# AQA Geography Skills Unit 4A

Revision for Unit 4A of the AQA Geography A level exam

- Created by: alex
- Created on: 12-06-13 16:18

## Section A

**The Fieldwork Investigation - River Liza/Ennerdale Study**

Aim - Investigate changes in channel characteristics downstream of the River Liza

Hypothesis:

- River discharge will increase with distance downstream (velocity x cross sectional area)
- Cross-sectional area will increase with distance downstream
- Hydraulic radius will increase with distance downstream (cross sectional area/wetted perimeter)

Method (for hypothesis)

**Velocity**

- record the time taken for a float to travel a known distance (1m) - used an orange/squash ball, drops just below the surface preventing influence of air resistance
- using a flow meter or a turbine on a stick which gives a result in m/s
- velocity increases downstream and becomes a laminer flow, the volume of water increases and less friction with river bed and bedload

## Section A

**The Fieldwork Investigation - River Liza/Ennerdale**

**Cross- sectional area**

- average width x depth
- width - measure the straight line distance from one bank to another - 3 for average
- depth - use stratified sampling, at regular intervals record the depth using a metre ruler

**Wetted perimeter**

- measure along the wetted banks and bed along the cross section of the river, record the distance

Sites chosen (10)

- source was located at approx 660m
- 8km in length
- stratified sampling used - over whole course in order for comparison

## Section A

**Risk Assessment (identify initial risk -> controll measure -> reasses level of risk)**

Drowning

- Initially high level risk
- reduced by staying below the knee
- being careful of overhanging cliffs
- awareness of deep areas e.g. pools and meanders
- making sure access is safe and secure - going in groups of at least 2
- checking local weather report

Broken/twisted ankle

- initially medium risk
- walking boots cover ankle, well fitted
- clear routes etc

Getting lost etc

- only going to 600m
- first aider/kit/phone/compass/navigation etc

## Section A

**The Ennerdale Valley - River Liza study**

- 8km in length from source to mouth
- 2 hostels in the valley e.g. black sail hut
- has the significant features
- tributaries (small) - high beck, low beck, scarth beck
- eyots and braided streams
- misfit stream in middle course - bigger flood plain than river would make

Data -

- 10 sites for spearmans rank
- why present - to compare, visualise changes, show trends
- line graph for depth and width, inversed axis for depth
- display graphs on each site on map - GIS
- proportional lines for width
- Does support hypothesis for discharge (cumecs) - site 3, 0.037, site 10 1.187
- Doesn't support hypothesis for cross sectional area m2 - site 1, 0.02, site 9, 2.5, site 10 2.24

## Section A

Spearmans Rank Correlation Test

- between -1 and 1, closer to 1 a positive strong relationship
- rank with 1 at lowest number (highest if time is a variable - as it is slowest)
- strong relationship - not neccessarily mean one variable has caused the changes in other

Chi -squared Test

- used to examine spatial distributions
- compares the data that have ben collected (observed) against a theoretical random distribution of those data (expected)
- null hypothesis 'there is no significant difference between the observed distribution and the expected distribution'
- if falls outside of 95% , we cannot be sure that any relationship did not occur by chance, the relationship is too small to be statistically significant - collecting more data further.

Mann - Whitney U Test

- whether two sets of data originate from the same population (same distributions)
- null hypothesis and alternative hypothesis
- if lowest statistic for U is less than the critical value, null hypothesis rejected

## Section A - previous questions

Explain why the location of your fieldwork was appropriate for the investigation

- aim- to investigate changes in channel characteristics downstream of the river liza
- in accordance to bradshaw model
- caused a need for a number of sites upstream and downstream - used ennerdale valley
- has the features of upper, middle and lower course
- allowed 10 sites to occur throughout the river using stratified sampling
- river located in the lake district national park preventing human intervention on the river
- small scale - health and safety whilst allowing the collection of reliable data that may have been more difficult to access on a larger valley
- aims informed using a selection of textbooks to find agreed theory as well as bradshaw

Assess the usefulness of one method used to collect data for the investigation

- collect discharge for investigation
- in order to do this need width and depth (cross sectional area) and velocity
- finding a mean width for each site (tape measure), using stratified sampling with 10 intervals for depth.
- for velocity - a brightly coloured visible float, calculated time took to travel 1 m, average
- however, this was affected by air resistance, high chance of human error

## Section A - previous questions

Analyse the strenghts and limitations of this method in meeting the aim(s) of your investigation

