Planning Stages of the Investigation

 I am going to investigate ‘How and why do the hydrodynamics (characteristics) of the River Alderbrook, Solihull change downstream?’

The Bradshaw model explains how characteristics of a river should change downstream. Therefore, the hypothesises/aims can be drawn from this model  

·        the river should get wider downstream

·        the depth should increase downstream

·        The velocity should increase downstream

Theoretically, all these river characteristics are linked and consequently there should be a positive correlation between them.

Task:- Draw the relevant sections of Bradshaw model below.

We studied the River Alderbrook, located in Brueton Park, in the suburbs of Solihull. The length of river we studied was one kilometre in length. The location of the river that we studied was chosen for several reasons; it is easily accessible from Solihull Sixth Form College as it is located only metres down a pathway. Furthermore, the scale of the river is appropriate for the fieldwork investigation we are conducting, as the characteristics, such as width can be determined using a standard tape measure and the readings generating are accurate as the tape can be held tort over a short distance. The most important factor is that it is a very safe river as there are not strong current and no hazardous chemicals are used nearby that could possibly leak into the River Alderbrook. A pilot survey was taken of the area to determine the equipment needs and the distribution of groups and number of sites available. We were aware that groups had visited before and secondary data was available in the Geography dept.

There are many risks involved when studying a river, though these do depend on the size of the river. The obvious risk is drowning, though there was very little risk of this occurring in the River Alderbrook due to is small depth.  Also, plants and animals can cause harm, the best possible way of preventing any injury is to avoid any animals and do not touch or eat any plants. There is a risk that is very difficult to avoid, slips and falls as many people fall over without causing serious injury to themselves. The best way is to avoid areas that appear dangerous e.g. steep embankments and carry a first aid kit in order to be prepared for any eventuality. With all untreated water there is a risk that it can carry water borne diseases, the best way to avoid these is not to drink the water and to wash hands as soon as possible.

Data Collection

The area in which we investigated the River Alderbrook is Brueton Park. The actual river is situated along the south boundary of the park that neighbours Solihull Sixth form college, the playing fields and Solihull nature reserve. The flood management in place means that if the discharge becomes too great the water will be channelled towards the playing fields and nature reserve in order to keep the floodwaters away from rare trees located in the park. The River Alderbrook originates in Tudor Grange Park, which is south of Solihull town centre and travels through Brueton Park before reaching a confluence, where it joins the River Blythe.  This is located near the lake in Brueton Park (as shown on the map).

We used a number of pieces of equipment in order to collect accurate and precise data. To measure the velocity we used a hydroprop, the amount of time for the propeller to spin from one end to the other is recorded and this is then utilised to calculate the velocity. To measure the time amounted we required a stopwatch. The most basic yet important piece of equipment we used were wellington boots and waders. To measure the wetted width we used a tape measure as it could quite easily stretch the distance between the two banks. However, when measuring the river’s depth a tape measure was not appropriate, as it would just be carried away by the flow of the river, so we used a metre stick instead. To record all the data we collected we had created recording sheets, prepared before the fieldtrip, meaning that when we measured the data it could immediately recorded accurately.

We decided to use this sampling method as it should clearly show the progression of river changes downstream as outlined by Bradshaw, as theoretically all points taken along the river would be equally spaced apart. The idea behind the investigation is to show the change in the river and therefore we felt this method was the only way in which to conduct the data collection process. We could have used the random sampling method but it would not have shown the progression downstream and would be almost impossible to sort into data that would be sufficient to answer the question at hand.

When doing this we measured the river width at 5 points across and the river, to use the average depth, this would give us a more accurate results for water depth. Finally, also at these points we recorded the amount of time taken for the hydro prop propeller to move along the screw threat. This time can be used to calculate the velocity of the river by dividing the length of the screw threat by the amount of time taken for the propeller to move the distance.

We used systematic sampling, as there were four groups who each measured five sites along the transect of the river, working down the river and therefore twenty sites between the whole class as a minimum. This method of sampling would enable us to collect a fair sample that would avoid bias and give more reliable data on which to base our conclusions. Ideally these sites would be spread equally along the whole stretch of the river in order to show the accurate progression of the river downstream. (here’s some Evaluation already) However, this did not happen, as we did not have enough time to measure the distance between sites equally and it is almost impossible to locate evenly spaced positions with expensive specialist equipment. Furthermore we did not sample the whole river as the source is located in Tudor Grange park, at least a fifteen minute walk which means we would not have enough time to sample the whole length as it would have probably taken a whole day or even longer. Also some areas of the river are inaccessible, as they were too deep or dangerous and a long length of the river is channelized which means the results would be almost identical along that transect.

Were Pools and Riffles considered as part of the sampling. Explain this in the space;

As so little rainfall had occurred for the previous 5 weeks, the results were for low flow which may not give the normal results pattern because low flow causes greater variations when the bed load is a more prominent part than the water.

