Paper 4 Measurements

Question 1

What is the aim of measuring surface velocity?

Answer 1

To investigate the changes in the discharge of the river along its length
To investigate how the human management of rivers can affect discharge and velocity

Question 2

What are the limitations of the ‘float’ method?

Answer 2

It must be visible, durable and not affected by wind
User error means that the start and finish line of the object may not be exact
Throwing or pushing the object can affect results

Question 3

How can the accuracy of the ‘float’ method be improved?

Answer 3

The float can be placed upstream and start and finish lines can help to minimise errors

Question 4

How can the speed of flow be measured

Answer 4

Flow meter
OR
1. The impeller of a hydro prop is placed at 1/2 the depth of the river and then wound to the end of its shaft
2. With the impeller facing upstream, it is placed in the water and timed using a stopwatch to see how long it takes to reach the end of its shaft
3. The distance travelled is measured and the speed=distance/time equation is used to measured speed

Question 5

What are the limitations using a hydro prop?

Answer 5

The hydro prop may not be completely covered in shallow water
In turbulent flow it may be difficult to see the impeller

Question 6

How can the impeller be made more visible?

Answer 6

It could be brightly coloured

Question 7

How is channel width measured?

Answer 7

1. Stretch a tape measure taut across a river from the point the water meets the bank on one side to the point the water meets the bank on the other side
2. The tape should be kept parallel just above the surface of the water
3. Measure the distance in m

Question 8

What are the limitations and solutions to measure channel width?

Answer 8

Water at high flow could come into contact with the tape measure which would influence width measurement
The tape measure can be raised further above the water to avoid this problem

Question 9

Measuring depth

Answer 9

1. Divide the width of the river by 4
2. Use a meter ruler/ranging pole to measure the depth at these intervals
   Do not use unnecessary force and push the ruler into the sediment

Question 10

How is finding cross sections useful?

Answer 10

Allows you to compare straight and meandering sections of the same river

Question 11

How do you work out the cross sectional area of a river?

Answer 11

Multiply width by average depth

Question 12

Wetted perimeter

Answer 12

1. Use a chain to measure the distance that the water is in contact with the bed
2. Use a tape measure to measure the length of the chain
   The chain should be held tightly to the shape of the bed

Question 13

Gradient

Answer 13

1. Measure a 10m stretch of the river
2. Carefully hold 2 ranging poles in the river, 10km apart vertically
3. Line the clinometer at the top of one pole and aim it at the other
4. Measure the angle
   More than one person may be needed to achieve a steady reading

Question 14

How do you measure the size of a pebble?

Answer 14

1. Hold a ruler against each rock
2. Measure the longest axis and read off in cm/mm
   Callipers would be a more accurate way

Question 15

How do you measure the weight of a rock?

Answer 15

1. Weigh an empty plastic bag
2. Put each rock in the plastic bag and attach to a spring balance
3. Subtract weight of plastic bag

Question 16

How do you measure the roundness of a rock?

Answer 16

1. Put the rock next to a powers roundness index
2. Choose the category that best fits the appearance of the rock
   This is subjective so isn’t very reliable

Question 17

Why are measurements generally taken?

Answer 17

To measure how each feature changes downstream

Question 18

Surface velocity

Answer 18

1. Record time taken for an object to travel over set distance
2. The floats may be caught up behind stones or held in turbulence so it is a good idea to do the measurements at a minimum of 3 places across the stream many times
3. Use speed=distance/time to work out average speed for all measurements taken
4. Surface water flow is reduced by friction with the air so you should multiply your results by 0.85 to gain a more accurate idea of the speed for an overall stream

Question 19

List some safety precautions that should be taken when taking measurements

Answer 19

Protection from weather (rain jacket/hat/sunscreen)
Carry out experiments in groups
Carry out in daylight and wear reflective clothes
Check the safety of a study area
Carry a mobile phone

Question 20

What can be done to make measurements more reliable?

Answer 20

Away from human impact
More investigations along a site
Pilot study to make sure equipment is working
More rocks may be measured
More than one student can measure subjective data

Question 21

What are the two different techniques that can be used?

Answer 21

Systematic: samples at regular intervals and take a number of samples at each point across a river
Random: use random numbers or pick up stones which the pole touches