Rivers Revision

-We will revise the main topic areas of Water on the Land

Knowledge Checklist• Know the processes of erosion• Know the processes of transportation• Know how waterfalls and gorges are formed• Know how meanders and ox-bow lakes are formed• Know how flood plains and levees are formed• Know the factors that affect river discharge• Know the physical and human causes of flooding• Know a case study of a rich and poor country flood• Know how hard and soft engineering can be used in flood

management• Know how water is used in the UK with areas of surplus and deficit• Know a case study of a reservoir in the UK

The Profile of a RiverKey Idea: The shape of river valleys changes as rivers flow downstream due to the dominance of different processes.

Processes of erosion – hydraulic action, abrasion, attrition, solution; vertical and lateral erosion.

Processes of transportation – traction, saltation, suspension and solution.

Deposition and reasons for it.

Long profile and changing cross profile.

The Water Cycle

It is the main input to the drainage basin

• The long profile of a river is a cross section from its source to its mouth. This whole area is known as the drainage basin.

• They are divided into three sections:– Upper course– Middle course– Lower course

• River gradient decreases gradually as the river flows downstream (ie. It becomes less steep)

The long profile and the drainage basin

• A river basin is the area of land drained by a river and its tributaries

• Watershed – an area of higher land separating two drainage basins

• Source – the place where a river begins• Tributary – a smaller river joining a larger one• Confluence – the place where two rivers join• Mouth – the place where a river enters a lake or

the sea

Drainage Basin Key words

Processes of Erosion

Transportation

• Material is carried in the river in four ways:• Traction: large stones are rolled along the river bed• Saltation: smaller stones ‘bounce’ along the river bed• Suspension: small particles of silt and clay float through the

water• Solution: minerals are dissolved in the river

Deposition

Deposition is the dumping of material and happens when the river loses its energy. This may be during a dry spell, on the inside of a river bend, or when the river reaches the sea (readon for more on this).

The Long Profile of a River

L.Ob: to describe how a river changes from source to mouth

Think about the 2 pictures of rivers:

why are they so different?

Features at the 3 stages of a river

Why?

SOURCE

MOUTH

UPPER COURSE MIDDLE COURSE LOWER COURSE

Waterfalls

Rapids

Interlocking spurs

V-shaped valley

Vertical erosion & transportation

Lateral & vertical erosion, transportation, deposition

Transportation & deposition

MeandersSEAOx-bow lakes

Levees

Flood plain

River Severn – Source to Mouth Video

Upper Course

• Vertical erosion is the main process. • Valleys are v-shaped, interlocking spurs. • Waterfalls are formed. • Rapids are smaller scale feature formed

where finer bands of varying resistance of rocks are found.

Foundation Question

Higher Question

Upper Course – V-Shaped Valleys and Interlocking Spurs

Upper Section Landforms

Waterfalls• A waterfall is a place on a river where the water flows vertically• They tend to occur in the upper course of a river1. Softer rock erodes quickly, undercutting harder rock2. Harder rock erodes more slowly, forming overhang3. Overhang eventually collapses – the waterfall moves upstream4. Steep sided valley (gorge) is formed5. Plunge pool erodes under waterfall

Landforms in Middle and Lower Sections: Meanders

Formation of Meanders

Slow flow = loss of energy. Fast flow = lots of energy.

Low energy = deposition. High energy=erosion

Foundation and Higher Question

Meanders and Ox-Bow Lakes

Meandering streamflowing fromtop of screento bottom

Maximum erosion

Maximum deposition

Oxbow Lake

Oxbow cuttoff

Meander scars

Foundation Question

Higher Question

A DeltaSome rivers reach the sea in deltas, which form where river mouths become choked with sediment, causing the main river channel to split into hundreds of smaller channels or distributaries

Deltas only form under certain conditions

• The river must be transporting a large amount of sediment• The sea must have a small tidal range and weak currents• The sea must be shallow at the river mouth

Famous deltas consist of the Mississippi delta, The Ganges and Brahmaputra delta (Bangladesh) and of course the Nile delta.

Flood Plains and LeveesWhen a river continually floods, it spreads silt across the flood plain. Often this material piles up to form levees. Sometimes, humans make artificial levees to mimimise the impact of flooding.

FloodHydrograph

DIS

CH

AR

GE

(cu

mec

s)

RA

INF

AL

L m

m

time

LAG TIME

Peak Rainfall Peak Discharge

River DISCHARGE

• Discharge is the volume rate of water flow, which is transported through the river channel.

• Measured in cumecs (cubic metres per second)

The Flood Hydrograph – A = floods quickly (flash flood)

B = slower rate of discharge, less likely to flood

WHAT FACTORS AFFECT THE DISCHARGE LINE?

Factors Affecting Water in a River

• Amount and type of rainfall• Previous weather conditions• Land use• Temperature• Rock type• Relief

Describe 5 factors that might affect the lag time (time it takes river to flood)

Describe 5 factors that might affect the lag time (time it takes river to flood)

• 1 = Deforestation1 = Deforestation• 2 = Urbanisation2 = Urbanisation• 3 = Relief of land3 = Relief of land• 4 = Dam Building4 = Dam Building• 5 = Industry/Agriculture5 = Industry/Agriculture

Contrast the hydrographs (3)

Explain why the two hydrographs are different (4)

Foundation

Higher

FloodingPhysical Factors Human Factors

Prolonged Rainfall Deforestation

Snowmelt Impermeable materials

Heavy Rainfall

Relief

Frequency of Flooding

Flooding in the UK appears to be happening more often!

Case Studies

• You need to know too flood case studies!– Rich Country (Worcestershire, England)– Poor Country (Bangladesh)

MEDC: UK Floods 2007

Write a quick case study….Write a quick case study….

What caused the floods? What were the What caused the floods? What were the main effects? What are the solutions?main effects? What are the solutions?

FLOODING IN AN LEDC – Bangladesh Case StudyFLOODING IN AN LEDC – Bangladesh Case Study

IMPORTANT DATES and DEVELOPMENT INDICATORS for BangladeshIMPORTANT DATES and DEVELOPMENT INDICATORS for Bangladesh

CAUSES of the flood:CAUSES of the flood:

EFFECTS of the flood on People and Environment:

Remember SHORT and LONG TERM

EFFECTS of the flood on People and Environment:

Remember SHORT and LONG TERM

MANAGEMENT RESPONSES – can they reduce the impact?:

MANAGEMENT RESPONSES – can they reduce the impact?:

Hard Vs Soft EngineeringPage 92 of book

Raise levees

Dredge river beds

Straighten rivers

Hard Vs Soft Engineering

Better warning systems

Zone off some areas

Model answers and mark scheme

For more past papers and info visit the OCR ‘A’ Geography website

http://www.ocr.org.uk/qualifications/gcse/geography_a/documents.html

Managing Water in the UK

• What causes the water stress?

• How can we be more efficient with water?

(6)

Reservoir Case Study• You need to know one case study of a reservoir that provides water to people in

the UKKielder Reservoir is in book- Biggests man-made reservoir in Europe.- Was poor farmland, large valley with steep sides.- Lots of rainfall and low population.- Wild habitats were limited so little environmental damage.- Supplies NE of England wit water.- Lots of leisure industry there. Good for economy.

Past Paper Questions

Click for examiners mark scheme

Model answers and mark scheme

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Model answers and mark scheme

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