Rivers and flooding

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The Water Cycle and River Sources

The water cycle is the continuous movement of water around the Earth, and all river water ultimately comes from precipitation.
Precipitation reaches rivers as rainfall, runoff down slopes, melting of glaciers or snow, or seepage from underground aquifers.
The headwaters are the smaller streams that feed a river and make up its source; they may be small and flow rapidly down mountain sides.
Some water seeps into underground aquifers and can still feed rivers through the water table, which is why rivers can flow even during droughts.
Melting snow and glaciers in higher regions add water to rivers, especially in summer, helping to maintain a continuous supply downstream.

Drainage Basins and Watersheds

A drainage basin (or watershed) is all the land uphill of a river that feeds it with water.
Drainage divides are ridges of higher land that separate drainage basins; water on one side flows into one set of rivers, and water on the other side flows into another.
An example is the Continental Divide of the Americas in the Rocky Mountains: water on the western side flows into the Pacific Ocean, while water on the other side flows into the Atlantic Ocean.
Rivers flow in channelled watercourses and merge at confluences to form larger drainage basins.

River Processes: Erosion

Hydraulic action is the force of water against the river bed and banks, which can break off material.
Abrasion is when rocks and sediment carried by the river scrape and wear away the bed and banks.
Attrition is when rocks carried by the river collide and break into smaller, smoother pieces.
Solution is when acidic water dissolves certain types of rock, such as limestone.

River Processes: Transportation and Deposition

Rivers transport material in several ways: traction (rolling large rocks), saltation (bouncing small stones), suspension (fine particles carried in the water), and solution (dissolved material).
Deposition occurs when a river loses energy and drops its load, often where the flow slows down.
Material deposited by rivers is called alluvium (or sediment), and it can shape the landscape, forming deltas and islands where flow slows.
Rivers regularly overflow their banks and flood, spreading nutrients onto the surrounding land.

Landforms of the Upper Course

In the upper course, rivers often flow rapidly down steep slopes and erode vertically, creating V-shaped valleys.
A waterfall can form where a river flows over a vertical drop, often because softer rock erodes faster than harder rock, creating a step in the river's long profile.
Where a river carves through a plateau, a canyon can form, with cliffs on either side.

Landforms of the Middle and Lower Course

Rivers seldom run straight; they meander (bend), and the locations of their banks can change frequently.
Ox-bow lakes are formed when a meander is cut off from the main river channel.
Floodplains are flat areas of land next to a river that are built up by alluvium deposited during floods.
Deltas form at the mouth of a river where the flow slows and sediment is deposited, often creating new land.

Causes of Flooding

Flooding happens when a river overflows its banks and covers the surrounding land.
Heavy or prolonged rainfall can quickly add large amounts of water to a river.
Snowmelt in spring or summer can also increase river discharge.
Human activities such as urbanisation (which creates impermeable surfaces) and deforestation can increase flood risk by reducing infiltration and speeding up runoff.

Effects of Flooding

Flooding can spread nutrients onto floodplains, which can benefit agriculture.
However, floods can cause damage to homes, businesses, and infrastructure.
Floods can also lead to loss of life and displacement of people.
The effects of flooding can be social, economic, and environmental.

Flood Defences: Hard and Soft Engineering

Hard engineering involves building structures such as dams, levees, and canals to control rivers and prevent flooding.
Hard engineering can be effective but may be expensive and can harm river ecosystems by eliminating habitats and reducing the amount of alluvium flowing downstream.
Soft engineering works with natural processes, for example by restoring floodplains or planting trees to increase infiltration and reduce runoff.
Soft engineering is often cheaper and more environmentally friendly but may be less effective in extreme floods.
Other methods include regulation of industrial and agricultural pollution, dam removal, and sewage treatment to improve water quality and restore river habitats.

Rivers and People

Rivers have sustained human and animal life for millennia, including the first human civilizations.
Rivers provide resources such as food, transportation, drinking water, and recreation.
Humans have engineered rivers to prevent flooding, irrigate crops, perform work with water wheels, and produce hydroelectricity from dams.
People associate rivers with life and fertility and have strong religious, political, social, and mythological attachments to them.
Rivers and river ecosystems are threatened by water pollution, climate change, and human activity.

