Geography - sampling the river holford

• 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