Rivers, Floods and Management AQA
Jan 29, 2016
Rivers, Floods and Management
AQA
Contents
Hydrological cycle and river dischargeRiver processesProfiles and characteristicsLandforms of fluvial erosion and depositionCauses and impacts of floodingFlood management strategiesExam questions
The drainage basin
Lesson 1
The drainage basin and hydrological cycle (lesson 1)
Lesson objectives
• Students develop skills of OS map reading and identifying key river features on an OS map.
Success criteria
To recognise 4 different
patterns of drainage basin.
To apply knowledge to an
OS map and identify 3
different drainage
basins and their pattern
Starter: Identify the key features of the drainage basin
Watershed
Main river channel
Source
Confluence
Tributary
Mouth
Task: Annotate the drainage basin to define the key word labels.
The watershedmouth
Drainage basin or catchment area Definition: What is a drainage
basin?
An area of land (also called the catchment area) drained by a river and its tributaries
The drainage basin
Types of drainage basin
The rectangular drainage pattern. Streams follow the path of least resistance and thus are concentrated in places where exposed rock is the weakest.
Trellis drainage patterns look similar to their namesake, the common garden trellis.
Parallel drainage patterns form where there is a pronounced slope to the surface. Tributary streams tend to stretch out in a parallel-like fashion following the slope of the surface.
A dendritic drainage pattern is the most common form and looks like the branching pattern of tree roots.
Using Ordnance Survey maps
Tasks: 1.Using the OS map of Snowdonia, identify as three
different drainage basins.
2. Having achieved this, write down the name of the main river channel that the drainage basin belongs to.
3.Now, identify the drainage basin pattern for each identified.
Plenary:
In your books, drawn the four different drainage basin
patterns that you have learnt about this lesson (without
referring to your class notes!)
Annotate each one identifying:
• Watershed
• Main river channel
• Source
• Confluence
• Tributary
• Mouth
Please print the following reading from the shared area, make key notes revision cards for next
lesson: Drainage basin: River Ouse
The drainage basin and hydrological cycle (lesson 1)
Lesson objectives
• Students develop skills of OS map reading and identifying key river features on an OS map.
Success criteria
To recognise 4 different
patterns of drainage basin.
To apply knowledge to an
OS map and identify 3
different drainage
basins and their pattern
Drainage basin processes
Lesson 2
Drainage basin processes
Lesson objectives
• To identify key processes of a drainage basin.
• Students be able to work out and construct soil moisture budget.
Success criteria
• To be able to identify drainage basin processes.
• To contribute thinking of geology and the soil moisture budget.
• Examine how this year’s summer weather will affect the usual British Isle moisture budget.
Starter:
Task:
Write down 5 words that you would use to
describe this summer’s weather.
Examine the impacts of this on our drainage
basins.
The drainage basin as an open system
The drainage basin forms part of the hydrological cycle, and can be described as an ‘open’ system involving a series of;
Inputs
Outputs
Stores
Transfers
Can you define these terms?
Ways in which water enters the system
Ways in which water leaves the system
Ways in which water is held in the system
Ways in which water is moved through and within the system
Task:
Complete the handout of a typical drainage basin.
In order to complete this you will need 4 different colours.
Assign each shape in the key with a colour and then colour
the shapes accordingly in the diagram.
Now, label each shape with the correct process.
Elements of the systemName each store Name each transfer Name the Input Name each Output
Surface storage - lakes, rivers, sea, depression storage
The water table (position varies)
Saturated or impermeable rock
Interception by vegetation
Soil water storage
Groundwater storage
Throughfall + stemflow
Infiltration
Throughflow
Surface (overland) runoff
Percolation
Groundwater (base) flow
Precipitation
Evaporation
Transpiration
The water balance
This is the balance between inputs and outputs in the drainage basin.
It is expressed as:
P + Q +E (+/-), where;
P = precipitation
Q = run-off
E = evapotranspiration
(+/-) = change in storageThe graph shows the main features of the water balance – average monthly precipitation and potential evapotranspiration levels
Task: Draw this model out, ensuring that it takes half an A4 page.
Understanding the water balance graph
In which month(s) is there a water surplus, and why is this?
Jan, Feb, March, April, Oct, Nov, Dec, when precipitation exceeds potential evapotranspiration
What is soil recharge and when does this occur?
The replacement of soil moisture lost during drier periods; during autumn in the UK (Oct and Nov)
Field capacity is attained after soil recharge. What exactly is field capacity?
It’s the maximum amount of water soil can hold
Understanding the water balance graph
Q. Why is a water deficit not shown on this graph?
A. In the UK, precipitation (nearly) always exceeds evapotranspiration
Q. How might water balance graphs be a) useful?, and b) difficult to construct?
A. They can be useful in predicting river regimes and managing drainage basins. It is however difficult to accurately measure evapotranspiration
Task: Underneath your diagram of the water balance graph,1.Explain what the graph shows (you must refer to each process along the course of the year)2.Strength and weakness of using this graph
Plenary:
Peer assess your study buddy’s work using this mark scheme
Drainage basin processes
Lesson objectives
• To identify key processes of a drainage basin.
• Students be able to work out and construct soil moisture budget.
Success criteria
• To be able to identify drainage basin processes.
• To contribute thinking of geology and the soil moisture budget.
• Examine how this year’s summer weather will affect the usual British Isle moisture budget.
The Storm Hydrograph and factors affecting shape of
hydrographs
Lesson 3 Please bring the following reading and supporting revision cards to next
lesson:
River hydrographs
Lesson 3
Lesson objectivesTo understand the impact of
land use, time of year,
slope, intensity of rain,
geology, previous weather
on hydrograph shape.
Success criteriaTo be able to plot
precipitation and discharge
using two different scales.
To apply base flow, run off
and flood concepts to the
graph.
To identify the features of
flashy and subdued
hydrographs and suggest
reasons why a flashy
hydrograph or subdued
hydrograph would occur.
Starter: Identify the key features of the storm hydrograph
Discharge and the storm hydrograph
• A hydrograph shows changes in a river’s discharge over time
• A storm hydrograph shows this information following a rainfall event
• Name the main features of the hydrograph
Time (hours)
Discharge (cumecs)
rainfall
?Rising limb
?Falling limb
?Peak discharge
?Lag time
?Storm flow
?Base flow
What factors affect river discharge?
Size and shape of drainage
basin
Porosity of soils underlying basin
Geology:permeability of underlying
rock
Drainage density
Vegetation: type and seasonal variations in
cover. Deforestation
Drainage basin relief
Factors affecting discharge
Precipitation: intensity and
duration. Antecedent rainfall.