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1.What is the name for water that flows in a natural channel?
Easy
- AA stream
- BA lake
- CAn aquifer
- DA delta
2.Which of the following is the correct order of a river's course from source to mouth?
Easy
- AUpper course, middle course, lower course
- BLower course, middle course, upper course
- CMiddle course, upper course, lower course
- DUpper course, lower course, middle course
3.Most rivers flow from north to south.
Easy
True or false?
4.Which of the following are processes of river erosion? (select all that apply)
Medium
- AHydraulic action
- BAbrasion
- CAttrition
- DDeposition
- ESolution
5.Match each river feature with its correct description.
Medium
- Meander
- Ox-bow lake
- Delta
- Floodplain
- A bend in a river
- A curved lake formed when a meander is cut off
- A landform built of sediment where a river enters a sea or lake
- Flat land beside a river that floods
6.Put these stages in the formation of a waterfall in the correct order.
Medium
- Soft rock is eroded faster than hard rock
- A step or drop forms in the river bed
- The river plunges over the drop, creating a waterfall
- The waterfall retreats upstream, forming a gorge
7.Which of the following is a hard engineering flood defence?
Medium
- ABuilding dams
- BAfforestation
- CFloodplain zoning
- DWetland restoration
8.Which of the following is a human cause of flooding?
Medium
- ABuilding on floodplains
- BHeavy rainfall
- CSnowmelt
- DStorm surges

