Physical Fieldwork: The River Holford

What is the enquiry question?

How does the channel cross profile and velocity of the RIver Holford change with distance downstream?

What are factors that need to be considered when choosing a suitable question / hypothesis for an enquiry?

You firstly need to decide what you want to find out - it has to be linked to the specification you're studying and done at the location you have mind.

The title is what you want to find out, normally phrased as a question.

The hypothesis is a statement based on the geographical title question.

What questions can you ask yourself to check the feasibility of your study?

Is the subject matter narrow enough? - if its too wide no solid conclusions can be made.

Can you collect the data you need? Eg do you have the correct equipment?

Is there sufficient time to collect the data?

Is there access to the data collection area? Eg in a very rural or overgrown environment.

Do you need permission to carry out the Fieldwork?

Is it safe to carry out?

What is the theory / concept underpinning our study? (Bradshaw)

The Bradshaw Model

It displays several graphs on one axis and shows what happens to the river from source to mouth in theory.

It suggests that discharge increases substantially, and average velocity, width and depth also increase with distance downstream.

This makes sense as with more water there will be less of the RIver in contact the bed and bands, so less friction.

The Bradshaw model therefore indicates that there are several factors that will change with distance downstream.

What is the theory / concept underpinning our study? (Hjulstrom Curve)

The hjulstrom Curve shows the relationship between velocity and the river processes of erosion, transportation and deposition

For the majority of particles, the larger the particle the faster the water needs to travel in order to eroded and transport.

Based the measurements we’re taking, we would judge this on the shape of the bed of the crosss profile and would expect slower velocity and larger particles (a more uneven depth) in the upper course.

What types of sampling was used in your enquiry?

Systematic - samples taken at regular / fixed intervals, for example every 3rd person that walks by. Used when measuring cross section of river.

Stratified - knowing something in advance and selecting a sample based on desired characteristics. We used this to choose data collection sites: some in upper, middle and lower course.

Justify the choice of the Fieldwork question.

This question was chosen as we are studying theoretical channel cross profiles and what happens to velocity in rivers, so it is sensible to see/test if its true in real life.

Where was the Fieldwork carried out?

The source is at Lady’s Fountain in a steep valley which remains steep for some time.

It then works its way into a flatter area where flooding is a risk. Due to this, straighter drainage channels have been built.

The investigation was carried out at 10 different sites from source to mouth.

The river was only 7.2kms long so samples were taken along the river in one day.

Describe the risk involved and how these may be reduced.

Fast river flow - do not enter the water if it’s above wellies height. Use a metre stick to check depth of river. Keep throwline in case emergency.

Ticks- we are going in winter and they'll be less likely to be around. Given a leaflet on information about what to do if you get one. Wear long sleeves and trousers.

Briefly describe what using location maps for an enquiry.

Secondary qualitative data

Equipment neeed is a map or digital login.

Log on to digimaps and find the desired place of study. Snip the image to word and add arrows to show north. Label the map.

Its crucial to know where you are going, and don't get lost.

Time consuming

Briefly describe calculating river width for an enquiry.

To calculate the cross-sectional area.

Need tape measure.

Pull tape taut across the river from bank to bank at the water level.

Undercutting of banks may make measuring difficult.

Explain the method and sampling measuring RIver depth in detail.

Collects primary quantitative data.

Equipment: tape measure, metre ruler.

Stratified to find each site.

Systematic sampling used to find measuring points across the river at each point. Divide by 6 (to get 5 equal points).

At each point, measure the depth with the metre ruler and record.

What are the limitations and justification of measuring RIver depth?

Needed to draw an accurate cross sectional area and see how depth changed downstream.

Limitations: human error due to undercutting banks making judging the edge of the bank difficult (when measuring width to find the measuring points). If the ruler was flat on to the current, it appeared higher than it was due to splashing.

Explain the sampling methods and equipment for measuring RIver velocity in detail.

Primary quantitve data.

Equipment: advanced flowmeter with hydropop and impeller.

Stratified to find each site.

Systematic sampling - width divided by 4 to get 3 points across the river to account for variances in speed and find the average.

Explain the method for measuring RIver velocity in detail.

Put the impeller 1 inch below the surface, switch on the flowmeter (ensuring it its switched to water measuring in MPs), wait 10s and read off and record the data. Leaving the impellar in the water, take the next reading wait 5s, take the next reading and reeat for 3rd time.Move to a new section and repeat. Repeat for a third time at a final point.

Justify the use of and explain the limitations of calculating river velocity.

Needed to calculate river velocity. The avrage allows greater accuracy.

Limitations: People stood in the flow Infront may slow the river down (inaccurate reading), impellar getting stuck particularly in shallow areas or where theres a lot of debris and leaves.

What equipment is used to measure the gradient and clast shape?

Gradient - clinometer (eye hold thing)

Clast size - callipers, identification chart.

What is the cross sectional area of the river holford at the sites you selected? How did you calculate this?

Upper course example, site three: 792cm².

Middle course example, site nine: 5120cm².

Lower course example, site ten: 4620cm².