Land use
How do these factors affect the storm hydrograph?
Factor Effects on Hydrograph
High intensity, long duration of rainfall, or antecedent rainfall
Snow melt
Porous soils and / or permeable rock
Impermeable rock / frozen ground
Small drainage basin
Elongated drainage basin shape
Steep slopes within drainage basin
Summer vegetation
Deforestation
Steep rising limb as infiltration capacity of soil exceeded
Greatly increased discharge, especially if ground frozen
Less steep or ‘flashy’ hydrographs
Reduced lag time and steeper rising limb
Faster response, so shorter lag time and steeper rising limb
Slower passage to river, so longer lag time
Faster passage to river, so shorter lag time and steeper rising limb
Interception higher - slower response, peak discharge lower
Faster response and higher peak discharge
time
discharge (cumecs) and rainfall (mm)
Shorter lag time as water quickly reaches the channel via surface runoff, through drains, sewers etc
Steeper rising limb due to impermeable surfaces
Urbanisation and the storm hydrograph
Higher peak flow as less water is ‘stored’; more water reaches the river
Rural
Urban
Flashy and subdued hydrographs
Task 1: Identify the differences between A and B.Task 2: Describe and explain the conditions under which A and B may occur
Plenary:
To complete the exam question handed out
to you. Answer this question on the
resource.
Lesson 3
Lesson objectivesTo understand the impact of
land use, time of year,
slope, intensity of rain,
geology, previous weather
on hydrograph shape.
Success criteriaTo be able to plot
precipitation and discharge
using two different scales.
To apply base flow, run off
and flood concepts to the
graph.
To identify the features of
flashy and subdued
hydrographs and suggest
reasons why a flashy
hydrograph or subdued
hydrograph would occur.
Valley profiles Lesson 4 and 5
Please print, read and produce revision
cards for the following:
River long profiles and valley cross
profiles
Lesson 4 and 5
Lesson objectives
• Students to be able to fit a cross profile to the long profile of a river.
• To understand Long profile (thalweg) and cross valley profiles and variation.
Success criteria
• To know the basic long and cross valley shapes.
• To understand what causes irregularities (knick points)
• To compare and contrast general profile with example of Afon Glaslyn.
Starter: Describe the changes to this channel from source to confluence along its long profile.
The long profile
• The long profile illustrates changes in altitude from the source of a river along its entire length to the mouth
• The idealised model is smoothly concave (a river will achieve this once it has achieved a balance between erosion and deposition), with a steeper gradient in the upper course becoming progressively gentler towards the mouth
Height (m)
60 Distance from sea (km) 0
A
B
C
How would the processes of erosion, transportation and deposition change from A, through B, and to C?
The changing cross-profile
A
B
C
Height (m)
60 Distance from sea (km) 0
A B C
Upper course Middle course Lower course
OS map skills
• Locate Afon Glaslyn on the OS map of Snowdonia.
• Identify:
Source, mouth, flow direction,
stores, valley shape and channel
pattern.
Plenary
• Draw the long profile of any river from the Snowdonia OS map on graph paper. You will need to ensure that your scale fits onto the graph paper!
Lesson 4 and 5
Lesson objectives
• Students to be able to fit a cross profile to the long profile of a river.
• To understand Long profile (thalweg) and cross valley profiles and variation.
Success criteria
• To know the basic long and cross valley shapes.
• To understand what causes irregularities (knick points)
• To compare and contrast general profile with example of Afon Glaslyn.
The River Processes
Lesson 6 and 7
Lesson 6 & 7
Lesson objectives
• To understand the significance concerning the river processes
Success criteria
• To know what the river processes are
• To examine the relationship between the river processes and river formations and landforms
Starter: Which of these sediments will be entrained first? Why?
River processes
1. FLUVIAL EROSION
The break-up of rocks by the action of the river
2. TRANSPORTATION
The movement of eroded material
3. DEPOSITION
The laying down of material which has been transported
by the river
Think…
What key processes do you think determine the size, shape and features of a river channel?
As we consider these processes, remember that a river’s discharge and velocity will have an impact on rates of erosion, transportation and also upon deposition
Tip
Put a new title in your book: River Processes
Key question:
What two types of energy will dictate the
rate of erosion, transportation and
deposition?
At any one time the dominant process operating within the river depends on the amount of energy available. This is governed by the velocity of the flow and the discharge within the channel.
Entrainment velocity: the critical erosion velocity (velocity required to pick up and transport sediment)
Remember...
River processes
FLUVIAL EROSION
The break-up of rocks by the action of the river
TRANSPORTATION
The movement of eroded material
DEPOSITION
The laying down of material which has been transported
by the river
What are the main processes
of fluvial erosion?
Attrition Abrasion / corrasion
Corrosion / solution
Hydraulic action
Definitions
EROSIONAL PROCESS
DEFINITION EFFECT ON RIVER
Corrasion / Abrasion
Attrition
Hydraulic action
Corrosion
Task: Using the cards, complete the table.
Scraping, scouring and rubbing action of the load carried by the river
Process where pebbles knock together and get smaller and more rounded
Frictional drag and pressure created by moving water as it is forced into cracks
Where the naturally weak acidic water dissolve some carboniferous rocks such as limestone and chalk
River banks wear away
Sediment load size decreases
Removal of loose material - river banks undercut and collapse
An increase in the dissolved load (solution)
Abrasion
Hydraulic Action
Corrosion
Attrition
ErosionAbrasion: The scrapping, scouring and rubbing action of materials carried along by the river.
Rivers carry rock fragments in the flow of the water or drag them along the bed of the river channel.
Abrasion is the most effective in short turbulent periods when the river is at bankfull or in flood.
During times when the river level is low, the load consists of small particles, e.g. Sand grains and these tend to smooth the surface of the river channel.
ErosionHydraulic Action: caused by the power of moving water. It is the movement of loose unconsolidated material due to the frictional drag of the moving water on sediment lying on the channel bad.
As velocity increases, turbulent flow lifts a large number of sand-sized particles from the channel floor.
Hydraulic action is particularly successful at removing loose material in the banks of meanders , which can lead to undercutting and collapse.
May also cause rocks to fragment along joints and other lines of weakness.
Erosion
Corrosion: Is the most active on rocks that contain carbonates such as limestone and chalk.
The minerals in the rock are dissolved by weak acids in the river water and carried away in solution.
Erosion
Attrition: Reduction in size of fragments and particles within a river due to actions like corrosion.
