To what extent does the Baye de Clarens river correspond to the Bradshaw model in terms of downstream change?

This field work links to “Part 2 - Freshwater – issues and conflicts” of the IB syllabus, following the sub-topic “Drainage basis and flooding”. This investigation will allow us to gain knowledge in a real-world geography context. The aim is to investigate how the “Baye de Clarens river”, in the Canton Of Vaud Switzerland correlates with the Bradshaw model in terms of downstream change, therefore answering the field work question : To what extent does the Baye de Clarens river correspond to the Bradshaw model in terms of downstream change ? The “Baye de Clarens” river has its source above the hamlet of Bains-De-l’Alliaz in the municipality of Blonay at an altitude of around 1205 m above sea level. The river’s torrent is approximately 8 Km long (“Wikiwand - Baye de Clarens”). Conveniently, the river is near our school allowing easy access to the sites investigated.

To focus this investigation, I have created three hypotheses about the Baye de Clarens river that I will be testing with the data collected. I have based these hypotheses on the Bradshaw model, a geographical model which depicts the changes that occur as a river flows from its source to its mouth (“River Processes”). This model gives an approximation of how a river usually changes as it progresses.

The cross-sectional area of the river will increase downstream as the volume of water will rise, increasing velocity and therefore its erosive power.

Sediments will have an increased sphericity as the river flows downstream as their irregular edges are removed by abrasion and corrosion. The farther a particle is moved, the more rounded and spherical it becomes. Load particle size will therefore decrease.

Discharge and average velocity will increase due to erosion, conjoining tributaries and surface runoff caused by weather systems and drainage systems.

The data was collected from 16 sites along the river that were identified based on accessibility and security. This was done to ensure that the investigation could be carried out safely. We calculated the distance (km) from the source to each site. The data collected at each site will allow the hypotheses to be answered.

The data was recorded on an application created prior to the data collection. At every site, our GPS location would be recorded as well as our data. The data collected could then be transferred to Excel for data procession.

Apparatus -

• Dog treat
• Tape measure
• Stopwatch

To calculate the velocity of the river at each of the 16 locations, the float method was used. A dog treat would float along a predefined distance. The dog treat was thrown upstream from the starting point into the water. Once it attained the starting point the stopwatch was started and once it passed the end point the timer was stopped. The time (in seconds) was calculated for the float to attain the determined distance. A dog treat was used because it floats, its biodegradable and therefore wouldn’t have polluted the river in any way. Hence, it was then possible to calculate the water’s velocity by the following equation -

\(V=\frac{D}{T}\)

The V represents velocity, D being displacement also known as the distance travelled by the dog treat and T being the time taken for the dog treat to reach the end point. This method was repeated three times at each site allowing us to calculate average velocity leading us to more accurate results.

Apparatus -

• 100 cm ruler
• Tape measure

Depth and occupied width were measured to calculate the cross-sectional area at each site. To measure the occupied width, a tape measure was held on each extremity of the river bank. Depth was recorded 10 times at each site. It was measured at every tenth of the way from one side of the riverbank to the other. To explain this concisely, at the fifth site, the width was 200cm. A tenth of 200cm is 20cm, so the measurement started at 0 and then went across 20cm every time to measure the channel depth at that point. This was done until the other side of the riverbank was reached. Hence, systematic sampling was used to measure depth since our measurements were conducted with a fixed periodic interval. With the data collected, the cross-sectional area of the river could be calculated with the following equation - Average depth × actual width.

Apparatus -

• Rock sphericity indication chart.

At each site 10 sediments were collected from the riverbed using random sampling. Our sample size for each site was large which allowed us to obtain a range of data. During the selection we looked away to avoid bias choices created by human instincts. For each sediment, the length and the sphericity were recorded. We could then compare how the sediments size had changed from the source of the river to the mouth. The sediments at the source were angular and as we reached the mouth of the river, they became more spherical. Sphericity was measured by comparing the sediment with an indication chart.

The cross-sectional area of the river will be the first hypothesis being compared to Bradshaw’s model, secondly it will be the load particle size and the sphericity of the sediments and finally the average velocity and discharge along the river. The data collected is presented below.