Discharge m³/s Rainfall mm 1 AQA GEO4B Geographical Issue Evaluation Skills Photocopiable/digital...

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Discharge m³/s Rainfall mm 1 AQA GEO4B Geographical Issue Evaluation Skills Photocopiable/digital resources may only be copied by the purchasing institution on a single site and for their own use © ZigZag Education, 2013

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Page 1: Discharge m³/s Rainfall mm 1 AQA GEO4B Geographical Issue Evaluation Skills Photocopiable/digital resources may only be copied by the purchasing institution.

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Dis

char

ge m

³/s

Rain

fall

mm

AQA GEO4BGeographical Issue Evaluation

SkillsPhotocopiable/digital resources may only be copied by the purchasing institution on a single site and for their own use  

© ZigZag Education, 2013  

Page 2: Discharge m³/s Rainfall mm 1 AQA GEO4B Geographical Issue Evaluation Skills Photocopiable/digital resources may only be copied by the purchasing institution.

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Geographical Investigation

Graphical Techniques

Hydrograph

Bar Chart

Line Graph

Simple

Comparative

Compound

Divergent

Pie Chart

Radar Graph

Climate Graph

Proportional circles

Kite & radial diagrams

Scattergraphs

Triangular graphs

Logarithmic scales

Basic SkillsAnnotation

Photos

OS maps

Base maps

Graphs

Diagrams

Sketch maps

Use of overlays

Literacy skills

Investigative Skills

Identify geographical questions

Data selection & collection

Sampling methods

Random

Stratified

SystematicQualitativeQuantitativePrimarySecondary

Processing data Interpreting data

Risk assessment

Drawing conclusions & assessing validity

Evaluation

Evaluate geographical information

Evaluate geographical issues

Statistical Techniques

Spearmann Rank

DisparityInterquartile range

Standard deviation

Mean, Median, Mode

Comparative testsChi Squared

Mann Whitney U test

Cartographical Skills

GIS

Choropleth

OS maps1:25,000

1:50,000

Isoline maps

Dot maps

Base maps

Sketch maps

Town centre plans

Proportional symbol maps

Flowline

Desire line

Trip lines

Synoptic charts

Use of ICT

Remotely sensed data

Digital images

Photos

Satellite images

Data Presentation

GIS

Statistics

Use of databases

Census

Environment Agency

Met Office

Page 3: Discharge m³/s Rainfall mm 1 AQA GEO4B Geographical Issue Evaluation Skills Photocopiable/digital resources may only be copied by the purchasing institution.

You can be asked to undertake any one of the skills shown on the previous slide.

However, some are going to be more appropriate to the pre-release material than others.

Do make sure that you are familiar with all of the different calculation methods and that you take a calculator and full maths set (protractor, compass, ruler) into the exam.

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WHAT SKILLS DO I NEED?

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STREAM ORDER HIERARCHYThis is a simple method of classifying the size of a stream based on the number of tributaries it has of certain sizes.

When two tributaries of the same size meet, the stream moves up the hierarchy, e.g. when two first-order streams meet, they create a second-order stream.

However, if a first-order and a second-order stream meet they simply remain a second-order stream. It needs the meeting of two second-order streams to create a third-order stream.

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SIX-FIGURE GRID REFERENCES

Top Tips: Read ‘along the corridor and up the stairs’ to get the four-figure grid

reference. Use a ruler to measure exactly how far across the square you need

to go (you need to subdivide each square into 10 segments). On a 1:25,000 map, 4 mm is 1 segment across. These form your

third and sixth numbers of the six-figure grid reference. Don’t forget, if what you are looking for is on the line then the third

(if going along) or sixth (if going up) number is 0.

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DRAWING A CROSS-SECTION

1. Identify the cross-section on your OS map (if possible, draw a faint pencil line so you don’t lose your place).

2. Look at how the contour lines change across your profile; follow them round until you find out their height.

3. What would you expect the land to be doing either side of the river?

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60

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40

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20

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00 50 100 150 200 250 300 350 400 450 500

1. Use the scale on the OS map to help you understand the distance you will be travelling – 4 cm = 1 km, therefore 2 cm (the distance of the transect given in the question) = 500 m. 4 mm = 50 m.

2. Plot your axis labels on your graph – along the horizontal axis needs to be your distance (0–500 m going up in 50 m intervals). Along the vertical axis needs to be the height of the land – check your transect – what’s the highest point shown?

3. Now make your first plot (0 m – the start of the transect should be 60 m high.)4. Now measure 4 mm (50 m from the start of the transect). What is the height of the land?

Plot this in the correct place on your graph.

DRAWING A CROSS-SECTION

x

x

60m

6. Now continue working your way along the transect line and plotting the heights.

7. Finally, join the crosses up with a smooth curve.

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COMPLETED CROSS-SECTION

River

Distance in metres across the cross section

Hei

ght o

f lan

d (m

)

Page 9: Discharge m³/s Rainfall mm 1 AQA GEO4B Geographical Issue Evaluation Skills Photocopiable/digital resources may only be copied by the purchasing institution.

PLOTTING A FLOOD HYDROGRAPH

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How to plot it:1. Choose a suitable scale for the

axes – you can have one scale for rainfall and another for discharge.

2. Plot the rainfall as bars first.3. Plot the discharge as a line.4. Identify the peak rainfall

(highest amount).5. Identify the peak discharge

(highest amount).6. Calculate the lag time (time

between peak rainfall and discharge).

