At site numbers four, five, six and eleven the cross sectional area has been measured at around 20mm. Similarly, a reading of around 60mm has been taken at site numbers eight to ten. Measurements at the remaining sites suggests an increase in distance downstream, increases the cross sectional area. The scatterplot as a whole gives little indication of any relationship between the two variables, cross sectional area and site number. Once again, the SRCC reinforces this conclusion, r = -0.021. As does the significance level (0.948), this surpasses the 0.05 confidence level considerably. i.e. there is virtually no relationship between the two variables and a high probability that the coefficient has occurred by chance.
In conclusion, hypothesis two cannot be accepted. i.e. cross sectional area does not increase further downstream. Geographical theories suggest that the hypothesis should be accepted, due to several reasons. Firstly, both the catchment area input (through processes such as surface runoff) and tributary input increases further downstream, the channel is eroded and made larger so to accommodate for the increased volume of water in the channel.
The reasons for the results not corresponding with geographical theories, as well as problems and solutions encountered, for scatterplots showing site number against both discharge and cross sectional area, are in the following paragraph. Firstly, the stretch of the river Lyd that the study was carried out did not contain any confluences with tributaries. As mentioned above, the input from tributaries is a main contribution to an increase in discharge downstream, without any tributaries in the data collection zone, the volume of the river or the discharge will not increase.
The lack of tributaries affect the cross sectional area as well, as the more water in the channel the larger the cross sectional area will be. Also, the size of the river channel will not increase due to the lack of erosion taking place (as there is not a large quantity of water), as a larger river channel (providing it is full) means a larger cross sectional area.
As shown in Figure 1.1, Parkend (nearest town to where the study was completed) is about half way along the Lyd’s course and the stretch extended to just before Bream; therefore it is not surprising that there is not a large increase in discharge in this small section of the river. To overcome this, the course should be divided into several sections and an average discharge then calculated. These new results would represent the discharge far better. When these results are plotted on a scatterplot, a more clear correlation may be visible.
Hypothesis Three: The larger the wetted perimeter, the greater the discharge. On four occasions while the wetted perimeter is between 150 – 250mm, the discharge is slightly below one thousand cumecs. The remaining eight points show a strong positive correlation, indicating that an increase in wetted perimeter also means an increase in discharge. Four of the eight points in this correlation are clustered when the wetted perimeter is 50mm and the discharge is 1000 cumecs. Figure 3.3 as a whole provides an indication of a fairly strong correlation between wetted perimeter and discharge.
Due to the relatively high ‘r’ value of 0.734, the SRCC also suggests that there is relationship between the two values. The significance level (0.007) is significantly below the 0.05 confidence level. i.e. there is 95% chance that the relationship between the two variables has occurred not by chance and because there is a correlation. If the study were to be undertaken again, a similar set of results would be collected.
In conclusion, hypothesis three is can be accepted. i.e. the larger the wetted perimeter, the greater the discharge. Geographical theory states the above hypothesis should be accepted. This is because the bigger the river channel, the water capacity of the channel also increases meaning more water can flow downstream, this is displayed in Figure 2.5. If the channel size i.e. wetted perimeter is bigger, then a greater volume of water can be transferred downstream at a quicker rate and hence discharge is greater.
As 4.1 demonstrates a possible reason for one of the weaker points in the correlation (site number 10) is the fact that a natural barrier/dam had built up in the river. This could have been due to debris not being able pass a certain obstacle during flood conditions or for another reason.