The fragments strike one another as well as the river bed. Particles become smoother, smaller and more rounded as they move along the river channel.
These smaller fragments therefore are found more commonly downstream.
Erosion• Vertical erosion: dominant in
the upper course of the river where the river is trying the cut down to reach either its base level of sea level.
• Depending upon meters above sea level will depend on its potential energy and ultimately the shape of the landscape.
• When the discharge level and velocity of the river is high, the river cuts down into its valley mainly by abrasion and hydraulic action. Such rivers often produce steep-sided valleys.
Erosion• Lateral erosion: Dominant in the
middle to lower course of the river channel.
• As the cannel reaches flatter land, the river’s energy erodes laterally.
• This may result in the formation of meanders.
• The channel will also become wider and deeper.
• Hydraulic action is prevalent here. • The strongest current of the water
is on the outside of the meander bend and causes undercutting, resulting in the banks collapsing.
2. River Transportation
Solution: Dissolved minerals within water
A river transports it’s load in four main ways.
Suspension: Very small particles of sand and silt (0.001 – 0.99 mm diam) carried in the flow
Traction: Large stones and boulders (> 100 mm diam) rolled along river bed
Saltation: Small stones (1.0 – 99.99 mm diam) bounced along river bed
Extension: Write a small paragraph underneath your diagram, explaining why you think different types of sediment are transported in a particular way.
Transportation
• River competence: the maximum size (calibre) of load a river is capable of transporting.
• River capacity: total volume of sediment a river can transport .
What calibre of sediment would you expect to be transported in the
upper, middle and lower course of a river?
What factors would you need to take into account?
Under what conditions will a river deposit its load?
When there is an increase in the size of the sediment load caused by a landslide or tributary delivering larger particles
In flood conditions, when a river overflows onto its floodplain
There is shallow water, e.g. on the inside of a meander bend
When river discharge is reduced due to a period of dry weather
3. Deposition
When there is a decrease in the gradient and / or velocity of the river e.g. at river mouth, or when entering a lake
Task: In your book, give yourself a heading ‘Deposition’. In the middle of your book write the following question. In pairs, develop some ideas that considers this question. You have 5 minutes!!
Deposition• A river deposits when it not longer has the competence (maximum size
(calibre)) of load a river is capable of transporting.• Any reduction in river velocity will reduce competence and the material will
begin to be deposited (starting with the coarsest sediment as this requires a lot of energy to remain suspended), e.g. gravel, pebbles, boulders.
• Very fine sediment may never be deposited in the channel and may be carried all the way out to sea via the estuary.
Deposition occurs when:
1. Sudden reduction in gradient
2. River enters a store
3. Discharge has been reduced
4. Shallow water (e.g. Meander bend = build up of sediment)
5. Sudden increase in calibre
Profile of dynamic equilibrium
Relationship between erosion and
deposition.
A river is always trying to reach a profile of
dynamic equilibrium.
If a river achieved this, how would the long
profile appear?
The long profile
• The long profile illustrates changes in altitude from the source of a river along its entire length to the mouth
• The idealised model is smoothly concave (a river will achieve this once it has achieved a balance between erosion and deposition), with a steeper gradient in the upper course becoming progressively gentler towards the mouth
Height (m)
60 Distance from sea (km) 0
A
B
C
How would the processes of erosion, transportation and deposition change from A, through B, and to C?
Ways in which changing processes affect the valley profile
Erosion Transportation Deposition
A (Upper course)
B (Middle course)
C (Lower course)
Hydraulic, attrition. Vertical erosion dominant
Mostly attrition, some hydraulic. Vertical erosion decreases + lateral begins
Some lateral erosion on outside of meanders
Mostly large boulders. Some in suspension + solution
Saltation and traction of smaller bed-load. Suspension increased. Some in solution
Smaller sized bed-load of sand and gravel, transported in suspension
Large bed-load only
Coarser material builds up in braiding, slip-off slopes and floodplain
Mostly fine material deposited on levees, floodplain and slip-off slopes
Task: Using the cards, complete the table.
The changing cross-profile
A
B
C
Height (m)
60 Distance from sea (km) 0
A B C
Upper course Middle course Lower course
Bradshaw’s model Bradshaw’s model illustrates the main changes expected down the long profile of a river
Upstream Downstream
dischargedischarge
occupied channel widthoccupied channel width
water depthwater depth
water velocitywater velocity
load qualityload quality
load particle sizeload particle size
channel bed roughnesschannel bed roughness
gradientgradient
Task: Examine Bradshaw’s
model of changing channel
characteristics based on your knowledge of
river processes
Upstream Downstream
dischargedischarge
occupied channel widthoccupied channel width
water depthwater depth
water velocitywater velocity
load qualityload quality
load particle sizeload particle size
channel bed roughnesschannel bed roughness
gradientgradient
Plenary:
With reference to Afon Glaslyn, annotate the
diagram to show the different processes at
work.
Lesson 6 & 7
Lesson objectives
• To understand the significance concerning the river processes
Success criteria
• To know what the river processes are
• To examine the relationship between the river processes and river formations and landforms
The Hjulstrom Curve
Lesson 8
Lesson 8
Lesson objectives
To be able to apply
knowledge of erosion,
transportation and
deposition to a theoretical
model
Success Criteria
Complete an annotated
diagram of the Hjulstrom
Curve
To know how to use and
understand a logarithmic
scale.
Starter:
1. Identify the three river processes.
2. Define ‘River competence’
3. Define ‘Entrainment velocity’
4. Define ‘Profile of dynamic equilibrium’.
The Hjulström curve shows the relationship between river velocity and the size of particles which can be eroded, transported and deposited.
The Hjulström curve
F. Hjulström collated data from 30 experimental studies into the competence of different flow velocities (competence is the maximum particle size which can be transported at specific velocities)
1. Silt/sand are picked up (entrained) at the lowest velocities.
2. Clays are as difficult to pick up as pebbles - although they are small particles they are very cohesive and the claybed is very smooth.
3. Large boulders are dropped very easily.4. Clay particles can be transported in suspension at
very low velocities.
1
2 3
4
Task: Draw an enlarged version of the Hjulstrom curve in your book, take up half a page (you can use the image in your text books).
Task:
Annotate your Hjulstrom curve to explain what the model shows and refer to
examples.
Semi-log graphs are used to show data that have a particularly wide range of values. For example, a semi-log graph allows us to compare things that differ enormously in size. This example allows us to compare Oceania and East Asia in terms of their trends in absolute population growth. This comparison would not be feasible using ordinary graph paper.