- Strengths - measurement of discharge at each of the 10 sites allowed changes in channel characteristics to be observed, the average at each site allowed, process was conducted at a similar way at each site, depth width and velocity were recorded in upper middle and lower course of the river e.g. velocity did increase from 0.02 (site 2) to 0.53 (site 10)
- Limitations - the data will not take into consideration the impacts of river features, such as pools, when collecting therefore not being reliable.Anomalous results expected due to human error e.g. cross sectional area anomaly at site 8
- Overall, this method allowed an overall evaluation of changing channel characteristics according to velocity with a trend that related to the Bradshaw model

Evaluate the investigation in light of its aims and underpinning geographical theory

- Strengths - allowed 10 sites to be selected, location allowed upper and lower course to be studied and compared for analysis, allowed quantitative data to be collected. Enough data was collected to disprove the null hypothesis
- Limitations - our hypothesis did not evaluate any qualitative measures such as channel bed roughness, due to restrictions of health and safety the stratified sampling technique was interrupted by access etc, would be more reliable if more sites and data, compared with other rivers would allow complete analysis

## Section A - previous questions

Assess one method used to analyse your data. Explain why this method was suitable for your purposes.

- Spearman's rank - compared relationship of discharge and distance from source
- rs = 0.983 which was above the 95% and 99% level showing a significant strong positive relationship - suitable for showing discharge changes with respect to distance - aim,
- produced a figure between -1 and +1
- did not happen by chance
- close to 1 showing a strong correlation

Describe one technique that you used to present your data. Explain why this was an appropriate technique to use.

- Used a bar graph with inversed axis to present depth - gave visualisation for each site allowing a comparison to occur and trends to be seen as well as features e.g. meander
- scatter graph for discharge (dependant variable) and distance from source (independant variable)
- draw a line of best fit to show correlation and relationship, shows the linear relationship
- allowed anomalies to be seen
- only takes into account the two variables however
- GIS (geographic information system) technology allows presentation of bar graphs on map

## Section B

**Graphical Skills**

Simple Line Graph - to show a single set of data

Comparitative Line Graph - comparing two sets of data on the same axis

Compound Line Graph - if information can be sub - divided into two or more sets of data

Simple Bar Graph - show a single series of data using categories

Comparitative Bar Graph - two sets of datas (bars) on the same graph

Compound Bar Graph - show how the total in any one bar is divided up between a number of subtotals

Scatter Graphs - nature of the relationships between two sets of variables, best fit line allows analysis of data to be made

Pie Charts - total divided to seperate components (percentagex360), proportional circles

Triangular Graphs - a scattergraph that shows three variables and how they are interrelated

## Section B

**Graphical Skills**

Kite Diagrams - trends in a visual way, central line has a value of 0

Radial Diagrams - use 'polar coordinate' graph paper, can show orientations as given by the points on a compass or continous cycles such as daily and annual progressions

Logarithmic Scales - used with a very large range of data making an arithmetic graph difficult draw and unclear to read or when an arithmetic graph would result in a parabolic relationship. Helps to show rates of change

Dispersion Diagrams - 'box and whisker plots', used to show a spread of numbers around a mean value

## Section B

**Cartographic Skills**

Proportional located symbols - used to show a limited number of points or areas - not for spread or distributions

Flow Lines - portray movements or flows, size of flow used along routes is shown by the thickness of the lines used

Desire Lines - shows the strength of desire to mover from particular areas, lines of proportional thickness, do not show movement along particular routes, generalise the movement

Trip Lines - can be used to show regular trips

Chloropleth - show spatial distributions using shadings of different densities to represent different divisions

Isoline Maps - join points on a map of equal value e.g. contours, isobars (pressure), isotherms (temperature) and isohyets (rainfall).

Dot Maps - represent spatial distributions by using dots of equal size, they show actual numbers, however, they may be confusing when placed into different areas

## Section B

Measures of Central Tendancy

- Mean - sum of total values/ frequency
- Median - middle value for a set of data when arranged in order of size n+1/2
- Mode - most common value
- Normal distribution- Mean=Mode=Median
- Skewed distribution- mode will be at the point of the highest frequency, median and mean will lie to the right of the mode on the graph
- Interquartile range - spread of values around the median
- Standard deviation - the average amount by which the values in a data set vary from the mean for that set.
- In a normal distribution 68% of values lie within +_1 of the mean, 95% within 2SD, 99% within 3SD
- Spearman's rank - how two sets of data are related
- Box and Whisker plots - comparisons of sets of data and averages

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