Physical fieldwork

• Aim


  How and why do the characteristics of the river Chess change with distance downstream?
• Knowledge that underpins this fieldwork

  -Bradshaw model

  -shows how different aspects of river change downstream from source to mouth

  + give an example e.g bedload size decrease
• Why is it a suitable topic for a fieldwork enquiry?

  -Low risk as it is a small river therefore low velocity

  - easily accessible

  - lots of data to collect

  - can be done within a day

  -gentle terrain
• Risk assessment


  1. Drowning/ slipping: shallow areas + grippy shoes e.g wellies

  2. Insect bites and getting stung: insect repellent

  3. Illness from river (wails disease): cover cuts and wear wellies
• How to measure width

  Tape measure in meters. However it is unclear where river starts and ends (may be boggy with vegetation). Different at all points in river

  
  

  systematic sampling
• How to measure depth

  Tape depth at increments of ten. There may be vegetation or big rocks. Accessibility issues

  
  

  systematic sampling
• How to measure velocity (1)


  Use a flow meter (m/s). Inaccurate if someone is in the way or there are lots of weeds.
• How to measure velocity (2)

  Use a dog biscuit. Set out ten meters with measuring tape and time with stopclock. Human error in timing. Wind might affect it and it might get stuck.
• How to calculate bedload size

  Use a calliper and ten rocks. Biased (people only pick up big rocks). If a rock is flat and skinny what do you measure.

  
  

  random sampling
• How to calculate bedload roundness


  Classify using a chart. Subjective.
• Example question: justify one primary data collection method used in relation to the aims of your enquiry (3)

  Measuring river width shows how it changes down stream. Measured with a tape measure. Created by lateral erosion due to abrasion and hydraulic action. Limitations: unclear of real bank with vegetation and boggy ground (especially if there is a slip off slope. However it is simple and involves no bias.
• Why is calculating mean useful

  Cancels out anomalous results. Takes all samples into account. Representative of all data
• Limitation of calculating mean

  Anomaly disrupts whole data set
• How to calculate median

  Put all value in order. (n+1)/2
• How to calculate UQ and LQ

  Use median and number of values either side.

  (n+1)/2
• One strength if IQ range


  Includes whole data set. Shows spread of data from high to low. Doesn't just show one value.
• Why do we use box plots to represent range, median and IQ range

  Summarises data from multiple sources and displays many results in a single graph. Allows for comparison = more effective decision making.

  
  

  good as it includes central tendency and dispersion
• Effectiveness of cross profiles

  -good visual representation

  -can see anomalies

  misleading if a different scale is used
• Effectiveness of central tendency

  -includes anomalies = incorrect result throwing off value of the mean

  -only one figure from whole set so can't see range of data (better shown as a box plot)
• Effectiveness of dispersion


  -IQ range, range and median all displayed on boxplots. Visual comparison of multiple values
• Average bedload size at site 1

  44.7 mm
• Average bedload size at site 2

  61 mm
• Width at site 1

  7.3 m
• Width at site 2

  4.5 m
• Improving bedload measurements


  -moving sites further apart

  -broader data set
• Improving river width and depth measurements

  -moving further down river

  -broader data set