The logarithmic scale compresses the range of values. It gives more space to smaller values and reduces the amount of space for the larger values. Thus it can show relative growth quite clearly.
On the scale there are ‘cycles’ of values. Each cycle increases by a larger amount, usually to the power of 10. With this example, the first cycle increases by 10 each time to 100, the second cycle increases by 100 to 1000 and so on.
Plenary:
Complete a detailed A5 revision card to
demonstrate what you have learnt this lesson.
Lesson 8
Lesson objectives
To be able to apply
knowledge of erosion,
transportation and
deposition to a theoretical
model
Success Criteria
Complete an annotated
diagram of the Hjulstrom
Curve
To know how to use and
understand a logarithmic
scale.
The River Tees
Lesson 11In order to support your work on the River Tees,
you will need to print and use the following
reading:
Flood and River basin management: River
Tees
Lesson 11
Lesson objectives
• To understand the formation of and profile of the River Tees
Success criteria
• Produce key notes from the video to inform your case study
River Tees Landforms case study
• Watch the 30 minute video about river landforms and features along the River Tees.
1.Location (source and mouth)
2.Features along the profile of the Tees
3.Landforms along the profile of the Tees
4.Management and reasons for management
River Tees case study
• Location• Length of the River Tees• Upper course formations and landforms• Middle course formations and landforms• Lower course formation and landforms• Management
Tip
You must show evidence of research and further reading.
You must also provide annotated images specific to the formation
and landforms along the river Tees.
Lesson 11
Lesson objectives
• To understand the formation of and profile of the River Tees
Success criteria
• Produce key notes from the video to inform your case study
River Landforms
Lesson 12 and 13
Lesson 12 and 13
Lesson objectives
To understand and explain
the formation of river
landforms
Success Criteria
Produce a 3 min
PowerPoint presentation
and revision hand out for
next lesson
Starter: Annotate this image as best you can from what you learnt last lesson
Presentation task
Aim:
In pairs or groups of three, prepare a 5 minute presentation
that explains the formation of a river landform.
Requirements:
1. You must produce a 3 minute presentation.
2. You must produce a key point revision handout for each member of the class (including images).
3. You must print out your PowerPoint presentation slides onto a handout page and submit to me with a copy of your revision handout.
What your assessed work must include:Presentation:
1. Identification of landform and location along the profile of the river
2. What it is
3. What they look like
4. Geographical formation (river processes)
5. An example
6. Include relevant annotated images
Revision handout
1. The step by step formation of the landform
2. Images of the formation
3. River processes
4. Example
This must be ready to
present next lesson
– please save work
onto a memory
stick
Landforms
• Upper course: V-shaped valleys and interlocking spurs Potholes and Rapids
• Upper/ Middle course: Waterfalls and Gorges
• Middle course: Meanders and Oxbow lakes
• Middle/ Lower course: Channel braiding and Eyots (island bars)
• Lower course: Floodplains, levees and deltas
Plenary:
Assess each group’s presentation using the
peer/ self assessment feedback sheets.
Provide feedback to each group.
Lesson 12 and 13
Lesson objectives
To identify and explain
the formation of river
Landforms along the profile
of a river
Success CriteriaSynthesise knowledge using tree
diagram.
Create a story board or flow diagram that
examines the formation of river landforms
from source to confluence of a river
Challenge: Incorporate Bradshaw’s
model.
Assess own progress and what you
learnt by completing a past exam
question using the Zones of Relevance
Challenge: Evaluate whether these
features are affecting a river’s profile of
dynamic equilibrium
Synthesising information: Landforms of fluvial erosion
Erosional
Features
Meanders
Interlocking
spurs
PotholesWaterfalls
& rapids
Middle and
lower course
Upper
course
River
terraces
Ox-bow
lakes
Lesson 12 and 13
Lesson objectives
To identify and explain
the formation of river
Landforms along the profile
of a river
Success CriteriaSynthesise knowledge using tree
diagram.
Create a story board or flow diagram that
examines the formation of river landforms
from source to confluence of a river
Challenge: Incorporate Bradshaw’s
model.
Assess own progress and what you
learnt by completing a past exam
question using the Zones of Relevance
Challenge: Evaluate whether these
features are affecting a river’s profile of
dynamic equilibrium
In areas of resistant rock (e.g. on Exmoor), meandering streams and rivers will be incised into the landscape, forming interlocking spurs.
Interlocking spurs
V-shaped valleys and interlocking spurs
Predominantly vertical erosion results in a v-shaped valley.
Rapids are formed by variations in rock resistance
Bourke’s Luck Potholes, South Africa
Potholes provide evidence of fluvial erosion
What is the most dominant type of erosion here?
Abrasion
Where there are depressions / fissures, fine particles and larger boulders (‘grinders’) may become trapped and swirled around by the current
In resistant rock, potholes require hundreds to thousands of years to form
Potholes
Soft rock
Soft rock
Broken piecesof hard rock
RiverHard rock
Waterfalls
Where do waterfalls form?
Usually where there is varying resistance in the types of rock or where there is a fault running across a river.
Which processes operate?
Usually there is considerable hydraulic action due to the falling water. Abrasion is also likely to occur to create the plunge pool at the base of the waterfall
Which feature is formed as the waterfall retreats upstream?
A gorge or canyon
High Force Waterfall, upper Teesdale, Yorkshire
• Tallest waterfall in England at 22m high
• 500m gorge downstream
How was it formed?
Resistant band of igneous rock (Whin Sill) overlying softer sandstone, limestone, shale and coal seam
Water erodes softer rock more quickly, creating an overhang and plunge pool
This eventually collapses and the waterfall retreats upstream
Can you remember how to describe the formation of ox-bow lakes?
What are these features, and what do they represent?
Ox-bow lakes. These show the former course of the river
Erosion (E) and deposition (D) around a meander (a bend in a river)
More erosion during flood conditions. The meander becomes bigger
The river breaks through during a flood. More deposition causes the old meander to become an ox-bow lake
Meanders
Meanders
Straight sections contain riffles or bars in the middle of the channel, where a ridge of bed load has been deposited in the middle of the river’s bed because the water velocity is slower here.
0.2 m/sec0.1 m/sec
• Sinuous bends in the river• Surface flow to outer bank and sub-
surface return to inner bank = helicoidal flow
• Velocity across the meander varies and is related to depth
• The fastest flowing water (the ‘thalweg’) is near the outside of the bend, where the water is deepest
• Here, erosion occurs creating a river cliff• On the shallower inside slower moving
water allows deposition to occur and a slip-off-slope or point bar forms
Outside of meander
Inside of meander
They are unstable and mobile features. When discharge and velocity increase they are easily eroded, and their position changes
The area where the sand or gravel is deposited is known as a point bar (also knows as an eyot)
Fluvial deposition – braided rivers
What is braiding and under what conditions does it occur?
