The precision was maintained successfully. We did this by keeping the tape measure tight at both edges. The two people measuring the width kept the tape measure 20cm above water level (Figure 2). This was done to ensure that results were accurate because if the width was measured at water level the current of the water will interrupt the measurement, making it harder to have a firm grip which hence will lead to inaccuracy in the results. Likewise, holding the tape measure higher would result in a ‘wiggly’ affect, which requiring a firm grip which is hard and can easily be lost, which will again lead to inaccuracy.
2 - Channel Depth:
According to the Bradshaw Model, the channel depth is expected to increase moving downstream from the source.
To measure the channel depth we will be using a metre ruler, this is appropriate and accurate because we already know, being told by our instructor, that the locations we will investigate along the River Calder do not have a high volume of water.
The first person in the group will vertically mantle the ruler (900) on the channel bed, simultaneously keeping their eye levelled with the water as best as they could and this was done in-order to avoid inaccuracies, one of which are ‘bow-waves’. Keeping their eyes levelled with the water will help them to stop being disillusioned into thinking that he held the ruler straight when it was actually bending in a different angle. Once the first person was comfortable in mantling the ruler correctly, the second person in the group insured that the first person’s mantling was indeed straight, if this was so, then the Channel Depth was measured and recorded.
As we went along the river’s course, we decided to keep consistency in our measurements. This was done by have a 50cm stretch to suit the time we had at the location, remembering that we also had other factors to measure. On the other hand, if we chose to increase the spacing to 75cm, for example, it would be harder to keep and we will also degrade the accuracy of our overall results, this is because measuring the depth will also help us to explain the discharge’s hypothesis as the channel depth can be used to draw work out and draw a surface-area graph, which is in the Discharge formula. Examples of these graphs are located in the Data Presentation part of the coursework folder.
3 – Water Velocity:
According to the Bradshaw Model, the velocity of the water is expected to increase moving downstream.
In order to measure the water’s velocity, we vertically mantled two ranging poles opposite of each other, 10 meters apart – this helped us when timing the ‘orange peel’ as it travelled from one ranging pole to the other. The time it takes the orange peel to travel is the time that will be substituted in the Velocity formula: Velocity (m/s) = Distance/time. The distance will always be 10m in all of the sites, except to site 2, where it was 1m – this was because site 2 had a substantially smaller channel width, leading to a sparse and drought supply of water and hence we reduced the stretch between the two ranging poles. Distance was kept the same during the substitution.
We thought an orange peel will be an effective objective to use because of its lightweight which will allow it to easily flow, and its bright colour, which will make it easily distinguishable.
The ‘shouters’ are the people in our group which will help the person with the stop-watch to accurately time the ‘orange peel’ as it travels from one ranging pole to the other.
Our method was straightforward, we had one person who aligned the orange peel in the same line as the orange peel, and once the timer was ready, the person who held the orange peel would allow it to flow; the timer was informed of this by a person from our group, preferably the person who held the orange peel.
Once the orange peel is placed in the water, the person on the left pole shouts “start!” and, likewise, when the orange peel reaches the opposite ranging pole, the timer is prompted to stop by a “stop!” This process was repeated five times in order to obtain an accurate average.
4 - Gradient
According to the Bradshaw model the river’s gradient is expected to slightly decrease going downstream.
Some of the method traits used to measure the water’s velocity (3) was used to measure the gradient too: the same ranging poles with the same stretch.
In order to measure the angle of the gradient’s slope, I have used a clinometer gun. I had to hold the gun accurately against the red stripe on the ranging pole in the upper-stream, pointing it to other ranging pole, in the downstream, where the other person from my group stood, doing exactly the same thing. In order to measure the angle, whilst we correctly aligned the clinometer gun, we pulled the trigger – this gave us the angle where of the steepness of the river’s slope – or gradient.
This method was repeated three times to get an accurate average.
5 - Discharge
According to the Bradshaw Model, the Discharge will increase heavily going downstream.
We will not actually work out the Discharge during our geographical investigation, as the method will simply be using the surface area, obtained via using the Channel Width and Depth and the Velocity, which is obtained by using the velocity formula.
I will work out the total surface area by drawing the sea-bed of each site. This will be done by using the results from the Channel Width (1) and the Channel Depth (2) of the river at each of the five sites. The results are shown in the Data Presentation section of the coursework folder.
An example of the cross sectional of the river bed is clearly shown in Figure 4. As you can see, the channel bed starts and ends triangular and the middle-sections are made up of trapeziums.
In order to work out the total cross-sectional area, I will have to work out the area of each shape in the surface bed with the appropriate formula and these are:
Area of a triangle: - ½(a+b)
Area of a trapezium: - ½(a+b) h
To get the total cross-sectional area, I must then add up all of the values, or in other words, using the following formula:
Cross sectional area = total area of triangles + total area of trapeziums
Using the total surface area, we can then calculate the Discharge for each of the five sites using the following formula:
Discharge (Cusecs) = Cross-sectional area (m2) * Velocity (m/secs)
6 - Bed load size
According to the Bradshaw Model, the Bed-load size is expected to decrease going downstream.
We have investigated this factor by sampling 20 pebbles from each of the five locations. This was done by ‘dividing’ the river (dependant on width) into five sections (Figure 5) and then picking five stones/pebbles (the type of rock is determined by the bed-load roundness (7)) from each section. This would give us an overall total of 100 pebbles.
100 pebbles are an appropriate amount because sampling more will prove very time consuming and sampling less would not give accurate results. This method of sampling is called representative sampling.
To insure our sample is reliable, each person from our group would pick one stone, the first stone that the person’s hands touches is the stones that will be sampled. The stone’s b-axis will then be measured using a cm ruler. The b-axis, because it’s a measurement of the horizontal, will help us determine the size of the rock and how its attributes change from the upper to the lower course, a larger stone would mean a bigger bed load size as larger stones take more space. After the first stone’s b-axis was noted, it will be left in a separate corner to ensure that it is not measured again, which can result in unnecessary repetition in our results. This method will then be repeated until100 are collected from each site.
7 - Bed-load roundness
According to the Bradshaw Model, the bed load roundness is expected to increase going downstream.
The bed-load roundness was measured by using the same rocks obtained by measuring the bed-load size. These were the rocks which were ‘put aside’ to avoid repetitiousness in our results. After we have finished measuring the bed-load size, the rocks were accumulated from the site which we were at that time.
People in my group, including myself, started to note the roundness of the pebbles whilst trying to fit their roundness in the most appropriate category shown in Power’s Roundness Chart (Figure 6). This proved very subjective and it was hard to come up with a decision which most of us agreed on since it was very ambiguous to differentiate between, say, a Sub-angular and a Sub-rounded rock. Because we were running out of time, it was decided to simplify Power’s Roundness chart into 3 categories, thus to make it easier to agree on a final decision, the three simplified categories are: angular; sub-angular and rounded.
After doing this, we were able to agree about a rock’s roundness more fluently, although it was still subjective. After an agreement we would tallied the result in a table according to roundness and site location.
Global results have proven very subjective with different groups giving a different overall percentage of the rocks’ roundness. This was one of the few parts where we had to trust each others’ initiatives to give accurate deductions. This data will be interpreted more closely in the Data Interpretation part of the coursework folder.