Results

·        The river should get wider further downstream.

·        The depth should increase down stream.

·        Velocity should increase downstream.

The best possible outcome would produce a positive correlation for all three.

The Bradshaw model that can be easily compared to the river and conclusions can be drawn from the information collected. However, the study only showed a snapshot of the river on one DRY day in autumn so a picture of the changes in the river throughout the year cannot be seen; we have only studied a quick snapshot of the river. The only way to generate a clear picture of the river throughout the year would be to take at least one measurement per season.

Many areas of the river were virtually impossible to access due to overgrown vegetation or fallen trees. This affected the enquiry as this meant some areas could not be measured and data could not be recorded which does not show the whole progression of the river. Furthermore, we were limited by the amount of time allocated to actually perform the enquiry; this also meant the whole river could not be measured, which actually originates in Tudor Grange Park.

Data Refinement and Display

(Need to upload images of Scattergraphs

please refer to Orange Booklet until images appear)                                                                                                                                

I have used scattergraphs to display our findings

JUSTIFICATION 1. all the others types of graphs available would not be appropriate for the way in which I intend to display my findings, e.g. if a pie chart was used it would be almost impossible to determine any trends as you move downstream and it would not be possible to understand the correlation between the sets of data.

2. Scattergraphs enable you to create a trend line (line of best fit) which can easily help you to determine if there is a correlation between the data.

3. Scattergraphs are more suitable than a simple line graph as if numbers are identical (as shown in the graph above) it would look incredibly messy and very difficult to interpret.

4. A scattergraph must be used for a river because it is not continuous data (Pools and riffles) so each site is not necessarily linked to the previous site so a line graph is incorrect due to the changes in the channel. A scattergraph enables the reader to determine patterns, trends and the relationship between two sets of data, clearly demonstrated by the graph which compares wetted width and depth.

5. Another way in which I displayed my data was using a table, this is appropriate as it allows you to compare directly the data collected from each category e.g. velocity/wetted width/depth/site number. It is also easy to comprehend as it is displayed neatly in columns and therefore the data can be easily distinguished.  From my knowledge and experience I have no better way in which to display the data collected. My use of presentation and sorting was appropriate for the task at hand.

Description, Analysis and Interpretation

Scattergraph 1 – This shows the relationship between the distance downstream and the wetted width of the River Alderbrook. By studying the trend line it is clear to see that there is a slight increase in the wetted width of the river downstream towards the confluence. Although, there are a few anomalies where the wetted width is less than the width upstream, the trend does continue to increase.  Firstly,  further downstream more water joins into the river as tributaries and through flow from the surrounding park and playing fields, which immediately increases the river’s discharge. With a greater discharge the river has greater erosive (abrasion) power over the river’s banks as it can carry large amounts of rocks and pebbles which results in wider banks as soil and rocks are removed. The depth remains around 150 mm between sites two and six as this part of the river is managed, it is channelized quite deeply so if a large discharge is carried down the river it will take longer to flood and less amounts of water will flood the surrounding area. This graph produces a positive correlation which is correct according to the Bradshaw model. As expected the highest wetted width was 340 cm, found at site number 20 (closest to the confluence), but the lowest wetted width was 70 cm, found at site number 16. The lowest wetted width was surprising as you would expect the further you move downstream the wider the river would become. The discharge of water remains the same as the depth increases to 0.38 m. This site could be considered as an anomaly as it does not occur anywhere along the river’s course. The wetted width ranges by 270 cm, which is very large considering these measurements were only taken along a small length of river, 1 kilometre. 

Scattergraph 2 – This shows the relationship between the distance downstream and the depth of the River Alderbrook. The trend line clearly shows there is a large increase in the depth downstream. However, there is an anomaly at point twenty as the depth decreases quite rapidly because the river has reached the confluence of the River Blythe. The river Blythe is dammed for an ornamental pool and flows more slowly than normal. As the river decrease in speed less materials can be held, and therefore rocks and sediment are deposited on river bed which results in a smaller depth at this point in the river. Throughout the rest of the river the depth increases up to this point as pebbles and rocks transported along the river floor cause abrasion as well as the hydraulic action of the water, creating a deep channel in the centre of the river. The depth is almost the same between points two and six, 0.1 metres as this is the managed sites of the river, consequently the characteristics of the river at this point are almost identical.  The largest depth is 0.39 m at site number 18 and the lowest depth is 0.08 m at the sites 2, 3 and 4. Generally, these results are what you would expect as you move further towards the confluence the depth should increase, but actually at the confluence the depth is less due to deposition as the river slows when the River Alderbrook and Blythe meet. Three sites along the river have the same lowest depth because these are along the managed section of the river and therefore the width remains the same and the discharge is likely to be basically the same as it is only over a very short distance. The range of depth is 0.31 m which is not a great difference, but is what is expected along a short stretch of river.