7. Is the rising limb gentle or steep?

8. Is the falling limb gentle or steep?

9. What is unusual about the Wansbeck hydrograph? Can you suggest why?

10 20 30 40 50 60 70 80

Hours from start of storm

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2

3

4

5

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Rai

nfal

l (m

m)

0

50

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150

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350

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0

Dis

char

ge (

m³/

s)

Rainfall River flow

Peak Rainfall

Peak Discharge

Secondary discharge peak

1st Peak Rainfall

Lag time = 3 hours

Stee

p ris

ing

limb

Steep falling limb

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This graph shows the distribution of data around the mean or median.

It is plotted as a line with a series of dots recorded if there are several pieces of data that are the same.

The points are NOT joined up.

HOW TO PLOT A DISPERSION GRAPH

Rainfall data for 5th–7th September

Note how the number of hours when there was no rainfall recorded really skews the mean and median data.

Mean

Median

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1. The mean is very straightforward; this is the average – add up all the data and then divide by the number of pieces of data you have.

2. For the median, you need to put all your data in order. Then find the middle number – this is the median. If you have an odd number of data sets this is easy, e.g. I have 51 sets of data so the median number will be the data found at number 26 as I count up. If you have an even number of data sets, you will need to split the difference between the two middle numbers, so if you have 50 sets of data you need to add the data you find at 25 to the data you find at 26 and then divide it by 2 to get your answer.

3. The mode is the most frequent number, so if in a list of numbers ‘15’ occurs five times and the other numbers only occur once or twice, then 15 is the mode.

CALCULATING THE MEAN, MEDIAN AND MODE

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This is a method used to show the spread (dispersion) of a set of data around the median. It is calculated by finding the difference between the upper and lower quartiles, which shows where 50% of all data is found.

The smaller the interquartile range, the more the data is grouped around the median showing that there is not much variation between the data.

INTERQUARTILE RANGE

Using the formulae provided, state the upper quartile (UQ), lower quartile (LQ) and the interquartile range (IQR) for your completed dispersion diagram.

UQ = th position in the rank order =

LQ = th position in the rank order =

IQR = UQ – LQ =

n = number in the sample3.2 mm

0.0 mm

3.2 – 0.0 = 3.2 mm What does this tell us about the spread of rainfall over these three days?

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1. Standard deviation is used to show the amount of clustering of each individual value around the mean. Its symbol is σ (the Greek letter sigma).

2. A low standard deviation shows that the data is clustered around the mean value, whereas a high standard deviation shows that the data is widely spread with some figures being significantly lower or higher than the mean.

3. The formula is easy: it is the square root of the variance. The variance is the average of the squared differences from the mean.

4. To calculate the variance: Work out the mean () (the total of all the data divided by the number of pieces of

data = n). Then subtract the mean from each number and square the result (the squared

difference). Then work out the average of the squared differences. Now you can calculate the standard deviation by square-rooting the variance. Then you need to decide whether your data is clustered or not.

STANDARD DEVIATION

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Time River flow (cumecs)

00.00 57 01.00 67.3 02.00 78.5 03.00 85.7 04.00 93 05.00 99.2 06.00 107 07.00 124 08.00 145 09.00 169 10.00 191 11.00 217 12.00 243 13.00 269 14.00 297 15.00 337 16.00 357 17.00 324 18.00 304 19.00 275 20.00 241 21.00 215 22.00 206 23.00 213

-139.57-129.27-118.07-110.87-103.57-97.37-89.57-72.57-51.57-27.57-5.5720.4346.4372.43100.43140.43160.43127.43107.4378.4344.4318.439.4316.43

19479.78

16710.73

13940.52

12292.16

10726.74

9480.92

8022.79

5266.41

2659.47

760.10

31.02

417.38

2155.75

5246.11

10086.18

19720.58

25737.78

16238.4

11541.2

6151.27

1974.03

339.66

88.92

269.94

4714.7 = 196.57 199337.84

= Standard deviationX = Individual value = Meann = Number in the sample = Sum of

𝜎=√∑ ( 𝑋− 𝑥 )2

𝑛

= √8305.74 = 91.14

This standard deviation result shows a wide spread around the mean showing considerable fluctuation in discharge during the day.

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Scatter graphs can be used to show the relationship between two data sets. However, it is only a ‘best fit’ relationship. For accuracy, Spearman Rank Correlation Coefficient can be used to prove the strength of a relationship.

Once points are plotted, a line of ‘best fit’ can be drawn. The pattern of the scatter graph shows the relationship between the data. With a positive relationship, as one set of data increases, so does the other. With a negative relationship, an increase in one data set causes a decrease in the other.

SCATTER GRAPH

0 5 10 15 20 25 30 35 40 4505

1015202530354045

0 5 10 15 20 25 30 35 40 450

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10

15

20

25

30

35

40

45Positive Relationship Negative Relationship

Line of Best Fit

Page 16: Discharge m³/s Rainfall mm 1 AQA GEO4B Geographical Issue Evaluation Skills Photocopiable/digital resources may only be copied by the purchasing institution.

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Cumulative frequency is when the data of one section is added to the data of the next section to give a running total.

This is particularly useful for giving an idea of how rainfall builds up over time and for showing why the ground would eventually become saturated leading to overland flow.

When plotted, cumulative frequency leads to a curve on a graph.

WHAT DO WE MEAN BY CUMULATIVE FREQUENCY?

0 5 10 15 20 25 30 350

10

20

30

40

50

Figure 2 – 5th September

Cumulative rainfall (mm)

Dis

char

ge (c

umec

s)