Plus de questions

9.Which of the following are landforms found in the lower course of a river? (select all that apply)
Medium
- AFloodplain
- BDelta
- CWaterfall
- DV-shaped valley
- EOx-bow lake
10.Match each river process with its correct description.
Medium
- Hydraulic action
- Abrasion
- Attrition
- Solution
- The force of water hitting the river bed and banks, forcing air into cracks
- Rocks carried by the river scrape and wear away the bed and banks
- Rocks carried by the river collide and break into smaller, smoother pieces
- Chemicals in the water dissolve certain types of rock
11.Put the following stages in the formation of a meander in the correct order, from first to last.
Medium
- Fastest current erodes the outer bank, forming a river cliff
- Water flows faster on the outside of a bend and slower on the inside
- Deposition on the inside of the bend forms a slip-off slope (point bar)
- The river bend becomes more pronounced over time
12.Which of the following is a soft engineering flood defence?
Medium
- ABuilding embankments along the river
- BConstructing a dam upstream
- CAfforestation in the drainage basin
- DStraightening the river channel
13.What is the main difference between a tributary and a confluence?
Medium
- AA tributary is a smaller river that joins a larger one; a confluence is the point where they meet.
- BA tributary is the point where two rivers meet; a confluence is a smaller river that joins a larger one.
- CA tributary is an artificial channel; a confluence is a natural channel.
- DA tributary flows into the sea; a confluence flows into a lake.
14.All rivers flow from north to south.
Easy
True or false?
15.Which site is most likely to be in the lower course of the river?
Medium
- ASite A
- BSite B
- CSite C
- DCannot tell from the data
16.What is the most likely reason for the decrease in average sediment size from Site A to Site C?
Medium
- AIncreased erosion of the river bed
- BAttrition as particles collide and break into smaller pieces
- CDeposition of large boulders in the lower course
- DA decrease in river discharge
17.Why does water in a drainage basin eventually flow into the same river?
Medium
- ABecause all the land in the basin slopes downhill towards that river
- BBecause the river flows uphill to collect water from the surrounding land
- CBecause the drainage divide pushes water into the river
- DBecause aquifers pump water into the river
18.What is the main reason a river can continue to flow during a drought?
Medium
- AWater seeps from underground aquifers into the river where the water table is higher than the river
- BRainfall continues to fall heavily during droughts
- CGlaciers always melt quickly during droughts
- DThe river flows uphill to find water
19.Which process directly adds water to a river from a glacier?
Easy
- AMelting of snow and ice
- BPrecipitation
- CRunoff
- DSeepage
20.Why does a waterfall form where a river flows over hard rock above softer rock?
Medium
- AThe softer rock is eroded faster, creating a vertical drop
- BThe hard rock is eroded faster, creating a vertical drop
- CThe river deposits sediment to build a step
- DThe river flows uphill over the hard rock
21.What is the main effect of a river overflowing its banks and flooding the surrounding area?
Medium
- AIt spreads nutrients onto the land
- BIt carves a deep canyon
- CIt creates a waterfall
- DIt forms a drainage divide
22.Why can building a dam on a river harm river ecosystems downstream?
Medium
- AIt traps sediment, lowering the amount of alluvium flowing downstream
- BIt increases the amount of alluvium flowing downstream
- CIt causes the river to flow faster downstream
- DIt removes all water from the river downstream
23.Which human activity has helped to improve river water quality?
Medium
- ARegulation of industrial and agricultural pollution
- BBuilding more dams
- CIncreasing sewage discharge
- DRemoving all levees
24.Which of the following are effects of rivers on the landscape? (select all that apply)
Medium
- AForming deltas and islands
- BCarving canyons and valleys
- CSpreading nutrients when they flood
- DCreating drainage divides
- ELowering the water table
25.Which of the following are threats to river ecosystems? (select all that apply)
Medium
- AWater pollution
- BClimate change
- CHuman activity such as dam building
- DSewage treatment
- EDam removal
26.Rivers flow downhill because of gravity.
Easy
True or false?
27.Water on the western side of the Continental Divide of the Americas flows into the Atlantic Ocean.
Medium
True or false?
28.Match each river term with its correct description.
Medium
- Tributary
- Confluence
- Drainage basin
- The area of land where surface water flows to a common outlet
- A river that feeds into another river
- The place where two rivers meet
29.Put these stages in the formation of a waterfall in the correct order, from first to last.
Medium
- A river flows over hard rock above softer rock
- The softer rock is eroded faster, creating a vertical drop
- The river plunges over the drop, forming a waterfall
- The waterfall retreats upstream as the hard rock is undercut
30.Which statement about rivers is correct?
Medium
- AAll rivers flow from north to south.
- BRivers flow downhill because of gravity.
- CRivers only flow during the rainy season.
- DRivers always flow in straight lines.
31.What is a tributary?
Medium
- AA river that flows into another river
- BThe place where two rivers meet
- CA ridge that separates two drainage basins
- DA type of flood defence
32.Why can a river continue to flow during a drought?
Medium
- ABecause it is fed by groundwater from the water table
- BBecause it is fed by precipitation from the water cycle
- CBecause it is fed by a glacier
- DBecause it is fed by a tributary
33.A student writes: 'Because rivers flow downhill under gravity, most rivers in the world flow from north to south.' Which statement best evaluates this interpretation?
Medium
- AIt is correct: gravity pulls water towards the south.
- BIt is incorrect: a river's direction is set by the downhill slope of the land, not by compass direction.
- CIt is correct for rivers in the Rocky Mountains but not elsewhere.
- DIt is incorrect because rivers always flow from south to north.
34.A drainage divide runs north–south across a region. A town lies on the western side of the divide. Which statement about the water falling on the town is most likely to be true?
Medium
- AIt will flow into the same set of rivers as water on the eastern side.
- BIt will flow into a different set of rivers from water on the eastern side.
- CIt will not flow into any river because it is on a ridge.
- DIt will flow north because all rivers flow north to south.
35.A table shows average sediment size at three sites along a river: Site A (upper course) 40 mm, Site B (middle course) 12 mm, Site C (lower course) 3 mm. Which process best explains the decrease in average sediment size from Site A to Site C?
Medium
- AHydraulic action breaking rock from the river bed.
- BAttrition wearing particles down as they collide with one another.
- CSolution dissolving the sediment in the water.
- DDeposition of large particles in the lower course.
36.A map extract shows a river flowing through a wide, flat valley with a broad floodplain and a settlement built close to the river bank. Which part of the river's course is this most likely to be?
Medium
- AUpper course
- BMiddle course
- CLower course
- DSource
37.A short extract from a river study states: 'The river here flows over a band of hard rock above softer rock. The softer rock is eroded more quickly, leaving an overhang that eventually collapses.' What landform does this extract describe?
Hard
- AA meander
- BAn ox-bow lake
- CA waterfall
- DA delta
38.A data table shows the number of days a river flooded in a town over four decades: 1970s – 2 days; 1980s – 3 days; 1990s – 5 days; 2000s – 9 days. Which statements are supported by this evidence? (select all that apply)
Medium
- AThe number of flood days generally increased over the period.
- BThe 2000s had more flood days than the 1970s.
- CThe river never flooded in the 1970s.
- DFlooding was caused by deforestation in the 2000s.
- EThe 1980s had fewer flood days than the 1990s.
39.A river's drainage basin is the area of land uphill of the river that feeds it with water.
Easy
True or false?
40.What is the name for the boundary of higher land that separates two drainage basins?
Easy
- AA drainage divide
- BA confluence
- CA tributary
- DAn aquifer
41.What is the term for the study of the movement of water on Earth?
Easy
42.Complete the sentence about drainage basins.
Easy
The boundary between two drainage basins is called a ____, and the area from which water drains into a river is its ____.
43.On a map with a scale of 1:50,000, two towns are 4 cm apart. What is the real-world distance between them in kilometres?
Medium
44.What is the name for the boundary that separates two drainage basins?
Medium
45.On a map with a scale of 1:50,000, two points are 6 cm apart. What is the real-world distance between them in kilometres?
Medium
46.Complete the sentence about the water cycle.
Medium
Water enters rivers through ____, which includes rainfall, snowmelt, and runoff.
47.What is the name for a ridge of higher elevation land that separates two drainage basins?
Easy
48.What is the term for the smaller streams that feed a river and make up its source?
Medium
49.On a map with a scale of 1:50,000, two points are 8 cm apart. What is the real-world distance between them in kilometres?
Medium
50.Complete the sentence about river flow.
Easy
Rivers flow downhill because of ____, and their direction is determined by this force.
51.What is the name for the study of the movement of water as it occurs on Earth?
Easy
52.What is the term for the study of the effect of rivers on the landscape?
Easy
53.Explain how a meander can eventually become an ox-bow lake.
Hard
54.Explain how a waterfall forms and retreats upstream.
Hard
55.Explain why a river can still flow during a drought.
Hard
56.Explain how human activity can threaten river ecosystems.
Hard
57.Explain how the shape of a river valley changes from the upper course to the lower course.
Hard
58.On a map with a scale of 1:50,000, two towns are 4 cm apart. What is the real-world distance between them in kilometres?
Medium
- A4 km
- B2 km
- C3 km
- D1 km
59.On a map with a scale of 1:50,000, two points are 6 cm apart. What is the real-world distance between them in kilometres?
Medium
- A3 km
- B5 km
- C4 km
- D2 km
60.On a map with a scale of 1:50,000, two points are 8 cm apart. What is the real-world distance between them in kilometres?
Medium
- A4 km
- B5 km
- C6 km
- D3 km

