Field Physical Flashcards
What was the title of our enquire for physical ?
How does the cross section of the river ogmore change downstream
What factors were considered when selecting enquiry ?
Measurable: river was easily accessible using wellies and it was possible to use a wide range of fluvial techniques across many locations of the river ogmore
Specific: 2.5km stretch of river was accessible and uninterrupted by human factors
Timescale: by using a stratified sampling where we take equal amounts of samples in each course of the river, to show variation along the river
What was the underpinning geographical theory ?
Bradshaw model formed our hypothesis
Width should increase going downstream, more tributaries joining so increased discharge, and therefore more energy, more lateral erosion, such as hydraulic action and abrasion
Depth should increase
Velocity should increase, more lateral and vertical erosion increases the width and depth of the river, meaning less water is affected by friction of the river bed and banks, so less drag force, so water flows faster
What were our hypothesis ?
- Width of the river should increase downstream
- Depth of the river should increase downstream
- velocity of the river should increase downstream
What were the advantages and disadvantages of the location we chose ?
+:
River was shallow enough to access using wellies
Footpaths run along the river allowing safe and easy access
25km long so there is enough variation in cross section to be accessed
-:
Passes through Bridgend, where there is heavy management of the river and is inaccessible here
Cannot take any samples closer to the source from site 1 as becomes too steep, and mouth since it was too deep
What is the risk assessment associated ?
extreme weather - appropriate clothing (waterproof clothing, sunscreen)
slips trips and falls - take care when walking in the river as bed may be slippery, wear wellies with good grip
drowning - walk in the river (do not run), be aware of team mates
How and why did we measure width and depth ?
- systematic sampling of a single width measurement for each site
- hold the measuring tape, bank it bank, perpendicular to the river, hold tight to prevent it being pulled away by the water and to get an accurate reading
- leave tape measure to measure depth
- systematically sampled using 11 depth measurements across the width of the river, (divide width by 10 and take measurement at each interval)
- use a ruler perpendicular to the river bed
Justification: - both are needed to work out the cross-sectional area of the river
- width sets up a transect for depth measurements
How and why did we measure velocity ?
- systematically took measurements across the width and took an average
-used a hydro prop and a stopwatch to see how long the propellor took to reach the end when placed into the river
justification: - velocity is a key factor In determining erosional power, and therefore cross-sectional area
Why we use secondary data ?
- We can use NFRA river station to collect secondary data, alongside our primary data to improve the reliability of our results
- allowed us to gather data from sites we were unable to access
- however data may have been collected under other conditions and could possibly out of date
How did we present data for width ?
- scatter graph
- allowed us to demonstrate a relaxation ship between 2 variables (width and distance from the source )
- kind of best fit helped to understand the strength of correlation, depending on how many data points are close to the line of best fit
- geolocated the data to get an accurate distance from the source
How did we present data for depth ?
- constructed bar graph
- allowed us to demonstrate a relationship between 2 variables depth and distance from source
- allowed us the clearly show the difference between sites, shows how the rate of change varies with distance from the source,
- geolocated the data to get an accurate distance from the source
How did we present data for average velocity and csa ?
- we used depth and width to calculate the csa and the velocity was imported into ArcGis, where we overlayed the data onto a map, where the size of the circle represented cross sectional area and colour represented velocity
- this can help us to identify patterns of the 2 variables downstream, this can be compared to the Bradshaw model
What are the qualitative data methods ?
- field sketches can be used to identify landforms in an enquiry
- for this, we can sketch the main landforms and label them from what we can see
- this allows us to be able to identify features from where it may be difficult to collect results e.g steep hill, deep rivers
- also, physical descriptions of the sizes of sediments can indicate velocity and key processes, e.g lateral and vertical erosion
What were the conclusions (including results) for width ?
- We can confirm our hypothesis as from site 1 to 5, the mean width increases from 0.5m to 20m
- this confirms Bradshaws model which says width would increase downstream, since increased velocity would lead to higher levels of erosion (hydraulic action)
- furthermore, we would expect the rate of the increased width to be higher than the depth, since lateral erosion more dominant downstream
What were the conclusions (including results) for depth ?
- can confirm our hypotheses as from site 1 to 5 depth increases from 0.05m to 1m
- this follows Bradshaw model, as higher discharge will lead to more vertical erosion, however lateral erosion becomes the dominant process
- this causes the rate at which the depth increases to be less than the width