It describes a section where the river has been forced to split into several channels separated by islands. It occurs in rivers supplied by large amounts of sediment load and / or rivers with variable / rapidly fluctuating discharges
The river becomes very wide in relation to its depth
Levees
Describe the process of levee formation shown in diagrams (a) – (d)
(a) During times of high discharge, the river floods. The competence of the river decreases as velocity is reduced when the river breaks the banks. Heavier, coarse material is deposited first
(b) Small banks of deposited material build up
(c) Subsequent floods result in further deposition on these banks and the bed of the river
(d) Raised banks, called levees are created and the river flows at a higher level than the floodplain
Deltas
• Feature of deposition at river mouth
• Velocity (and therefore competence) decreases on entering a lake or the sea
• They occur where river sediment load is very large, and where there are weak currents and / or small tidal range. The rate of deposition thus exceeds the rate of removal.
• Flocculation occurs as sea water and fresh water mix
• Clay coagulates and settles on the river bed
• Sorting of deposits occurs into topset beds (larger heavier material), foreset beds (medium graded particles) and bottomset beds (finest particles)
Curving shoreline and dendritic pattern of drainage, e.g. Nile
Fingers of deposition build out into sea along distributaries, e.g Mississippi
Pointed ‘tooth-like’ delta; material spread evenly on either side of channel, e.g. Tiber
Lesson 12 and 13
Lesson objectives
To identify and explain
the formation of river
Landforms along the profile
of a river
Success CriteriaSynthesise knowledge using tree
diagram.
Create a story board or flow diagram that
examines the formation of river landforms
from source to confluence of a river
Challenge: Incorporate Bradshaw’s
model.
Assess own progress and what you
learnt by completing a past exam
question using the Zones of Relevance
Challenge: Evaluate whether these
features are affecting a river’s profile of
dynamic equilibrium
Plenary:
Mark scheme
Lesson 12 and 13
Lesson objectives
To identify and explain
the formation of river
Landforms along the profile
of a river
Success CriteriaSynthesise knowledge using tree
diagram.
Create a story board or flow diagram that
examines the formation of river landforms
from source to confluence of a river
Challenge: Incorporate Bradshaw’s
model.
Assess own progress and what you
learnt by completing a past exam
question using the Zones of Relevance
Challenge: Evaluate whether these
features are affecting a river’s profile of
dynamic equilibrium
Process and impact of rejuvenation – knick points,
waterfalls, river terraces and incised
meanders.
Lesson 14, 15 and 16
Lesson 14, 15 and 16
Lesson objectives
To examine the causes of
rejuvenation and how a
rejuvenated valley can be
recognised.
Success criteria• Produce a 3 min PowerPoint
presentation and revision hand out for next lesson
• To be able to define ‘rejuvenation’.
• To produce an annotated diagram showing the causes of and effects of rejuvenation.
• To relate coastal terms Isostatic recovery and Eustatic Change.
• To be able to draw and annotate between Ingrown and Entrenched form of Incised meanders.
Starter:
Draw diagram showing formation the of a
meander & Ox Bow lake, a Delta and a
Waterfall, then annotate.
Significant breaks in slope (Knick points) along a river’s long profile may be due to rejuvenation.
What is rejuvenation?
It occurs when there is a fall in sea level (relative to land) or the land surface rises. Vertical erosion increases and, starting from the sea, the river adjusts to the new base level. The knick point (where the old profile joins the new) thus moves upstream
original sea leveloriginal long profile
What feature will be found here?
A waterfall
relative fall in sea level (or rise of land surface)
new sea level
knick point
new long profile
Rejuvenation
Rejuvenation may also be caused by the sea eroding through and creating a breach in the coastal geology, e.g. River Lyn on the north Devon coast.
Original course of River Lyn
Breach in coastal geology
Knick point waterfalls
Present – day village of Lynmouth
‘Valley of the rocks’
Rejuvenation
Renewed energy from rejuvenation results in increased vertical erosion and incised (deepened) meanders
Steep river cliff
Inside of meander slopes
gently
When incision is less rapid and lateral erosion is occurring, meanders become ingrown, e.g. the River Wye at Tintern.
FLOW
Entrenched meanders have a symmetrical cross-profile (rapid uplift) whereas ingrown meanders are more asymmetrical (slower uplift)
Ingrown and entrenched meanders
What are the differences in form between entrenched and ingrown meanders?
When incision is rapid and vertical erosion dominates, an entrenched meander is formed, with steep sides and a gorge-like appearance
Floodplains and terraces
Are floodplains features of erosion or deposition?
River terraces result from which process?
BothRejuvenation forms river terraces
How are they formed?
• Lateral erosion
• Meander migration
• Valley widened
• Deposition of sand and silt during floods
How are they formed?
• Following rejuvenation, river sinks into former valley
• Old floodplain left at higher level
• Several stages of rejuvenation can create several terraces, e.g. lower course of the River Thames
What are they?
Remnant of former floodplain
Terrace
Floodplain
Bedrock
http://www.bbc.co.uk/learningzone/clips/river-terraces/402.html
Plenary:
Lesson 14, 15 and 16
Lesson objectives
To examine the causes of
rejuvenation and how a
rejuvenated valley can be
recognised.
Success criteria• Produce a 3 min PowerPoint
presentation and revision hand out for next lesson
• To be able to define ‘rejuvenation’.
• To produce an annotated diagram showing the causes of and effects of rejuvenation.
• To relate coastal terms Isostatic recovery and Eustatic Change.
• To be able to draw and annotate between Ingrown and Entrenched form of Incised meanders.
What causes flooding?Lesson 19
Lesson 19
Lesson objectives
To understand and be able
to calculate flood frequency
and recurrence interval and
apply to concept of flood
magnitude.
Success criteria
• Design a mind map showing the causes of flood (human and physical)
• To complete flood
frequency calculations.
Starter: Causes of river flooding
What physical and human factors contribute
to flooding?
Human factors
Excessive, prolonged rainfall
Saturated soil Deforestation
Urbanisation
Physical factors
Snow melt
Frozen soil
Local relative rise in sea level / storm surge
Steep gradientImpermeable rock
High drainagedensity
Flooding occurs when a river exceeds its bankfull discharge
River managementShort, intense rainfall event
Plenary:
Complete the flood risk and recurrence
interval calculations.
