Pebble Roundness
Hypothesis
I predict that the further down stream you go the less angular the stones will be, this may be because the further down stream you go the greater the velocity and the greater the velocity the faster the stones travel, and the more they knock against the sides and bed of the river, therefore eroding the edges of the stones.
Method
To find pebble roundness, I will need to:
- Select ten pebbles at random from the bottom of the river.
- I will then select how round the pebble is using the table below.
- I will then need to find the:
Mode ~ most frequent
Median ~ the number in the middle when all the numbers are wrote out numerically.
Mean ~ the average
I will repeat this for all the sites.
Results
Conclusion
The results back up my hypothesis, the further down the stream we went, the rounder the stones became this was due to the increase of velocity the further down stream you went which lead to the increase of friction therefore the more erosion which leads to rounder stones.
This experiment wasn’t very accurate as you may have picked out 10 sharp stones, you could make this experiment more accurate by picking out more stones, and then finding the average.
Cross-Sectional Area
Hypothesis
I think the cross sectional area will start off small and increase as you go down stream, this is because as you go down stream more water joins the river making it wider and therefore increasing the cross-sectional area.
Method
To find the cross-sectional area I will need to find the width and depth of the river. To do this I will:
- Width: I will measure across the top of the water between the two banks
- Depth: I will then take the depth at 10 equal intervals across the river. Once I have the information, I will average out the depth.
- Once I have the depth I will use the following equation to workout the cross-sectional area:
Width (in metres) X av depth (in metres) = Cross-sectional area
Results
Conclusion
My hypothesis was correct the further downstream we went the greater the cross-sectional area became.
Measuring the width and depth a couple more times in the same area, then finding the average could have improved the experiment.
Discharge
Hypothesis
I think the discharge will increase the further down stream you go, this is because there is more water in the river the further down stream you go, increasing velocity. The width also increases due to more water entering the river from streams, this increases the cross-sectional area, and therefore there is more discharge. (The more water in the river, the more discharge there is likely to be)
Method
To measure the discharge I will need to take the results from the velocity and cross-sectional area and use the following equation:
Velocity X cross-sectional = discharge
I will repeat this an each site.
Results
Conclusion
My hypothesis was correct the further down the stream we travelled the greater the discharge; this was due to the increase in amount of water in the river.
The method was an accurate way of collecting data to find out discharge.
Valley Side Slopes
Hypothesis
I think that the further down stream you go the less sloped the valley side gets this is because at the beginning of source of a river the slopes are very mountainous and as you go downstream the area becomes less mountainous therefore the slopes are smaller.
Method
To find the valley side slopes I will need to:
- Place a pole at the bottom of the river a further 10m upstream I will place another pole.
- I will then place the clinometer onto the pole and look through up
- I will line the clinometer up with the other pole and record the reading
- I will then move the first pole a further 10m from the second and repeat step c.
I will then repeat this for the other sites.
Results
Conclusion
My results agreed with my hypothesis, the valley side slope did decrease. However, we could not get a reading for site two as there was a fence obstructing the way, and a road blocked the right side of sight three.
This is a good way to measure valley side slop however things such as fences may obstruct the way.
Channel Width and Depth
Hypothesis
The further down stream you go the wider and deeper the stream gets. This should be because the further down stream you go the more water there is in it because of small streams joining to it, this means there’s more erosion which means the stream gets wider and deeper.
Method
To find the width and depth of the channel I will need to:
- Width: I will measure across the top of the water between the two banks
- Depth: I will then take the depth at 10 equal intervals across the river. Once I have the information, I will average out the depth.
Results
Conclusion
My hypothesis results didn’t match my hypothesis as site two and site three had the same depths this was because site 2 was on a bend so the water on the bend would have been deeper making the average depth higher.
This was not a totally accurate way of collecting data as bends may affect the results also the river could have changed without you realising if your interval between measurements was large. You could improve this by taking measurements more frequently.
Geography Field Trip:
Rivers
By: Rebecca Roberts 10x
Introduction
In October, we went to Snipedales, to collect information about rivers. With the information we have collected, I have been able to work out the following at three different sites:
River Velocity
Cross-sectional area
Discharge
Pebble Roundness
Valley side slopes
Channel Width and Depth
With the information, we have found out with have been able to get a better view on the way a river changes as it goes down stream.
