Revision:Edexcel - Applied Geographical Skills Exam - Lemon River Field Work

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River Lemon

Background Facts

• Steep Gradient- 350m Drop
• Small Drainage basin
• Management on the river-Dam, Channelisation, Culvert
• Lack of vegetation in Dartmoor
• 16km long
• High drainage density
• Granite bedrock- impermeable
• Short lag time-flashy
• Basing out aims on the theoretical model: Bradshaw model.
• It shows how some river variables change going from upstream to down stream.

Aims

• Main aim is to test the Bradshaw model on the river lemon.

Sub-aims

• Velocity should increase
• The discharge should increase
• The amount of rock (Load) should increase
• The cross sectional area of the river should increase
• The efficiency (hydraulic radius) should increase
• The roughness of the channel (manning ‘n’) should decreases
• The friction should also decrease
• The turbulence should decrease
• The size of the rock should decrease
• The gradient should decrease

The reasons why to tested Bradshaw’s model is to see if there is a pattern for ALL rivers, to try to predict for floods, it effects us –flood plains—Farming—food chain, the impact of humans on the river. Also aquatic Species- Plant/Flora and Animal/Forna. Oxygen content in the river-turbulence.

Methodology

• on A3 sheet*

Data Analysis

Graphs

Velocity:

• Increases
• From 0.23 to 0.42 m/sec
• Range= 19m/sec
• The biggest increase is between site 1and 2
• Steady

Gradient:

• Decreases
• From 0.037 to 0.003 Meters
• Range= 0.034
• The graph is very steady

Cross sectional area:

• Increases
• From 0.040to 2.2 meters 2
• Range= 2.16
• Biggest change is between sites 1 and 2
• A very steady graph

Discharge:

• Increases
• From 0.01 to 0.95 m3/sec
• Range=0.94
• The graph is very steady

Wetted perimeter:

• Increases
• From 0.8 to 8 meters
• Range= 7.2
• Biggest change is between 1 and 2
• Steady but levels of rapidly after site 2

Hydraulic radius (efficiency):

• Increases
• From 0.06 to 0.27
• Range= 0.21
• Once again biggest change after site 1, but levels off after site 2

Manning ‘n’ (roughness):

• decreases
• From 0.18 to 0.056
• Range
• Steady drop

Turbulence:

• Decrease
• Site 1 results are quite steady but site 2 is very high at the fist measurements but then are very low for the rest. And site 3 results are mainly high
• So it fluctuates

Bed Load Size:

• increases
• fluctuates a lot
• group 2 had site 2 with the biggest rock and also with group 4 but the other groups increase in order.

Bed Load Shape:

• gets rounder and smother
• site 1 has a lot more angular rocks that in site 3

Between these variables there are patterns, we can test these patterns using a method called “Spearman’s Rank test”. This finds out wither the is a relationship between two variables exist. I will test the two variables wetted perimeter and manning ‘n’.

Spearman’s rank Formula =

This is a positive relationship so as manning ‘n’ decreases so does the wetted perimeter.

But to scientifically test if the relationship works I can check it with the degrees of freedom from a table. 0.64 is between 5% and 2% so it is not a certain thing but it is quite a good relationship.

Conclusion

From the analysis, Size of bed load, hydraulic radius, wetted perimeter, discharge, velocity and cross sectional area, all increase as going down stream.

But turbulence, manning ‘n’ and gradient should decrease. As all of the aims matches with the results so I can accept that Bradshaw’s model works with the river Lemon.

Limitations

To get better results we could have:

• done the tests for longer periods
• done the tests at different times of the year
• before/after rainfall
• river itself, rock type, size, location

The limitations of Bradshaw’s model are that it does not show any relationships between the variables. And the words around the model don’t really tell us much about the river and how those words affect the river and the variables.

For a future study we could:

• test a larger river
• concentrate on one point of the river
• do equal points down the river
• Concentrate on only one or two variable to get more detailed results.
• See if there is a relationship between two similar rivers in different locations. Or possibly with say the rock type changed.

Also See

• Edexcel - Applied Geographical Skills Exam - Exeter Field Work

Comments

These notes are aimed at students studying for Edexcel (A) Applied Geographical Skills exam, though will be suitable also for people studying with different exam boards and at different levels.

They were originally submitted by AbzDaDon in this thread on TSR Forums.