Lesson 19
Lesson objectives
To understand and be able
to calculate flood frequency
and recurrence interval and
apply to concept of flood
magnitude.
Success criteria
• Design a mind map showing the causes of flood (human and physical)
• To complete flood
frequency calculations.
Flooding in an MEDC
Lesson 20 and 21
Lesson 20 and 21
Lesson objectives
• To assess the causes an impacts of flooding in an MEDC.
Success criteria
• Design MEDC case study.
High risk areas; Shrewsbury, UKStarter: Examine the map below and identify causes of flooding in Shrewsbury town and the socio-economic impacts.
Shrewsbury lies inside an incised meander loop of the River Severn. The town centre lies above the floodplain but some of the main transport routes lie vulnerably low, and recent development has taken place on low lying floodplain
Boscastle, Cornwall
Suggest the ways in which the physical geography of the area may increase the speed of onset and severity of flooding
Study the photograph which is looking upstream from Boscastle harbour towards the village of Boscastle.
Impact of flash flooding in Boscastle, - August 2004
• Intense low pressure weather system caused localised heavy thundery downpours
• 200mm rain fell in 24 hours (most between midday and 5pm on the 16th) on high ground to the east.
• Already saturated catchment – rapid runoff• Boscastle lies in a deep valley just
downstream of the confluence of the rivers Valency and Jordan
• 2m rise in river levels in one hour• Debris caught under narrow bridge caused 3m
high wave of water which burst down main street when bridge collapsed
• 70-80 cars swept away, significant structural damage, 100 people air lifted to safety but no loss of life
Southern Britain, July 2007
Normal Jet stream
June – July 2007
Causes;
• Abnormal track of jet stream
• Rainfall totals for May-July highest since 1776
• Infiltration / percolation capacity minimal
• Exceptional rainfall on 20th July – event only expected once in several hundred years
Consequences;
• Flash floods across southern England; especially lower Severn and upper Thames catchments
• Drainage systems overwhelmed and transport networks severely disrupted - £25 million damage to Gloucestershire’s road system – the year’s budget!
• 45, 000 households lost power; 350,000 lost running water – £1billion cost to water industry
• £3 billion damage covered by insurance. Equivalent amount uninsured loss
• 50% crops lost in affected areas – shortages and price increases
• 3 people died
MEDC flooding case study structure.1. Title2. Images3. Map location (annotated identifying
obvious human/ physical causes, floodplain and flood risk area)
4. Causes (explained, interdependent links)
5. Impacts – Short term(social, economic, environmental)
6. Impacts – Long term (social, economic, environmental)
7. Management strategies – What has been put in place to reduce risk and impacts of flood in future?
TIP
Include statistics e.g. cost of damage and claims made, numbers injured/ killed.
Plenary:
Identify 1 cause and 3 impacts of flooding in
your chosen MEDC case study to share with
the class.
Lesson 20 and 21
Lesson objectives
• To assess the causes an impacts of flooding in an MEDC.
Success criteria
• Design MEDC case study.
Flooding in an LEDC
Lesson 22 and 23
Lesson 22 and 23
Lesson objectives
To assess the causes and
impacts of flooding in
Bangladesh (2007).
Success criteria
• Design LEDC case study.
Starter: High risk areas - Bangladesh
Major rivers converge?
?Himalaya Mountains; (monsoonal) rainfall and snow melt
?
Storm surges, especially during cyclones / hurricanes. Also local sea level rises of 7mm/year
80% of country occupies low-lying delta < 1m above sea level
What are the human influences?
• Deforestation
• Agricultural practices
• Densely populated
• Urbanisation – Dhaka population over 1 million
• Embankments built (road and river) – have prevented back-flow of flood water and increase siltation in drainage channels
• Low GDP and lack of investment
?
Explain why these factors have been identified as causes of flooding?
Flooding in Bangladesh, 2004Exceptionally high rainfall totals in the monsoon of 2004 led to widespread flooding in July and August
Consequences of flooding
38% land area flooded – worst floods for 6 years
800,000 ha agricultural land flooded – small scale farmers severely affected
Capital city, Dhaka Flooded.
36 million people made
homeless (nearly 29% of total population)
800 dead by mid-September
Spread of disease Flood waters mixed with
raw sewage caused diarrhoea outbreak
Infrastructure severely Damaged – damage to roads, bridges, school
and hospitals estimated at $7 billion
$2.2 billion estimated cost
of damage (4% of GDP
for 2004)
LEDC flooding case study structure.1. Title2. Images3. Map location (annotated identifying
obvious human/ physical causes, floodplain and flood risk area)
4. Causes (explained, interdependent links)
5. Impacts – Short term(social, economic, environmental)
6. Impacts – Long term (social, economic, environmental)
7. Management strategies – What has been put in place to reduce risk and impacts of flood in future?
TIP
Include statistics e.g. cost of damage and claims made, numbers injured/ killed.
Add a paragraph at the bottom explaining why the impacts suffered from floods are different between MEDCs and LEDCs (based on our examples).
Plenary:
Identify 2 causes and 3 impacts of flooding
in Bangladesh ready to present to the class.
Lesson 22 and 23
Lesson objectives
To assess the causes and
impacts of flooding in
Bangladesh (2007).
Success criteria
• Design LEDC case study.
Flood management strategies
Lesson 24
Lesson 24
Lesson objectives
• To examine the use of hard and soft flood management strategies.
Success criteria
• To complete hard and soft engineering worksheet
• Begin Case Study
Starter:
Think of 5 questions beginning with the letter ‘W’
that you could ask about this image
Task 1:Hard and soft engineeringHow would you define the following key terms?
Hard engineering:
Strategies involve the building of structures or alteration of
the course / structure of the river. The aim is to reduce the
frequency and magnitude of flood events, and therefore
reduce the damage that floods cause.
Soft engineering:
Abatement strategies which aim to work with natural
processes, and be more sustainable solutions to flooding
Task 2:
• Using your text book and completing further research, complete the handout showing you different methods of hard and soft engineering to manage river flooding.
• You must include the following in each annotation box:
1.What it is
2.Aim
3.Named river where used
4.Advantages
5.Disadvantages
Flood management
Hard engineering strategies involve the building of structures or alteration of the course / structure of the river
The aim is to reduce the frequency and magnitude of flood events, and therefore reduce the damage that floods cause
1. Can you describe the measures shown in the diagram opposite?
2. What might be the advantages and disadvantages of hard engineering methods?
After the disastrous Lynmouth floods of 1952, the river was managed. What management can you see in the photograph?
