Question 2 Flashcards
State the aim of your investigation (2 marks)
To investigate the hydrological changes down the long profile of the River Ogmore in line with Bradshaw’s model.
State one hypothesis that you sought to test (2 marks)
One hypothesis tested, in line with Bradshaw’s theory, was ‘velocity with increase with distance downstream’. The null hypothesis was ‘there will be no change in velocity with distance downstream’.
Briefly outline the theory that underpinned your aim (4 marks)
Bradshaw’s model underpinned our study. Bradshaw suggests that hydrological features change with distance downstream. Hydraulic radius, wetted perimeter, cross sectional area, velocity will all increase, while gradient, bedload and channel roughness will all decrease. We wanted to see if a river less than 20km from source to mouth displayed the same hydrological changes.
After measuring the velocity and the bedload, the Hjulstrom curve also helped us to understand which channel processes were operating at each river site.
Describe the location of your fieldwork and outline why this was a suitable site for your investigation (6 marks)
The aim of the investigation was to consider the hydrological changes of a river along its entire long profile. The River Ogmore, Margam, South Wales was a suitable site due to its long profile length (approximately 20km from source to mouth) and its width and depth. Its relatively short long profile ensured the entire river could be sampled via a stratified sample, within the confines of a 8 hour day. Giving a representative sample of the entire course. Its depth and width – no deeper than 1 metre at the final mouth site – ensured the river could be accessed easily and with relatively low risk. Each site was easily accessible via foot.
Outline the risks associated with carrying out your fieldwork and assess the effectiveness of strategies used to minimise the risks (5 marks)
Risks included slipping on the river bed, drowning, hypothermia, adverse weather, Weil’s disease, twisted ankles. Risks were minimised by conducting a risk assessment – each risk was given a measure of severity from 1 to 5, and appropriate precaction was taken to reduce likelihood. Precautions were also given a score 1 to 5. The difference between the two was calculated. Precautions to minimise risk included wearing sturdy footwear, waterproofs, weather forecasts, trained first aiders, washing hands before eating, covering cut hands. Precautions were effective at managing risk and reducing the possibility of severe accidents.
Describe one method of primary data collection used in this investigation (5 marks)
Velocity was measured at each site by first taking a tape measure to find the width of the river. The width was then divided into three systematic sample sites to obtain three velocity readings for each site. A mean average of the three readings would give a more accurate measure of velocity for the entire cross profile. A hydroprop was placed in the river up stream of the recorder and at a depth of 15cm, this was to reduce frictional drag and air resistance. The impeller was reset each time and the time was taken for it to move down the thread. A simple calculation was used back in the lab to work out the velocity in m/s.
Discuss the limitations of your primary data collection method (5 marks)
Human error could have meant the impellor was not properly reset prior to each reading affecting the accauracy of the data. The hydroprop may not have always been held at 15cm depth. Inconsistency could have crept in here and affected the validity of the data. If held too high in the water – surface drag would reduce the reading. If held too low in the water – frictional drag with the bed and banks would come into play. Sample size was only three velocity readings at each site. More samples would have ensured a more rigorous data sample. There was also a huge reliance on the hydroprop/impellor being accurate and scientifically sound. Could have used more than one technique to measure velocity (orange, tape measure, stop watch and/or a flowmeter). This would have increased reliability of data.
Justify both your sample size and sampling method (5 marks)
The sampling method used was stratified sampling. Sites totalled 8, and were selected in the lab before embarking upon the field in line with Bradshaw’s theory and our chosen hypotheses. Stratified sampling ensured that the sites were representative of the entire long profile – and its upper, middle and lower hydrological features and changes. It was felt 8 sites were adequate to provide a reliable and valid data set and exhibit the predicted hydrological changes – whilst being achievable in an 8 hour day.
What role did secondary data play in your study (4 marks)
The Met Office website (www.metoffice.org.uk) was used to obtain weather reports and rainfall measurements for the Ogmore area. This was used for risk assessment purposes, to ensure the discharge was within a safe level for the field day and also as part of the analysis. Rainfall data was used alongside discharge readings to identify links and patterns.
What role did quantitative and qualitative data play in your study (4 marks)
Quantitative data formed the majority of my primary data (width (m), velocity (m/s), hydraulic radius, wetted perimeter (m) etc). This was correlated to distance downstream through Spearman’s Rank coefficient. Qualitative data was in the form of Power’s Index. Sediment was noted as angular, sub-angular, sub-rounded and rounded.
Outline the role ICT played in your study (4 marks)
ICT was used throughout the study. Google Earth located the study sites and provided drainage basin background information (land use, tributaries, size and shape of basin).
The Met Office website provided rainfall data, which was used alongside discharge data to identify patterns and correlations.
An Excel spreadsheet was used to calculate hydraulic radius, cross sectional areas and discharge automatically. It also was used to create scatter graphs and Spearman’s Rank values.
Outline and justify the use of one or more techniques used to present your results (4 marks)
Each hypothesis compared and investigated relationships between two variables (velocity v distance, bedload v distance, HR v distance)
The ‘twin variable hypotheses’ lent themselves to scatter graphs (x/y data plotting), used alongside Spearmans – in order to prove/disprove hypotheses and accept/reject Bradshaw’s theory.
Scatter graphs graphically present relationships; a line of best fit expresses strength and reliability of correlations while highlighting anomalies. All important for valid analysis.
Outline and justify the use of one or more techniques used to analyse your results. (7 marks)
Each hypothesis compared and investigated relationships between two variables (velocity v distance, bedload v distance, HR v distance)
The ‘twin variable hypotheses’ lent themselves to scatter graphs (x/y data plotting), used alongside Spearmans – in order to prove/disprove hypotheses and accept/reject Bradshaw’s theory.
Scatter graphs graphically present relationships; a line of best fit expresses strength and reliability of correlations while highlighting anomalies. All important for valid analysis.
Spearman’s correlation coefficient gave a statistical significance to the correlation. I could prove or disprove hypotheses to a significance of 95% or 99%, depending on the critical value. This gave statistical weight to my conclusions.
Drawing upon your findings, explain how your enquiry improved your understanding of the topic (6 marks)
River systems must be treated on an individual basis. Not all river systems will fall into Bradshaw’s neat theory. Textbook theory is often too neat and reductionist, and should be treated with appropriate level of scepticism. The real world is often more complex.
Complexity of real world requires rigorous methodologies. For example the river load methodology only took into consideration randomly selected bedload. Lacked rigor as suspended sediment was not tested for. Hjulstrom’s curve should have been considered more when designing hypotheses.
With specific reference to your results, summarise the main conclusions of your study (6 marks)
Velocity increased with distance downstream with a statistical significance of 99%. This proved Bradshaw’s theory was correct regarding velocity and distance down the Ogmore.
Hydraulic radius increased with a significance of 95% - this showed that channel efficiency was greater as we moved closer to the river mouth.
Bedload and distance downstream did not correlate with any statistical significance. The null hypothesis was accepted. Evaluation proved that the methodology only took into consideration bedload and changes in the x axis. Whereas suspended sediment was not considered. It was felt suspended sediment would have been a better indicator of changes in channel processes.
