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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
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 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
Continues…..
Model answers and mark scheme
Continues…..