Cottages now set back from river bank
Entry of East Lyn tributary is under a
wide bridge to prevent damming
Channel has been straightened
Building of concrete
revetment to increase speed of river flow in time of flood
Lynmouth – flood controls
What are the arguments for and against hard engineering? Outline the impacts for each.
Plenary: Hard engineering
FOR AGAINST
Reduction in flooding and therefore protects property
Takes water away from towns more quickly
Increase in water supply e.g. on the Nile
Improved navigation e.g. Mississippi
Allows energy to be created e.g. hydroelectric power on the Colorado
Can lead to destruction of habitats along river bank
Can be visually intrusive
It can dramatically increase peak discharge, duration and timing of floods downstream
Where meanders have been straightened, the river will try to re-establish itself
Straightening courses can lead to greater upstream erosion and downstream deposition
Lesson 24
Lesson objectives
• To examine the use of hard and soft flood management strategies.
Success criteria
• To complete hard and soft engineering worksheet
• Begin Case Study
Case study: The Three Gorges Dam, China.
Lesson 25
Lesson 25
Lesson objectives
• To examine the use of a dam in managing flood risk
Success criteria
• Produce a detailed case study
Starter:Identify as many impacts as a result of this
method of hard engineering.
Impact of the Three Gorges dam, China
• Largest ever river hard engineering project
• Dam completed in 2006; 2.3 km long and over 100m high, with reservoir (660km by 1km) behind
• Project due to complete in 2009, at a cost of an estimated £25 billion
Defence Criticism
Produce HEP for 13 million people Cost
Reduce the flood risk for 15 million people
1.2 million people relocated to newly built settlements following reservoir creation
Improve navigation for faster, cheaper and safer shipping
Cultural monuments lost due to creation of reservoir
Boost local economic growth Downstream sediment supply decreased by 50% - increased erosion
Improved water supply Disruption to habitats and environment
The Three Gorges Dam
Hard Engineering case study structure
• Title
• Method of engineering
• Map location and images
• Name of river
• Aim: Why it was built, what was the need? (include flood magnitude and frequencies – any socio-economic/ environmental issues that prompted it?
• Size and cost of dam
• Labour and cost in its maintenance
• Benefits (socio-economic, environmental)
• Disadvantages (socio-economic, environmental)
• Conclusion
Plenary 1: Past exam question (15 marks)
Plenary 2: Keyword test
Define:
Hard engineering
Soft engineering
Afforestation
Rejuvenation
Profile of dynamic equilibrium
Erosion
Hydraulic radius
Percolation
Base level
Drainage basin
Lesson 25
Lesson objectives
• To examine the use of a dam in managing flood risk
Success criteria
• Produce a detailed case study
Case study: Restoration schemes, River Quaggy
Lesson 27
Lesson 27
Lesson objectives
• To examine the impacts for the use of river restoration schemes
Lesson criteria
• Produce a detailed case study
Starter: What are the impacts associated with this method of engineering?
What is soft engineering?
Soft engineering
Abatement strategies which aim to work with natural processes, and be more sustainable solutions to flooding
• Afforestation
• Contour ploughing and strip farming to reduce runoff
• Floodplain zoning to allow (economically less valuable) areas to flood naturally
• Conservation and restoration schemes; returning rivers to their original state and protecting, e.g. bales to improve water quality
• Forecasting and early warning, e.g. Environment Agency flood watch and risk maps. Some small-scale community projects in Bangladesh have resulted in early warning systems and lives are being saved
River restorationThe River Cole near Swindon underwent a restoration project between 1994 and 1996. The aims were to change the water course back to a more natural state, improve water quality and manage bank side vegetation and habitats. The main strategies are shown below
River Restoration: River Quaggy, UK
http://www.qwag.org.uk/quaggy/restoration.php
Soft Engineering case study structure
• Title
• Method of engineering
• Map location and images
• Name of river
• Aim: Why it was constructed, what was the need? (include flood magnitude and frequencies – any socio-economic/ environmental issues that prompted it?
• Size and cost of project
• Labour and cost in its maintenance
• Benefits (socio-economic, environmental)
• Disadvantages (socio-economic, environmental)
• Conclusion
Plenary: Plan out your answer for this 15 mark question
MarkschemeThere is a need to make clear why soft engineering strategies are preferred to hard engineering or vice versa.
This is the likely route so there should be reference to the advantages of soft engineering and possibly also the
disadvantages of hard engineering. There will probably be some description of the relevant strategies that may
be adopted. Alternatively, candidates may disagree with the statement and provide
advantages of hard engineering and disadvantages of soft engineering. The final option is to perceive the
complementary nature of the two approaches and discuss this aspect. Advantages of soft engineering are
likely to refer to its greater sustainability, its limited interference with a natural system, the ability to improve
the environment at times and to work with natural systems so that wetlands and habitats may be
restored/created, the relative affordability. Disadvantages of hard engineering relate to the extent to which
there is change to the natural system and questions over its sustainability – the large scale of building dams and
their environmental impact, as well as economic and social costs. Similarly, channelisation means that the flood
risk may be increased downstream and habitats destroyed. Advantages of hard engineering
may relate to their effectiveness, especially in the short term, associated schemes for HEP, irrigation which
give other advantages. Disadvantages of soft engineering relate to ineffectiveness in already built-up
areas, the fact that flood warnings allow preparation but are not preventing damage from flooding. They will be
seen as reducing the scale of risk rather than preventing flooding. The actual content will depend on the
specific strategies considered and whether there is exclusive discussion of soft Engineering strategies only.
There may be reference to case studies – such as River Quaggy, London, Lincolnshire, Oxfordshire (Cherwell),
Ouse, Jubilee River Channel, Carlisle, Three Gorges Dam, Colorado etc.15 marks)
MarkschemeThere is a need to make clear why soft engineering strategies are preferred to hard engineering or vice versa.
