physical

• why did we choose chesham

  • accesible from a416 - only 20 mins away
  • parking in chesham
  • all study sites are within 2.5km within eachother so are walkable
  • river chess is safe - knee high
• What are we measuring

  • how width and depth change going downstream
  • how velocity changes going downstream
  • how sediment size changes as you go downstream
• what does bradshaws model state

  • discharge, channel width, channel dept, velocity and load INCREASE DOWNSTREAM
  • particle size and channel roughness DECREASE DOWNSTREAM
• What is systematic sampling

  • collecting data in an orderly way
  • every 500m
• what is stratisfied sampling

  • selects a sample which is reprisentative of each different groups
  • chose sites considering health and saftey
• why did we use those types of sampling

  • ensure we collected data at regular distances which are safe and accesible from the river
• why would we expect the river to get wider and deeper

  • there is more lateral erosion due to more abrasion and hydrulic action
• why would we expect velocity to increase

  • steeper gradient - water gains momentum
• method to measure width

  • stand on both sides of the river with one person on each side holding the tape measure TIGHT
  • left to right
  • face upstream
• how to measure depth

  • take 5 readings with a metre stick every 20cm
  • put narrow side of ruler in the flow
  • divide the width by 6
• how to measure sediment size

  • random sampling
  • take 15 random pieces of sediment and measure the longest side of rock with ruler
• how to measure velocity

  • speed = distance/time
  • measure over a width of 10m
  • measure wiht a stopwatch 3 times and calculate a mean
  • take 3 at edges and 3 in the middle
• why where sites 2 and 4 faster 


  • they where channelised - faster flow of water
• why may site 7 be inaccurate

  • it was a branch of the river , not the main channel
• why does depth not follow bradshaws model

  • used stratisfied sampling so we only went to sites which where safe ie knee height
• how to present data

  • cross section - line graph
  • bar graph to compare sites
  • Scattergraphs to show the relationship between two sets of data. For example, the river width and discharge