🌀 FLUVIAL LANDFORMS: MIDDLE COURSE
PAGE 1 OF 5 — THE RIVER MATURES
MIDDLE COURSE
FROM YOUTH TO MATURITY
The middle course lies downstream of the steep upland upper course you studied in Topic 10. Here the river's gradient becomes gentler, so velocity falls and the channel begins to widen rather than deepen. Lateral erosion (sideways cutting) replaces vertical erosion as the dominant process. The river erodes its outer banks and deposits sediment on inner bends, building a flat floodplain on either side. Discharge is higher than upstream because tributaries have joined the main channel. On the Bradshaw Model, this is the maturity stage: lower gradient, smoother flow, and a mix of erosion and deposition. Landforms such as meanders and eventual oxbow lakes characterise this section. The river is still eroding overall, but it now shapes the landscape sideways as well as downward.
↔️ LATERAL VS VERTICAL
In the upper course, vertical erosion deepens the valley. In the middle course, lateral erosion widens the channel and floodplain while meanders migrate across the landscape.
MATURE!
GENTLER GRADIENT
- A gentler gradient means the river loses height slowly over distance, reducing flow velocity compared with the upper course.
- Lower velocity means less energy for vertical downcutting and more time for sideways erosion on bends.
- Increased discharge from tributaries gives the river volume to transport finer sediment by suspension.
FLOODPLAIN
- A floodplain is the flat land beside a river, built up by repeated deposition when the channel overflows in flood.
- Floodplains are often fertile farmland because fresh silt and clay enrich the soil after each flood event.
- The floodplain widens as meanders migrate and eroded material is spread across the valley floor.