Geog 2 - Cowside Beck

1. Our Hypothesis
1. Velocity will increase downstream because the increase in cross sectional area resulting from added water (tributaries and run off) will increase the efficience as friction is reduced due to the increase in hydraulic radius.
2. Pebble roundness will increase downstream - because of increased attrition and abrasion
3. Pebble size will decrease downstream - because attrition and abrasion breaks up sediment and bedload as it is transported downstream
4. Bradshaw's Model
  1. Predicts how river behaviour changes downstream showing that some variables increase and others decrease
  2. "It was useful because it allowed me to base my hypothesis on these concepts and gave me ideas that I could test, and to see to what extent these ideas are evident in a real river, and if there are any other factors that are important, like geology and land use."
2. Location
1. "Cowside Beck flows through a hilly limestone area in the Yorkshire Dales National Park. It flows into the River Wharfe about 5km south of Kettlewell."
2. 5 km long, has a very distinct upper, middle and lower course.
3. Relitively unchanged by human activity
4. Risk assessment - river is safe - never fast flowing or more than wellington heigh deep with stable banks
  1. Safe and easy access points
3. Risk Assessment
1. Drowning in deep water - river is not very deep, has flat river terraces to either side (easy to step out to the side), worked in groups so nobody was alone if they fell
  1. Action - Member of staff supervised each group with a throw rope, survival blanket and spare dry clothes to prevent hypothermia
2. Forecast hot - took suncream and fluids to prevent dehydration and sunburn
3. "We also recognised that risks were ongoing and were prepared to modify or cancel the data collection at any time. EG a bank had become unstable at a sample site since the pre-visit so we moved the site downstream by 10 metres"
4. Data Collection
1. One method - Pebble roundness (increase downstream)
  1. 1. Systematically picked 11 pebbles along the bed width divided by 11 to give correct intervals. Did this at 3 sample sites.
    1. 2. Laid out at the side of the river in order from left to right
      1. 3. Compared each pebble to the Powers Scale, gave score between 1 and 6 (1 very angular.) The same person did this to help with consistence and recorded the results on a frequency table.
        We then photographed the pebbles to give further visual evidence to compare back in college. Then safely returned the pebbles back to the river.
4. Strengths/weaknesses
1. Worked well - quick and easy, systematic sample allowed representation of the full channel width
2. Choosing 11 pebbles from 50cm intervals gave us a big enough sample size for statistical significance
3. Using the Power's index gave us a quick visual technique HOWEVER it was subjective and relies on a value judgement which led to some inconsistances within the data.
4. "To reduce the limitation nest time, I would standardise the Power's scores more by getting everyone in the group to agree on a score and also using a couple of pebbl;es per site to be checked by all groups to act as a moderator.
5. Data presentation
1. Proportional divided circles
  1. 1. Chose radius of 3cm for my largest mean pebble size - workes well visually on the map. Calculated a constant by dividing the 3cm by the square root of largest pebble size. Gave me 0.9. 0.9 was then cused to calculate the other radii, by multiplying it by the root of each mean pebble size.
    1. 2. Drew circles using compass next to 3 sample sites on base map of Cowside Beck.
      1. 3. Created pie chart inside each circle. To calculate angle, divide frequency by the total number of pebbles (66) then multiplied by 360. Then constructed angles using a protractor working clockwise. Repeated the same technique for the other circles for consistency.
        4. Then shaded in the 6 segments in different colours and creased a key.
7. Advantages/disadvantages
1. Easy to construct, clear and visual, easy to compare between 3 sites due to the map. The diameters showed the decrease in mean size from 11.1 to 9.1cm
2. Best way to show roundess. 6 Categories is perfect as it is easy to calculate the angle. Having 3 pie charts on the map made this easy to spot anomolies such as site 2 where angular material had washed in from scree slopes.
3. Anomalous data distorted the averages. A graph showing the range of sizes at each site might have been better. Pie charts did not show individual values but can be resolved by writing the percentages in each segment.
8. Data Analysis
1. Spearman's Rank
  1. 1. Drew table and ranked 18 velocities in the first column from lowest to highest. Wrote in the corresponding average pebble roundness and ranked from highest to lowest.
    1. 2. Next colum - calculated and recorded differences in the rank. Squared the differences (808.5) and used this to work out the formula. (0.166)
      1. 3. Checked for statistical significance by using a critical values table. My result was less than 95% certain of being a valid correlation therefore accepted my null hypothesis of no relationship between velocity and pebble roundness.
2. "One possible problem with Spearman's is that I could have made a mistake in my calculation. However a major disadvantage is that the result swallows up anomalous data in the middle course where scree falls increase angularity, explaining this weak relationship. So I think it is important to use a scatter graph as well to analyse the data successfully."
3. Advantages - ideal due to the relationship being linear. 18 pairs of data is also enough for significance. Quick and easy, gives numerical value and is therefore objective, allowing you to see the strength of the relationship. More reliable than using a line of best fit on a scatter graph as this is subjective and can be misinterpreted.
9. Results and coclusions
1. 1.Partly followed the Bradshaw's model. Velocity did increase downstream slightly from 0.09 to 0.32 m/s.
  1. However site 2 was faster than expected due to human intervention - straightened to speed up flow.
2. 2. Mean pebble size decreased but only from 11.1 to 9.1cm
  1. "My results would be useful to other people/geographers as it shows that Bradshaw's ideas are partly evident in real life, but not always because of local factors like human intervention and geology."
3. 3. Pebbles got rounder but located divided circles showed some anomalous data in the middle course near Darnbrook farm - 17/66 had scores of 1 to 2 (very angular) - due to scree slopes.
4. "Overall I was able to achieve my aim in testing Bradshaw's model, however to further validate my conclusions I would also like to extend my investigation to sampling another stream in the locality and collect larger sample sizes to improve significance."

Nächster

Geog 2 - Cowside Beck

Beschreibung

Zusammenfassung der Ressource

ähnlicher Inhalt

	Erstellt von anniehopley13 vor etwa 10 Jahre