River Field Work

• Measuring the width of a river

  1. Stretch tape measure from one bank to the other

  2. Measure width from inside bank edge to far bank edge
• Measuring the width of a river

  • Poles placed on each bank/side
  • Tape measure stretched/taut/perpendicular/at right angles to bank
  • Measure where river touches the bank
• Measuring the depth of a river

  1. Stretch tape measure from one bank to the other

  2. Use metre ruler to record depth from riverbed to water surface

  3. Take measurements at regular intervals across the river
• Measuring the depth of a river

  • Rest ruler/rod on river bed
  • Ruler/rod vertical
  • Measure where water level is
  • Equally spaced depth measurements across river
• Width and depth of a river

  Increase downstream (towards the mouth)
• Reasons why width and depth increase downstream

  • Increased volume of/ more water downstream
  • Tributaries join main river
  • Bed and banks are eroded
  • Channel eroded by abrasion/corrosion/hydraulic action
  • Bedrock may be weaker so increases rate of erosion
• Plotting river cross-section information

  1. Measure values down from zero at the top of the graph

  2. Join the dots to create a scale picture of a slice through the river
• Cross-sectional area (CSA)

  Width x average depth
• Measuring the size of pebbles in a river

  1. Put pebble into 'teeth'/ jaw / mouth of callipers

  2. Adjust/close callipers to hold/touch pebble

  3. Use scale of callipers / look at reading on scale/ measure gap between 'teeth' with ruler
• Measuring the roundness of pebbles

  Use information from the Powers Index of Roundness chart / compared pebble with the chart
• Weaknesses of selecting rocks at random

  • Rocks selected may not be typical of the rocks at that site / anomaly
  • All rocks may have been taken from same area of river bed / not across channel / taken from same place
  • Not a fair / reliable sample / students choose rock / bias
• Reasons why rocks generally become rounder and smaller downstream

  • Attrition / pebbles crash into each other / river bed / bank
  • Corrosion / solution / dissolves rocks
  • Smaller / rounder pebbles are moved further downstream because they are easier / lighter to transport
• Measuring the velocity of a river using floating objects

  1. Measure length of river (10 m) / divide into sections / ranging poles to mark out section / set up start and finishing points

  2. Put orange / dog biscuit / float / floating object into river

  3. Time float moving over distance

  4. Repeat and calculate average / repeat across river channel

  5. Calculate velocity by dividing distance by time
• Measuring the velocity of a river using a velocity meter/flowmeter

  1. Put velocity meter / propeller / it below surface of river / in / into river / in / into the water

  2. Propeller must be facing upstream / nothing in front of propeller

  3. Read / look at digital / velocity reading / display / speed is shown on display

  4. Take several readings over time and calculate average / take readings across river channel and calculate average
• Why a velocity meter/flowmeter gives more accurate readings than a floating object

  • Floats gets stuck in channel / hit objects / vegetation in channel
  • Operator error / error in calculation when using a floating object
  • Measurements are not easy to take at different points across river / float does not move in straight line
  • Floats are affected by wind
  • It only measures surface velocity
• How to improve methods used in fieldwork

  • Repeat the experiment: to check accuracy
  • More time to do the experiment that is repeat the procedure several times and over more days
  • Sample size: increase the sample size
  • More students to do the experiment: other students take the same measures at the same time, or to check each other's measurements
  • More sites: to test the hypothesis
  • Improvement on sampling methods: To systematic sampling or stratified if, these were not the ones used in the first place
  • Use digital instruments: these are likely to be accurate compared to traditional methods of measuring