Notes de révision

## Rivers and Flooding — Revision Notes **The water cycle** moves water around the Earth. All river water ultimately comes from **precipitation** — rainfall, runoff down slopes, melting glaciers or snow, or seepage from aquifers. **Drainage basin (watershed):** all the land uphill of a river that feeds it with water. **Drainage divides** are ridges of higher land separating basins — e.g. the Continental Divide of the Americas: west flows to the Pacific, east to the Atlantic. **Headwaters** are the smaller streams that feed a river and make up its **source**. **Tributaries** feed into larger rivers; the meeting point is a **confluence**. Rivers also gain water from **groundwater** via the **water table** (where the river sits lower than the water table, water flows in — so rivers can flow in droughts) and from **glacier melt**, which supplements snow melt in late summer. **River processes** - **Erosion:** hydraulic action, abrasion, attrition, solution — carves rock and soil into canyons and valleys. - **Transportation** of sediment (**alluvium**). - **Deposition:** where flow slows, alluvium shapes the landscape, forming **deltas** and islands. **Landforms by course** - Upper: V-shaped valleys, waterfalls (softer rock weathers faster, creating a vertical drop). - Middle: meanders (rivers seldom run straight; banks shift frequently). - Lower: ox-bow lakes, floodplains, deltas. **Flooding:** rivers may regularly overflow their banks, flooding surrounding land and spreading nutrients to it. **Flood defences** - **Hard engineering:** dams, canals, levees and other engineered structures — but these eliminate habitats, have caused extinctions, and reduce alluvium flowing through rivers. - **Soft engineering:** regulation of industrial and agricultural pollution, dam removal, sewage treatment — improving water quality and restoring habitats. **Threats:** water pollution, climate change (less snowfall means less summer water), and human activity. Rivers have sustained life for millennia, providing food, transport, drinking water and recreation. **Key idea:** rivers flow downhill, directed by gravity — not all from north to south.