This is the likely route so there should be reference to the advantages of soft engineering and possibly also the
disadvantages of hard engineering. There will probably be some description of the relevant strategies that may
be adopted. Alternatively, candidates may disagree with the statement and provide
advantages of hard engineering and disadvantages of soft engineering. The final option is to perceive the
complementary nature of the two approaches and discuss this aspect. Advantages of soft engineering are
likely to refer to its greater sustainability, its limited interference with a natural system, the ability to improve
the environment at times and to work with natural systems so that wetlands and habitats may be
restored/created, the relative affordability. Disadvantages of hard engineering relate to the extent to which
there is change to the natural system and questions over its sustainability – the large scale of building dams and
their environmental impact, as well as economic and social costs. Similarly, channelisation means that the flood
risk may be increased downstream and habitats destroyed. Advantages of hard engineering
may relate to their effectiveness, especially in the short term, associated schemes for HEP, irrigation which
give other advantages. Disadvantages of soft engineering relate to ineffectiveness in already built-up
areas, the fact that flood warnings allow preparation but are not preventing damage from flooding. They will be
seen as reducing the scale of risk rather than preventing flooding. The actual content will depend on the
specific strategies considered and whether there is exclusive discussion of soft Engineering strategies only.
There may be reference to case studies – such as River Quaggy, London, Lincolnshire, Oxfordshire (Cherwell),
Ouse, Jubilee River Channel, Carlisle, Three Gorges Dam, Colorado etc.15 marks)
• Level 1 (Basic) 1-6 marks
Identifies soft and/or hard engineering strategies.
Refers to simple reasons why soft engineering is better.
Some use of appropriate terminology present at the higher end.
Coastal flooding response – if relevant, generic aspects.
• Level 2 (Clear) 7-12 marks
Describes strategies and advantages and / or disadvantages of soft and / or
hard engineering.
Begins to discuss why soft engineering strategies are better (or an alternative
option).
Uses strategies to illustrate points – will illustrate one aspect only or with
imbalance e.g. advantages of soft engineering may be discussed with no
reference to hard engineering.
Case study material may be included in a descriptive way.
Appropriate geographical terminology is used.
• Level 3 (Detailed) 13-15 marks
Clear, purposeful discussion that seeks to put a case for/against soft engineering
or is aware of the complementary nature of the strategies.
Advantages and disadvantages of soft and hard engineering are discussed.
Strategies are effectively used to illustrate concepts.
Case studies are used to make points.
Specific terminology is used throughout.
Lesson 27
Lesson objectives
• To examine the impacts for the use of river restoration schemes
Lesson criteria
• Produce a detailed case study
Flood prediction and warning – Floodplain zoning, role of
Environment Agency(also methods of soft
engineering)
Lesson 28
Lesson 28
Lesson objectives
• To assess the use of flood prediction and warning and the importance of it, with specific reference to the Environment Agency (EA).
Success criteria
• Complete floodplain zoning diagrams
Starter: How useful is this floodplain informationchart in informing flood risk?
Floodplain zoning
Draw and annotate your own floodplain
zoning map, annotate each zone and
explain the importance of a floodplain zone
map.
Land use management on the floodplain (method of soft engineering)
PredictionFeet
above SLMagnitude
RecurrenceInterval (years)
796.8 1 57.00
792.3 2 28.50
791.4 3 19.00
791 4 14.25
789.9 5 11.40
789.8 6 9.50
789.7 7 8.14
789.6 8 7.13
789.5 9 6.33
789.4 10 5.70
785.1 20 2.85
782.8 30 1.90
779.5 40 1.43
774.1 50 1.14
All flood protection methods are designed to cope with certain magnitudes and frequency of floods
Hydrologists try to predict the likelihood of future flooding by examining historical discharge and flood records
What is flood recurrence?
The average number of years between floods of a certain size is the recurrence interval or return period
Study the data shown to understand the recurrence intervals
The Environment AgencyWhat does The Environment Agency do?
• Monitoring of water levels and flows
• Building and maintenance of flood defences on coast and rivers
• Use of radar rainfall data combined with discharge data to predict flood risk and issue flood warnings through; media, automated messages to risk groups, flood-line for the public
• Implements and coordinates incident plans
• Produce flood risk maps
• Advises planners and developers on flood risk
• Develops information, e.g. on the website about flood risk and what to do in the event of, and aftermath of a flood
The Environment AgencyFlood prediction software• Helps to model likely outcomes, warnings may be issued in terms of the
potential severity of the flood risk and the areas that could be affected.• The Environment Agency’s England and Wales flood mapping system
is based on the National Flood Risk Assessment (NaFRA), which uses a method called Risk Assessment for Strategic Planning (RASP) – Risk-based probabilistic approach which factors the location, type, condition and performance of flood defences into the risk assessment.
• People concerned can call Floodline Direct to receive a service called Flood Warnings Direct (automatic telephone warnings).
• People in high risk areas e.g. Cumbria, receive automatic phone warnings to alert inhabitants in potential flood risk zones. Flood wardens ensure temporary defences are in place and evacuations carried out when necessary.
Plenary: Exam question 1How can planners help to restrict flood damage? (6)
They can stop the water getting to the settlement, by building a
reservoir and controlling the discharge. This was done when the Aswan Dam was built on the River Nile. They can also make sure that towns and cities are
not built too near a river which is likely to flood.They can also
make sure that there are enough sandbags to stop the floods
affecting the nearby buildings.
Good use of appropriate term; could just have said “water”
Suspect choice of example; prior to
Aswan being built the farmers relied on floods to provide
fertile alluvium. How much damage was
done?
Naïve; there are very few ‘new’
settlements whose location
can be determined by
planners. Impossible for every riverside
settlement have a stock - again, rather naive
Over-simplistic answer, with some poorly
chosen examples (2/6)
Where? needs to be upstream
Typical answer
Exam question 1
How can planners help to restrict flood damage? (6)
Planners can restrict the amount of building on the floodplain of river, or of buildings near to the
river (as at Lynmouth). They can alter the channel of the river the river to straighten and speed up its flow. They can allow water
meadows to flood, storing water, which can also be achieved by
upstream retention e.g. reservoirs.
Useful additional
detail
Always a good idea to add a named
exampleAgain, complex sentence
allows point to be developed
fully
Two examples combined in the one sentence
Although only three sentences, each is full,
with examples.
Would score as 3 x 2.
Specimen answer
Exam question 2Examine the physical factors responsible for flooding.
(25)
Points to consider
1. Introduction could attempt to classify the causes, e.g. climatic, geomorphological, to indicate range of factors, and structure of essay.
2. Range of detailed examples needed, from MEDCs and LEDCs
3. Essay should demonstrate that many floods are multi-causal.
4. Maps and diagrams integrated into text discussion
5. Answer should be well structured and well written, with appropriate use of specific vocabulary. Conclusion could consider changing physical factors likely to make flooding more likely, e.g. global warming.
Lesson 28
Lesson objectives
• To assess the use of flood prediction and warning and the importance of it, with specific reference to the Environment Agency (EA).
Success criteria
• Complete floodplain zoning diagrams