Describe the data / graph which shows how river depth changes with distance downstream.

The graph starts at the upper course and shows there is a small depth and width of the RIver - the average depth (of site 3) is 4.4cm.

By the middle course (using site 9 data), this has greatly increased to 12.8cm.

At the lower course (site 10) it is 15.4cm.

Site 10, in theory, should appear a lot wider than site 9. It does not appear this way because there was human intervention before site 10, where the river was split into two channels.

There was also an attenuation basin around site 8, so site 9 may be smaller / more shallow and slower than expected.

Describe what the Bradshaw model suggests about how river depth changes with distance downstream.

They increase with distance downstream (as does channel width) so channel cross section also increases,

Describe the data / graph which shows how velocity changes with distance downstream.

The overall trend is a weak positive correlation.

At site 1, the velocity was 0.13 m/s, compared to site 10 where velocity was 1.9 m/s.

This is because the Bradshaw model shows the velocity of flow in the river will increase with distance downstream, as tributaries feed the river with water. An increased discharge and less friction between the water and bed and banks of the RIver results in a higher velocity.

Anomalies were present as there was evidence of ‘slowing the flow’ in the upper course to prevent flooding by using dead trees in the channel.

On the lower course, the river has been contained by the car park in a narrower, deeper channel made by humans (human intervention).

Describe the data / graph which show how clast size has changed with distance downstream.

The mean clast size in the upper course (site 3) is 6.5cm, the middle course mean (S9) is 5.3cm and the lower course (S10) mean is 4.1cm. this shows how clast size decreased due to the course of a river downstream.

According to the Bradshaw model, the sediment gets smaller with distance downstream due to fluvial erosional processes.

How did width change with distance downstream?

Overall, the river got wider with distance downstream.

At site 3, it was 180cm, site 9 was 400cms and site 10 was 300cms.

There was a slight difference to what should be expected as before site 10, human intervention occured where the river was split into two, so the overall size was likely to decrease.

This agrees with the Bradshaw model, which suggests width increases with distance downstream.

What sites were affected by human intervention and why?

The river has been made deeper and less wide by the carpark near kilve beach.

The river has been split into two channels to go around the water treatment plant near kilve beach (before site 10).

Attenuation basins have been made to hold water in section before the village of Holford to prevent flooding there.

Overall, how does the channel cross profile and velocity change with distance downstream on the River Holford? What is the impact where human intervention has taken place?

Overall, channel cross profile has got wider, deeper, and faster with distance downstream, as shown by sites 3, 9 and 10.

However, there were sections affected by human intervention, meaning sies such as site 10 were less wide, fast and deep as site 9, which was less affected.

However, site 10 was still faster, deeper and wider than site 3.

Describe how to measure the gradient.

Two people of similar heights standing 5m each side from where the width was measured in the middle of the RIver. Person walking downstream should use the clinometer, angling it at the other person at eye height.

Evaluate the method for data collection of the width of the river.

The method was very appropriate and did find the width clearly.

It was effective in answering the question, as it allowed me to see that width increased with distance downstream overall, as the Bradshaw model suggested, and that human intervention affected it.

Problems with the data collection method included human error - the undercutting of the banks means it was difficult to judge where the edge the river bank was in places.

It could be improved by making sure the tape was tight, and that we decided in advance what counted as the ‘edge’ to be more consistent.

Evaluate the method for data collection of the depth of the river.

Was very appropriate method as found the depth.

Was effective as I saw depth largely increased with distance downstream, agreeing with the Bradshaw model.

Problems with data collection method - if the ruler was flat on to the current, it appeared higher than it actually was due to splashing.

It sometimes sunk into the mud at the bottom.

How may the method be improved - ensure the same person did the measurements so they were always measured the same. Make sure it was firm on the river bed.

Evaluate the method for data collection of the velocity of the river.

Very appropriate - it indeed found the speed of the RIver.

Very effective - was able to see that velocity increased, although it wasn't as clear.

Problems with method - leaves in the way. People stood upstream in the flow may have slowed it down. Impellar getting stuck, particularly in shallow areas or where there was lots of debris.

How could it be improved - I could have used a dog biscuit or orange as a float on the surface and measured out a distance and timed it. (Velocity = distance/time). This would reduce the problems experienced with more sophisticated experience and human error.

Evaluate the method for data collection of the gradient of the river.

Appropriate as correctly measured the gradient.

Not effective as the data was not used.

The gradient measures the long profile (not directly answering the question on the cross profile).

What are suggestions for other data that could've been used in the enquiry?

Rather than just cross profile and velocity, you could include long profile (and therefore data on the gradient that wasn't used).

Could also use clast size data and how thi changed.

How may the enquiry be extended / improved further?

Using the hjulstrom Curve theory to test conclusions further - Bradshaw model was regularly used, however.

Taking the measurements at different times of the year - our data was only collected on one day. You could explore how time of year affected the enquiry question.

Collecting data more than once could would allow for difference in river velocity - rainfall overnight or another dry day will affect the amount of water in the channel.