Geography - sampling the river holford

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  • Sampling the river Holford
    • Sampling strategies
      • Random = Randomly choosing points
      • Stratisfied= We select points which are in different groups eg/ types of rock
      • Systematic = Where points are chosen based off a system eg/ every km along
      • Opportunity= We sample wherever we can eg/ safe areas
    • We measured the velocity at a variety of locations
      • Why?
        • We needed  to see how it varied at different locations + how it was influenced by different factors
      • How?
        • We used a flowmeter to measure the water speed in m/s
          • You face the oncoming flow
        • You face the oncoming flow
        • We did it 3 times for validity at equal spaces across the channel
          • The systematic sampling of the width reduces bias
        • The systematic sampling of the width reduces bias
        • We used a stopwatch to measure time taken for the impeller to spin along the thread
        • Evaluation
          • It didn't function as well in slow/ shallow water
          • It got stuck
          • Stopwatch= human error
          • we could increase the number of measurements across
          • Could repeat + measure in different depths
          • Quite accurate; better than floating object
      • We measured the channel shapes -- width, depth and wetted perimeter
        • Why?
          • To calculate the efficiency, using hydraulic radius. This shows whether it influenced velocity
        • How
          • For the depth we used a meter ruler at 7 spaces across the channel
          • For the width + wetted perimeter we used a tape measure across the channel and the banks
          • This is a systematic way of sampling
        • Evaluate
          • Take more depth measurements to show how the shape varied
          • Human errors
          • water height varied whilst measuring
          • generally accurate
      • We measured the gradient
        • Why?
          • To see if it affected velocity
        • How?
          • We used a clinometer -- this showed the slop angle in degrees between 2 points
          • We measured it from 5m apart in the river
        • Evaluate
          • May not have pointed at the same height -- human
          • Should be further apart
      • Secondary Data we used
        • We used  secondary data such as OS maps and British geology maps
        • We used secondary data because we wanted to find out about different rock types as well as the overall height of the land and the location


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