Primary Data
Secondary Data
Data you collect your self
You gather information that other people have collected
Equipment used and for what
- ## 25m measuring tape (to measure width of river from bank to bank)
How did we measure velocity of a river
- Used a measuring tape downstream at 10m length
- Place a table tennis ball (object that floats)
- Use a stop watch to time how fast the flow of water carried the ball 10 meters
- Repeat and calculate a mean to exclude anomalies and increase reliability
How did we measure sediment size
- Take a piece of sediment from the river bed and measure with a ruler along its longest axis
- At each site, take a sample of stones every 50cm across the river channel (systematic)
- Or take a handful of stones every 50cm across the river channel (random)
When do we use secondary data
When the river becomes too wide and deep for us to measure safely
IF we didn’t have enough time
How to carry out risk assessment
Check the river was ankle depth or less
Wear wellies to avoid cutting on sharp objects in the river
Hypothesis - Channel size
- As you travel from the source to the mouth, the channel size will get wider and deeper due to increased erosion
Hypothesis - Discharge
- As you travel from the source to the mouth to the mouth, the river’s discharge (total water flowing) will increase because there are less large rocks to slow the water down and more tributaries join the river
Hypothesis - Sediment size
- As you move from the source to the mouth the size of the sediment in the river decreases because of erosion processes
What data needed processing
To find velocity, we had to use the equation - Velocity = distance/time, so distance would remain 10 each time, and time in seconds will vary
What processes cause the river channel to increase
- Lateral erosion by stones, hits the side of the river and causing abrasion
- Hydraulic action will widen the river
- Further downstream, there is more water which gives more power to erode
Bradshaw model
Theoretical model that shows how a river’s characteristics change as it goes downstream.
Why does velocity increase significantly downstream
- At the source, channel is narrow so there is lots of friction with the river bank, as well as larger rocks in the river, to slow the water down
- Further downstream, the river is wider and much deeper, so there is less friction and less large rocks to slow the water down
Why does sediment size decrease downstream, and why do some results not show this
- the further away from the source, the more distance sediment has had to travel and it would have eroded more by attrition
- Some results don’t show this because the 3 sample sites are too close together to show much change
What made our results reliable (sediment size)
- Each group measured 5 stones every 50cm across the river channel. This meant that we took hundreds of measurements. We use these to calculate a more accurate, mean average
We sampled at 3 different sites to allow us to see if sediment sizes had changed
What made our results less reliable (sediment size)
- Samples weren’t very random
- Because we were biased towards sampling sediment that fitted easily in the hand
- A lot of particles of sediment were too small to measure with a ruler
How could we improve results (sediment size)
- Use callipers to more accurately measure smaller sediment
- Use a small spade to scoop up sample
What made our results reliable (velocity)
- We repeated 3 times to calculate a mean
- We times over 10 meters, which is a long enough distance to get a proper idea of the velocity that the water is travelling
What made our results less reliable (velocity)
- Was hard to measure 10 meters downstream because the river bends so much
- The table tennis ball kept getting stuck on rocks and bumping into the river bank, making the time longer and unrepresentative of its actual velocity
How can we improve results (velocity)
- Use a flow meter to more accurately measure the river velocity
- Ignore the anomalous results
