Paper 4 - River measurements

Question 1

How do you measure the width of a river?

Answer 1

stretch a tape measure taut at 90° to the channel, take reading from bank to bank

Question 2

How can you get a mean depth of a river?

Answer 2

-use a metre stick
-hold vertically upwards at regular intervals across a channel’s width
-read the length where it comes out of the water
-calculate mean of all readings

Question 3

What is the wetted perimeter?

Answer 3

entire length of the bed and riverbank that is in contact with the water

Question 4

How would you find the wetted perimeter?

Answer 4

-use a chain and lay it along the channel’s width, making sure it touches the riverbed
-mark where it comes out of the water, pull the chain out and measure the length between the 2 markers

Question 5

How do you measure a river’s velocity?

Answer 5

-use ranging poles, stick them vertically in the riverbed, time how long it takes for a float to move between them and use d/t to find velocity

-or use hydroprop with impeller and flowmeter to digitally read velocity, pointing the propeller upstream with nothing blocking it

-measure from different depths to calculate mean

Question 6

What are the advantages of using a flowmeter to measure river velocity?

Answer 6

-simpler equipment to set up and use
-more precise and accurate results
-readings aren’t affected by wind (unlike a float)
-can measure velocity at different depths

Question 7

How do you find an estimate for a river’s discharge?

Answer 7

-find width
-find mean depth
-multiply to get an estimate for the cross-sectional area (m²)
-multiply cross-sectional area by river velocity (ms⁻¹) to get discharge (m³s⁻¹)

Question 8

Can be applied to both coasts and river questions

How do you measure pebble shape and size?

Answer 8

-use random selection to get pebble
-use callipers and measure long axis of the pebble from the scale
-compare to Power’s Roundness Index for shape

Question 9

How can you measure the gradient of a river?

Answer 9

-use ranging poles (vertically in river) and set them a certain distance apart (record this distance)
-put clinometer on the top of one pole, look through the sight and aim at the top of the other pole
-take angle reading and repeat to take a mean