Floodplains and Levées
Part of River Processes and Landforms — GCSE Geography
This deep dive covers Floodplains and Levées within River Processes and Landforms for GCSE Geography. Revise River Processes and Landforms in Physical Landscapes in the UK for GCSE Geography with 15 exam-style questions and 22 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 9 of 18 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 9 of 18
Practice
15 questions
Recall
22 flashcards
🌿 Floodplains and Levées
The floodplain is the flat, wide valley floor that flanks the lower course of a river. Far from being a dangerous accident of nature, it is an entirely predictable product of thousands of years of river activity — and one of the most agriculturally productive landscapes in the UK.
How Floodplains Form
Floodplains form by two processes working together over long timescales:
- Lateral meander migration — as meanders erode their outside banks and migrate across the valley, they gradually plane off the valley floor, creating a flat, wide surface. The river works across its own floodplain over centuries, reworking the entire width.
- Overbank flooding and alluvium deposition — when the river overtops its banks during high discharge, it spreads across the floodplain. The sudden drop in velocity causes deposition of alluvium (fine silt and clay). Each flood adds a thin layer of sediment to the floodplain surface. After thousands of floods, a deep, extraordinarily fertile layer of alluvial soil has accumulated. This is why floodplains are prime agricultural land — the Thames Valley, the Vale of York, and the Somerset Levels are all built on flood deposits.
How Levées Form
Levées are natural embankments of sediment that build up alongside the river channel on the floodplain. They form through a selective deposition process during flooding:
As the river floods, it immediately loses velocity as it spreads out across the floodplain — the shallow flood water moves much more slowly than the main channel flow.
The biggest, heaviest particles in the load require the highest velocity to be transported. They are the first to be deposited, immediately beside the channel where the velocity drop is sharpest. This coarse sediment builds up closest to the river.
Very fine particles — silt and clay — remain in suspension even in slow-moving floodwater, and are deposited further from the channel across the wider floodplain.
With each successive flood, more coarse material is deposited alongside the channel. Over time, these natural embankments — levées — can rise 2–5 metres above the surrounding floodplain, raising the river bed above the level of the land on either side. This creates a dangerous situation: if the levée is breached, the flooding is sudden, deep, and extensive because the land behind the levée is lower than the river.
Levées are found beside many UK lower-course rivers, including sections of the River Severn and River Thames. Human engineers often strengthen natural levées with earth embankments and concrete flood walls to improve flood protection.