlements sit on them. The same process that makes the soil good is the flooding that makes building there a risk, and the two cannot be separated.
Water flows fastest on the OUTSIDE of a bend, so it erodes there, cutting a river cliff. On the inside it is slow, so it deposits, building a slip-off slope. Year by year the bend gets tighter and migrates sideways. Eventually the neck of the loop is so narrow that a flood cuts straight across it, the loop is abandoned, and it becomes an OXBOW LAKE. The whole sequence follows from where the water is fastest.