Statistical Correlation

 The scatter graphs show trends but a more accurate measurement of the correlation can be found with a statistical correlation test such as Spearman Rank.

We carried out such a test on the first set of data Wetted Width and produced an answer of +0.4. This was a weak positive correlation; however when we tested the reliability of this result is was not acceptable when measured on the reliability graph.  The results for the River depth was +0.6, again a moderate positive result. Only having 20 sites was really a bare minimum data set that has been unreliable. Had more sites been use to collect our data (50?) we would have a more reliable pattern and possibly shown a results similar to the Bradshaw Model.

In the space below sketch out the reliability graph for Spearman ranks using page 574 in Waugh textbook and plot your results.

Conclusion and Evaluation

The Bradshaw model predicts that all three should increase further downstream.

Depth, velocity and wetted width should increase as you move further downstream as the discharge increases as more water flows into the river, which theoretically should increase all of the characteristics. However, from our investigation it is clear that this is not always true.

Aim 1.  The width will increase downstream. The results showed a weak correlation, therefore the river Alderbrook with these limited results did not conform to the Bradshaw model. The reasons are that to little data was collected, also the river has been significantly changed by human activity. The river has been channelized in one section and used for flood defence with a levee and gabions in another area. Most extra water is added from urban run-off via under-ground channels/pipes and there are only a few natural tributaries that would help maintain a nature pattern.

Aim 2. The depth increases down stream. The scatter graph showed a modest positive trend and the Spearman rank result of +0.6 was a moderate positive results but not reliable. Again the results were not very supportive of the Bradshaw Model. This maybe due to the low flow in the river and the limited amount of data. The Pools and riffles in the river may also up-set the data set because they were a very common physical feature down our river and may have been another significant factor in the inconsistent results. Explain the impact of Pools and Riffles on the results.

 3. The velocity increases downstream. Our results showed the velocity did not increase downstream. Reasons

I analysed the relationship between the wetted width and velocity. I found that as wetted width increases the velocity decreases, this does not show what you would expect, but I think that if the river study was conducted over the whole length of the river a positive correlation would be produced. Yet again, our investigation has produced results that contradict the Bradshaw model. Overall, I felt I was able to explain how the hydrodynamics of the River Alderbrook change as you move downstream, that wetted width, velocity and depth are related and how the hydrodynamics correspond to the Bradshaw model.

Evaluation

I felt our data collection methods were very efficient, but there were some ways in which the sampling and collection could be improved.

• The hydroprop was not very accurate in low flow conditions as it was frequently half submerged. Another data set after rainfall would have been more reliable.  Also, we could have measured more river characteristics such as, bank width, bed load and hydraulic radius.
• In terms of sampling, the methods could be easily improved. The distances between the different sites could be measured, so the sites selected would be less biased.  The sites that we selected were often biased as we chose to measure positions where the river was either easily accessible or not too deep as we were only wearing wellingtons.
• Furthermore, we only took readings on one day in year, only giving us a snapshot survey of what the River Alderbrook is like.
• To improve our investigation and to study the change in the river throughout the year measurements could be taken once every season. By doing so we could generate a picture of the River Alderbrook’s river regime and it would also help to remove unreliable data.
• Finally, to produce more conclusive analysis on the changes of the hydrodynamics of the River Alderbrook, we could have surveyed the whole length of the river that would result in more site readings being taken. By doing so we may have been able to understand why some of the anomalies occurred and would result in more accurate conclusions.

The strengths of our investigation were; the weather was good meaning that during the study rain would not alter the river discharge as we measured different sites along the river. We collected enough data to produce statistics and graphs that enabled us to draw conclusions to the sub-questions that we chose. Also, having relatively accurate data helped us to draw substantial conclusions from the study that we conducted, if the data had been incorrect or unreliable it would be almost impossible to draw substantial conclusions. We were able to take accurate readings as we were provided with suitable equipment. Finally, the river study was of an appropriate scale, as it was not too wide, deep and the velocity was not too great, which could have compromised safety when taking readings.

The weaknesses of our investigation were; we did not plan the investigation in full depth e.g. we did not assign exact sites to different groups; we just chose the most easily accessible areas. Pools and Riffles were not always taken into account when collecting data; this would have significantly affected our results with only 20 sites. In addition, the majority of the class had never conducted a study like this before meaning it took a longer amount of time as people became used to the method. As mentioned before, not all areas along the river were accessible, consequently the whole river was not sampled meaning some areas where not measured and did not contribute to the final data and therefore the sampling method was not systematic. This point was further backed by the fact that we did not measure the distance between sites, as a result of this not all the sites were spread out equally, meaning trend lines may not have been one hundred per cent accurate.