Key Stage 3 geography · Physical geography

KS3 rivers, drainage basins and flooding: a guide for parents

In Key Stage 3, pupils study hydrology, which is how water moves through the environment, and how rivers shape the land. They learn the drainage basin as a system, the processes of erosion, transport and deposition, the landforms along a river’s course, and why rivers flood and how people manage that risk. It matters because flooding affects thousands of homes in the UK, and the topic shows how physical processes and human decisions interact.

Rivers and drainage basins, explained

The study begins with the water cycle and the idea of a drainage basin, the area of land drained by a river and its tributaries. Pupils learn that a drainage basin is a system with inputs (rainfall), stores (such as soil, rock, lakes and vegetation), flows (surface runoff, infiltration, throughflow and groundwater flow) and outputs (evaporation, transpiration and the river reaching the sea). The edge of the basin is the watershed. Seeing the basin as a system helps pupils to predict how a change, such as cutting down trees or building roads, would alter how fast water reaches the river.

Rivers do three jobs. Erosion wears away the bed and banks through hydraulic action (the force of water), abrasion (rocks scraping), attrition (rocks knocking together and becoming smaller and rounder) and solution (dissolving). Transport moves material by traction (rolling), saltation (bouncing), suspension (carried within the water) and solution. Deposition happens when the river loses energy, for example when it slows or the water level falls, and it drops its load. Larger stones are dropped first and fine silt last.

Along a river’s course, from source to mouth, these processes produce a pattern of landforms that pupils learn to link to the long profile. In the upper course the river is steep and cuts downwards, making V-shaped valleys, interlocking spurs, rapids and waterfalls. In the middle course it cuts sideways and forms meanders, bends that migrate across the valley, and sometimes oxbow lakes when a meander is cut off. In the lower course the river is wide and slow, and deposits sediment to form a floodplain and levees. Where it meets the sea it flows into an estuary, or in some places builds a delta. The programme of study does not name a river, so schools choose one, often a river near them or a well-known example such as the River Tees.

The study of flooding usually brings in the storm hydrograph, a graph showing a river’s discharge over time after a storm. Pupils learn to read the lag time between peak rainfall and peak discharge, and the rising and falling limbs. A short lag time and a high peak make flooding more likely. Physical factors include heavy rain, steep slopes, impermeable rock and saturated soil. Human factors include building on floodplains, covering land with tarmac and concrete, and removing trees. Management falls into hard engineering, such as dams, embankments and channel straightening, and softer approaches, such as planting trees, restoring wetlands, floodplain zoning and natural flood management.

Pupils are expected to look at real places. Schools choose the case studies, and many compare a flood event in a high-income country with one in a low-income country, to consider impacts and responses. The aim is to show how complex systems interact, and to judge who gains and loses from each decision. For example, protecting a town with a wall can increase flood risk further downstream.

Words your child will hear

Drainage basin: The area of land drained by a river and its tributaries.
Watershed: The boundary of high ground between two drainage basins.
Tributary: A smaller river that flows into a larger one.
Confluence: The point where two rivers meet.
Discharge: The volume of water passing a point in a river each second.
Meander: A bend in a river that becomes more curved over time as the outside is eroded and the inside is built up.
Floodplain: The flat land either side of a river that floods when the river overflows.

What the National Curriculum says

The programme of study for Key Stage 3 says:

Pupils should be taught to understand, through the use of detailed place-based exemplars at a variety of scales, the key processes in physical and human geography
Physical geography relating to: geological timescales and plate tectonics; rocks, weathering and soils; weather and climate, including the change in climate from the Ice Age to the present; and glaciation, hydrology and coasts
Pupils should become aware of increasingly complex geographical systems in the world around them.

Objectives from the National Curriculum in England, © Crown copyright, used under the Open Government Licence v3.0.

A model answer: why do towns flood faster than countryside?

Explain why a river flowing through a large town may flood more quickly after heavy rain than a river in open countryside.

Identify the surfaces. In a town, roofs, roads and car parks are impermeable, which means water cannot soak into the ground. In the countryside, grass and soil are permeable and water can infiltrate.
Explain what happens to the rain. In the town, water runs over the surface as surface runoff, which is the fastest route to the river. In the countryside, much of it soaks in and moves slowly through the soil.
Add drains. Town drains and gutters send water straight to the river through pipes. Plants also intercept rainfall and take up water, and the town has fewer of them.
Link to the hydrograph. More water reaches the river in a shorter time, so the lag time is short and the peak discharge is high.
Conclude. A high, quick peak means the river is more likely to burst its banks soon after the rain starts, giving people less warning.

Impermeable surfaces and drains send rainwater rapidly to the river as surface runoff, instead of letting it infiltrate. This gives a short lag time and a higher peak discharge, so the river is more likely to flood, and sooner, than one in open countryside.

Common mistakes and how to help

Thinking rivers always flow from north to south

Maps are drawn with north at the top, and pupils think of downhill as down the page.

What helps: Rivers flow from higher to lower ground, whatever the compass direction. Trace rivers on an atlas map. Many British rivers flow east or south-east, and some of the biggest in the world flow north.

Confusing erosion with deposition on a bend

Both happen on the same meander, so pupils reverse which bank does which.

What helps: On the outside of the bend the water is faster and deeper, so it erodes and makes a river cliff. On the inside it is slow and shallow, so it deposits material and makes a slip-off slope.

Believing floods are caused only by heavy rain

Rainfall is the visible trigger.

What helps: Land use, soil type, slope and drainage all change how fast water reaches the river. Ask what else about the place made the rain turn into a flood.

Thinking a bigger flood wall always solves the problem

It is the obvious solution to protect one place.

What helps: Walls and straightened channels can send water faster downstream and raise the risk there. Discuss the costs and who benefits, as an evaluation answer requires.

How to help at home

Make a miniature drainage basin. Crumple a large sheet of paper, flatten it slightly and draw over the ridges with a washable pen. Use a spray bottle of water and watch the ink run into valleys. The ink lines mark out the rivers and tributaries.
Test the surfaces. On a dry day, pour a jug of water onto a paved area and the same amount onto a lawn. Which one runs off, and which soaks in? Link what you see to infiltration, surface runoff and urban flooding.
Follow a river on a map. Use an atlas or a paper map to trace a local river from its source to the sea, naming tributaries and towns. Ask where the steepest part is and where you would expect meanders and a floodplain.
Visit a river safely. Stand on a bridge or a safe bank with an adult and look at the river’s width, speed and the size of the stones on the bed. Do not go in or near fast water. If possible, compare an upland stretch with a lowland one.
Talk about local flood risk. Ask your child where water would go in a heavy storm near your home, such as down the road or into drains. Discuss what could reduce the risk, such as planting trees or using permeable paving.

Builds on

Key Stage 2: Climate zones, biomes and vegetation belts
Key Stage 2: Rivers and the water cycle
Key Stage 2: Mountains
Key Stage 2: Volcanoes and earthquakes
Key Stage 2: Settlements and land use
Key Stage 2: Economic activity and trade
Key Stage 2: Natural resources