River Tillingbourne Fieldwork

Aim of investigation

- To investigate the characteristics of the River Tillingbourne change on its journey from source to mouth

- To investigate how the physical and human characteristics of the River Tillingbourne's drainage basin affect the level of flood risk to settlements along the course of the River

What is the Bradshaw model?

How a 'typical' river's characteristics will change on its journey from source to mouth. The model predicts changes

Channel size (width, depth, cross sectional area, wetted perimeter)

More water is added to the channel via tributaries, surface runoff, through flow and groundwater flow

How does Channel size change downstream

Increases

Gradient

As river enters its middle course, it loses GPE, and the dominant direction of erosion changes from vertical to lateral

How does gradient change downstream

Decreases

Hydraulic action (channel efficiency)

The smoother channel downstream, the more efficient at transporting water. (Less water affected by friction with bed and banks)

How does Hydraulic action change downstream

Increases

Velocity

Average velocity flow is greater due to more efficient channel shape and less friction

How does velocity change downstream

Increases

Discharge

Discharge = Cross Sectional Area x Velocity.

- Both of these increase downstream, so discharge also increases

How does discharge change downstream

Increases

Load size

Prolonged effects of attrition along the river's course results in the material becoming smaller

How does Load size change downstream

Decreases

Load roundness

the prolonged effects of attrition along the river's course results in material becoming smoother

How does load roundness change downstream

Increases

Two things that affect flood risk

Discharge and Landscape gradient

How does Discharge change downstream (and therefore flood risk)

- Increases

River is more likely to exceed bank full discharge during a flood event

How does landscape gradient change downstream (and therefore flood risk)

- Decreases

Flat areas are more likely to be affected by flooding as water can spread over a larger area

What is the hazard of drowning and how to manage

- River

Assess to flow conditions before entering river.

Do not enter above knee height

What is the hazard of Weil’s disease and how to manage

- River

Cover open cuts with plasters.

Wear washing up gloves (optional)

What is the hazard of Slips, trips and falls and how to manage

- uneven ground

Wear appropriate footwear

Stick to footpaths

Watch where we put our feet

What is the hazard of Road traffic and how to manage

- Country roads

Walk in single file when walking alongside country lanes

Keep to pavements

What is the hazard of Road traffic accident and how to manage

- Transport

Wear seatbelts at all times on minibuses

What is the hazard of Sunburn and how to manage

- Weather

Check the weather forecast before departure

Wear sun cream and hats if appropriate

What is the hazard of getting cold and wet and how to manage

- Weather

Check the weather forecast before departure

Bring layers and waterproof clothing if appropriate

What is the first research question?

How does river discharge change with distance downstream?

What is the equation for discharge

Discharge = width x depth x velocity

RQ1: How to measure the width

Stretch a tape measure from one side of channel to other, at right angles to direction of flow.

RQ1: How to measure the depth

- Divide width of cross-section by 6 for division intervals.

- Measure 5 regularly-spaced measurements.

- This is an example of systematic sampling

- Use metre ruler to measure depth for river at these points.

RQ1: How to measure the velocity (m/s)

- Lay a tad measure out for 10 m along the river bank

- Drop cork in middle of the river at start of 10m

- Start stop watch and stop when cork reaches end of 10m

- Repeat twice

- Speed= distance/time

What is the second research question?

How does load size and shape change with distance downstream?

How to find the stones in systematic sampling

- Using the same method as the depth in equidistant intervals

How to measure sediment size (cm)

- Put each piece in Vernier callipers and close jaws around it

- Measure the long axis of stone

- Read length of callipers scale

How to measure sediment shape

- Compare each piece of sediment to Power's index

- assign it to one of the six categories: very angular, angular, sub-angular, sub-rounded, rounded, very rounded.

What is the third research question

Is the flood risk greater in the lower course of the River Tillingbourne?

Primary data of seeing the flood risk.

Field sketches from the first and final site you visit.

- containing relevant details about the river: channel shape, vegetation type, landscape gradient etc.

- Should have time and date and direction you were facing

Secondary data of having flood risk

- flood risk maps from Environment Agency

Data presentation for RQ1

- Scatter graph to show distance downstream and cross sectional area

- Scatter graph to show distance downstream and velocity

- Scatter graph to show distance downstream and discharge

Data presentation for RQ2

- Proportional circle map to show sediment size/ angularity changing downstream

Data presentation for RQ3

- Annotated photographs

- Field sketches showing flood risk/ channel dimensions.

Data Analysis RQ1

- Bradshaw model suggests ...

- Plotted scatter graph with discharge against distance downstream

- We got a positive correlation

- We testes strength of this relationship with Spearman's rank test.

What was the Spearman's rank value compared to ours?

- Our Spearman's rank value was 0.851 which was higher than the critical value at the 95% significance level.

- Therefore, we can conclude that there was a statistically relationship between distance downstream and discharge.

Data Analysis RQ2

Describe and explain using data from the table, linking to geographical theorem and processes (erosion) how sediment size changes downstream.

RQ1 Conclusions

Does the data collection agree with the Bradshaw model that we would expect discharge to increase with distance from the source?

RQ2 Conclusions

- Does the data collection agree with the Bradshaw model that we would expect the load size to get smaller/ less angular with distance downstream

RQ3 Conclusions

Does your data collection agree that flood risk is greater nearer the mouth of the River Tillingbourne

Strengths for RQ1

- 5 equidistant depth measure is representative of channel

- Tape measure held taught

- Cork floated on top of water near source, good for shallow depth

Weaknesses for RQ1

- Could be difficult finding bottom of the channel because of the load

- Cork gets stuck

Improvements for RQ1

- Use a flow meter

- Use and orange

- Do more velocity measurements

Strengths for RQ2

- Used calliper for accuracy

- Systematic sampling across river

- 5 samples per site

Weaknesses for RQ2

Power's roundness index is subjective and open to interpretation

Improvements for RQ2

- Take more samples

- Calculate volume of the sediment

- Have the same person describing roundness each time to reduce bias

Strengths for RQ3

- Visual representations of the site

- Qualitative primary data to support secondary data

Weaknesses for RQ3

- Rainfall data was not taken within the Tillingbourne catchment