AS Fieldwork Report
To investigate the downstream changes in channel variables at Ashes Hollow Stream. Hypothesis
“Discharge increases with Distance from Source”
Location and description of the location
Ashes Hollow Stream is an area fairly untouched by human activity, with safe, easy access and the Stream is shallow due to being in the Upper Course of the river. Methodology
Wear suitable footwear, act sensibly
Diseases and Illness
Death, Weil’s Disease
Wash Hands, Wear Gloves
Get Wet, Cold, Hypothermia
Plenty of layers, Waterproof coat
General safety tips;
Take mobile phone and leave contact details
Work in groups
Tell someone how long you are going to be
We used Stratified sampling because we thought it would give us the biggest changes in regards to our hypothesis. To do this we chose a sample area both before and after 4 separate confluences on Ashes Hollow. Cross Sectional Area
Needed to calculate discharge; Q = CSA x V
1. Measure the width of the stream, using a tape measure. Make sure the tape is taught and 90˚ to the bank, avoiding the overhanging bank. 2. Divide the width by 10 (to give a systematic sample). Then measure the depth using a meter ruler, orientating the ruler parallel to the stream flow to minimise drag. 3. Calculated the mean depth and multiply by the width to get average CSA. 4. Pros: Gives an estimate of CSA and allows comparison downstream. 5. Cons: Bedload caused problems getting true reading of depth. Velocity
Needed to calculate discharge; Q = CSA x V
1. The hydro prop was placed in the water and the time taken for the impeller to travel the distance of the rod was taken. 2. This measurement was repeated at 3 equidistant places across the river and an average time taken. The velocity was calculated using the equation: (0.0277+3.281) ÷ Mean Time. 3. Pros: The measurements are more accurate than alternative methods. 4. Cons: If the hydro prop is used in shallow water the impeller may not be covered, in turbulent flow the user may find it difficult to see the impeller, obstructions may disrupt river flow. Discharge
The Velocity and Cross Sectional Area are multiplied together to get the discharge value. Data Presentation
Identify patterns of change downstream (2 Variables)
1. Draw 2 axis (X axis is Distance from Source, Y axis is Discharge). 2. Plot the data.
3. Insert a line of best fit- Calculate mean for each axis and plot a straight line between the points (going through team). 4. Pros: Good for showing trends and anomalies + assessing strength and relationship. 5. Cons: Can be difficult to identify patterns.
The Graph shows that as the distance from the source increases so does the discharge however there is no clear pattern in the data, making it hard to draw a more solid conclusion. Data Analysis
1. Write down your Alternative Hypothesis (What you are looking for) and your Null Hypothesis (the opposite). 2. Write down the results from the two variables you are comparing. 3. Rank Variable 1 from highest to lowest.
4. Rank Variable 2 from highest to lowest.
5. Find the difference (d) between the ranks for Variable 1 and Variable 2. 6. Square the value of d to get d2 for each site (in order to remove negative values). 7. Sum the values of d2 to give Σd2 and count the pairs of data to get n. 8. Insert the values into the SRCC equation and calculate the test statistic Rs = 1 – 6Σd2
9. Refer to the table of critical values to assess the significance level for your result, and then decide whether to accept or reject your null hypothesis. 10. Pros: Clearly shows if there is a relationship between the two variables and the strength of the relationship as well. 11. Cons: Time Consuming
The results of the SRCC showed that there is no significant correlation between Discharge and Distance from the Source. The Discharge doesn’t increase because at sites 5, 6, 7 and 8 there are rocky outcrops which increase the size of the Bedload in the river. This increases the friction, decreasing the river efficiency. This in turn decreases the velocity of the river which means the discharge doesn’t increase. Also the increased Bedload size also reduces depth, affecting the discharge negatively.
We could have also had this result because we only looked at a relatively small area, entirely within the upper course of a river. Evaluation
I believe that the results we took were mostly accurate, however if we were to repeat the investigation then I would either like to use more sites or spread out the current number of sites in order to properly test our hypothesis in accordance with Bradshaw’s model. Another way we could improve our investigation would be to repeat it at several different times throughout the year and take overall averages so that various seasons and weather patterns are taken into consideration, which would increase the accuracy of the results we take.
Also when we did our investigation there were a lot of groups all taking results both sides of our group which could have disrupted the river and modified our results, so if we did it again we would wait until the river was clear of other groups.