River: A natural flow of freshwater that flows on or through land towards another body of water downhill (a lake, an ocean, or another river).
Stream: Water that flows in a natural channel; a channel may also be called a watercourse.
Hydrology: The study of the movement of water as it occurs on Earth.
Water cycle: The continuous processes by which water moves about Earth; all river water ultimately comes from precipitation.
Precipitation: Water entering rivers as rainfall, runoff down a slope, melting of glaciers or snow, or seepage from aquifers.
Drainage basin (watershed): All of the land uphill of a river that feeds it with water.
Drainage divide: A ridge of higher elevation land separating drainage basins; water on one side flows into one set of rivers, and water on the other side into another.
Headwaters: The smaller streams that feed a river and make up the river's source.
Tributary: A river that feeds into another river.
Confluence: The place where a tributary meets the river it feeds into.
Aquifer: Underground store of water that can feed rivers via the water table.
Water table: The groundwater beneath the surface of the land stored in the soil; water flows into rivers where the river's elevation is lower than the water table.
Erosion: Wearing away of the river's bed, carving rock and soil into canyons and valleys; types include hydraulic action, abrasion, attrition and solution.
Alluvium: Sediment carried by rivers; it shapes the landscape, forming deltas and islands where flow slows down.
Deposition: Dropping of carried sediment where a river's flow slows down.
Meander: A bend in a river; rivers seldom run a straight course and their banks can change frequently.
Waterfall: A vertical drop formed where softer rock weathers faster than harder rock, creating a difference in elevation.
Flooding: When a river regularly overflows its banks and floods the surrounding area, spreading nutrients to it.
Hard engineering: Engineered flood defences such as dams, canals and levees; they can eliminate habitats, cause extinctions and reduce alluvium flowing through rivers.
Soft engineering: Measures such as regulation of industrial and agricultural pollution, dam removal and sewage treatment, which improve water quality and restore river habitats.

Cartes mémo

What is a river?

A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river.

What is the water cycle?

The water cycle is the continuous processes by which water moves around the Earth.

How does water enter rivers?

Water enters rivers through precipitation, including rainfall, runoff from slopes, melting of glaciers or snow, and seepage from aquifers.

What is a drainage basin?

A drainage basin is an area where surface water eventually flows to a common outlet.

What is a drainage divide?

A drainage divide is a ridge of higher elevation land that separates drainage basins, causing water on one side to flow into one set of rivers and water on the other side into another.

What are the headwaters of a river?

The headwaters are the smaller streams that feed a river and make up the river's source.

What is a tributary?

A tributary is a river that feeds into another river.

What is a confluence?

A confluence is the place where two rivers meet.

What is the bed of a river?

The bed of a river is the bottom of the river channel, typically within a river valley between hills or mountains.

What is a meander?

A meander is a bend in a river; rivers seldom run straight but instead meander, and the locations of their banks can change frequently.

What is an ox-bow lake?

An ox-bow lake is a curved lake formed when a meander is cut off from the main river channel.

What is a floodplain?

A floodplain is the flat area of land adjacent to a river that is regularly flooded when the river overflows its banks.

What is a delta?

A delta is a landform formed where a river slows down and deposits sediment, often at its mouth where it meets a larger body of water.

What is hydraulic action?

Hydraulic action is the erosion process where the force of water alone dislodges and carries away rock and soil from the river bed and banks.

What is abrasion?

Abrasion is the erosion process where rocks and sediment carried by the river scrape and wear away the river bed and banks.

What is attrition?

Attrition is the erosion process where rocks carried by the river collide with each other, breaking into smaller, smoother pieces.

What is solution?

Solution is the erosion process where soluble minerals in rocks are dissolved by river water.

What is transportation in a river?

Transportation is the movement of eroded material (sediment) downstream by the river.

What is deposition?

Deposition is the process where a river drops its carried sediment when its energy decreases, often where the flow slows down.

What is a V-shaped valley?

A V-shaped valley is a narrow valley with steep sides, formed by river erosion in the upper course.

How does a waterfall form?

A waterfall forms where a river flows over a vertical drop, often caused by differences in rock resistance: softer rock erodes faster than harder rock, creating a step in the river's course.

What are the causes of flooding?

Flooding occurs when a river overflows its banks, often due to heavy precipitation, snowmelt, or when the ground is saturated and cannot absorb more water.

What are the effects of flooding?

Flooding can spread nutrients to the surrounding area, but can also cause damage to property, land, and human life.

What is hard engineering in flood management?

Hard engineering involves building artificial structures such as dams, levees, and canals to prevent flooding.

What is soft engineering in flood management?

Soft engineering involves working with natural processes to reduce flood risk, such as restoring floodplains or planting vegetation.

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